Louis' Solar Power Strategy

Antius · 2017-05-11 11:26:27

Louis has mentioned the possibility of thin-film solar modules (printed on plastic) as a near term alternative to nuclear power for Mars surface missions. In the thread for ‘ Industrial Plan for Mars - the first 20 years.’ he provided a link to the study that informs this opinion. I decided to review it and would like to thank him for bringing it to my attention.

http://www.sciencedirect.com/science/ar … 6509004834

The premise of the study is that by the time a manned Mars mission is carried out, photovoltaic technology will have evolved to the point where it is possible to print extremely thin doped amorphous silicon coatings onto any substrate. This should allow the manufacture extremely lightweight solar panels, with high mass power density. The study authors take this assumption to its logical conclusion and model the performance of minimum practical thickness flexible solar panels. These are amide polymer sheets with amorphous silicon coatings, some 67 microns thick. This would make the panels about two thirds the thickness of A4 printer paper, which is still considered to be sufficient to provide strength against puncture or tearing on sharp objects (i.e. rocks) if reasonable care is taken. The panels have mass of 0.07kg/m2 and the intention is to lay the panels on the Martian surface and weigh them down with rocks. A 100kWe average power system can be set up with about 132 man-hours of EVA. The study authors also assume that the panels will achieve efficiency 15%, which is a stretch on amorphous silicon thin-film panels produced to date, but might be possible with further development.

The conclusions are that at the most favourable location on Mars (31 degrees North), the assumed PV system would approximately match an SP-100 based nuclear power system in terms of time-averaged power-to-weight, provided the mission is capable of tolerating some amount of intermittency in its power supply.

Here are some potential issues as I see them:

1. The concept is not new. The study references a previous design study carried out in the 1980s. In the 30 years since, the technology for printing thin films onto flexible substrates has only recently been demonstrated at laboratory level, but is still far from commercialisation. About an inch square of the material has so far been produced by MIT (early 2017) and it is not yet known if large scale production is even possible at this point. The response of the PV printed surface to abrasion and radiation damage is not known at this point.

2. Thin-film technologies already exist, but typically do not achieve superior power-weight to ordinary cells because glass covers are needed to protect the fragile PV films from abrasion and radiation damage. This mission scenario is banking on the PV films maintaining performance long enough to complete the mission. In the real work, flexible thin-film solar panels have been produced and have area specific mass of 2-4kg/m2, almost two orders of magnitude greater than that assumed in the MIT study.

3. To achieve high power-weight, the mission design includes a regenerative fuel cell high along with 200-bar storage tanks, to cover stay-alive power requirements for the hab (10KWe). One of Louis’s objections to relying upon a single nuclear reactor was the potential for such a reactor to go offline, leaving the crew without stay-alive power. This is a concern for any system and power supply reliability should certainly have a bearing on mission architecture. However, it is difficult to make the case that a regenerative fuel cell with its numerous pumps, compressors, polymer/ceramic membranes, valves, etc. represents a more reliable power supply than a liquid metal cooled nuclear reactor. In the latter case, pumping may be achieved with MHD pumps or even natural convection, neither of which requires moving parts. Likewise, the sterling engine power conversion units are chosen specifically for their high reliability – they are mechanically simple components with only a few moving parts. The mission architects appear to realise this and present a number of possible power supply architectures, including solar with lithium ion storage, which somewhat degrades power-weight; and hybrid option, which uses a radio-isotope RTG to provide stay-alive power in the event of solar power system failure.

4. The acceptability of the system is dependent upon the ability of the mission to tolerate an intermittent power supply. Whilst it is possible to include energy storage systems to cover essential stay-alive power requirements for the hab, the architects appear to have decided that providing sufficient storage to maintain a flat diurnal power profile would require an unacceptable increase in power system total mass. This is not surprising; as such an effort would require some 1600KWh storage capacity for a 100KW continuous power supply, which would add some 6.4 tonnes to power supply mass budget if provided by regenerative fuel cells and 10.67 tonnes if Li-ion battery storage is used. What is more, storing such a large proportion of power would greatly increase the area of solar panels required, due to storage losses. The electrolysis + fuel-cell energy storage system is at best 50% efficient, maybe lower when pumping and compression losses are accounted for. Designing a system with flat power profile would therefore at least double the area of solar panels needed. In the case of Li-ion battery storage, the increase would be less dramatic, perhaps a 30-40% increase. But the storage system is heavier to begin with. By my calculations, using the authors assumptions to provide a system with flat diurnal power profile at the optimum location (31 degrees North) reduces effective system power-weight to ~10W/kg. This is only about half that of an SP-100 sterling power system doing the same job, but might still be tolerable at this location if it averts political / development difficulties of the SP-100.

5. Providing a flat power profile (non-intermittent) is important, because without it, energy hungry equipment such as propellant manufacturing effectively lay dormant for most of the day. The energy produced by a flat non-tracking array is effectively a sine function, reaching zero when the sun is at the horizon and reaching a maximum at noon. Even during the day, the power requirements of propellant production will be out of sync with the array output, with the array providing either too little power or too much. As the 100KWe average power system will produce the majority of its power over just 25% of the Martian day, this suggests that the propellant production facility must either be scaled up 400% in its production capability or the mission must accept that the same plant will take ~4 times as long to produce the same amount of propellant.

6. The study is based upon an optimum location on the Martian surface (31 degrees North). This is the region that achieves high annual insolation levels and the least seasonal variance of solar incidence. With tracking arrays, solar incidence varies by +/- 10% from year average over the course of a Martian year. For locations at different latitude, performance of the system drops off rapidly. At 30 degrees south for example, mass specific power is about 70% that of the equivalent northern location. At 60 degrees North & South, it drops to just 5W/Kg. None of these estimates account for the extra mass required to produce a non-intermittent power supply, which would reduce mass specific power even further. The authors conclude that for missions to latitudes substantially away from 30 degrees North (i.e. for global access) nuclear fission power supplies are required.

7. The system requires substantial deployment time - 132 man-hours of EVA for the 100KWe system that was modelled. Perhaps twice that, if a base load power supply is needed with substantial storage. This is a problem, as it suggests that propellant production can only start after the crew have arrived.

8. It is not clear what assumptions the study authors used when estimating the total mass of the panels. Their assumption appears to be that solar array panels can be produced with constant area mass of 0.07kg/m2, which is consistent with a 67 micron thick polymer film. However, real solar panels tend to discharge current at very low voltages, typically less than 1V for single cells, which are stacked in series to produce a 12V output. This can be done without excessive resistance losses because the cell aluminium backing and surface conductors are relatively thick, which reduces internal resistance. However, for very thin cells, internal resistance losses would be too high for significant numbers to be put in series. The discharge voltage would be low and thick conductors would be needed to carry current to an inverter-transformer to step up the voltage. Given the size of the intended collection area – 25,000m2, it is likely that a large number of inverter-transformer units would be needed, perhaps one for every few square metres of solar array. I do not know how small or compact these units could be made, but it is difficult to imagine that the mass of the whole system would remain as low as 0.07kg/m2.

9. The study is based upon the requirements for short-term surface missions, i.e. Mars Direct style missions. This negates concerns over the long-term survival of power systems. For the longer term requirements of a Martian base, the long term performance of a power system becomes more important. If radiation damage and abrasion result in rapid declines in system performance over a period of just a few years, the impact on power supply economics could be severe. For short-term missions, we are interested in base-load KW delivered per kg of power supply mass. For a base, we are just as interested in total KWh delivered per kg of power supply delivered to the surface. A liquid metal cooled nuclear reactor can deliver a flat power profile for a decade or more. It is not clear that these ultra-thin solar cells can do this when exposed to the high UV environment on the Martian surface.

10. It is an accepted fact that long-term human habitation of Mars must rely upon the use of native materials for whatever commodities human settlers may need. As all consumables on Mars must be manufactured (including air to breath) and low temperatures may necessitate energy intensive forms of agriculture (in particular, artificial light for crop growth) living on Mars will be energy intensive. The prosperity of the average Martian will depend upon cheap energy. A key input to the production cost of energy here on Earth is ‘Energy Return on Investment’ (EROI). This is the ratio between energy produced by a power plant over its lifetime, to the energy invested to produce the plant, mine its fuel and maintain it, etc. This is not a big issue for power systems provided for Mars Direct style missions, as the total size of the systems is small and the costs of manufacturing them are a small part of the total mission cost. If we are talking about power supply for a Martian town or city, the energy burden of manufacturing the power supply begins to grow significant, even if it is produced on Earth. If it is manufactured on Mars from local materials, a low EROI becomes especially burdensome and will substantially push up the local cost of power. Renewable energy systems tend to have low EROI, especially if energy storage is factored in to the calculation. This is reflected in high capital costs for these systems. For solar power, EROI is typically 2-10, depending on the technology used and this drops further when the energy costs and losses from storage are included. For fossil fuels on Earth, EROI varies between 20 and 80, depending upon the specific fuel. For nuclear power with centrifuge enriched PWR plants, EROI is about 100. I do not know what the EROI of the thin-film PV modules is; it may be much better than traditional solar, but historical experience suggests that this could be a problem if this technology must be mass produced on Mars as the dominant source of power to a growing settlement.

My conclusion to the assessment is that thin-film solar power is an interesting technology that may contribute to a future mission power supply. However, it would be premature to assume that nuclear fission is not needed for future mission architectures. Looking at the space solar power systems that we have available today, which have area specific mass of ~1kg/m2, a 100KW base-load power system for Mars at 31 degrees North, would weigh some 57 tonnes and mass specific power would be 1.8W/kg. This is about an order of magnitude heavier than an SP-100 Stirling system and the situation would be worse at less optimal locations.

Last edited by Antius (2017-05-11 11:55:06)

Dook · 2017-05-11 12:53:53

The only reason you need a lot of power is to make rocket fuel on Mars. It's a waste of time and energy to try to gather Mars salty ice to turn into fresh water that you then zap into rocket fuel. It's even more wasteful to try to produce steel, aluminum, glass, or other materials that don't provide more food, oxygen, or water.

Any exploration team will have a landed ERV to return home on. A settlement should not have to make rocket fuel because they should stay on Mars. Even if you do bring them home you would send them an ERV to come home in like the exploration teams would use.

We only need to power the Mars Hab, recharge the rovers, and power a buried habitat. We don't need a large nuclear reactor. We need a large RTG capable of about 15,000 watts an hour supplemented by solar arrays on the surface (two 10'x50' arrays, not a 300'x300 foot one), another array on top of the Mars Hab (30' circular to cover the regolith), and a thin solar array built in to the outside of the Mars Hab (maybe 360 watts an hour).

Growing inside will be energy intensive? Seven buried 25' circular habitats could have five 23 watt (100 watt equivalent) LED lights each. The inside walls, ceiling, and floor would be white to reflect light. That's 115 watts an hour per habitat, 805 total watts, for growing plants.

Last edited by Dook (2017-05-11 12:55:06)

Antius · 2017-05-11 13:37:09

Dook, I would rather this didn't turn into another endless discussion of 'Why its pointless to make anything on Mars'. On the subject of food, it would take about 1GJ of electrical energy to make enough food for 1 person for one day. It is an energy hungry activity. I carried out the energy analysis on a recent thread that you also contributed to.

Dook · 2017-05-11 13:52:49

When you did your plant energy study did you factor in reflected light?

Also, plants on the earth don't get a full 24 hours of sunlight, they get about 12 hours if they are grown in a field that has been cleared.

If you can't grow plants inside then how come all these people are growing marijuana in their garages?

SpaceNut · 2017-05-11 16:43:18

One thing that was missed is that the panels need to be weighed down with rocks, sand bags when laid flat on the ground ect.. which further can cause damage to these as the mars winds cause the panels to move against the rocks. The spacing between rocks may need to change due to the underlying ground which may not be the best to lay the panels onto...

louis · 2017-05-11 17:35:27

People may find this link better (I got a sign-in form with your link, Antius).

http://systemarchitect.mit.edu/docs/cooper10.pdf

Some observations in response...

I was taking the MIT study on trust, I'll admit. It's rather surprising if they were citing a technology that did not exist in even pilot form.

I think the PV panels suggested by MIT are averaging about 10 watts per sq. metre on Mars during hours of sunlight, so they were very low efficiency...

ULW PV power might not be there yet, but it's close...

http://newatlas.com/lightest-thinnest-s … mit/42092/

I think we need some of the Apollo boldness. Even if we can't get to 6 watts (or 3 watts for Mars, say) per gram, we might still have a very low weight system on offer within the next 10 years. We need to spray some money at the problem, in the way NASA did with Apollo-related problems in the 60s. In the context of something like a $15 billion mission, spending $500 million on getting the energy system right, is perfectly reasonable. We could get as low as 3Kws per Kg...which I would estimate would mean about 70 Kgs to achieve the 100KwE constant recommend by MIT for a 6 person mission. But even if it were ten times that - 700 kgs - that would still be very cost-effective in the context of a Mars mission.

Antius wrote:

The conclusions are that at the most favourable location on Mars (31 degrees North), the assumed PV system would approximately match an SP-100 based nuclear power system in terms of time-averaged power-to-weight, provided the mission is capable of tolerating some amount of intermittency in its power supply.

I looked into the location issue...there isn't really much difference between the low 20 degrees and 31 degrees in terms of output.

Antius wrote:

The concept is not new. The study references a previous design study carried out in the 1980s. In the 30 years since, the technology for printing thin films onto flexible substrates has only recently been demonstrated at laboratory level, but is still far from commercialisation. About an inch square of the material has so far been produced by MIT (early 2017) and it is not yet known if large scale production is even possible at this point. The response of the PV printed surface to abrasion and radiation damage is not known at this point.

I think we have to be careful not to confuse commercial viability on Earth and mission viability on Mars. If we had to lay 25,000 metres and pay $50,000 for every square metre, that would only be $1.25 billion out of a mission cost of $15 billion (and it would be delivering savings on other aspects - initial tonnage launch, whether we are talking about conventional solar or nuclear power). I am not suggesting it will cost that much, but I expect full development will be in the hundreds of millions of dollars range.

Antius wrote:

Thin-film technologies already exist, but typically do not achieve superior power-weight to ordinary cells because glass covers are needed to protect the fragile PV films from abrasion and radiation damage. This mission scenario is banking on the PV films maintaining performance long enough to complete the mission. In the real work, flexible thin-film solar panels have been produced and have area specific mass of 2-4kg/m2, almost two orders of magnitude greater than that assumed in the MIT study.

The Mars weather environment is in many respects extremely benign. Even the highest speed winds have little force compared with on Earth. If you really could get down to 70 Kgs for 25,000 sq. metres, then there would be no reason not to pack 5 replacement systems for your mission.

Antius wrote:

To achieve high power-weight, the mission design includes a regenerative fuel cell high along with 200-bar storage tanks, to cover stay-alive power requirements for the hab (10KWe). One of Louis’s objections to relying upon a single nuclear reactor was the potential for such a reactor to go offline, leaving the crew without stay-alive power. This is a concern for any system and power supply reliability should certainly have a bearing on mission architecture. However, it is difficult to make the case that a regenerative fuel cell with its numerous pumps, compressors, polymer/ceramic membranes, valves, etc. represents a more reliable power supply than a liquid metal cooled nuclear reactor. In the latter case, pumping may be achieved with MHD pumps or even natural convection, neither of which requires moving parts. Likewise, the sterling engine power conversion units are chosen specifically for their high reliability – they are mechanically simple components with only a few moving parts. The mission architects appear to realise this and present a number of possible power supply architectures, including solar with lithium ion storage, which somewhat degrades power-weight; and hybrid option, which uses a radio-isotope RTG to provide stay-alive power in the event of solar power system failure.

I was citing the MIT study as an example of how one might construct a PV based power system. I wouldn't say it was my approach.

I have long favoured methane/oxygen production. The point about that is that it can be begun years in advance of humans landing with pre-landed automated machines. When humans arrive they have a ready made alternative power source. I am not averse to use of small RTGs as well as back up. We will of course also have chemical batteries in place which will provide bridging power over several sols or more in event of power failures.

We should also investigate use of ULW solar reflectors to improve the efficiency of the PV systems.

Antius wrote:

The acceptability of the system is dependent upon the ability of the mission to tolerate an intermittent power supply. Whilst it is possible to include energy storage systems to cover essential stay-alive power requirements for the hab, the architects appear to have decided that providing sufficient storage to maintain a flat diurnal power profile would require an unacceptable increase in power system total mass. This is not surprising; as such an effort would require some 1600KWh storage capacity for a 100KW continuous power supply, which would add some 6.4 tonnes to power supply mass budget if provided by regenerative fuel cells and 10.67 tonnes if Li-ion battery storage is used. What is more, storing such a large proportion of power would greatly increase the area of solar panels required, due to storage losses. The electrolysis + fuel-cell energy storage system is at best 50% efficient, maybe lower when pumping and compression losses are accounted for. Designing a system with flat power profile would therefore at least double the area of solar panels needed. In the case of Li-ion battery storage, the increase would be less dramatic, perhaps a 30-40% increase. But the storage system is heavier to begin with. By my calculations, using the authors assumptions to provide a system with flat diurnal power profile at the optimum location (31 degrees North) reduces effective system power-weight to ~10W/kg. This is only about half that of an SP-100 sterling power system doing the same job, but might still be tolerable at this location if it averts political / development difficulties of the SP-100.

I didn't see the MIT crew mention a pre-landing scenario. For me this has always been key. By the time humans arrive there will be a fail safe power supply ensuring life support for the whole mission period, even if there were a coterminous dust storm reducing power output by 90% (likelihood? - at the very most extreme end of probability). I accept that in that extreme scenario nuclear has the edge as you can do a lot more. But any mission plan has to assume a more benign environment at best...for instance you still want to go exploring but you can't do that with your nuclear reactor and less you put it in a Rover which creates a whole lot of other problems.

Antius wrote:

Providing a flat power profile (non-intermittent) is important, because without it, energy hungry equipment such as propellant manufacturing effectively lay dormant for most of the day. The energy produced by a flat non-tracking array is effectively a sine function, reaching zero when the sun is at the horizon and reaching a maximum at noon. Even during the day, the power requirements of propellant production will be out of sync with the array output, with the array providing either too little power or too much. As the 100KWe average power system will produce the majority of its power over just 25% of the Martian day, this suggests that the propellant production facility must either be scaled up 400% in its production capability or the mission must accept that the same plant will take ~4 times as long to produce the same amount of propellant.

I don't think that follows really unless the vast majority of your power is being used to produce propellant. I am not a great fan of making propellant on Mars at an early stage.

Another way of looking at it is that nuclear cannot give you that mid-sol oomph you might want to conduct industrial experiments like smelting.

Antius wrote:

The study is based upon an optimum location on the Martian surface (31 degrees North). This is the region that achieves high annual insolation levels and the least seasonal variance of solar incidence. With tracking arrays, solar incidence varies by +/- 10% from year average over the course of a Martian year. For locations at different latitude, performance of the system drops off rapidly. At 30 degrees south for example, mass specific power is about 70% that of the equivalent northern location. At 60 degrees North & South, it drops to just 5W/Kg. None of these estimates account for the extra mass required to produce a non-intermittent power supply, which would reduce mass specific power even further. The authors conclude that for missions to latitudes substantially away from 30 degrees North (i.e. for global access) nuclear fission power supplies are required.

For Mission One, I think I would accept that. But it's irrelevant. Given there is little variation between the low 20s north and 31 north, that is still a huge, huge area you can choose from on the planet.

Antius wrote:

The system requires substantial deployment time - 132 man-hours of EVA for the 100KWe system that was modelled. Perhaps twice that, if a base load power supply is needed with substantial storage. This is a problem, as it suggests that propellant production can only start after the crew have arrived.

If you really want propellant production, it could start 6 years before any humans land. But as explained, I don't think that is a top priority, if we assume a Space X style Red Dragon capability (it's completely irrelevant if you assume a Space X ITS capability which can land 450 tonnes!).

Antius wrote:

It is not clear what assumptions the study authors used when estimating the total mass of the panels. Their assumption appears to be that solar array panels can be produced with constant area mass of 0.07kg/m2, which is consistent with a 67 micron thick polymer film. However, real solar panels tend to discharge current at very low voltages, typically less than 1V for single cells, which are stacked in series to produce a 12V output. This can be done without excessive resistance losses because the cell aluminium backing and surface conductors are relatively thick, which reduces internal resistance. However, for very thin cells, internal resistance losses would be too high for significant numbers to be put in series. The discharge voltage would be low and thick conductors would be needed to carry current to an inverter-transformer to step up the voltage. Given the size of the intended collection area – 25,000m2, it is likely that a large number of inverter-transformer units would be needed, perhaps one for every few square metres of solar array. I do not know how small or compact these units could be made, but it is difficult to imagine that the mass of the whole system would remain as low as 0.07kg/m2.

I would agree with that...that is something I wondered about (in a less specifically technical way)...they seemed to be underestimating the amount of associated equipment and cabling...the bigger the area, the more cabling you would need I would have thought. When discussing their proposal I have tended to throw in a load of extra tonnage for all the associated equipment. I think on the basis of their estimate, I suggested a figure of 4 tonnes might be reasonable.

Antius wrote:

The study is based upon the requirements for short-term surface missions, i.e. Mars Direct style missions. This negates concerns over the long-term survival of power systems. For the longer term requirements of a Martian base, the long term performance of a power system becomes more important. If radiation damage and abrasion result in rapid declines in system performance over a period of just a few years, the impact on power supply economics could be severe. For short-term missions, we are interested in base-load KW delivered per kg of power supply mass. For a base, we are just as interested in total KWh delivered per kg of power supply delivered to the surface. A liquid metal cooled nuclear reactor can deliver a flat power profile for a decade or more. It is not clear that these ultra-thin solar cells can do this when exposed to the high UV environment on the Martian surface.

Full consideration of these issues will simply replay the nuclear v PV debate. I concede that nuclear power is quite attractive in the very early stages because it appears to offer an energy guarantee (so long as you take along at least two reactors). But it is v. inflexible. The likelihood is that any supposedly "nuclear" mission is going to start packing some PV as well. Beyond the first couple of missions, I genuinely believe that nuclear is not the right answer to Mars's energy needs. I think that we will develop solar reflector with steam (or CO2) turbine technology and possibly biofuels early on to provide a guaranteed energy supply (always using methane as a back up). There's no way a Mars community of 20 will be knocking out nuclear reactors but they could quite easily be producing solar reflectors, steam engines and bio fuels.

Antius wrote:

It is an accepted fact that long-term human habitation of Mars must rely upon the use of native materials for whatever commodities human settlers may need. As all consumables on Mars must be manufactured (including air to breath) and low temperatures may necessitate energy intensive forms of agriculture (in particular, artificial light for crop growth) living on Mars will be energy intensive. The prosperity of the average Martian will depend upon cheap energy. A key input to the production cost of energy here on Earth is ‘Energy Return on Investment’ (EROI). This is the ratio between energy produced by a power plant over its lifetime, to the energy invested to produce the plant, mine its fuel and maintain it, etc. This is not a big issue for power systems provided for Mars Direct style missions, as the total size of the systems is small and the costs of manufacturing them are a small part of the total mission cost. If we are talking about power supply for a Martian town or city, the energy burden of manufacturing the power supply begins to grow significant, even if it is produced on Earth. If it is manufactured on Mars from local materials, a low EROI becomes especially burdensome and will substantially push up the local cost of power. Renewable energy systems tend to have low EROI, especially if energy storage is factored in to the calculation. This is reflected in high capital costs for these systems. For solar power, EROI is typically 2-10, depending on the technology used and this drops further when the energy costs and losses from storage are included. For fossil fuels on Earth, EROI varies between 20 and 80, depending upon the specific fuel. For nuclear power with centrifuge enriched PWR plants, EROI is about 100. I do not know what the EROI of the thin-film PV modules is; it may be much better than traditional solar, but historical experience suggests that this could be a problem if this technology must be mass produced on Mars as the dominant source of power to a growing settlement.

"The prosperity of the average Martian will depend upon cheap energy." That's where you went wrong I think. In the early settlement, nothing will be "cheap". I think the EROI is misleading. The EROI on a nuclear power plant manufactured on Earth to Mars-compliant spec and then imported from Earth to Mars is less than zero - much less.

The EROI concept is not very instructive. We could if we wished, even on Earth, build a solar plant in the desert that then powered diggers that dug up sand and powered factories to purify the sand dug up into silicon and make PV panels and then start again...your EROI would rapidly begin to approach infinity. It's just ignoring things like humans, land values, practical products and so on.

Antius wrote:

My conclusion to the assessment is that thin-film solar power is an interesting technology that may contribute to a future mission power supply. However, it would be premature to assume that nuclear fission is not needed for future mission architectures. Looking at the space solar power systems that we have available today, which have area specific mass of ~1kg/m2, a 100KW base-load power system for Mars at 31 degrees North, would weigh some 57 tonnes and mass specific power would be 1.8W/kg. This is about an order of magnitude heavier than an SP-100 Stirling system and the situation would be worse at less optimal locations.

My conclusion is that:

(a) You have ignored the potential of a pre-landing PV based energy storage. This could deliver large quantities of energy available to humans on landing. This could be available on Sol One of Mission One. It is not clear nuclear power would be available on Sol One of Mission One.

(b) Thin-film solar technology has not been developed as effectively as it might because it doesn't make much economic sense on Earth. This is one of the reasons why space projects are good because they oblige us to work hard in these neglected areas. My opinion is that if we throw $500million at the problem in a co-ordinated, Apollo-style way then we will be able to make use of a light weight PV technology on Mars. I doubt it's going to come in at 3 watts a gram...but even 3 watts per 10 grams would be fantastic.

(c) Nuclear power offers the illusion of security but it is v. inflexible. We would need at least two reactors to be built and delivered to Mars to ensure fail-safe energy but would likely still require supplementary PV and chemical batteries (so probably about 8 tonnes in total??) . The system has not been built as far as I know and would require much development and testing before being used on Mars.

(d) Nuclear is definitely not the future of Mars. A small Mars settlement won't be able to build nuclear reactors. They will build solar reflectors and steam (or CO2 vapour) engines and before long their own PV panels (this might be quite simple if 3D printing of solar panels is developed as seems likely).

Antius · 2017-05-12 06:55:46

Take a look at this reference, in particular the cross-section of the conceptual solar cell:

https://infoscience.epfl.ch/record/1338 … er_329.pdf

It is less than 60microns thick. The silicon film is 0.39 microns thick. At this thickness, the breakdown voltage of silicon is only 11.7 volts. This is a problem, because resistance losses build up rapidly at such low voltages, even in thick conductors. Notice also that the aluminium backing plate is only 1 micron thick. That represents a lot of internal resistance and a big voltage drop over even a relatively small cell.

My impression is that much of the excitement generated so far have been based on the high power-weight of individual cells. Some engineers have extrapolated this to whole solar power systems, possibly without understanding the limitations that such systems need to deal with.

At voltages of 10V, each cell would need to be small and fit into a lattice of aluminium, which is in turn connected to thick aluminium conductors carrying power to the inverter. That implies a lot of extra weight. The cells would need to be sunken into the aluminium lattice. One could reduce the need for an aluminium lattice and power transmission cables by thickening the silicon sandwich (allowing voltage to increase) and increasing the thickness of the aluminium backing plate (increasing current capacity). But again, that increases cell mass. Either way, the twin issues of breakdown voltage of the silicon wafer and resistance losses in the metallic backing plate and silver atop the cell, place fundamental limitations on how thin a practical cell can be. It isn't clear that the authors of the study understand this problem.

Last edited by Antius (2017-05-12 07:27:56)

Antius · 2017-05-12 07:53:50

'"The prosperity of the average Martian will depend upon cheap energy." That's where you went wrong I think. In the early settlement, nothing will be "cheap". I think the EROI is misleading. The EROI on a nuclear power plant manufactured on Earth to Mars-compliant spec and then imported from Earth to Mars is less than zero - much less.

The EROI concept is not very instructive. We could if we wished, even on Earth, build a solar plant in the desert that then powered diggers that dug up sand and powered factories to purify the sand dug up into silicon and make PV panels and then start again...your EROI would rapidly begin to approach infinity. smile It's just ignoring things like humans, land values, practical products and so on.'

Louis, EROI is key to the cost effectiveness of power sources here on Earth and will be when we try to build anything on Mars. Do you really think that it is an accident that high EROI energy sources, such as coal, oil, gas, hydro, nuclear here on Earth, were exploited on an industrial scale long before low EROI energy sources such as wind, solar PV, tide, wave, etc? The critical problem with the these energy sources is low power density and that translates into a lot more infrastructure needed to do the same job. These problems have to do with the laws of physics, they are not a function of technology. Producing thin-film solar cells here on Earth, is an attempt at getting around the problem by reducing energy inputs into the manufacturing process. But the problem remains.

A small settlement won't be manufacturing much of anything. But in terms of a colony, as numbers do start to increase towards thousands, it will no longer be affordable to support that many people with imports from Earth. High value imports are different, because you have some hope of paying for them. We may for example be able to afford to import high burn up nuclear fuel and core barrels from Earth if the more massive power conversion systems can be made on Mars. If 3D printers are as good as you say they are, I don't see why that won't be possible. Nuclear reactors are boilers after all.

In terms of the energy requirements of Mars colonisation, do you seriously believe that they won't be even higher per capita than they are here on Earth? On a planet where we need to manufacture breathable air and provide steel pressure domes to keep it from disappearing? A planet where it is difficult to grow food without artificial light?

Last edited by Antius (2017-05-12 08:02:09)

GW Johnson · 2017-05-12 16:45:20

I still contend the arguments here derive from the disparity between what an exploration mission needs and does, versus what a base-building mission needs and does, versus what a colony-building mission needs and does. Until that disparity is clarified, pointless arguments will continue. As pointless as angels-on-the-head-of-a-pin.

There is a tad of overlap: during the exploration mission, you need to try out as many as possible of the technologies and equipment items that the base-building mission will need. You do not have to do this at full scale, and you'd best not bet your exploration crew's lives on these things, because Murphy's Law says at least some of these items will fail.

There is more overlap: you simply cannot start a colony from the very first landing, yo start it after a base has sustained itself for a while. Too much is unknown until you have actually "been there and done that" at both stages. The scale and needs of exploration versus base-building versus colony-building colony-building are multiple factors of 10 different.

Better to explore properly at very small scale and set up the base-building mission. Then the base-building mission proves out the necessary technologies at base scale. Once that is done, you scale them up and start building your colony. Each is going to require shipments of one or another amount of stuff from Earth to get going, no way around that.

Don't bite off any more than you can chew in any one step. That's my advice.

That advice is from an old guy who learned very much more from the school of hard knocks, than any other school. An old guy with a BS, an MS, and a doctorate in engineering. Who spent 20 years in aerospace defense work doing things never done before, and has dabbled in it ever since.

I suspect that at least some that wisdom and experience applies to Mars missions.

GW

Last edited by GW Johnson (2017-05-12 16:51:33)

Oldfart1939 · 2017-05-12 16:52:32

GW Johnson wrote:

I still contend the arguments here derive from the disparity between what an exploration mission needs and does, versus what a base-building mission needs and does, versus what a colony-building mission needs and does. Until that disparity is clarified, pointless arguments will continue. As pointless as angels-on-the-head-of-a-pin.
There is a tad of overlap: during the exploration mission, you need to try out as many as possible of the technologies and equipment items that the base-building mission will need. You do not have to do this at full scale, and you'd best not bet your exploration crew's lives on these things, because Murphy's Law says at least some of these items will fail.
There is more overlap: you simply cannot start a colony from the very first landing, yo start it after a base has sustained itself for a while. Too much is unknown until you have actually "been there and done that" at both stages. The scale and needs of exploration versus base-building versus colony-building colony-building are multiple factors of 10 different.
Better to explore properly at very small scale and set up the base-building mission. Then the base-building mission proves out the necessary technologies at base scale. Once that is done, you scale them up and start building your colony. Each is going to require shipments of one or another amount of stuff from Earth to get going, no way around that.
Don't bite off any more than you can chew in any one step. That's my advice.
That advice is from an old guy who learned very much more from the school of hard knocks, than any other school. An old guy with a BS, an MS, and a doctorate in engineering. Who spent 20 years in defense working doing things never done before, and has dabbled in it ever since.
I suspect that at least some that wisdom and experience applies to Mars missions.
GW

Words of true wisdom!

It's pretty easy to get ahead of the learning curve in aspirations. But, since Murphy has been invoked, remember that MURPHY WAS AN OPTIMIST!

SpaceNut · 2017-05-12 17:57:33

GW Johnson wrote:

I still contend the arguments here derive from the disparity between what an exploration mission needs and does, versus what a base-building mission needs and does, versus what a colony-building mission needs and does. Until that disparity is clarified, pointless arguments will continue.

Murphy says we are trying to run before we can walk but due to mars long duration mission we are forced to question how long is long enough in each phase of Mars before we loss interest on the one that we are on or mission being done within the mission cycle.

GW Johnson wrote:

There is more overlap: you simply cannot start a colony from the very first landing, you start it after a base has sustained itself for a while. Too much is unknown until you have actually "been there and done that" at both stages. The scale and needs of exploration versus base-building versus colony-building colony-building are multiple factors of 10 different.

What really makes it a base? Mission overlap at the beginning is just one of the reasons that mars is cancelled really quickly as no one is staying to keep a landing site going.

As for colony building it not only is about more people being there and staying its about useable real estate to which man can use to sustain those that are staying behind...

GW Johnson wrote:

Better to explore properly at very small scale and set up the base-building mission. Then the base-building mission proves out the necessary technologies at base scale. Once that is done, you scale them up and start building your colony. Each is going to require shipments of one or another amount of stuff from Earth to get going, no way around that.

The moons missions were small scale as they were time limited mars even when walking due to the duration will not be small...

louis · 2017-05-12 18:28:05

I have some disagreements with some of what you say there GW!

1. The arguments may be pointless in the sense that we don't (most of us) have any influence over the decisions to be taken, but I think the arguments are highly relevant. What is done at an early stage will determine the rest of Mars's history. Look at the USA's history - the decision was taken in the 17th century to turn to slavery to solve the manpower problem...no turning back from the consequences of that. Likewise, it is a big decision to go nuclear - with all that means for centralisation of control, monitoring and so on.

2. Murphy's law applies to both nuclear and PV - and any other power source.

3. It's not clear why an exploration mission per se is necessary. It may desirable but we will know well before humans land, what conditions obtain in the landing area and we will have a very good idea of resources available in the surrounding area. The humans can direct robot diggers from their base. Of course it will be irresistible to have an EVA for geologists to get up close to the ground. But it won't be strictly necessary.

4. In my view the colony does start with the first landing of humans on Mars. That's the starting point. They will be growing food (not meeting all their needs, but perhaps something like 3% of their nutritional needs). They will be gathering resources e.g. iron ore. They will be beginning experiments in industrial processing and construction. They will be 3D printing. A colony is simply a continuous settlement, it doesn't require permanent residents, just permanent residence. I am not sure we disagree in reality, this is perhaps more a semantic point, but in terms of explaining the mission to humanity on Earth, I think it is important this is differentiated from a flags and footprints mission.

5. I do however agree we shouldn't bite off more than we can chew...which is why I would rule out attempting to produce all the food requirements or undertaken long distance human exploration or trying to produce rocket propellant for return craft.

GW Johnson wrote:

I still contend the arguments here derive from the disparity between what an exploration mission needs and does, versus what a base-building mission needs and does, versus what a colony-building mission needs and does. Until that disparity is clarified, pointless arguments will continue. As pointless as angels-on-the-head-of-a-pin.
There is a tad of overlap: during the exploration mission, you need to try out as many as possible of the technologies and equipment items that the base-building mission will need. You do not have to do this at full scale, and you'd best not bet your exploration crew's lives on these things, because Murphy's Law says at least some of these items will fail.
There is more overlap: you simply cannot start a colony from the very first landing, yo start it after a base has sustained itself for a while. Too much is unknown until you have actually "been there and done that" at both stages. The scale and needs of exploration versus base-building versus colony-building colony-building are multiple factors of 10 different.
Better to explore properly at very small scale and set up the base-building mission. Then the base-building mission proves out the necessary technologies at base scale. Once that is done, you scale them up and start building your colony. Each is going to require shipments of one or another amount of stuff from Earth to get going, no way around that.
Don't bite off any more than you can chew in any one step. That's my advice.
That advice is from an old guy who learned very much more from the school of hard knocks, than any other school. An old guy with a BS, an MS, and a doctorate in engineering. Who spent 20 years in aerospace defense work doing things never done before, and has dabbled in it ever since.
I suspect that at least some that wisdom and experience applies to Mars missions.
GW

louis · 2017-05-12 18:33:56

Yes, I am more in sympathy with your viewpoint SpaceNut.

The nature of a Mars mission requires us to do a lot of stuff in terms of life support, technical maintenance and so on. The mission will be more likely to be uccessful if we plan for a wide range of capabilities e.g. robot rovers, automated atmospheric extraction of water, production of methane, and a small element of food production. Mission One will last about 700 days - that's a lot of time on our hands if we don't do something. With a crew of 6 that's 4200 person days...a lot of work time. We can accomplish much with the help of robots, 3D printers and automated processes.

SpaceNut wrote:

GW Johnson wrote:
I still contend the arguments here derive from the disparity between what an exploration mission needs and does, versus what a base-building mission needs and does, versus what a colony-building mission needs and does. Until that disparity is clarified, pointless arguments will continue.
Murphy says we are trying to run before we can walk but due to mars long duration mission we are forced to question how long is long enough in each phase of Mars before we loss interest on the one that we are on or mission being done within the mission cycle.
GW Johnson wrote:
There is more overlap: you simply cannot start a colony from the very first landing, you start it after a base has sustained itself for a while. Too much is unknown until you have actually "been there and done that" at both stages. The scale and needs of exploration versus base-building versus colony-building colony-building are multiple factors of 10 different.
What really makes it a base? Mission overlap at the beginning is just one of the reasons that mars is cancelled really quickly as no one is staying to keep a landing site going.
As for colony building it not only is about more people being there and staying its about useable real estate to which man can use to sustain those that are staying behind...
GW Johnson wrote:
Better to explore properly at very small scale and set up the base-building mission. Then the base-building mission proves out the necessary technologies at base scale. Once that is done, you scale them up and start building your colony. Each is going to require shipments of one or another amount of stuff from Earth to get going, no way around that.
The moons missions were small scale as they were time limited mars even when walking due to the duration will not be small...

louis · 2017-05-14 18:31:43

Antius,

I don't think EROI is as useful as you claim. It is almost a truth by definition. We wouldn't pursue agriculture if it led to us expending more calories in harvesting that we gained in food. Clearly there has to be an energy surplus, but in as much as it's true, it isn't very helpful.
We've got loads of coal in the UK, but we've given up on digging it out of the ground. The chief reason we've given up is not because the coal is any less energy rich or requires more energy now to be extracted (far from it, compared with 100 years ago). But humans in the UK demand better remuneration, and we have to expend a lot of time and effort on health and safety. So we get Chinese peasants to dig it out in China, or blast it in open cast mines in Australia.

I don't accept that "A small settlement won't be manufacturing much of anything." This is really a prejudice that comes from Earth-based thinking, where there is no real (economic) reason to manufacture on a small scale. But on Mars there is every reason to manufacture on a small scale, to avoid the costs of importation of mass and to speed up the creation of a successful settlement. We'll be spending billions on getting humans there...why wouldn't you spend hundreds of millions on providing them with the wherewithal to create a small scale industrial infrastructure that enables them in short order to manfacture tools, utensils, machines, batteries, electrolysis units, electrical circuits, rocket fuel, basic rockets, rovers, bricks, steel items ,clothes, furniture, white goods, plumbing, photovoltaic panels, solar reflectors and so on?

In the context of a colonisation effort that will cost maybe £50 billion over 30 years, whether the energy system costs £500 million or £750 million is not very relevant. What is relevant, is ensuring that it is the right energy system and that humans on Mars can manufacture their own energy systems within a few years.

I am not saying that per capita energy usage will be less than on Earth, on average, but I am saying that it is probably the easiest thing to get right. Per capita energy usage will be high certainly to begin with, especially as we will initially be relying on indoor agriculture. Life support is demanding of energy, but on the other hand, the early settlers won't be driving private cars hundreds of miles, going on holiday, fitting out their homes with energy intensive products, using paper or watching mega size TVs.

Eventually the need for water recycling will be reduced as we locate copious supplies of water, we may find natural sources of methane on Mars, so we don't have to manufacture it, we will learn how to farm on Mars without artificial lighting systems (though perhaps with solar reflectors), and oxygen will be produced as a by product of farming and various industrial processes. The Mars-specific factors in high energy usage will have been much reduced.

But I have no doubt that the early colonists will after 10 years or so be able to fully meet their own energy needs through solar-driven turbines, manufacture of PV panels and manufacture of methane.

Antius wrote:

'"The prosperity of the average Martian will depend upon cheap energy." That's where you went wrong I think. In the early settlement, nothing will be "cheap". I think the EROI is misleading. The EROI on a nuclear power plant manufactured on Earth to Mars-compliant spec and then imported from Earth to Mars is less than zero - much less.
The EROI concept is not very instructive. We could if we wished, even on Earth, build a solar plant in the desert that then powered diggers that dug up sand and powered factories to purify the sand dug up into silicon and make PV panels and then start again...your EROI would rapidly begin to approach infinity. smile It's just ignoring things like humans, land values, practical products and so on.'

Louis, EROI is key to the cost effectiveness of power sources here on Earth and will be when we try to build anything on Mars. Do you really think that it is an accident that high EROI energy sources, such as coal, oil, gas, hydro, nuclear here on Earth, were exploited on an industrial scale long before low EROI energy sources such as wind, solar PV, tide, wave, etc? The critical problem with the these energy sources is low power density and that translates into a lot more infrastructure needed to do the same job. These problems have to do with the laws of physics, they are not a function of technology. Producing thin-film solar cells here on Earth, is an attempt at getting around the problem by reducing energy inputs into the manufacturing process. But the problem remains.
A small settlement won't be manufacturing much of anything. But in terms of a colony, as numbers do start to increase towards thousands, it will no longer be affordable to support that many people with imports from Earth. High value imports are different, because you have some hope of paying for them. We may for example be able to afford to import high burn up nuclear fuel and core barrels from Earth if the more massive power conversion systems can be made on Mars. If 3D printers are as good as you say they are, I don't see why that won't be possible. Nuclear reactors are boilers after all.
In terms of the energy requirements of Mars colonisation, do you seriously believe that they won't be even higher per capita than they are here on Earth? On a planet where we need to manufacture breathable air and provide steel pressure domes to keep it from disappearing? A planet where it is difficult to grow food without artificial light?

Last edited by louis (2017-05-14 18:33:50)

louis · 2017-05-16 05:30:01

http://www.nextbigfuture.com/2015/09/na … power.html

I think this sort of system could be used for automatic deployment in a pre-landing scenario where we need PV power to produce water, methane, CO, oxygen and other gases from the atmosphere.

This would be a high efficiency system. Probably 500 Kgs of solar array would be enough to do the job.

Antius · 2017-05-22 04:02:54

Louis, apologies for the late reply. I am going to stick purely with the topic of EROI in this post and take up other points later on.

For any human economic activity, basically anything that requires the processing or manipulation of matter, energy is a non-substitutable input. The relationship between economic production and energy use is so tight that the GDP of a country is basically a measure of the amount of work being carried out in that country – by definition, the amount of refined energy brought to bear on tasks that are valuable to human beings. Improving efficiency can reduce primary energy inputs, but this is achieved by improving the conversion of primary fuels into useful work – something that obviously has impassable limits – not a reduction in the amount of work being carried out. Many countries have shown declining trends of GDP vs primary energy, because they have gradually substituted higher grade fuels for lower grade fuels. The relationship between GDP and electricity use is basically a straight line, because electricity is close to 100% efficient in producing mechanical work. Take a look at the following graphs to see how important this relationship is. Notice that the relationship is particularly tight for electricity:

For the world (electricity): http://notrickszone.com/wp-content/uplo … Caryl1.gif

For world regions (electricity): http://www.ourenergypolicy.org/wp-conte … 3/02/4.png

World energy consumption vs GDP: https://gailtheactuary.files.wordpress. … al-gdp.png

Here is an excellent article on the topic from Euan Mearns’ website: http://euanmearns.com/electricity-and-t … f-nations/

This is not well understood in political circles. It has become popular amongst left-wing elites to talk about decoupling the link between rising energy consumption and economic activity. This is clearly impossible, because less energy means less work and less GDP by definition.

Back onto the topic of EROI (Energy Return on Investment). This is a ratio between the amounts of energy invested to produce and maintain a means of energy production, against the amount of energy provided over its useful life. One of the difficulties with calculating EROI is defining system boundaries, i.e. where does one stop with the analysis. For example, most people would agree that the energy needed to manufacture the steel and concrete that goes into a power plant should be part of an EROI calculation. But, what about the energy people use to drive to work? What about the energy needed to build the road leading to the power plant? The energy used in every step of building all of the many components in a power plant should be part of the EROI calculation, but can often only be estimated. One reaches the point where further investigation must be caveated with estimates. Perhaps most contentiously, what about the employees working in that industry? Since the employees do nothing else for the economy other than support that specific power industry, should the energy consumption of their lifestyles be factored in to the EROI calculation? In a holistic analysis they probably should.

Why is EROI important? Let’s use a simplistic model. Imagine the output of an energy system from an energy flow point of view. Let’s say that an energy system provides 100 units of energy output per year. With an EROI of 5, some 20% of that energy must be reinvested, say in maintaining the energy system. Out of an initial 100 units, there are now 80 remaining for other uses. A large share of what remains must go into running and maintaining essential systems for society. This is things like transport, food production, heating, etc. This is why electricity production beneath a certain threshold is associated with sharply declining living standards (see link below).

https://www.euronuclear.org/e-news/e-ne … -print.htm

Let’s say another 50 units are used to meet these basic needs. That leaves the final 30 units available for consumption of luxuries and investment in new capital. Here is where EROI gets interesting for several reasons.

1. Remember economic activity and energy consumption are tightly linked. Lower EROI energy sources require more investment in people power, maintenance and physical infrastructure. This makes their output more expensive financially, and as can be seen, there is less of it.

2. The smaller the energy surplus available after paying for the energy and meeting essential functions, the less energy is left other for other things, like luxury items, research and new investment in capital. The final item is essential if the colony / nation intends to expand living standards (economic growth) or expand carrying capacity (population).

3. If a nation / colony wishes to expand its carrying capacity, its ability to manufacture and its infrastructure generally, this will require both an energy investment in new infrastructure and new energy supply in order to meet the needs of the new people and new infrastructure. With a low EROI energy source, not only is there less energy available to invest in expanding the energy source, but the returns are lower.

Past human civilisations have tended to collapse, because the EROI of their energy sources (mainly food energy) declined and became too low to maintain the systems that they had in place. They could no longer maintain roads, buildings, armies to protect them, trade links, etc. This is becoming a severe problem for modern industrial societies. As the fossil fuel era has continued, the EROI of fossil fuel resources has declined progressively. Once abundant onshore conventional oil and gas resources are increasingly substituted by lower EROI resources as they deplete – such as deep offshore oil & gas, fractured shale oil, tar sands, etc. and renewable energy sources are increasingly used in the electricity sector. The reduced energy surplus is placing a severe strain on economies, as it is becoming difficult to maintain existing infrastructure whilst maintaining the investment needed for new economic growth. As a result, the wages of workers and ordinary people are being squeezed. The slowing of global economic growth, increasing income inequality and the continuing debt crisis are all symptomatic of this.

For a Mars colony, it is clearly important that high EROI native energy resources are developed. Not only must we maintain existing infrastructure keeping us alive, but we must also expand infrastructure sufficient to keep up with population growth. What is more, due to the extreme cost of importing materials and infrastructure from Earth, there is a strong need to manufacture as much as possible of what is needed using Martian resources. This increases energy requirements for a growing Martian base – energy requirements that will be high in the first place.

Renewable energy sources generally have low EROI, because the energy source is poor in power density and additional infrastructure is needed to deal with problems of intermittency. On Earth, an EROI of 7 is considered to be the limit of economic usability without subsidy. Hydropower generally has EROI far above that, because the energy density of flowing water is quite high, compared say to the energy density of moving air (i.e. wind power). It is therefore little surprise that hydropower is an established energy technology, and has been exploited to its limits in most places, whereas wind power has struggled to gain market share without subsidy.

Last edited by Antius (2017-05-22 04:33:35)

Oldfart1939 · 2017-05-22 09:15:29

On most of these threads, we seem to be co-mingling 2 different scenarios; long term development, and the immediate short term needs of the first few exploratory missions. I have to discriminate between the two in order to make any sense whatever of some of these concepts. I'm hearkening back to the "Old Original Mars Direct Plan," that was postulated some 29 years ago, and the immediate power required MUST be supplied by the most easily initiated system., without need of several advance landings by robotically operated solar array dispersion systems. Nuclear. For the first several landings on Mars, the explorer-pioneers will not be spending time trying to be green on the red planet. There is far too much to accomplish.

As time passes and more bodies arrive, there will be more available labor for such undertakings as building huge solar power farms. Using the EROI concept stated by Antius, nuclear will be overwhelmed by energy needs, if no ISRU can be developed for a sustainable supply of fissionable material. I seem to recall reading that Mars holds large quantities of Thorium, which, by the way, is my long term choice of nuclear power.

louis · 2017-05-22 11:24:41

Antius,

I think there are some rather misleading assertions in your reply, which I will deal with below.

1. GDP is not a reflection of work done. The Irish Republic has had a problem with it GDP figures as they are very misleading. Ireland has a low corporation tax and so lots of head offices are based in Dublin and profits flow through there (which get counted as part of GDP) but they hardly touch the ground, as it were...the money is not being invested in Ireland. Same goes for those countries more normally thought of as tax havens. Same goes for the UK - a finance centre where the amount of energy being used to generate profit is very small (basically just what you need to run all those trading computers in the City). Equally energy rich countries produce huge energy surpluses but don't put the energy to work, they export it. They receive huge payments for the energy but the amount of work done is relatively low. Germany uses hugely more electricity than the UK because it is a huge manufacturing nation.

2. Germany and Denmark are both relying more and more on (domestically produced) energy that is gives less return on investment than some hydrocarbons. Both countries are very successful manufacturers. Whereas countries like Saudi Arabia and Libya though rich in oil and gas are pretty useless at producing goods the rest of the world wants to buy. There's a paradox for you. There wonderful EROI advantage hasn't magically delivered a sophisticated industrial infrastructure.

3. I do not doubt that the EROI reflects some very basic truths but so do lots of other things...The need to overcome the effects of gravity is one such. The need to maintain revenue for any activity involving expenditure is another.

4. What sort of population level on Mars are you talking about? For the purposes of this discussion, I am thinking about maybe up to 1000 (at the end of maybe 20 years of settlement development). Could a colony of 500 make nuclear reactors? I doubt it. Even if they could from a technical point of view, it would be a dangerous undertaking which would require them to expend huge amounts of time and effort in ensuring health and safety. But could they make solar reflectors plus steam-driven or other electricty generating turbines? Answer yes, most definitely. Could they make their own PV Panels? Answer yes, as long as we ensure they have the material purification facilities in place. Your approach is condemning the Mars settlement to always be importing its energy source and it would displace other tonnage which would be much more useful e.g. 3D printing machines and other small scale manufacturing machines.

Antius wrote:

Louis, apologies for the late reply. I am going to stick purely with the topic of EROI in this post and take up other points later on.
For any human economic activity, basically anything that requires the processing or manipulation of matter, energy is a non-substitutable input. The relationship between economic production and energy use is so tight that the GDP of a country is basically a measure of the amount of work being carried out in that country – by definition, the amount of refined energy brought to bear on tasks that are valuable to human beings. Improving efficiency can reduce primary energy inputs, but this is achieved by improving the conversion of primary fuels into useful work – something that obviously has impassable limits – not a reduction in the amount of work being carried out. Many countries have shown declining trends of GDP vs primary energy, because they have gradually substituted higher grade fuels for lower grade fuels. The relationship between GDP and electricity use is basically a straight line, because electricity is close to 100% efficient in producing mechanical work. Take a look at the following graphs to see how important this relationship is. Notice that the relationship is particularly tight for electricity:
For the world (electricity): http://notrickszone.com/wp-content/uplo … Caryl1.gif
For world regions (electricity): http://www.ourenergypolicy.org/wp-conte … 3/02/4.png
World energy consumption vs GDP: https://gailtheactuary.files.wordpress. … al-gdp.png
Here is an excellent article on the topic from Euan Mearns’ website: http://euanmearns.com/electricity-and-t … f-nations/
This is not well understood in political circles. It has become popular amongst left-wing elites to talk about decoupling the link between rising energy consumption and economic activity. This is clearly impossible, because less energy means less work and less GDP by definition.
Back onto the topic of EROI (Energy Return on Investment). This is a ratio between the amounts of energy invested to produce and maintain a means of energy production, against the amount of energy provided over its useful life. One of the difficulties with calculating EROI is defining system boundaries, i.e. where does one stop with the analysis. For example, most people would agree that the energy needed to manufacture the steel and concrete that goes into a power plant should be part of an EROI calculation. But, what about the energy people use to drive to work? What about the energy needed to build the road leading to the power plant? The energy used in every step of building all of the many components in a power plant should be part of the EROI calculation, but can often only be estimated. One reaches the point where further investigation must be caveated with estimates. Perhaps most contentiously, what about the employees working in that industry? Since the employees do nothing else for the economy other than support that specific power industry, should the energy consumption of their lifestyles be factored in to the EROI calculation? In a holistic analysis they probably should.
Why is EROI important? Let’s use a simplistic model. Imagine the output of an energy system from an energy flow point of view. Let’s say that an energy system provides 100 units of energy output per year. With an EROI of 5, some 20% of that energy must be reinvested, say in maintaining the energy system. Out of an initial 100 units, there are now 80 remaining for other uses. A large share of what remains must go into running and maintaining essential systems for society. This is things like transport, food production, heating, etc. This is why electricity production beneath a certain threshold is associated with sharply declining living standards (see link below).
https://www.euronuclear.org/e-news/e-ne … -print.htm
Let’s say another 50 units are used to meet these basic needs. That leaves the final 30 units available for consumption of luxuries and investment in new capital. Here is where EROI gets interesting for several reasons.
1. Remember economic activity and energy consumption are tightly linked. Lower EROI energy sources require more investment in people power, maintenance and physical infrastructure. This makes their output more expensive financially, and as can be seen, there is less of it.
2. The smaller the energy surplus available after paying for the energy and meeting essential functions, the less energy is left other for other things, like luxury items, research and new investment in capital. The final item is essential if the colony / nation intends to expand living standards (economic growth) or expand carrying capacity (population).
3. If a nation / colony wishes to expand its carrying capacity, its ability to manufacture and its infrastructure generally, this will require both an energy investment in new infrastructure and new energy supply in order to meet the needs of the new people and new infrastructure. With a low EROI energy source, not only is there less energy available to invest in expanding the energy source, but the returns are lower.
Past human civilisations have tended to collapse, because the EROI of their energy sources (mainly food energy) declined and became too low to maintain the systems that they had in place. They could no longer maintain roads, buildings, armies to protect them, trade links, etc. This is becoming a severe problem for modern industrial societies. As the fossil fuel era has continued, the EROI of fossil fuel resources has declined progressively. Once abundant onshore conventional oil and gas resources are increasingly substituted by lower EROI resources as they deplete – such as deep offshore oil & gas, fractured shale oil, tar sands, etc. and renewable energy sources are increasingly used in the electricity sector. The reduced energy surplus is placing a severe strain on economies, as it is becoming difficult to maintain existing infrastructure whilst maintaining the investment needed for new economic growth. As a result, the wages of workers and ordinary people are being squeezed. The slowing of global economic growth, increasing income inequality and the continuing debt crisis are all symptomatic of this.
For a Mars colony, it is clearly important that high EROI native energy resources are developed. Not only must we maintain existing infrastructure keeping us alive, but we must also expand infrastructure sufficient to keep up with population growth. What is more, due to the extreme cost of importing materials and infrastructure from Earth, there is a strong need to manufacture as much as possible of what is needed using Martian resources. This increases energy requirements for a growing Martian base – energy requirements that will be high in the first place.
Renewable energy sources generally have low EROI, because the energy source is poor in power density and additional infrastructure is needed to deal with problems of intermittency. On Earth, an EROI of 7 is considered to be the limit of economic usability without subsidy. Hydropower generally has EROI far above that, because the energy density of flowing water is quite high, compared say to the energy density of moving air (i.e. wind power). It is therefore little surprise that hydropower is an established energy technology, and has been exploited to its limits in most places, whereas wind power has struggled to gain market share without subsidy.

louis · 2017-05-22 11:34:51

I always try to be specific about the timeframe and population. I agree it is very important to distinguish what period we are looking at.

As for Mission One...

To try and rule out pre-landing of supplies is absurd. Pre-landing has a number of advantages not least, in relation to energy, that you know it has been deployed successfully. When you are carrying your nuclear reactor to the surface, you have no idea whether all the training and design is going to pay off and you are going to have a successful deployment. When do you deploy BTW? In LMO prior to touch down, on touch down, at some point after touch down? How will it be deployed? Very importantly as well, do you rely entirely on one nuclear reactor to work? Or do you take two? Or do you take some other energy system with you? How is the nuclear reactor going to work with an exploration rover?

Medium term (first 20 years)...

As explained in my reply to Antius, a colony of 1000 would find it extremely difficult to safely manufacture nuclear reactors. But manufacture of solar reflector plus turbine and PV panels would be very much within their capability as long as we provide the right equipment.

Longer term (20-100 years)

Geothermal, solar power satellite (energy beamed to the surface), and methane capture will all be good energy sources from an EROI point of view. I doubt nuclear will get a look in.

Oldfart1939 wrote:

On most of these threads, we seem to be co-mingling 2 different scenarios; long term development, and the immediate short term needs of the first few exploratory missions. I have to discriminate between the two in order to make any sense whatever of some of these concepts. I'm hearkening back to the "Old Original Mars Direct Plan," that was postulated some 29 years ago, and the immediate power required MUST be supplied by the most easily initiated system., without need of several advance landings by robotically operated solar array dispersion systems. Nuclear. For the first several landings on Mars, the explorer-pioneers will not be spending time trying to be green on the red planet. There is far too much to accomplish.
As time passes and more bodies arrive, there will be more available labor for such undertakings as building huge solar power farms. Using the EROI concept stated by Antius, nuclear will be overwhelmed by energy needs, if no ISRU can be developed for a sustainable supply of fissionable material. I seem to recall reading that Mars holds large quantities of Thorium, which, by the way, is my long term choice of nuclear power.

kbd512 · 2017-05-22 13:57:47

For Mission 1, small nuclear reactors can be pre-packaged and pre-assembled into small units that only require emplacement in a crater and attachment of a power cable. That's the extent of what's required to bring the plant online. There is no requirement for multiple cargo landings with these types of fission reactors.

A colony of 1000 people will use something like 10MWe, so 2 to 3 of the 4MWe SAFE-400 evolutionary reactor designs. Mind you, these reactors are not much physically larger than SAFE-400, even if they weigh more. Just like SAFE-400, there's no requirement for anything more sophisticated than emplacement and attachment of power cables. Each reactor can be delivered with a single Falcon Heavy or whatever other heavy lift rockets are available at the time.

Providing multi-MW continuous power systems using solar power is more fantastic than small fission reactors assembled on Earth and shipped to Mars. Here on Earth, the power grid can tolerate use of resource-inefficient PV panels and wind farms because there's already so much fossil fuel and nuclear power infrastructure built to provide base power.

Long term, geothermal energy and beamed power are absurd substitutes for molten salt fission reactors, although solar concentrators using molten salts fall within the realm of feasibility. The only reason fission reactors, solar power, and wind farms exist is that plentiful and readily available fossil fuels were available to permit the development and use of more advanced power production technologies. We're starting with no fossil fuel infrastructure on Mars.

Solar farms large enough to see from orbit are not mass-viable replacements for a fission reactors the size of shipping containers or smaller, to say nothing of the non-existent grid scale battery technology required for electrical power storage.

Oldfart1939 · 2017-05-22 16:16:26

Louis-

I never stated there would be no pre human mission landings. I'd insist they contain something other than solar panels. Habitats. Food. And more FOOD. Moxie units, nuclear reactors. kbd512 did an excellent job of stating my thoughts re: the usefulness of yet-to-be-discovered geothermal power, and the absolute absurdity of the battery pack required for your solar dreams.

GW Johnson · 2017-05-22 16:35:19

Here's a notion I hope is resolved before men go to Mars, but WILL get resolved regardless shortly after, at some cost in lives, if not resolved properly before that first trip.

Some things work quite well as solar-powered items, especially if not needed at night, which reduces the battery size you need. It would be easier to just bring those devices than to string the power line from a nuke plant. And there's nothing wrong with that, as long as you can do without whatever-this-toy-is for the weeks- or months-long duration of a major Martian dust storm, such as the one that covered the entire planet for months in 1969 when our first orbiter (Mariner 9?) arrived.

There are other things that simply cannot be done that way, or else people die! You need these things night and day, and you need them regardless of whether the daytime sun is obscured or not. Solar simply cannot do that job, because the battery gets ridiculous very, very quickly. Thus, there is simply NO excuse not to rig those things to a nuke generator. Period. End of issue.

What that really means is you take a mix of both power supplies, each tailored to how critical continuous operation is.

So I suggest: accept reality. Just get on with it. Nuke and solar.

Otherwise, you might as well be arguing about how many angels can sit on the head of a pin.

GW

Last edited by GW Johnson (2017-05-22 16:40:39)

louis · 2017-05-22 17:04:44

Well I can't see why you would preclude an energy system from pre-landing.

Oldfart1939 wrote:

Louis-
I never stated there would be no pre human mission landings. I'd insist they contain something other than solar panels. Habitats. Food. And more FOOD. Moxie units, nuclear reactors. kbd512 did an excellent job of stating my thoughts re: the usefulness of yet-to-be-discovered geothermal power, and the absolute absurdity of the battery pack required for your solar dreams.

SpaceNut · 2017-05-22 17:47:13

Another part of the solar question has to do with the amount of energy required to keep the batteries from freezing. The next is to get the biggest bang for the mass as going with low effieciency cells at oe extreem and the highest level of efficiencey does not make for the best performance for the mass as its somewhere in the middle.

As for solar on a preloaded cargo delivery the AtK panels would fit that bill to keep the unit powered and systems working.

Once a crew is on the planet and using the contents of the cargo landers then repurposing the extra power for use is a leg up on that next delivery as we can keep doing the same until we need something much larger than what we can send.

louis · 2017-05-22 17:50:14

How small are these nuclear reactors? Have any ever been built? Or are you referring to RTGs? Has the Safe-400 actually been built (I can't find anything on the net suggesting it has) - so is this an untried design?

Electricity from solar can easily be stored in batteries. The reason it isn't done on Earth much is because it is an expensive option. The revenue cost of providing battery storage on Mars will be zero for Mission One. Cost doesn't come into it. Lithium batteries can store nearly 12Kwhs per Kg. So a tonne will give you 12000 KWhs. Power can also be stored as methane and overnight as hot water or heated bricks. The intermittent nature of solar power is a red herring in terms of judging the overall effectiveness of the system.

Not sure why you think nuclear reactors are such a great option longer term. At one of our major UK nuclear facilities, Sellafield, there are 10,000 people employed!!! That's how labour intensive a nuclear power industry is. A solar power satellite microwave beam system could be pretty much completely automated.

Geothermal works fantastically well in Iceland...so it if is a practical option on Mars, there's no reason to think it won't work well there.

It sounds to me like you are going to condemn the people of Mars to being dependent on energy imports from Earth for many years as there is no way that they will be able to manufacture nuclear power facilities.

Furthermore, given the absolute necessity of life support on Mars, if your nuclear reactor fails, the people die. Or are you going to invest in battery technology as well.

kbd512 wrote:

For Mission 1, small nuclear reactors can be pre-packaged and pre-assembled into small units that only require emplacement in a crater and attachment of a power cable. That's the extent of what's required to bring the plant online. There is no requirement for multiple cargo landings with these types of fission reactors.
A colony of 1000 people will use something like 10MWe, so 2 to 3 of the 4MWe SAFE-400 evolutionary reactor designs. Mind you, these reactors are not much physically larger than SAFE-400, even if they weigh more. Just like SAFE-400, there's no requirement for anything more sophisticated than emplacement and attachment of power cables. Each reactor can be delivered with a single Falcon Heavy or whatever other heavy lift rockets are available at the time.
Providing multi-MW continuous power systems using solar power is more fantastic than small fission reactors assembled on Earth and shipped to Mars. Here on Earth, the power grid can tolerate use of resource-inefficient PV panels and wind farms because there's already so much fossil fuel and nuclear power infrastructure built to provide base power.
Long term, geothermal energy and beamed power are absurd substitutes for molten salt fission reactors, although solar concentrators using molten salts fall within the realm of feasibility. The only reason fission reactors, solar power, and wind farms exist is that plentiful and readily available fossil fuels were available to permit the development and use of more advanced power production technologies. We're starting with no fossil fuel infrastructure on Mars.
Solar farms large enough to see from orbit are not mass-viable replacements for a fission reactors the size of shipping containers or smaller, to say nothing of the non-existent grid scale battery technology required for electrical power storage.

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