Installing solar electricity

Back before Christmas (see posting dated 2 December 2009) I wrote about having solar hot water panels fitted to my roof. At the time they were installed to one side, not centrally, to leave space for solar electricity panels to be added later. Well, that’s now been done – my panels were installed last week. The whole job took two and a half days, excluding the erection/dismantling  of the scaffolding.

As before, because my house is east-west oriented, I’ve had to have two sets of panels, and thus two control mechanisms. This adds to the initial cost of course, and the estimate is that I will get 85-90% efficiency compared with a south-facing roof installation. The design of the system is dependent on the amount of roof available, so I have ended up with six panels at the front and six at the back.

The company I used was JHS Power Solutions Ltd.  The case study currently up on their website is my friend Caroline, who lives just across the allotments from me, and who recommended this company to me. She has 10 panels facing south, giving roughly the same generating capacity as my 12 panels split east-west. I have Sanyo panels, with an estimated annual yield of 2064 kWh. The total cost of an installation varies with the number of panels fitted, and the fact that mine is an east-west system added about £800 to the overall cost because of needing two control systems.

If I had arranged to have the water and electricity panels fitted at the same time, I could probably have saved £800 or so in scaffolding costs – but that had to be balanced against time and convenience in fitting the work around the rest of life. The total cost of this work was about £15,000, of which I will get £2,500 back as a grant from the government’s Low Carbon Buildings scheme. I didn’t claim a grant for my solar hot water – if I had done, I would have received £400 for that and only £2,100 for the solar electricity; there’s £2,500 in total available to each household. I didn't need to obtain planning permission because my house isn't a listed building and I don't live in a conservation area.

The final result looks like this at the front:

And like this at the back:

The electrical connections are fixed under the roof tiles, and the tile replaced:

Long brackets are fixed to support the panels:

The panels are fixed on:

And then the brackets are trimmed to fit:

Getting these panels up onto the roof was much easier than lifting the solar hot water panels – that took four men, two ladders and ropes! These are much lighter and can be carried up by one person:

Each array of six panels is wired up in series, producing direct current (DC). Our houses are wired up to work on 240v alternating current (AC) so the power from the panels passes through an inverter to convert it to AC at the correct voltage for the house. The east-west orientation means that the front and back panels will be producing different voltages, so each has to have its own inverter. These are installed up in the loft, out of the way, alongside an isolation switch – if an electrician were working on something in the house, the solar power would have to switched off, as well as the mains power.

The inverters are very clever boxes of sophisticated electronic tricks that manage the interaction between the solar power and the mains electricity grid – ‘renewable’ this may be, but low-tech it ain’t! The displays on the boxes give readouts of electricity being generated at the moment, and total electricity generated since they were commissioned.

There’s another control system in the front porch, alongside the meter and fuse box – plus another isolator. The readout here shows total electricity generated (both arrays amalgamated) as here the two outputs are combined and fed into the house or the grid:

The solar power generated is used first in the house. If the house needs, in total, more power than the panels are generating at that moment, then the balance is drawn in from the grid; if the house need less, the excess is exported to the grid. You are paid for everything you generate, even if you use it yourself; and from 1 April this year, there will be a ‘feed-in tarriff’ which means that this payment will be raised to provide an incentive for householders to install solar or wind power. You will receive more per kWh for what you generate than you pay per kWh for what you consume from the grid. These payments are handled via your electricity company.

Although most people aren’t motivated first to do this for financial reasons, the new arrangements certainly change the financial equation so that it really does pay to be green. The Guardian’s ‘Money’ supplement last Saturday carried a major article by Miles Brignall, ‘The brightest investment?’ arguing that there is now enough financial benefit to make this a positive option on those grounds alone, as the average pay-back time will be reduced to only 10 years.

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