3 ms·

* Round-trip energy efficiency: I can't see a system taking electrical input to produce liquid air on the way in and similarly to run a turbine generator on the

* Round-trip energy efficiency: I can't see a system taking electrical input to produce liquid air on the way in and similarly to run a turbine generator on the other end without having substantial losses both ways... I believe Tesla is around 88% on their system. Well you can just power an engine on the temperature gradient. That's going to incur some losses though. This seems to be the downside of storing energy cooling stuff, you have to fight the second law of thermodynamics both ways.

ncmncm 5y ago
You get to run both a heat engine, on the temperature difference, and a turbine, on the resulting boiled-off gas. So, you get benefit of thermodynamics both ways. Furthermore, the heat engine uses heat pumped out and saved from liquifying the gases. It is typically a mistake to assume people behind an innovative development, that they are spending $150M on, are idiots.
- AtlasBarfed 5y ago
  Is that analogous to how turbochargers can get ICE engines to exceed carnot limits?
  - ncmncm 5y ago
    Turbochargers run in open-cycle engines that are not bound by Carnot limits. Diesels run on the Rankine cycle, and gasoline engines run on the (similar) Otto cycle. Both of those take in cold air and exhaust hot air, so can be more efficient than an engine that runs a fixed supply of working fluid around the Carnot cycle. Turbo- and super-charging enables an engine with a given displacement to take in more air, and thus can burn more fuel, than one that must fill cylinders with no more than ambient air pressure; and can thereby deliver more power. It doesn't change the engine's thermodynamic profile.
- contravariant 5y ago
  In the end you're still powering something by letting something cold grow warm, so I'm not seeing how you could avoid the second law of thermodynamics. I suppose that in theory the cooling step would be where you could recoup your losses a bit by using an efficient heat pump, but getting the coefficient of performance greater than 1 could be pretty difficult for such extreme temperature differences.

ncmncm 5y ago

You get to run both a heat engine, on the temperature difference, and a turbine, on the resulting boiled-off gas. So, you get benefit of thermodynamics both ways. Furthermore, the heat engine uses heat pumped out and saved from liquifying the gases. It is typically a mistake to assume people behind an innovative development, that they are spending $150M on, are idiots.

AtlasBarfed 5y ago
Is that analogous to how turbochargers can get ICE engines to exceed carnot limits?
- ncmncm 5y ago
  Turbochargers run in open-cycle engines that are not bound by Carnot limits. Diesels run on the Rankine cycle, and gasoline engines run on the (similar) Otto cycle. Both of those take in cold air and exhaust hot air, so can be more efficient than an engine that runs a fixed supply of working fluid around the Carnot cycle. Turbo- and super-charging enables an engine with a given displacement to take in more air, and thus can burn more fuel, than one that must fill cylinders with no more than ambient air pressure; and can thereby deliver more power. It doesn't change the engine's thermodynamic profile.
contravariant 5y ago
In the end you're still powering something by letting something cold grow warm, so I'm not seeing how you could avoid the second law of thermodynamics. I suppose that in theory the cooling step would be where you could recoup your losses a bit by using an efficient heat pump, but getting the coefficient of performance greater than 1 could be pretty difficult for such extreme temperature differences.