We’ve been thinking about the economics of putting PV panels on the roof, particularly to offset the power requirments of the ground source heat pump, which takes 2.8 kW when it’s running. Although we are getting this electricity from Good Energy who use only renewable sources, it still costs a lot and anyway the capacity isn’t currently there for the whole country to use renewables. So, a good idea but a pity it’s so expensive since it could help our commitment to saving 10% of our emissions as part of the amazing 10:10 campaign. We were also worried about the degree of shading by trees – more on that later.
What has suddenly changed the cost equation is the Labour government’s introduction of the Feed-in Tariff. This pays 41.3p for every kW we generate. What’s so amazing is that they pay this much (around 3 times the cost we buy it at) whether we use it or export it. So we have a double saving. It’s a no-brainer for middle class families that have the space and capital to invest in it.
So I looked around for a reputable installer, having heard there were a lot of pirates out there. I came up with Ardenham Energy of Aylesbury, who have turned out to be excellent. Following a site survey, they quoted £11,316 to install 16 panels with a total output of 2.88kW. This included the scaffolding and the rather complex electrical installation, since 2 inverters to be needed for this capacity.
Very important at this stage is their expert prediction of the likely annual output in practice. They estimated this at 2,448 kWhours. This would provide a feed-in tariff of £1,011, a saving of £147 and an export return of £37, making a total each year of £1,195. So the system would pay for itself in 10 years and provide this much income and savings thereafter. And of course it would be mean that a proportion of our electricity use would be entirely emission free.
The only snag that arose was the discovery that the current generation of inverters have the strange property that if even one of the 16 panels is in shade, the output of all of them is reduced. There is a new generation of inverters to avoid this but they were not available at the time.
So we accepted the quotation.