3 ms·
Nice idea. For a summary, this is an energy storage project, where the energy is stored in tanks of high and low temperature fluids. Temperature differentials
by mnw21cam 9y ago
Nice idea.
For a summary, this is an energy storage project, where the energy is stored in tanks of high and low temperature fluids. Temperature differentials can be generated by heat pumps, and can be converted back into useful energy by heat engines.
However, the theoretical maximum energy efficiency of this unit, assuming no heat losses from the tanks, will probably be poor compared to LiIon or pumped storage (of the gravity type), simply due to the fact that heat engines are strictly limited in efficiency to the Carnot efficiency (and are usually much less efficient than that).
Depending on the temperatures involved, I'd be surprised if it can return as much as half the energy that is put into it.
Also, conflation of energy and power in the article.
- maxerickson 9y agoThe energy is surplus at time of storage, lower storage cost can end up making more sense than higher efficiency.
- URSpider94 9y agoYou're forgetting something on the Carnot cycle efficiency, which is that the efficiency of the storage cycle can be GREATER than unity. Heat pumps (of which this is an example) can move more than one joule of heat per joule of input power. I agree that the output efficiency (Joules of power : Joule of heat) is going to be low, given the relatively small temperature differential between the reservoirs, but the round-trip efficiency might not be that bad.
- URSpider94 9y agoTo correct my own comment, Joules are of course units of energy, not power...
- usrusr 9y agoHeat/cold storage is very efficient when you have direct consumers for heating/cooling: charge the insulated tanks in times of electrical surplus, heat/cool when needed. Mixed application installations (e.g. campus-scale air conditioning and hot water, generously overprovisioned to allow some paid grid stabilization work on the side) might be an economic sweet spot even with terrible cycle efficiency. In any case, for grid storage, price per effective capacity will remain the key metric as long as the storage market is not saturated. Tanks scale pretty good.
- aphextron 9y ago>However, the theoretical maximum energy efficiency of this unit, assuming no heat losses from the tanks, will probably be poor compared to LiIon or pumped storage But Li-ion is orders of magnitude more expensive than what they're proposing (no matter how cheap the cells are getting), and couldn't possibly be deployed at this scale. It's more useful for stop-gap loads when you need instant discharge. Pumped hydro is only possible when the local geography is perfect for it and there is an abundance of water. The reality is that our future will require a host of different technologies like this working in synergy to provide grid scale energy storage. No single solution will become the standard.
- Retric 9y agoEV batteries are at $227 / kwh and are on target to hit $100 per kWh in 2020. Because, costs tend to drop as production ramps up. Average american uses 35 kwh per day. 5% of US daily grid storage is an excessive goal, but assuming 100$/kwh would only cost 3,500$ / person. Assuming they last ~15 years that's under 20$/month which is clearly a deal killer, but not exactly impossible. PS: Hydro storage is generally a much better option, but as a supplemental option batteries could be very useful.
- deleted 9y ago[deleted]
- maxerickson 9y agoDo you say 5% but then calculate the cost for 100%?
- Retric 9y agoI was unclear, I meant even 100% is not impossible. Though, I suspect 5% is a vastly more reasonable upper bound.