On Mon, 25 Feb 2013 10:48:53 -0800 (PST), Tom wrote:

But you name any energy system that is efficient. Input always greatly
exceeds output.

Ultimately the laws of of thermodynamics says that always has to be the case,
provided you prefix "output" with "useful".

What about heat pumps? Output input every time?

When installed and running yes (though air source are crap overall with air
temps between about freezing and a few degrees higher).

I think that PV has such a high manufacturing energy cost, poor conversion
effciency and only work for a few hours a day (on average) from a low energy
density source that they are going to really struggle to recoup a significant
amount of the energy used to make 'em.

Solar Thermal is better, lower manufacturing energy cost, conversion
effciency double if not more than that of PV, much better chance of becoming
energy posistive.

--
Cheers Dave.
Nr Garrigill, Cumbria. 421m ASL.