Lindsey's Comments

The claimed efficiency looks unbelievably high. How is it achieved and has it been independently verified. I would have expected to see a figure nearer 50% for conversion from electricity to compressed air then back to electricity again.

How much energy is expected to be stored in the final phase test bag?
(You don't measures energy in kW so there is some sort of error in the last line.)

Thanks Michael, a good article. Now I would like to see you do a comparison of micro-inverters with the technology you have explained . (Efficiency, cost, reliability, simplicity etc.) Here in New Zealand we have a 230 V 50 Hz system. Apart from a reduction in I2R losses wire size for wire size and W for W probably slightly biasing the results towards micro-inverters I suspect it doesn't affect the argument much.

Here in New Zealand, there is no subsidy for electricity generated from wind. Neither is there any legal requirement that a certain percentage has to be generated by renewable – and emissions charges have not yet cut in. Yet wind is competing head on with the alternatives – indeed it is the majority of new generation that has been added to the grid in the last few years. While about 2/3 of our electricity is hydro, a significant chunk of the rest is geothermal and we have conventional thermal generation as well, perhaps it is explained because we have better wind resources than many other countries.

Interesting. It is not just electricians and solar panels. Massachusetts has what look very like trade-protection rules around installation of gas fired clothes dryers that we haven't run into anywhere else in the world.

Ralph and Michael, you do not mention the algae option – or include it in your figure 1.
Any comments?

Remeber that emissions of CO2 often accompany geothraml fluids at various rates. See  http://www.beehive.govt.nz/speech/nz+geothermal+association+agm where New Zealand values for different fields feeding our geothermal power stations are quoted.  They range from 35 g/kWh to 600 g/kWh.  The latter value is worse than combined cycle gas generation but better than coal-based electricity.

It is not clear why the article omitted full-scale hydro from the "renewables" list - unless it is only discussing so-called "new" renewables.  Here in New Zealand (1st 1/4 2007 data) 66% of electricity generated (not generating capacity, note) was from hydro and wind (most of it hydro).  Geothermal (6%) and biomass generation brings the total to 74%.  Total annual consumption for NZ (year ending March 2007) was 40,146 GWh.Data is from the Aug 2007 "Energy Watch" journal (see www.energywatch.org.nz).Fastest growing sector is wind (in GWh/year terms not just in % increase of that sector).  Second would be geothermal.