> >Or we will have to harness the solar power that lands on our roofs for
> >free! When you consider the amount of insolation available on the
> >average roof, it seems quite ridiculous to ship gas (sometimes
> >literally) across the world to heat water for a shower.

The landing may be free but the utilisation usually isn't.

Unsubsidised crystalline silicon photovoltaic energy is about twice
grid parity cost now with a substantial degree of spread in the break
even point due to insolation levels and local power prices. Some
alternative systems are suggesting substantially lower pries now (eg
Cadmium Telluride) but long term viability is in doubt.

Small scale solar thermal is often marginal. When i have costed
domestic systems over the years the pay back periods or IRR are
usually long and low to the extent that maintenance uncertainties make
them very doubtful. Grid supply scale solar thermal - with a  seconday
conversion to electricity, is marginally viable at present with new
stations being bult in especially well suited areas (eg new plant at
Guila bend in Arizona (memorable town to me for the most uncomfortable
"sleep" I ever had)).


                   Russell
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