3 ms·

It's a cool idea. The big advantage might be in being cheap, simple, and non-toxic, so that it can be easily deployed in less-prosperous areas and with less exp

It's a cool idea. The big advantage might be in being cheap, simple, and non-toxic, so that it can be easily deployed in less-prosperous areas and with less expertise. It seems probably even simpler than the "concrete stacking battery" whose name I forget. But... >with currently available technology the process of converting heat back into electricity only has an efficiency rate of 30% Yes they're recovering heat as well, which is great when it works. But in general 30% is not great. This probably only makes sense to use when you have huge amounts of nearly-free power. Like if you massively overbuilt solar/wind (which could be a plausible thing to do!) or nuclear.

unwind 4y ago
I thought heat output was the main effect, thus the talk about "district heating pipes" in the list of components. With nuclear power generation I thought there was no need to store energy, since it can generate at all times and ramp up/down pretty quickly.
- breischl 4y ago
  I'd say the marketing on at least this article is more geared at the electric energy. Heat is a form of energy for sure, but not a big enough one that it could "transform clean energy". Nuclear can be ramped, but typically is not. I haven't dug into why, but I get the impression it's partially economic - the plants are very expensive to build and the marginal cost of a few hours of fuel is so low that they prefer to just run all the damn time. I think there may be some technical reasons as well. In general if you look at how utilities operate, they will ramp down literally everything else before the nuclear plants. That probably applies less to the Small Modular Reactors people keep talking about, but those are still not really a factor.
Schroedingersat 4y ago
30% of that noon day summer sun looks pretty good on a cloudy day mid winter. In some places where mid-winter PV output is 1/4 of summer, it *already* makes sense to overbuild by a factor of 4. Keeping 30% of the summer energy would double the winter output. Of course this only makes sense if the electricity extracting bit is much cheaper than wind.
- breischl 4y ago
  Indeed! But getting ~80% back from batteries or pumped hydro looks even better[1]. Or, the ~90% that EnergyVault claims[2]. I'm very much pro-renewables and pro-storage, but that doesn't mean that all forms of storage are equal. This one has certain advantages (cheap, simple, tough), but the roundtrip efficiency kinda sucks compared to some other options. And I'm guessing (without checking) that the 30% is for short-term storage (eg, overnight). In which it will drop over time, as the battery inevitably leaks heat into the environment. I'd guess that after 6 months (summer to winter, as you mentioned) it will lose a non-trivial amount of energy so the efficiency will be even lower. [1] - Actual rates from deployed systems from the EIA: https://www.eia.gov/todayinenergy/detail.php?id=46756 https://www.eia.gov/todayinenergy/detail.php?id=46756 [2] - https://www.energyvault.com/newsroom/energy-vault-announces-commercial-availability-of-transformative-utility-scale-energy-storage-technology https://www.energyvault.com/newsroom/energy-vault-announces-...
  - Schroedingersat 4y ago
    Laege scale thermal storage has surprisingly low losses to the point where a 10GWh scale system can disregard them over a year. Cube square helps a lot here. Your heat engine is where you lose all the energy. Batteries are great and getting better. There's a reason most storage uses them, but they're ill suited to multi month storage due to cost. The best contender here is chemical fuels (which have similar efficiency penalties). Energy vault is, at best, a very poor subsitute for batteries. A 1000 tonne block on top of a 500m tall stack can store $20 worth of solar energy and might sell it for $80. If you use it annually, then you get $60/yr. If you use it 1000 times a year it might be viable compared to current generstion batteries, but that will change quickly as there's no real way to make it more economical. Ignore it and tell anyone who suggests using it as anything other than 4hr storage they're probably being scammed. Thermal batteries are the budget option. You can store about 5-20Wh/kg in whatever thing that's lying around that doesn't turn into a gas or become too corrosive. By every other metric they are terrible, but they are, in the most literal sense possible, dirt cheap (although you generally use low grade sand or maybe water because dirt is too valuable). The use case is mostly providing very cheap heat with energy that is not valuable enough to store with other methods. Insofar as using the concept for work (where the efficiency penalty lies), the logic would probably be something like: -- I have free energy noone wants (curtailed wind during midday summer) -- I have free sand noone wants (someone dug a hole and wants to get rid of it), but it costs me a little more to move it and build a silo than I will get paid to dispose of it. -- I have a free steam engine with its exhaust hooked up the district heating noone wants (a coal generator went bankrupt because renewables replaced it). I'll put the heat in sand, then make steam with it in winter (extracting 20-30% of the original energy as work), then pump 50-60% of the original energy into homes as heating (losing about 20% in the pipes and steam engine and some during storage).

unwind 4y ago

I thought heat output was the main effect, thus the talk about "district heating pipes" in the list of components. With nuclear power generation I thought there was no need to store energy, since it can generate at all times and ramp up/down pretty quickly.

breischl 4y ago
I'd say the marketing on at least this article is more geared at the electric energy. Heat is a form of energy for sure, but not a big enough one that it could "transform clean energy". Nuclear can be ramped, but typically is not. I haven't dug into why, but I get the impression it's partially economic - the plants are very expensive to build and the marginal cost of a few hours of fuel is so low that they prefer to just run all the damn time. I think there may be some technical reasons as well. In general if you look at how utilities operate, they will ramp down literally everything else before the nuclear plants. That probably applies less to the Small Modular Reactors people keep talking about, but those are still not really a factor.

Schroedingersat 4y ago

30% of that noon day summer sun looks pretty good on a cloudy day mid winter. In some places where mid-winter PV output is 1/4 of summer, it *already* makes sense to overbuild by a factor of 4. Keeping 30% of the summer energy would double the winter output. Of course this only makes sense if the electricity extracting bit is much cheaper than wind.

breischl 4y ago
Indeed! But getting ~80% back from batteries or pumped hydro looks even better[1]. Or, the ~90% that EnergyVault claims[2]. I'm very much pro-renewables and pro-storage, but that doesn't mean that all forms of storage are equal. This one has certain advantages (cheap, simple, tough), but the roundtrip efficiency kinda sucks compared to some other options. And I'm guessing (without checking) that the 30% is for short-term storage (eg, overnight). In which it will drop over time, as the battery inevitably leaks heat into the environment. I'd guess that after 6 months (summer to winter, as you mentioned) it will lose a non-trivial amount of energy so the efficiency will be even lower. [1] - Actual rates from deployed systems from the EIA: https://www.eia.gov/todayinenergy/detail.php?id=46756 https://www.eia.gov/todayinenergy/detail.php?id=46756 [2] - https://www.energyvault.com/newsroom/energy-vault-announces-commercial-availability-of-transformative-utility-scale-energy-storage-technology https://www.energyvault.com/newsroom/energy-vault-announces-...
- Schroedingersat 4y ago
  Laege scale thermal storage has surprisingly low losses to the point where a 10GWh scale system can disregard them over a year. Cube square helps a lot here. Your heat engine is where you lose all the energy. Batteries are great and getting better. There's a reason most storage uses them, but they're ill suited to multi month storage due to cost. The best contender here is chemical fuels (which have similar efficiency penalties). Energy vault is, at best, a very poor subsitute for batteries. A 1000 tonne block on top of a 500m tall stack can store $20 worth of solar energy and might sell it for $80. If you use it annually, then you get $60/yr. If you use it 1000 times a year it might be viable compared to current generstion batteries, but that will change quickly as there's no real way to make it more economical. Ignore it and tell anyone who suggests using it as anything other than 4hr storage they're probably being scammed. Thermal batteries are the budget option. You can store about 5-20Wh/kg in whatever thing that's lying around that doesn't turn into a gas or become too corrosive. By every other metric they are terrible, but they are, in the most literal sense possible, dirt cheap (although you generally use low grade sand or maybe water because dirt is too valuable). The use case is mostly providing very cheap heat with energy that is not valuable enough to store with other methods. Insofar as using the concept for work (where the efficiency penalty lies), the logic would probably be something like: -- I have free energy noone wants (curtailed wind during midday summer) -- I have free sand noone wants (someone dug a hole and wants to get rid of it), but it costs me a little more to move it and build a silo than I will get paid to dispose of it. -- I have a free steam engine with its exhaust hooked up the district heating noone wants (a coal generator went bankrupt because renewables replaced it). I'll put the heat in sand, then make steam with it in winter (extracting 20-30% of the original energy as work), then pump 50-60% of the original energy into homes as heating (losing about 20% in the pipes and steam engine and some during storage).