It is extremely rare that I feel that I can contribute anything useful 
to this knowledgeable list and so I must seize this opportunity. Sadly 
it is not a Linux related technical question and I feel I must wait many 
years for that to happen.
However there has been a revolution in PV panel economics since April 
1st (seriously) when the Government introduced extremely generous Feed 
in Tarifs.
 
http://www.energysavingtrust.org.uk/Generate-your-own-energy/Sell-your-own-energy/Feed-in-Tariff-Clean-Energy-Cashback-scheme
Anybody producing from wind or solar will get a payment of 41p per kwH 
generated whether you use it yourself or export it. To compare 
electricity costs about 11p /Kwh. In addition you get 3p /kwh for 
exported electricity. All this is guaranteed for 25 years and is tax 
free. It is looking like a 7-8% tax free return on an investment of 
about £9 - 10,000.
However critics such as George Monbiot say this is a waste of money 
because only the middle class benefit and non roof owners will have to pay.
I have been thinking of installing PV myself for some time for the "feel 
good factor" . To cut costs I was planning to import the equipment from 
Germany (surprisingly they generate over 50% of the worlds solar 
electricity) and install it myself but a self install would not qualify 
for the old grants. Unfortunately the feed in tariffs will not be paid 
to self installers either.
However having looked at what is required to become a certified 
installer I am toying with becoming one.
When I eventually get my PV panels, I want to do some serious domestic 
monitoring of energy in and out to see for myself whether this is a 
viable contribution to the climate problem. This would probably be based 
on something like the Sheeva plug or a using a Linksys router with Linux 
providing I can get some data into them. So any advice on current 
monitoring would be helpful.
Roger