Grid storage using heat pump and thermal storage

Interesting proposal. Insulating the storage vessels and plumbing and maintaining the stratification of heat will be among the technical challenges.

I'd really like to see a prototype... Carnot engines are limited to ~40% thermal efficiency... I know it's a heat pump but if that's how it's getting closer to the ~80% efficiency of pumped storage there must be an optimum band for operation.

nwdiver said:

I'd really like to see a prototype... Carnot engines are limited to ~40% thermal efficiency... I know it's a heat pump but if that's how it's getting closer to the ~80% efficiency of pumped storage there must be an optimum band for operation.

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Since a heat pump simply moves heat they can be as much as 300% efficient. So it is a very different way to measure efficiency and in this case I think it is the right way.

In a similar vein I heard a chemist show how EV will not work as even an 85 KWh pack only holds the same energy as 2 gal of gasoline implying range is terrible. While what he said is true with the gasoline engine being only 25% efficient versus 90% for an EV drive train it is like you have 9 gal of gas not 2.

dhrivnak said:

In a similar vein I heard a chemist show how EV will not work as even an 85 KWh pack only holds the same energy as 2 gal of gasoline implying range is terrible. While what he said is true with the gasoline engine being only 25% efficient versus 90% for an EV drive train it is like you have 9 gal of gas not 2.

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That made me chuckle. Classic case of reaching an incorrect conclusion because of a failure to look at the big picture and not include all relevant factors in the analysis.

dhrivnak said:

Since a heat pump simply moves heat they can be as much as 300% efficient. So it is a very different way to measure efficiency and in this case I think it is the right way.

In a similar vein I heard a chemist show how EV will not work as even an 85 KWh pack only holds the same energy as 2 gal of gasoline implying range is terrible. While what he said is true with the gasoline engine being only 25% efficient versus 90% for an EV drive train it is like you have 9 gal of gas not 2.

Click to expand...

Carnot's theorem, developed in 1824 by Nicolas Léonard Sadi Carnot, also called Carnot's rule, is a principle that specifies limits on the maximum efficiency any heat engine can obtain, which thus solely depends on the difference between the hot and cold temperature reservoirs.
Carnot's theorem states:The formula for this maximum efficiency is
Maximum Efficiency = Carnot Efficiency = (1 - Cold Temperature /Hot Temperature)
Where the each of the Cold Temperatures and the Hot Temperature are absolute temperature (measured in degrees Kelvin).

Carnot's theorem is a result of the second law of thermodynamics.

Applying Carnot's theorem to the proposed storage system (hot reservoir of 500 degrees C and cold reservoir of minus 160 degrees C) yields a theoretical maximum efficiency of around 85%.

The maximum efficiency of this heat storage system is therefore limited by its ability to generate and sustain the 660 degree C temperature differential between the two reservoirs. (Hence my previous observations relating to factors which could prevent the system from generating or maintaining the massive temperature differentials required to achieve reasonable efficiencies.)

See: http://en.wikipedia.org/wiki/Carnot's_theorem_(thermodynamics)
http://en.wikipedia.org/wiki/Heat_engine
http://en.wikipedia.org/wiki/Carnot_heat_engine
http://scienceline.ucsb.edu/getkey.php?key=4019
http://www.rapidtables.com/convert/temperature/celsius-to-kelvin.htm