Air-compressor efficiency ~ what percentage of efficiency?

We are working on a university project with a team of colleagues. We are working our way backwards from a compressed air tank to the energy grid powering the air compressor. We already have calculated the energy required to compress the air in the tank and we need an average air compressor efficiency in order to reach the energy required by the grid. However, searching around has got us nothing, we cant seem to find an average value of air compressors efficiency anywhere. Would it be accurate to assume an efficiency of 80-90% for a market existing air compressor or is it way off these values?
Thank you in advance for your time
Giannis Dafnomilis, Delft, Netherlands

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Bill says...

Giannis, I am sorry, but I cannot commit to a standard of 80-90% efficiency for compressors, as each make of compressor and the efficiency of the motor used in that model will vary. I just don't know what the range will be.

If it were me doing your project, and assuming that you will end up with a formula, why not offer results based on a range of compressor efficiencies? For example, if the compressor has an efficiency of 50%, then xxxx is the result. If 60%, then yyyy, and so on.

Or, pick the top 5 or 10 worldwide compressor manufacturers and ask them the average efficiency of their compressors.

Cheers,

Bill