Is that actually important, though? Does it mean inexpensive small-scale energy caching in off-grid areas is impossible? Would a truck-carried air tank (or bank of them) hooked to solar-powered compressors not actually work, or be cost-prohibitive?
But it does. The Wikipedia numbers [1] give a mass density for compressed air storage of 40 kJ/kg and volume density of 8 kJ/L. That's 0.011 kWh/kJ or 0.0014 kWh/L. So a 10,000 L tank gets you only 14 kWh, or ~$1.50 worth of energy.
