PG&E to compress air to store wind power

[Jason M. Hendler]

PG&E to compress air to store wind power:

Link

[pdt]

300 MW and 3 GWh! I wonder what that's going to cost...

[Jason M. Hendler]

300 MW and 3 GWh! I wonder what that's going to cost...

A whole lot less than 300 MW - 3 GW of batteries - that's for sure ...

All you need is a large compressor - the empty chamber within a salt or basalt formation is free.

[wtiger]

I wonder what the energy loss to the ground would be; since compressed air is much hotter than the same mass of uncompressed air while containing the same amount of energy. How much of the energy are you going to loose to the surrounding, much cooler, earth.

[pdt]

A whole lot less than 300 MW - 3 GW of batteries - that's for sure ...

All you need is a large compressor - the empty chamber within a salt or basalt formation is free.

Sure, but how much? Also, I wonder what the efficiency will be. I'm guessing it will be lower than pumped hydro due to the heat transfer issues mentioned in the previous post. 50%?

[Jason M. Hendler]

Since the compressed air tends to cycle in and out, there isn't sufficient time for significant heat transfer to occur, per articles I read years ago. There is usually one period of time during the day when wind is high and another when it is low and demand also fluctuates daily, so these systems aren't intended for long term storage.

Remember, air is a good insulator (vs. liquids and solids), so these systems are still efficient.

[pdt]

Looks like I had a good guess at 50%:

http://www.livescience.com/technolog...4-pf-caes.html

If heat storage is used, apparently ~70% efficiency is possible, of course, the heat storage hardware would add capital as well as maintenance costs.

It will be interesting to see how this all works out!

[Jason M. Hendler]

Put,

Great find. If they are looking for an efficient means to store heat, then liquid salt is the best answer.

70% is good when you are looking at cost efficiency, as this smoothing allows you to use fewer wind turbines and no batteries to meet demand.