Not just blowing in the wind: Compressing air for renewable energy storage

[kristopher]

9. Poor little nuclear loving wtmusic...

You would rather live in an alternate reality than admit that all the pieces are in place for a carbon free/nuclear free world, wouldn't you?

2.4.3.2. Round Trip Efficiency
A CAES unit powered by wind energy will be compared to other electrical storage options that might be considered for wind back up such as electrochemical or pumped hydroelectric storage. Such alternative storage systems are typically characterized by a roundtrip electrical storage efficiency ηRT defined as
ηRT = (electricity output)/(electricity input).

To facilitate comparisons of CAES to other electrical storage devices, a round trip efficiency can be introduced that employs an “effective” electricity input ≡ EM + ηNG*EF. The second term is the amount of electricity that could be have been made from the natural gas input EF, had that fuel been used to make electricity in a stand-alone power plant at efficiency ηNG instead of to fire a CAES unit. ...

For typical natural gas power systems, (heat rates in the range 6700-9400 kJ/kWh) CAES roundtrip efficiencies are in the range of 77-89% assuming a 1.5 ratio of output to input electricity and a heat rate of 4220 kJ LHV per kWh. An exergy analysis of conventional CAES systems indicates that 47.6% of the fuel energy input is converted into electrical work [71]. For this measure of the thermal efficiency, the roundtrip efficiency is 81.7%.

An alternative formulation ηRT,2 of an electrical roundtrip storage efficiency introduces an output correction term EF*ηNG. Instead of expressing the fuel input as an effective electrical input, the electrical output is adjusted by subtracting the assumed contribution to the output attributable to the fuel. Correspondingly the output attributable to the electrical input is ET - EF*ηNG [72].
Using the same assumptions as for ηRT,1 with the Zaugg efficiency for fuel conversion, ηNG = 47.6%, the round trip efficiency is 66%.

Thus, depending on the index chosen for its measure, the roundtrip efficiency for CAES is typically in the range 66-82%. This is in the same range as the roundtrip efficiencies cited for other bulk energy storage technologies such as pumped hydroelectric storage (74%) and Vanadium flow batteries (75%)

Compressed Air Energy Storage, Succar and Williams April 2008
http://www.princeton.edu/pei/energy/publications/texts/SuccarWilliams_PEI_CAES_2008April8.pdf