Donnacadh McCarthy

Eco auditor Donnacadh McCarthy has kitted out his home with every form of micro renewables you can imagine. He explains why solar thermal is one of his favourites:

I innocently thought installing solar-electric panels would sort out my house’s carbon emissions. 

I hadn't realised how much CO2 is involved in heating water. The average electric immersion heater uses the energy of 600 energy-saving bulbs. So when my gas boiler died I resolved to replace it with a solar hot-water system.

How did you go about making the decision?

I confess the decision-making process was quite complex. There was a whole range of technical decisions to be made: how many solar-heating panels, how big a tank, what type of back-up system, how to power the pump, planning permission. And while all this learning was going on, I was without hot-water.

I finally installed a single Filsol panel, with a 150 litre electric-immersion heater. This works by pumping anti-freeze in a pipe through the hot water tank, up to the roof solar panel, where it collects the sun’s heat and back down to the tank, where it heats the water - in techie terms, it is a heat-exchanger.

The pump is powered by a small solar electric panel, which kicks in when the temperature on the roof is more than 5 degrees hotter than the water in the tank.

How much of your hot water can be generated by solar?

Between early May and mid-October last year, my back-up immersion was not used once. The industry claims the systems provide up to 70 per cent of hot water needs and that has been my experience - but you need a warm-feed washing machine to use it for washing clothes.

Even on Christmas day, my tank was a respectable 20°C, requiring only a modest boost to shower in.

The world of solar hot-water, however, has the occasional shark in it.  I have had calls from people who had useless systems installed. Their panel was so far from their taps, the water was cold on arrival.

What advice do you have for finding a reputable installer?

Ensure your installers are Energy Savings Trust approved or members of the Solar Trade Association. Systems cost from about £2,500 - £5,000. There are grants of £400 available from the Low Carbon Building Programme (temporarily suspended since March 2007) and many councils have supplementary grants. In London, they're arranged by Solar for London.

When my system finally got installed, it was exhilarating to shower naked in hot water heated directly by the sun and not by nasty nuclear or fossil fuels.

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