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Geothermal may beat batteries for energy storage

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Re: Geothermal may beat batteries for energy storage

#41

Post by rnhmjoj »

jillesvangurp wrote: post #7

Interesting option. It's all about the cost and efficiencies in the end. Converting electricity into heat and then back into electricity is a lossy process that is constrained by the second law of thermodynamics. Basically generating heat is easy and efficient. But converting it back to electricity is typically less than 50% efficient. Basically, it's several energy conversions in one process: you use electricity to…

> But converting it back to electricity is typically less than 50% efficient.

It's generally much much worse than 50%. Say that you used a resistor to heat the water in a (perfectly insulated) boiler and want to know how much useful work you can extract from it, ideally. The answer is given by the exergy efficiency, which can be computed by attaching an imaginary heat engine to it, integrating the infinitesimal works δW = δQ⋅η_Carnot while the temperature drops from the initial T_boiler to T_ambient and dividing by the internal energy of the boiler.

The result is η_exergy = 1 - T_ambient/T_lmtd where

  T_lmtd = (T_boiler - T_ambient)/log(T_boiler/T_ambient)
is the logarithmic mean temperature difference. Even heating water to 90°C gives an efficiency of only 9%.

Re: Geothermal may beat batteries for energy storage

#42

Post by drewbeck »

Someone wrote: post #40
jillesvangurp wrote: post #19

Earlier quoted context omitted.

This article is about storing energy generated using renewables in reservoirs; not about tapping into geothermal energy. The issue with geothermal is not that the energy isn't there but that getting to it involves a lot of expensive infrastructure. It's cost effective in some parts of the world and not really cost effective (relative to cheaper solutions) in other parts of the world. Using this instead would mean hav…

> This article is about storing energy generated using renewables in reservoirs; not about tapping into geothermal energy. I think it’s about both. They plan to create reservoirs that heat water _and_ use them to store warm water. Also for the latter the outside heat source will provide energy. FTA: Enhanced geothermal systems (EGS) get around this geographical limitation by creating artificial reservoirs. Developers…

Yeah that last line is key — they’re not creating heat with the excess energy, they’re pumping water. The article doesn’t have much specifics but the implication is they’re achieving much higher efficiency than if they were doing electricity → heat → electricity

Re: Geothermal may beat batteries for energy storage

#43

Post by jbay808 »

rnhmjoj wrote: post #41
jillesvangurp wrote: post #7

Interesting option. It's all about the cost and efficiencies in the end. Converting electricity into heat and then back into electricity is a lossy process that is constrained by the second law of thermodynamics. Basically generating heat is easy and efficient. But converting it back to electricity is typically less than 50% efficient. Basically, it's several energy conversions in one process: you use electricity to…

> But converting it back to electricity is typically less than 50% efficient. It's generally much much worse than 50%. Say that you used a resistor to heat the water in a (perfectly insulated) boiler and want to know how much useful work you can extract from it, ideally. The answer is given by the exergy efficiency, which can be computed by attaching an imaginary heat engine to it, integrating the infinitesimal works…

> Say that you used a resistor to heat the water

If you're looking to maximize round trip efficiency, this is probably not a good starting point. Better to use a heat pump, as mentioned elsewhere.

Re: Geothermal may beat batteries for energy storage

#44

Post by elif »

Retric wrote: post #16
jillesvangurp wrote: post #7

Interesting option. It's all about the cost and efficiencies in the end. Converting electricity into heat and then back into electricity is a lossy process that is constrained by the second law of thermodynamics. Basically generating heat is easy and efficient. But converting it back to electricity is typically less than 50% efficient. Basically, it's several energy conversions in one process: you use electricity to…

Using batteries for the grid requires roughly the same amount of batteries as EV’s do. A 100kWh battery pack for a car * 1,000 charge cycles / 25 years = 4,000 kWh of battery per year * ~290 million cars. That’s enough to store almost 1/3 of all current electricity used in the US while ignoring busses and farm equipment etc. Of course actual cost depends on how much storage we need and future battery prices but addin…

As someone that charges lithium batteries for both cars as well as for my house, I can promise you there is 0% of me that wants to cycle my vehicle battery from 100 to 0 every day to arbitrage $1.80 of electricity.

Re: Geothermal may beat batteries for energy storage

#45

Post by elif »

moffkalast wrote: post #8
jillesvangurp wrote: post #7

Interesting option. It's all about the cost and efficiencies in the end. Converting electricity into heat and then back into electricity is a lossy process that is constrained by the second law of thermodynamics. Basically generating heat is easy and efficient. But converting it back to electricity is typically less than 50% efficient. Basically, it's several energy conversions in one process: you use electricity to…

I wonder if it would be possible to scale down pumped hydro to something the size of a tall water tower. Probably not worth it due to the small height difference and volume, and you'd also lose efficiency due to the smaller turbine, but I still do wonder what the actual figures are like for something like that. Especially in cost per kWh stored compared to lithium.

That's the problem with the US capitalist approach to renewable energy. "Can I downsize this to a scale that makes sense in our economic reality?" Dang, there dies another viable idea. Instead of changing the status quo we have some warm libraries and city halls.

Re: Geothermal may beat batteries for energy storage

#46

Post by rnhmjoj »

jbay808 wrote: post #43
rnhmjoj wrote: post #41

Earlier quoted context omitted.

> But converting it back to electricity is typically less than 50% efficient. It's generally much much worse than 50%. Say that you used a resistor to heat the water in a (perfectly insulated) boiler and want to know how much useful work you can extract from it, ideally. The answer is given by the exergy efficiency, which can be computed by attaching an imaginary heat engine to it, integrating the infinitesimal works…

> Say that you used a resistor to heat the water If you're looking to maximize round trip efficiency, this is probably not a good starting point. Better to use a heat pump, as mentioned elsewhere.

Yes, if you're counting the heat output as part of the useful energy, but parent was specifically talking about converting electricity into heat and back again.

Re: Geothermal may beat batteries for energy storage

#47

Post by ncmncm »

This is an example of "how can we keep X relevant in a world where it is not?" Geothermal is falling away because maintaining a steam turbine is expensive.

There are plenty of efficient storage options that don't depend on a steam turbine. Those are favored except where the storage medium is also a transportable, valuable product, as for ammonia. (Ammonia is burned in combined-cycle turbines already built to burn NG.)

Re: Geothermal may beat batteries for energy storage

#48

Post by CorrectHorseBat »

HPsquared wrote: post #14
VilleOr wrote: post #6

Earlier quoted context omitted.

Majority of geothermal enery comes from the decay of radioactive isotopes. It's not renewable, but there will be enough heat for millions of years.

It's not renewable, but exploiting it doesn't reduce the overall output. It's "not depletable", you could say.

How is that different from renewables?

Re: Geothermal may beat batteries for energy storage

#49

Post by swayvil »

rglullis wrote: post #33
swayvil wrote: post #30

Earlier quoted context omitted.

You got any examples of "friendly, nonfighting type competition" in the business world?

All of the oligopolies? Do you really believe that, e.g, tech companies are "fighting" each other? What about Big Pharma? The Food industry? In any case, you are arguing semantics. Competition can be friendly.

The tech, food and pharma industries fight each other tooth and nail.

I don't think this "friendly competition" happens in the business world. It's just an ordinary fight.

Re: Geothermal may beat batteries for energy storage

#50

Post by jbay808 »

rnhmjoj wrote: post #46
jbay808 wrote: post #43

Earlier quoted context omitted.

> Say that you used a resistor to heat the water If you're looking to maximize round trip efficiency, this is probably not a good starting point. Better to use a heat pump, as mentioned elsewhere.

Yes, if you're counting the heat output as part of the useful energy, but parent was specifically talking about converting electricity into heat and back again.

So am I. If you're going from electricity to heat for storage and back to electricity, you'll get better efficiency by using a heat pump to generate that stored heat. In general, sticking to processes that are as close to reversible as possible will be the most efficient.
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