Long Service Life Energy Storage Infrastructure

Calliban · 2025-04-04 17:09:04

Recent discussions on sustainability have led me to rethink long lived energy storage infrastructure. Specifically, if we can build energy storage infrastructure that takes centuries to wear out, then the rate of replacement in a steady state energy mix will be low. This means that marginal cost of infrastructure after an initial investment will also be small, even if the unit capital cost of energy storage infrastructure is high.

There are a number of options for energy storage that could potentially last a long time. My baseline target is a 100-year service life. Some options here might be extended even longer. My goal is to discuss each technology in detail and consider ways in which it might be used to improve sustainability. Globalisation of industry is breaking down. Increasingly, nations are coming to the realisation that the globalised trading system doesn't work for them and they seek to develop more self-sufficient economies. Energy storage systems will be examined in how well they can support this goal as well.

1. Thermal energy storage. This is most suitable in situations where heat is the desirable end product, but it can be integrated into thermal powerplants as well. It could be as simple as a tank of hot water, or a heated solid mass or a phase change material of some kind. The vessels involved need not be under heavy pressure, but they may undergo thermal cycling. Corrosion may limit operational life for some specific storage mediums (i.e. molten salts). But lifetime could still be long by human standards.

2. Flywheel energy storage. This stores mechanical energy as rotational kinetic energy. Using fibre reinforced polymers with high strength-weight, this can achieve impressive energy density. It has been used to power vehicles and as part of regenerative braking systems. For high energy density systems, charging tends to require AC induction, which is contactless. The flywheel rotates in a vacuum on magnetic bearings. The storage duration is limited by gyroscopic forces induced by rotation of the Earth.

3. Compressed air. We have discussed this extensively on this board. Compressed air may be a sustainable way of powering vehicles, because pressure vessels do not degrade in the way that batteries do. Energy density is limited to a few hundred KJ/kg. If storing at high pressure, interstage cooling is needed to avoid excessive energy losses. Likewise, the motor must employ interstage reheat to avoid discharging air cryogenic temperatures and wasting most of its work potential. The storage itself involves not moving parts and well maintained vessels should last a long time. This means that storage can be added cumulatively, increasing storage incrementally.

4. Compressed (other) gases. Compressed CO2 is interesting for static energy storage applications here on Earth. Interesting because under high pressure, CO2 will liquefy at room temperature, allowing it to be stored as a dense saturated liquid in compact vessels. Because CO2 is a trace gas in Earth's atmosphere, the expanded CO2 must be captured in a flexible container, from which it can be recompressed. However, energy storage density of the gaseous vented CO2 in low pressure tanks, may be as high as 22kWh/m3. This js because vented CO2 is cold. As the pressure vessels tend to dominate capital cost, L-CO2 has some important advantages over CAES. Because expanded CO2 needs to be collected and reused, this technology is unsuitable for distributed, direct mechanical energy use in small devices. This makes it different to compressed air, which can be vented from tools as it expands to provide mechanical power.

5. Underwater CAES. I thought this deserved its own category. It is similar to other CAES concepts, but air is stored in a vessel or flexible bag underwater. This takes advantage of the hydrostatic pressure of the surrounding water to maintain the air in a compressed state. This obviates the need for a pressure vessel, but requires installation of the storage vessel underwater. Using this technology, huge volumes of compressed air could be stored within ballasted concrete shells within lakes or offshore on the seabed. As compressive structures, properly coated concrete air storage vessels should last for generations.

6. Raised water. Large pumped storage schemes have been built in many countries. These have typically focused on absorbing excess electricity from the grid, pumping water into a mountain reservoir and releasing it through a pelton wheel turbine to regenerate electricity. Typical storage capacities exceed 1000MWh. The energy stored within an elevated mass of water is proportional to head height of the stored water. However, this does not preclude the use of smaller scale pumped storage between two reservoirs or between a water tower and a receiver tank. A significant advantage of this concept is the use of only a few moving parts. Valves are needed, a centrifugal pump and a turbine, with the later two potentially being the same component. Direct hydro is also possible, in which falling water directly drives mechanical equipment without electricity generation. If pumping was also achieved non-electrically, then the entire process can bypass electrical energy. This simplifies the machinery involved and makes it easier to build energy systems on a simpler resource base, using local resources.

7. Hydraulic accumulators. These can work in a number of different ways. The most common today are steel pressure vessels, containing a polymer bag which is usually filled with nitrogen. Other technologies replace the gas bag with a spring, or a piston seperating gas from the liquid. Another option is a raised weight acting on a piston. In all cases, liquid hydraulic fluid is pumped into the vessel under pressure. Energy is released by opening a valve, allowing pressurised hydraulic fluid to be pushed out. The pressurised liquid can drive a turbine generating electricity, or can power mechanical machinery directly without need for electrical energy generation. Hydraulic accumulators have relatively low energy density compared to compressed air energy storage. This is because liquids do not change volume very much under compression and the volume of any contained gas is limited to the volume of the vessel at ambient pressure. So accumulators have too low an energy density to be useful as energy sources for mobile applications, aside from the limited potential of braking energy recovery. But hydraulics use liquids under pressure, which have low compressibility. This has the advantage that very little energy is lost in this form of energy storage, because volume change of the liquid is negligible. Hydraulics can also discharge at very high power levels.

8. Cryogenic energy storage. This typically involves liquefying air, by repeated compression and reexpansion. Liquefied air can be stored in an insulated vessel at ambient pressure. Exposing the air to a low grade heat source, like waste heat from a power station or even ambient heat, produces high pressure air that can be expanded through a turbine generating mechanical or electrical power. Air liquefaction is more complex than most other energy storage processes. However, the potential energy density of stored liquid nitrogen is 620KJ/litre, or 172kWh/m3. This makes liquid air an energy dense storage medium, in spite if the difficulties of handling cryogenic liquids.

9. Vacuum energy storage. This is similar to CAES, but makes use of negative pressure. Energy storage density is very low - a maximum of 100KJ/m3. However, the storage vessels experience compressive forces, allowing vacuum tanks to be made from low embodied energy materials like concrete, stone or even compressed soil bricks. Vacuum can be created by pumping water out of a closed vessel, making vacuum energy storage a kind of negative hydraulic accumulator.

10. Energy storage in the lifting force of a bouyant balloon, beneath water (as per Terraformer's suggestion in Post #4).

11. Electrostatic energy storage devices (super-capacitors) as per Kbd512s suggestion in post #5.

Can anyone think of any more?

Last edited by Calliban (2025-04-05 15:09:27)

tahanson43206 · 2025-04-04 17:19:22

This post is reserved for an index to posts that may be contributed by NewMars members over time.

For Calliban... if your concept for posts to develop the topics comes to pass, the index post can contain direct links to the posts.

We did something similar for Dr. Johnson's course ("Traditional")

If you decide to pursue that idea, you can create the posts as empty buckets now, and fill them as you have time.

Index:
Post #3: Calliban: Hydraulic accumulators for static energy storage applications.
https://newmars.com/forums/viewtopic.ph … 61#p230861

(th)

Calliban · 2025-04-04 17:25:43

Thanks TH. My next entry will discuss hydraulic accumulators for static energy storage applications. I will post here tomorrow.

Terraformer · 2025-04-05 04:04:50

So: thermal, mechanical, gravitational potential, compression, and... a mix of compression and thermal (compressed/liquified gas with reheating)?

Hard to think of anything else that fits these. Maybe something using a balloon reeled down to the seafloor to exploit its buoyancy I guess. I'm sure I've seen something like that proposed before.

kbd512 · 2025-04-05 14:41:54

Electrostatic energy storage devices, which we know as "super capacitors", are an example of a long-lived electrical / electronic form of energy storage. Those devices can achieve 1M+ cycles with little loss of storage capacity, relative to electro-chemical batteries. If we can figure out how to get their energy density on-par with Lead-acid batteries while reducing manufacturing cost, perhaps with mass production, then I see a future which uses them as durable solid state electrical energy storage devices that provide us with our future mass electrical energy storage for data centers and computers. Super capacitors are typically based upon Carbon and plastic materials, which are reasonably plentiful. Graphene-based lab-scale super capacitors have achieved 50Wh/kg to 80Wh/kg.

As modern computers become increasingly photonic vs electronic, and photonic chips consume many times less electrical energy for a given compute capability, then these advance super capacitor devices can store the energy required to ensure that sophisticated AI-enabled super computing infrastructure continues to operate, even if the grid is less than totally stable, or worse, has to shrink because we cannot devote the personnel and logistical support to these "mega project" compute devices.

Computers are not going anywhere. They're here to stay. We do need to arrest the growth of power consumption associated with large data centers and AI, but then we need to power them through a combination power buffer / fast energy storage that precisely regulates voltage and enables them to continue operating, uninterrupted.

Calliban · 2025-04-06 05:56:32

Regarding hydraulic accumulators, here was my first sketch for what a large scale raised weight hydraulic accumulator might look like.

It was inspired by the old gasometres that were once a common sight around UK towns and cities. This hydraulic accumulator would store 3.7GJ of energy (1.03MWh). The structure would be 20m wide and 40m high, fully extended. The outer shell the accumulator is made from reinforced concrete.

I realised after I had finished drawing it, that a more efficient idea would be to make the raised weigyt out of reinforced concrete and use it to contain the hydraulic reservoir.

In this case, the reinforced concrete raised weight carries tensile pressure exerted on it be the hydraulic fluid. However, the hoop stress in the concrete is low due to its extreme thickness. The concrete can be reinforced using long stone fragments, such that the tensile strength of the stone contains the pressure. This accumulator would store 8.3GJ, or 2.3MWh. Under discharge, it could yield 96kW for 24 hours, or 2.3MW for 1 hour.

During operation, the wear surfaces of the accumulator are the piston ring and the steel liner around the inside of the hydraulic reservoir. As this start to wear, hydraulic fluid would gradually seep and run down the outside on the piston. So the piston ring will need to be replaced. Hydrauluc jacks will be needed to lift the weight off of the piston for this to be done.

Advantages of the raised weight hydraulic accumulator are extremely long service life. This would be limited only by wear of the hydraulic chamber steel liner. The device is capable of being charged with pressurised hydraulic fluid, which can be pumped mechanically. It will discharge pressurised hydraulic fluid as well, which can drive mechanical loads in homes or factories. So this energy storage system can bypass reliance on electricity altogether, if that is desirable. It will store mechanical energy from any prime mover that drives a pump. Liquids are incompressible, so wind turbines, hydropower or solar energy, can pump hydraulic fluid using single-stage positive displacement piston pumps. This is much simpler than producing compressed air at the same pressure, as no interstage cooling is required. The hydraulic fluid will most likely be a mineral oil. This can be reused almost indefinitely. Other advantages include technological simplicity, ease of construction and a very high potential rate of power discharge.

The main disadvantage of this concept is its relatively low energy density. The raised weight will have a mass of 28,200 tonnes. Assuming it is used to store and discharge 2.3MWh of energy per day, then total energy stored will be 84,000MWh over 100 years, or 3MWh/tonne. The embodied energy of concrete is estimated to be 1.11MJ/kg, or 0.308MWh/tonne. So it would take over 10 years for a raised weight accumulator to repay the energy needed to build it, assuming that it stores and discharges its full capacity every day. So this kind of infrastructure only makes sense if we have a very long investment window. If we are planning infrastructure that we intend to use for centuries, then a hydraulic accumulator is a gift to future generations. But no one would build one for quick returns on investment. It is also worth noting that this is static infrastructure. It cannot be part of a moving system like a vehicle, because of its low energy storage per unit mass.

The UK uses about 800,000MWh of electricity every day. So providing 1 day of storage would imply building 348,000 of these units. The amount of stone and concrete needed to build the raised weights would be nearly 10 billion tonnes. This is a huge amount, though a large part of this mass would be quarried stone. If we built 3500 units per year and built this capacity up over a century, then the annual stone and concrete needed would be more like 100 million tonnes. That is achievable. How much would it cost?

For large projects, concrete costs about $100 - 150 per cubic yard. That is $191/m3 or $80/tonne. Over 100 years, a tonne of concrete mix will store 3MWh of mechanical energy. So the added cost of storage is $0.0267/kWh. Which really isn't at all bad. This suggests to me that the trick to affordable energy storage is to build systems that last a very long time and to use them for a long time.

How much space would this take up? Each accumulator has a footprint of 20 x 20m and we need 348,000 of them. So: 348,000 x 20 x 20 = 139,200,000m2 or 54 square miles.

I think the liklihood is that raised weight hydraulic accumulators will have niche applications. One of their strengths is a high discharge rate. This makes them useful for power smoothing applications, in which a powerplant provides a steady power input and the load consumes much higher power, but only intermittently. Mechanical hammers and hydraulic presses are like that. Grid frequency control requires energy storage that is capable of activating and ramping up power very quickly. This fills the gap in generating capacity if a large powerplant disconnects from the grid and something is needed to provide power for the time it takes to bring another powerplant online. If an industry is using mechanical power from a wind turbine say, and wind level begins to drop, an accumulator could provide the power needed to finish an operation and make equipment safe. It can also provide high pulsed power for specific operations.

Last edited by Calliban (2025-04-06 07:23:36)

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Long Service Life Energy Storage Infrastructure

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