This easy-to-use interactive solar pv energy calculation software calculates the electrical energy and carbon dioxide emissions generated/saved in accordance with SAP2005 Appendix M. It can calculate for up to 4 different arrays on a building at varying orientations and sizes. The calculation does not take account of the recent feed-in tariffs.

On 1st February 2010 The Government confirmed the feed in tariffs which will come into force on 1st April 2010. For someone fitting a typical 2.5kW photovoltaic solar system to an existing home (at a cost of around £12,500), a payment of 41.3p per KWh generated will be paid whether that electricity is exported or used by the home owner. A further payment of 3p per kWh will be made for each unit not used and therefore exported to the grid. New-build properties fitted with solar panels will receive a lower tariff of 36.1p per kWh generated.

These tariff payments are guaranteed for 25 years and they are also index linked - i.e. they will rise in line with inflation. The typical 2.5kW system will generate tax-free payments of around £1000 per year, and so the payback on the investment will be around 12 years.

This also works out as a tax-free return on investement of 8% - far better than any bank account offers, and particularly attractive to those paying tax at the higher rate. Since the electricity generated can be used by the homeowners, they are also rewarded with a £150 reduction in their electricity bill with a 2.5kW system.

Therefore, if you are lucky enough to have £10-12,500 in the bank AND have a south (or nearly south) facing roof, you'll struggle to find a better financial investment than installing a PV solar array on your home, and you'll reduce your annual carbon emissions by approximately 1.1 tonnes.