Energy Return on Energy Invested for Solar PV

kbd512 · 2024-04-04 09:40:00

Calliban,

He doesn't seem to understand that we're saying LCOE of wind and solar plus storage, which becomes a hard requirement for a 70% renewables grid, is far in excess of the cost of all other competing options. We're also stating that the EROEI of photovoltaic electronics are far too low, unless ideally located in a desert, which excludes most parts of the world where people actually live.

The way I can tell that the LCOE, whatever he thinks it is, is still far too high, is that the rates paid by consumers have doubled or tripled anywhere there is a lot of renewable energy on the grid. True cost is not so easy to hide. Someone must always pay the bill for the equipment and services provided, and the consumer is always "that person".

He thinks the argument is being shifted, despite the fact that he's the one that keeps going back to LCOE, as if it makes EROEI irrelevant, to avoid addressing the fact that the LCOE is too high and the EROEI is too low, all at the same time. He's using future LCOE projections, which cannot be used to construct a new energy system, in the here and now. He's saying EROEI doesn't matter or that the calculations are wrong.

This is what hard core "green energy denialism" looks like.

His only coherent line of argumentation is that both could change in dramatic ways in the future. That's always a possibility, but doesn't address the "here and now".

He seems to have bought into the idea of the future possibilities of wind and solar, because he has no coherent arguments about the "here and now", unless all data that doesn't show what he wants it to show is wrong / bad / lies. He called the charts I posted "FUD", because they came from a website that doesn't support his beliefs about energy, but then provided a link to a study a couple of posts later, which used the exact same numbers from the website I posted the charts from. It's ridiculous.

SpaceNut · 2024-04-04 10:03:12

The problem with location and energy source is subsidized cost deflation that changes all values unless only measure is watts.

Calliban · 2024-04-04 10:20:31

I had previously wondered if using different materials would increase the EROEI for PV. We could make panels out of concrete and put them on soil berms instead of steel frames? We could use aluminium instead of copper wiring. The EROEI calculation in post #1 gave me some insight into why this isn't done. Over 80% of embodied energy is in the polysilicon. So changing panel and support frame materials makes very little difference. It could easily be counterproductive if it results in higher panel wastage or exposes the panels to other problems that lower performance or reduce working life. The thing that wouod make the most difference to PV EROEI would be large reductions in the energy cost of the polysilicon. If polysilicon can get down to the same energy cost as aluminium, it would roughly triple powerplant EROEI. I think thin film also shows promise. Efficiency is lower, but energy cost per m2 is much lower.

Last edited by Calliban (2024-04-04 10:21:40)

Spaniard · 2024-04-04 10:30:39

kbd512 wrote:

Calliban,
He doesn't seem to understand that we're saying LCOE of wind and solar plus storage, which becomes a hard requirement for a 70% renewables grid, is far in excess of the cost of all other competing options. We're also stating that the EROEI of photovoltaic electronics are far too low, unless ideally located in a desert, which excludes most parts of the world where people actually live.

These are two different debates.

An overall LCOE is different than a LCOE value standalone. And an integrated costs depends a lot of what kind of configuration you can build.
As I said before, current storage is still non competitive. You can build a model with only wind+solar+storage+curtailment but it would be significantly more expensive than current values.

BUT there are multiple configurations and multiple promising storage technologies claiming prices that reduce that price dramatically. Not only through batteries, but also other technologies.

In the meantime, overall LCOE analysis (not specific PV LCOE) using current prices, points a mix of natural gas with renewables as the cheapest combination, at least when natural gas prices are contained, and that's the reason why we are adding more and more renewables to the mix.

That's the "here and now".

kbd512 wrote:

The way I can tell that the LCOE, whatever he thinks it is, is still far too high, is that the rates paid by consumers have doubled or tripled anywhere there is a lot of renewable energy on the grid. True cost is not so easy to hide. Someone must always pay the bill for the equipment and services provided, and the consumer is always "that person".
He thinks the argument is being shifted, despite the fact that he's the one that keeps going back to LCOE, as if it makes EROEI irrelevant, to avoid addressing the fact that the LCOE is too high and the EROEI is too low, all at the same time. He's using future LCOE projections, which cannot be used to construct a new energy system, in the here and now. He's saying EROEI doesn't matter or that the calculations are wrong.

You are shifting because you claimed that the EROEI low values come from the high energy costs of the PV panel , while the LCOE of the PV itself is cheap.

There is no need to calculate a EROEI of PV + STORAGE for a full 100% model, as already LCOE of that model says that it's non competitive so only heavily subsidized pilot plants are mostly installed. Sometimes just for frequency because the cost for peak plants and regular storage has two different prices.
Well... Now we are installing the firsts renewables+storage, but the data is still coming, as it's too recent. That's because cheap batteries are also just too recent and the price still fluctuates, not a clear goal that has been surpassed and can be taken for granted.

kbd512 wrote:

This is what hard core "green energy denialism" looks like.

That's how the "skeptic" movements works.

kbd512 wrote:

He seems to have bought into the idea of the future possibilities of wind and solar, because he has no coherent arguments about the "here and now", unless all data that doesn't show what he wants it to show is wrong / bad / lies. He called the charts I posted "FUD", because they came from a website that doesn't support his beliefs about energy, but then provided a link to a study a couple of posts later, which used the exact same numbers from the website I posted the charts from. It's ridiculous.

Not only my "beliefs". But also a bunch of links of a lot more trustworthy source that a guy that name itself as "The Fracking Guy" on twitter with values a lot higher than any common source.

Calliban · 2024-04-04 10:56:58

Off topic from PV, this wind power technology is interesting.
https://www.windpowerengineering.com/sh … t-florida/

It is a ducted wind power concept. Air blows into a funnel, where is it accelerated through a venturi before entering a turbine. The things that make it interesting are that the turbine is compact, without need for extended blades and can sit close to the ground, where maintenance is easier. The funnel that collects the wind is entirely static. This means it could be made from brick, terracota or concrete. The machine structure could last a very long time, maybe centuries.

This is exactly the sort of engineering needed if we want to get high EROEI from a low power density energy source. Two ways of doing that are to: (1) Make the energy harvester out of low embodied energy materials; (2) Build it to last a very long time. As the body of the stucture can be built as a static masonry tower, I think this design is a good contender to meet both requirements.

I set up a thread titled Permanence Movement some months back. The idea is that one of the ways of keeping embodied energy costs to a minimum, is to build devices and infrastructure to last as long as possible. The Victorians understood this when they built bridges and buildings out of thick masonry. We are still using them today. However much they cost to build, they provide benefits over hundreds of years of use. We should be the same with everything we build. Planned obsolescence needs to be end. We should instead build like we want the thing to last until the sun explodes. This is really the essence of nation building. The lives of men are short. But nations live for centuries if not millenia. The way of building a prosperous nation on a limited energy base, is to add infrastructure that doesn't need to be replaced and has minimal ongoing maintenance cost. Rather like the cathedrals and castles of old.

Last edited by Calliban (2024-04-04 11:20:56)

kbd512 · 2024-04-04 12:01:58

Spaniard,

These are two different debates.

If we're talking about arriving at 70% wind and solar power generation, then no they are not. It's two different aspects of the same debate, both of which are required to evaluate the stated goal of 70% wind and solar energy generation. You are free to argue for whatever you think is best or easiest to achieve, but I am talking about publicly stated energy generation goals / policy according to EIA (America) and IEA (Global).

An overall LCOE is different than a LCOE value standalone. And an integrated costs depends a lot of what kind of configuration you can build.

You're not telling me anything I'm not already aware of. It's irrelevant to a grid with 70% energy generation from wind and solar, which requires fast storage.

I'm not going to debate the merits of how cheap jet fuel is or potentially can be, if only we ignore the fact that it requires a very expensive jet engine attached to an even more expensive jet airliner to make use of it.

As I said before, current storage is still non competitive. You can build a model with only wind+solar+storage+curtailment but it would be significantly more expensive than current values.

Then 70% wind and solar is non-competitive until we get that much cheaper fast battery storage.

BUT there are multiple configurations and multiple promising storage technologies claiming prices that reduce that price dramatically. Not only through batteries, but also other technologies.

I don't care about what people are claiming. I care about existing technology. A grid built today can only be built with the technology that exists today. Yes, the future is full of promise and potential. When that potential is realized, we can revisit the claims to see how closely they align with results.

In the meantime, overall LCOE analysis (not specific PV LCOE) using current prices, points a mix of natural gas with renewables as the cheapest combination, at least when natural gas prices are contained, and that's the reason why we are adding more and more renewables to the mix.

This implies a few things.

1. LCOE is worse than it looks because that wind and solar doesn't function without a gas turbine running 24/7/365, because the near-vertical drops in power output that are inherent to all renewables without fast storage. If you don't include the gas turbine in your LCOE, then you're not comparing costs on an operable grid. A grid with a large percentage of renewables but no gas turbine and no storage, simply doesn't function.

2. This implies limited CO2 reduction benefits from wind and solar, because it implies that the gas turbine is kept spinning at all times, because you cannot snap your fingers and spin-up a cold gas turbine to full output. They don't work like aircraft jet engines, even though they're based upon the same technology. You go from cold iron to full output in 60 seconds with an aircraft engine and that's a normal duty cycle. That's also why aircraft engines have proportionally shorter service lives and cost more to maintain. You try that with a gas turbine electric generator and you won't have a gas turbine for very long if you do that repeatedly.

3. EROEI of anything plus battery storage needs to be calculated.

You are shifting because you claimed that the EROEI low values come from the high energy costs of the PV panel, while the LCOE of the PV itself is cheap.

EROEI is directly tied to the high embodied energy cost (energy cost, not monetary cost) of PV panels.

PV could be very cheap, and it has to be to make any sense, but PV + storage or PV + gas turbine is not very cheap.

There is no need to calculate a EROEI of PV + STORAGE for a full 100% model, as already LCOE of that model says that it's non competitive so only heavily subsidized pilot plants are mostly installed. Sometimes just for frequency because the cost for peak plants and regular storage has two different prices.

We're doing 70% wind and solar. That is the only actual plan on the books- plans that are part of national and international energy policy, rather than someone's belief about what the policy should be. We can have a separate debate about what we think the policy should be. We've touched on it a few times.

Well... Now we are installing the firsts renewables+storage, but the data is still coming, as it's too recent. That's because cheap batteries are also just too recent and the price still fluctuates, not a clear goal that has been surpassed and can be taken for granted.

Are batteries going to fall below $25/MWh? That's about where natural gas is.

That's how the "skeptic" movements works.

All valid science requires a health dose of skepticism about fantastic claims that don't add up.

For example, if LCOE of wind and solar is so great, then why does the cost of electricity to the consumer go up everywhere it's implemented? The simple and obvious explanation is that however theoretically cheap a solar panel is, when you include all that "extra stuff" to make it part of a functional grid, then it's no longer cheap.

Not only my "beliefs". But also a bunch of links of a lot more trustworthy source that a guy that name itself as "The Fracking Guy" on twitter with values a lot higher than any common source.

If two different sources say the same thing, it doesn't matter which one you think is "more trustworthy", because you're not getting different information from either source. Whether you like "The Fracking Guy" or not, his industry is the one that enables your favored power solution to exist at all. Wind and solar don't function, at the present time, without cheap and reliable gas turbine power plants.

Calliban · 2024-04-04 15:29:21

This paper examines the embodied energy of lithium ion batteries.
https://www.researchgate.net/publicatio … _Batteries

Total = 1153.64Wh per Wh capacity. In other words, the battery must complete some 1200 charge-discharge cycles before it has stored as much energy as was needed to create it.

How much energy would be needed to make 1 day of electricity storage for a country like the UK? UK baseload is about 30GWe. So to store 24h of power would require 720GWh or 720,000,000,000Wh of storage. The embodied energy of those batteries would be 720GWh x 1153.64 = 830,631GWh. That is about equal to UK power generation for 3 years.

But here is the real kicker. On average, lithium ion batteries have an effective life of 300 - 500 charge-discharge cycles. So they can never actually store as much energy as it takes to make them before they wear out.
https://techiescience.com/lithium-ion-battery-lifespan/

This doesn't by any stretch make them a useless invention. But it does suggest that they aren't going to be able to provide a large part of grid energy storage for a planet powered by renewables. Electrochemical batteries just don't look very promissing from this perspective. It also suggests that powering transportation using lithium ion batteries is a losing proposition, because it will take substantially more energy to make the batteries than the cars will actually use in their lifetime. I knew lithium batteries were energy intensive to make. But I didn't know until today just how energy intensive they were. If the results of this study are true, it will be impossible for lithium batteries to scale up sufficiently to provide more than a tiny fraction of society's energy storage needs. Instead, batteries should be prioritised for applications where small amounts of high value power are needed in portable applications. Other options for grid and automotive energy storage, such as compressed air, should be prioritised over batteries.

Last edited by Calliban (2024-04-04 16:02:30)

Terraformer · 2024-04-04 16:14:52

Hmm. I've seen far higher figures given for lifecycles of Li-ion batteries, in the 2-5000 range. But I don't know what they were counting as a cycle. Keeping the depth of discharge shallow seems to extend their life quite a bit (I should probably charge my phone more often lol); but then, it reduces the effective amount of energy you're storing.

The sellers of this battery claim it can last 3000 cycles before losing 20% of its power. Of course, its also a pretty pricey battery at $500/kWh, so maybe they're just limiting the depth of discharge to achieve that...

kbd512 · 2024-04-05 01:41:53

The entire world uses about 3TW of constant power. To supply that much "firm power" from solar thermal, using 50MWe power plants of the kind already installed in Spain, we need 196t of Copper power per 50MWe solar thermal power plant. If each power plant is 100MWe, the Copper consumption drops by 30% for the power cables and 10% for the control electronics.

18,000,000,000,000W / 50,000,000W per solar thermal power plant = 360,000 50MWe solar thermal power plants

360,000 50MWe solar thermal power plants * 196t of Copper = 70,560,000t of Copper

131.5t of Copper in the power cables per plant, 64.7t in the generator / transformers / mirror control motors / etc per plant

18,000,000,000,000W / 100,000,000W per solar thermal power plant = 180,000 50MWe solar thermal power plants

92.05t of Copper in the power cables per plant, 58.23t in the generator / transformers / mirror control motors / etc per plant

There are Sun trackers / panel rotators available that don't use any electricity at all, so we can get rid of that ridiculous nonsense to save more Copper and energy and money.

180,000 100MWe solar thermal power plants * 150.28t of Copper = 27,050,400t of Copper

Current total global annual Copper production is 24,000,000t per year

We could provide 100% of the world's present electrical requirements from solar thermal power while only consuming a year's worth of global Copper production to do it. We can probably manage to do that inside of 10 years.

18,000,000,000,000W / 1,000,000W per 1MWe photovoltaic power plant = 18,000,000 1MWe photovoltaic power plants

18,000,000 1MWe photovoltaic power plants * 7t of Copper per 1MWe photovoltaic power plant = 126,000,000t of Copper

The Copper requirements for onshore and offshore wind turbines are higher (onshore) to a lot higher (offshore) than photovoltaics, but the capacity factors are also much better, so it could be a wash. One thing's for sure, though. There's a lot more toxic stuff and heavy mining required for electronics vs solar thermal power. I think we've spent enough time and money indulging our electronics enthusiasts. I think electronics are great. I really do. I have a job because I know how to program a computer. I'm not so enamored with computers and electronics that I think they should be used as the fundamental building blocks of globally scalable energy generating solutions. An all-mechanical solar thermal power system simply cannot fail the way electronics do. An AI-enabled computer virus is going to do a whole lot of nothing to a solar thermal water heater. If you want to "hack" the system, then you need direct physical access to millions of machines that have the computing power of an entire bag of hammers.

It's time to switch to solar thermal power plants to finally get this job done instead of endlessly chasing after non-solutions. Solar thermal requires a lot more metal than nuclear thermal power, but the metal requirements remain firmly within the realm of reason and global production capacity.

1. Right off the bat, 80% of the photovoltaic power plant's embodied energy is gone. There's no polysilicon.
2. 4.66X less Copper in sum total. No ridiculous "grid upgrades" that include a bunch of additional short-lived electronics are required.
3. A solar power plant lasts for at least 75 years, as opposed to 25 years, and power output doesn't appreciably degrade over time. That means 240% less embodied energy from making new polysilicon 3 times over the life of a solar thermal plant. When it comes time for recycling, you have monolithic metals that can be shredded, melted, and pressed / rolled into new sheet metal.
4. A solar thermal power plant requires no fast storage electrochemical batteries at all. If you include storage, aka "hot bricks" or "hot salt", then it also produces power at night.
5. A solar thermal power plant can supply electricity from a single large turbogenerator which provides a "spinning reserve", steam or hot water, potable water, desalinated water to replenish aquifers, feed process heat into Haber-Bosch for fertilizers, supply pumping power for water pressure and waste water treatment plants, and/or supply the heat and pressure to make more liquid hydrocarbon fuels from CO2 in seawater.

I will never understand why people feel the need to make simple things so pointlessly complex. The general idea is to get the job done, to do it quickly, with minimum fuss and mess, and then move on to the next job. For all the fixation over electrical efficiency, we've spent the past 40 years tinkering with our electronics, only to produce one of the most stunningly inefficient and complicated means of generating and delivering power known to man. That which makes a better computer does not make a better energy generating system.

Calliban · 2024-04-05 04:52:57

A solar thermal plant looks like a far more workable solution than a PV plant. I know we have discussed it in the past. I will dig into some of the old posts and see if I can find enough information for an EROEI assessment. It isn't something that will work everywhere. But the southern and western US states would appear to be a good place for it. A few thoughts:

1. This paper discusses the latent heat of melting of nitrate salts.
https://energy.sandia.gov/wp-content/up … ordaro.pdf

Sodium nitrate has a melting point of 308°C and a heat of melting of 197KJ/kg. The heat exchangers of the solar thermal powerplant could be constructed to contain steel tanks of nitrate salt. This would allow the heat exchangers to continue generating steam at 300°C even after the sun goes down. Nitrate salts don't wear out. So when we retire the powerplants, the salt can be removed and recycled into a new powerplant endlessly.

2. One thing I like about the solar thermal idea for producing synfuel, is that it is possible to concentrate assets. Hundreds of GW of plant could be built in Texas and New Mexico. This allows dedicated recycling capabilities to be built. We could have electric arc furnaces that deal specifically with the recycling of the of the specific steel grades used to manufacture different parts of the plant. And transport of components can be carried via rail. This allows the life cycle of the product to be closed in a way that just isn't possible with PV.

3. We have discussed the possibility of stored heat powered vehicles in the past. There are a number of different ways this could work. The liquid nitrogen powered vehicle has received some attention. We discussed a hot limestone heat battery a while back. A vehicle powered by a tank of hot sodium nitrate salt, generating power through a steam cycle is possible as well. It could be recharged by circulating hot oil through the tank from a hot rock solar heat store. The range of such a vehicle won't be great - probably no better than 30 miles. But this is a rugged and technologically simple solution, that is entirely mechanical. Could we set up a solar plant at a mine or construction site and recharge vehicles with heat?

4. It would be worth examining how well a solar thermal plant could work on Mars. Sunlight intensity is less than half that of Earth, but it is mostly sunny outside of dust storms. The thin atmosphere could allow for the use of thinner steel sections for concentrating mirrors, reducing the required energy investments. So EROEI due to weaker sunlight might not be much lower than on Earth. Dust contamination of mirrors would be an issue, as would dust abrasion of aluminium coatings. Corrosion of steel frames won't be an issue. But corrosion and erosion in the steam range will be no less a problem than on Earth. One thing that would greatly improve the efficiency of a solar plant on Mars would be the use of liquid sodium as the heat transfer fluid in the trough collectors. Using oils, pyrolysis limits temperatures to 400°C. So it is difficult to produce superheated steam. But sodium would allow higher primary side temperatures. A steam temperature of 500°C should be achievable, which would allow superheated steam to be raised. This increases the whole plant power density and may be enough to compensate for the lower sunlight intensity on Mars.

5. Regarding solar tracking. Depending on the day of the year, the Earth's axial tilt will result in the sun following a predictable path, with a predictable angle w.r.t the horizon. Assuming we can calculate this in advance, the mirrors could be adjusted by an entirely mechanical control system, rather like clockwork. This isn't neccesarily the most efficient way of doing things, as the electronics needed to track the sun and adjust mirror angle will not be a large or complex item even for a solar thermal plant generating hundreds or thousands of MWe. But a mechanical control system is non the less possible. For a large plant, manual control of mirrors is also possible, although it would be a boring job. Actuation of the mirrors could also be via mechanical means rather than electric motors. Several rows of mirrors could be linked by a chain link. Driving the mirrors could be done electrically, hydraulically or even using some sort of rope drive. Manual actuation by turning a wheel connected to chain link is also possible. The output of the solar plant generator could be electrical, hydraulic or pneumatic. So there is no inherent need for electricity or electronics to be involved in any way. It is just better if you to transmit power long distances and put it to a variety of uses. But there are situations where we could use purely mechanical power.

Last edited by Calliban (2024-04-05 05:44:59)

kbd512 · 2024-04-05 10:00:58

Calliban,

Let's re-run that energy calculation with no glass and no polysilicon. We're keeping all the other materials requirements the same, even though solar thermal uses dramatically less Copper. That makes our materials embodied energy 4,879,970MJ. I arrived at that figure by using your 5,929,970MJ figure for all the materials except the polysilicon, minus the 1,050,000MJ for the glass that we're not using, because we opted for polished metal.

Assume our overall plant efficiency is no better than 14.5%, same as the photovoltaics. Reality at the temperatures solar trough concentrators can reasonably generate is about 25%, but let's assume 14.5% for sake of argument. We're not going to grant any "extra credit" to the more efficient supercritical CO2 Brayton power cycle. We shall simply assume losses somewhere, somehow, and that this is the closest / most probable approximation to reality. Somebody puts this plant in a less than ideal location, somebody has made a Sun tracking calculation error, the "Sun God" doesn't love us, etc. Anybody who claims a radical efficiency improvements somewhere in the plant, is presumed to be a liar until proven otherwise.

We still get the same 125,675,736MJ from our solar thermal power plant, so 14.5% overall efficiency. Maybe someone can do better somewhere, but we're not counting on that to happen in the real world.

125,675,736MJ / 4,879,970MJ = 25.75:1 Energy Yield to Embodied Energy

We get 25.75 units of energy back for each unit of energy we dump into our solar thermal power plant. If we adjust Copper consumption downwards to match reality, then we're going to get an even greater energy payback. We recycle materials 3X less often to boot.

Our energy yield over 25 years matches, coal or gas or conventional oil.

Now let's do 75 years:

125,675,736MJ / 4,879,970MJ = 77.26:1 Energy Yield to Embodied Energy

That's about as good as a pressurized water reactor, but without the objections of our wildly irrational anti-nuclear activists.

This is why I don't care if the solution is solar thermal or nuclear thermal. EROEI is the same, before accounting for the 4.66X lower Copper consumption. After that's taken away, the energy yield looks even better. Almost all of the waste we're left to deal with is 100% recyclable metal, and if nothing is rusted or corroded, we skip recycling, because there's no need to do that.

Now let's do Energy Stored on Energy Invested:

Lead-acid Battery: 5:1
Lithium-ion Battery: 32:1
Pumped Hydro Storage: 704:1
Compressed Air Storage: 792:1

Why do we want to use solar thermal to compress air for air and hot water powered vehicles?

As with solar thermal and nuclear thermal, it's all about that golden bang-to-buck ratio when it comes to embodied energy cost and the cost to the consumer. Sometimes the most practical and effective solution isn't to throw more technology at the problem, it's actually less.

When you don't mandate polysilicon photovoltaic panels as your source of solar energy, you don't have to figure out how to recycle them, or if you can recycle them, because that pointless complication is irrelevant to your ability to generate the same amount of energy using a much simpler technology set that simply cannot fail in the same ways as photovoltaics and electrochemical batteries do.

That begs the question about what we actually mean when we say "efficiency"?

Photovoltaics, electronic wind turbines, and electrochemical batteries are the most efficient way of transferring the wealth of the average person, into the pockets of the people advocating for use of this technology set. If it comes to monetary cost to implement and use them to power society, embodied energy cost, cost to the consumer of the energy generated or stored, or cost to the environment from all the waste generated, they're pretty close to the least efficient ways of generating or storing energy. One could reasonably conclude that these electronic devices are very efficient in terms of bankrupting society, but outside of highly specialized applications like communications satellites or cell phones, they're not efficient at all for anything else.

SpaceNut · 2024-04-05 13:19:29

With my extended period of no power it's best to have a hybrid system of at a minimum of 240 kwhr of pure electrical a day for a family of 7 to take care of all needs. That energy crosses all air, earth, wind, fire and solar inputs for use stored in all forms that can be created and converted back to electrical after loses.

SpaceNut · 2024-04-06 18:56:58

I know that solar panels now come in a bifacial format and here is an article about them.
Two-faced solar panels can generate more power at up to 70% less cost

The panels can generate more than 36 mW per square centimeter—and the back panel produced nearly 97% of the power that the front panel did. That compares to 75%–95% for most bifacial panels currently on the market.

Now add solar reflection and the power increase even more.

Large amount of content at this sites article Solar Cheat Sheet: Your Guide to Getting Solar Panels

kbd512 · 2024-04-07 01:50:45

For 10MWe output level, supercritical CO2 gas turbines with a 500C turbine inlet temperature and 35C cooler exit temperature have a total or net efficiency, after all losses are accounted for in an actual test setup, of 28.3%. Larger scale turbines and/or higher temperatures are more efficient, but turbine inlet temperature and cooler exit temperature will be the driver of cycle efficiency at 100MWth+. The turbine component of a 10MWe sCO2 gas turbine is so small that a child can pick that component up with one hand.

Here's a photo of he 10MW Brayton cycle sCO2 turbine in-hand:

The background image shows a 300MW Rankine cycle steam turbine.

Here's an image of a 300MW Brayton cycle sCO2 turbine, made from plastic:

It should be fairly obvious how dramatically smaller it is than the 300MW Rankine cycle steam turbine shown in the first image.

10MW Brayton cycle sCO2 gas turbine vs 10MW Rankine cycle steam turbines:

Modern sCO2 power turbines and axial flux electric generators can be positively tiny and weigh very little, relative to steam turbines.

Wright Electric is putting 2MWe motor-generators through the FAA certification process that weigh 200kg. At 10kWe/kg, those turbines would weigh 10,000kg at the 100MWe output level. That means the powerhead and electric generator plant portion of a 100MWe solar thermal power plant would fit inside a single 20ft CONEX box. The heat exchangers would require another 2 to 4 20ft long CONEX boxes.

The link below is to a 500C solar thermal power plant that uses plastic for the mirrors, concrete for the support base, and pneumatic (compressed air) power to drive the mirrors. The mirrors don't use electricity and very little metal. The use of metal is confined to the helical receiver tube assembly above the mirror and mirror-like metallic coating on the plastic. It was constructed at Ait Baha, Morocco (30.2174°N, 9.1493°W, altitude: 256 m), and includes thermal energy storage directly below the mirrors in the form of a bed of compacted / crushed rock.

It generates 1,810,000,000Wh of thermal power per year from 2,400kWh/yr of direct normal insolation, from 5,880m^2 of mirror aperture area, so 307,823Wh/m^2, which makes direct hot air power 12.83% efficient at collecting thermal power, so 75,878.4Wh/m^2 at 24.65% efficiency, so 1,896,960Wh/m^2 over 25 years or 5,690,880Wh/m^2 over 75 years. This looks rather poor because air was the thermal power transfer medium.

We could obtain 600kWh of electrical power per year from the same area using 25% efficient photovoltaic panels. That seems to make photovoltaics look like the obvious choice, until we also consider the material requirements to do that. Material requirements for photovoltaics don't decrease as you scale-up, and they're already about 6X to 7X higher than a metal-based solar thermal setup. Beyond that, we'll note that stainless steel, plastic, and concrete were used. The solar thermal setup also had built-in thermal energy storage directly below the panels. That likely puts the materials embodied energy differential between 10X and 20X greater for the photovoltaics, which means the total power yield over time, relative to the solar thermal plus thermal power storage, was less than half that of a solar thermal system based on hot air. Air is about 1,000X less dense than supercritical CO2, so its thermal power transfer will be quite poor by way of comparison. Even so, at best, the energy yield from the photovoltaics without any energy storage is no better. That's what happens when you fixate on the end result- the electrical power output, but don't consider what's required to arrive at that result. Somehow a seemingly absurdly inefficient thermal energy system, albeit a very simplistic one that has very low embodied energy, ends up netting more energy over time.

A 1.2 MWth solar parabolic trough system based on air as heat transfer fluid at 500°C - Engineering design, modelling, construction, and testing

Let's presume 1.7X greater efficiency / more energy generated per unit area for solar thermal, even though we can generate 28.3% with 500C turbine inlet temperatures at the 10MWe scale, or 24.65% total efficiency at the 100MWe scale after all losses are accounted for, so 125,675,736MJ * 1.7 = 213,648,751MJ.

Solar Photovoltaic Energy Yields
125,675,736MJ / 30,811,536 = 4.08:1 (25 years) 14.5% efficiency
251,351,472MJ / 30,811,536 = 8.16:1 (25 years) 29% efficiency

Solar Thermal Energy Yields
213,648,751MJ / 4,879,970MJ = 43.78:1 (25 years)
640,946,253MJ / 4,879,970MJ = 131.34:1 (75 years)

Pressurized Light Water Reactor Energy Yields
75:1 (75 years; 83% Uranium enrichment)
106:1 (75 years; 100% Uranium enrichment)

The solar thermal embodied energy figure I presented still includes solar photovoltaic Copper embodied energy, at 7t/1MWe (294,000MJ/1MWe), even though solar thermal at the 100MWe scale, is only 1.5028t/1MWe (63,117.6MJ/1MWe). I left that in there in case engineers decide to "gold plate" a part of the solar thermal energy solution. Energy yield without the excess Copper is only 137.86:1 for any who are curious. What matters most is that supplying 100% of the 25,000TWh of consumed power via solar thermal at the 100MWe power plant scale, only requires a little bit more Copper than 1 year's worth of global production, rather than multiple years of production with photovoltaics or electronic wind turbines. Storing 24 hours worth of global electrical power consumption, using electrochemical batteries, also requires about as much Copper as the photovoltaics.

The enormous demand for energy-intensive and scarce materials is what has slowed the adoption of photovoltaics, wind turbines, and electrochemical batteries. The producers of said materials cannot keep up with demand. It's equally fallacious to think that the demands placed upon more efficient energy generating and storage systems will go down. There is no historical evidence to point to, which supports such an assertion. All available evidence indicates that the exact opposite will happen.

Energy yield is why I don't care if the solution is solar thermal or nuclear thermal. Either way, it's like having a 1950s era oil well that spews RP-1 grade kerosene out of the ground. The actual figures will be slightly better than what I have reported, but the difference over 25 to 75 years is negligible. 131:1 energy yield to energy input is about as good as any pressurized water reactor that presently exists. Advanced nuclear reactors could do better than that, perhaps 200:1 or greater for Thorium-based molten salt reactors, but any energy yield of 100:1 or greater is analogous to having a time machine that allows us to go back to the heydey of oil-based energy. For humanity to thrive, for technological advancements to take off like a rocket, a new era of cheap and abundant energy is required.

Anything over 100:1 allows us to synthesize cheap hydrocarbon fuels, to store CO2 sequestered from the oceans in CO2 tank farms, to stop extracting any coal or natural gas or oil to make materials or power vehicles, and to do lots of other things with the energy related to agriculture and sanitation.

Whenever you find yourself in an energy hole, the first thing you must do is stop digging, reassess what you're doing, and then work with physics instead of against it. All these electronic energy machines are trying to work against physics, to devise the most highly ordered and therefore efficient ways of doing something. That's why I call them "entropy machines". They're attempting to flip the bird to entropy and embodied energy using hydrocarbon fuel energy sources to overcome fundamental physics problems. All the fixation on electrical energy efficiency misses the broader point that there's nothing remotely efficient about trying to use electrical power to solve all energy-related problems.

Transitioning from 25% to 50% efficiency on the consumption side, to 75% efficiency, doesn't help you when the energy efficiency tied to actually doing that is orders of magnitude lower than what thermal power systems readily achieve. This is a physics problem, and we're not going to solve it by "consuming more", regardless of how we attempt to obfuscate what we're actually doing.

Calliban · 2024-04-07 15:42:37

This reference discusses parabolic trough in some detail:
https://www.researchgate.net/publicatio … _standards

It lists concentration factor as greater than 10, but less than 100. Let's assume that we can build a trough with a concentration factor of 70. What sort of temperature could we achieve with that sort of concentration factor? We can reach an estimate using the Stefan-Boltzmann equation.

Q = a.sigma.T^4

Where a = absorptivity (assume 0.9); sigma = Stefan-Boltzmann constant 5.67E-8; T = temperature (K).

I am going to assume grey body behaviour, i.e. absorptivity = emissivity. The maximum possible temperature is the equilibrium temperature of the trough tube. But we wouldn't want to operate the tube at that temperature, because it would be radiating as much heat as it received from the sun. Let us set collector tube efficiency at 75%. This means that it will radiate only 1/4 of the energy it receives from the sun. We can calculate the operating temperature that it would need to be limited to as a fraction of equilibrium temperature.

0.25 = T^4, therefore T = 0.707Te

Now calculating Te under full sun:

1000 x 70 = 0.9 x 5.67E-8 x Te^4

Te = 1082.2K

Operating temperature = 0.707 x Te = 765.13K (492°C).

To get to temperatures as high as 500°C is therefore possible with a parabolic trough. But it requires a high concentration factor of nearly 100 under full sun conditions of 1000W.m-2, or acceptance of a lower collector efficiency due to reradiation. We also need to account for the fact than there is always a temperature drop across heat exchangers.

I suspect that we may need to stick with a steam cycle for paraboluc trough collectors. The concentration factor doesn't seem to be quite high enough.

Point source dish type and solar tower collectors can achieve concentration factor of around 1000. There woukd be no problem reaching the 500+ degree temperatures needed for S-CO2 cycles using these technologies. In situations where high temperature process heat is needed at >1000°C, (i.e. cement manufacture) these collectors would be the ideal choice.

Last edited by Calliban (2024-04-07 15:53:55)

Terraformer · 2024-04-07 16:09:15

In the area of sacrificing efficiency for cost, how do Fresnel lenses compare?

kbd512 · 2024-04-07 17:52:11

Terraformer,

These costs are a bit dated now, but here you are:

Parabolic Trough Collector Cost Update for the System Advisor Model (SAM)

Edit: Fresnel lenses are included for you to compare costs.

Last edited by kbd512 (2024-04-07 17:52:58)

kbd512 · 2024-04-07 18:05:51

Development of an Advanced, Low-Cost Parabolic Trough Collector for Baseload Operation

SkyFuel is developing a commercial parabolic trough collector with:
LCOE of $0.09/kWhe in 2020
Capacity factor of 75%, suitable for baseload operation
Larger aperture than any trough in commercial operation today
Maximum operating temperature in excess of 500ºC
Ability to use molten salt directly as the HTF

For people who think LCOE means everything, which would only be true if photovoltaics and wind turbines provided capacity factors similar to regular baseload power plants, the parts that actually matter are "Capacity factor of 75%", "temperature in excess of 500ºC", and "use molten salt directly as the HTF".

Calliban · 2024-04-08 06:28:55

kbd512 wrote:

Development of an Advanced, Low-Cost Parabolic Trough Collector for Baseload Operation
SkyFuel is developing a commercial parabolic trough collector with:
LCOE of $0.09/kWhe in 2020
Capacity factor of 75%, suitable for baseload operation
Larger aperture than any trough in commercial operation today
Maximum operating temperature in excess of 500ºC
Ability to use molten salt directly as the HTF
For people who think LCOE means everything, which would only be true if photovoltaics and wind turbines provided capacity factors similar to regular baseload power plants, the parts that actually matter are "Capacity factor of 75%", "temperature in excess of 500ºC", and "use molten salt directly as the HTF".

Interesting. A problem with pushing tube temperatures to 500°C if that hydrocarbon oils start to undergo pyrolysis at those temperatures. The issue with using molten salts is materials compatability. What happens to steels when they are exposed to liquid salts for years? Do the salt ions migrate along grain boundaries making the metals brittle? Are there corrosion problems? These sorts of material uncertainties have scuppered molten salt reactor development for the past fifty years. A solar plant doesn't have the same regulatory overburden, but materials behaviour is still a technology risk that could be life limiting for the plant. Liquid sodium has compatability with steel, but ignites on contact with air and water. Gaseous coolants have poor volumetric heat capacity unless heavily pressurised. There aren't any easy options when temperatures go north of 400°C. Molten salt probably is the best bet, but how will it behave on contact with steels?

If capacity factor can get to 75% or greater, it should allow the plant to support a baseload capability. We would pair it with open cycle gas turbines, which woukd operate the other 25% of time. These have a low capital and operating cost but relatively high fuel cost. If you need backup but don't need it very often, that is the thing to use.

If a solar heat source can generate temperatures exceeding 500°C, then it could be used to generate bio-oils by pyrolysis of biomass. This is an intermediate technology that can plug gaps in liquid fuel supply whilst direct synthesis from CO2 is under development.

Last edited by Calliban (2024-04-08 06:39:36)

tahanson43206 · 2024-04-08 06:38:41

For Calliban re #44

Molten salt probably is the best bet, but how will it behave on contact with steels?

For many reasons, I'm hoping forum members will attempt to answer the question posed by Calliban. It appears that the company reported by kbd512 in Post #43 is making fairly significant bets they can harness these materials within the bounds of acceptable risk.

The answers ** should ** appear in literature at some point. If anyone finds updates, please post them here.

While most humans do not make investments in risky ventures like this one, we can all benefit from advances in understanding of how the Universe works.

Update from Index Post #2:
Index:
Post 35: A solar thermal plant looks like a far more workable solution than a PV plant.
Sodium nitrate has a melting point of 308°C and a heat of melting of 197KJ/kg.
Calliban: http://newmars.com/forums/viewtopic.php … 62#p221362

For Calliban ... is Sodium nitrate a candidate material for use in this application. Is anything known about it's suitability in a metal system?

Related question... the material will solidify throughout the system over night. Can solar energy melt all the material in the system by direct heat transfer when the Sun comes back up? Is this a practical idea, or is it limited to theoretical speculation?

Related question ... is there a record of anyone trying this concept anywhere on Earth, since the beginning of time?

If there ** is ** such a record, and if the experimenters were generous enough to report their observations, it sure would be helpful for the progress of this topic.

(th)

tahanson43206 · 2024-04-08 06:56:29

This is a continuation of Post #45, but separated to focus on a specific question ....

A working material that solidifies inside the machinery where it is used seems risky to me, so I am hoping forum members who know more than I do will be willing to investigate how such materials are used in the Real Universe.

One possible answer is to drain the material into a holding tank when the energy source is removed.

That would mean that the tank would have to be heated above the melting point of the material, before it could be returned to the energy collection pathway.

Perhaps that is a practical idea?

Is there a record of anyone on Earth having tried this, from the beginning of time?

Water is a working fluid that freezes below 0 degrees Celsius. Humans have devised techniques to extend the lower range of freezing of water.

Are there any records of how humans have dealt with the problem of water freezing inside machinery. Is it customary to drain water out when temperature will fall below the freezing point of whatever mixture is used to extend the lower range?

I know it is customary to drain water out of a house that has lost heat and when temperatures are expected to drop below the freezing point of water.

This topic seems well suited for posts that explore the capabilities of various materials for energy collection systems.

(th)

SpaceNut · 2024-04-08 06:56:31

The kilowatt reactors use molten salt for this reason as it remains stable in the conditions of moon and mars locations.

The towers in New Mexico that converts the reflected sun into energy.

https://en.wikipedia.org/wiki/National_ … t_Facility

https://en.wikipedia.org/wiki/Solar_power_tower

solar furnace is a structure that uses concentrated solar power to produce high temperatures, usually for industry. Parabolic mirrors or heliostats concentrate light (Insolation) onto a focal point. The temperature at the focal point may reach 3,500 °C (6,330 °F)

The rays are focused onto an area the size of a cooking pot and can reach 4,000 °C (7,230 °F), depending on the process installed, for example:
about 1,000 °C (1,830 °F) for metallic receivers producing hot air for the next generation solar towers as it will be tested at the Themis plant with the Pegase project
about 1,400 °C (2,550 °F) to produce hydrogen by cracking methane molecules
up to 2,500 °C (4,530 °F) to test materials for extreme environment such as nuclear reactors or space vehicle atmospheric reentry
up to 3,500 °C (6,330 °F) to produce nanomaterials by solar induced sublimation and controlled cooling, such as carbon nanotubes or zinc nanoparticles

Calliban · 2024-04-08 06:57:07

Here for example.
https://mat-research.engr.wisc.edu/rese … ten-salts/

Nitrates appear to have 'good' compatability with carbon steels.
https://www.calpaclab.com/carbon-steel- … ity-chart/

This is convenient as carbon steels are cheap. It isn't really specified here what 'good' really means. Does it mean years of operation before corrosion is a problem? I wonder if we can galvanise carbon steel tube for even better performance?

This silicone based oil is stable up to 430°C. So a trough system using this miggt be able to generate steam at 400°C.
https://www.fragol.de/en/heat-transfer- … 430-c.html

This company specialises in heat transfer fluids. Most oil based fluids only appear stable up to 400°C. But they have one molten salt based fluid that is able to operate up to 600°C. That is the sort of temperature we need. But long term materials compatability wouid need to be carefully considered.
https://globalhtf.com/heat-transfer-flu … ure-fluid/

Liquid sodium is being investigated as a CSP heat transfer fluid. It boils at 800°C, so primary pipework need not be pressurised.
https://www.sciencedirect.com/science/a … 4822003178

The problem here is that even small amounts of oxygen will react with sodium to produce highly abrasive sodium oxide. This will do bad things to steel pipework, heat exchanger tubes and pump impellors. Even so, as a high temperature heat transfer fluid it is one of the best options. It does have compatability issues with stainless steels because alloying elements tend to dissolve into the sodium. But this appears to be a very slow process. It wasn't considered to be a life limiting problem in faster breeder reactors operating at 550°C.

Last edited by Calliban (2024-04-08 07:36:34)

tahanson43206 · 2024-04-08 08:49:45

As a reminder, I am hoping a member of the NewMars forum can address the issue of solidification of coolant that has a melting point above room temperature. Perhaps the answer is available, but if anyone has written about the problem and it's practical solution, I've missed it.

If a material is used in a nuclear reactor, I assume it has to be melted before it is injected into the reactor?

It seems to me that a material that solidifies far below ambient temperature and which does not destroy the pipes in which it flows would be desirable. Some oils appear to have desirable properties along those lines, but I gather that oils can disassociate at elevated temperatures where the heat they carry would be most useful.

One question that I have about that situation is whether the oil reconstitutes itself after it disassociates, or if other compounds are formed when the material is cooled by the radiator through which it travels.

Oils are composed of carbon and hydrogen, in various combinations, so I would expect hot carbon and hydrogen to recombine as hydrocarbons after they cool.

The question I am asking is .... does it matter if oil disassociates? Can the subsequent hydrocarbons continue serving as coolant?

If that is the case, why not simply prime the system with whatever the end product would be?

(th)

SpaceNut · 2024-04-08 09:26:22

With no filtering system it would build up a plumbing issue called sludge as the carbon would build up as a solid.
water severs quite well even at those temperatures, but it's got to be nuclear grade pure.
Also, there are other gas combinations that do work well up to those temperatures but suffer the same issues of break down.

I did put up a concept of a much smaller trough hidden inside a voids topic as a decorative shell of a light house. Placing it vertically rather than horizontally.

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