In (solar) hot water?

Back in January I posted about some of the eco-friendly kit installed in my house. I’ve now had chance to get to grips with my solar water heating after quite a few months of use. So, what’s it like?

Photo: (Left) Roof-mounted, solar hot water panels; (right) info panel, with T1 (roof panel), T2 (tank bottom), T3 (tank top) temperatures given

First, the lack of instructions meant there was some trial-and-error involved in getting to know how to use the system. An important factor turned out to be to switch off the ‘mains’ hot water system. Of course, no one had told us this! Without that step, the solar hot water system doesn’t get a chance to run fully. The ‘mains’ gas will heat up the tank and the solar hot water will never – or very rarely – be pumped in to top up the tank with the ‘free’ hot water from the sun.

Second, in the climate of the North of England, even with quite a lot of sun, the hot water seems unlikely to ever go above 45 degrees C. By contrast, the ‘mains’ hot water is set to heat water to about 65. It’s an interesting test of what’s necessary and what’s tolerable to my family and I though. We get on fine with 45 degrees C for showers, washing and so on. It is noticeably cooler than, and not quite as relaxing as ‘mains’ heat. But it’s not a problem. Only when the temperature of the stored solar hot water drops to the low-30s do things get a bit uncomfortable – although this does shorten our shower times so we save on water then!

Third, three days in a row of overcast skies necessitates returning to the ‘mains’ system – albeit switching it on for 10 minutes is usually enough, given that the tank is not stone cold due to the buffer from the solar system.

I must say that having the kit has made me more acutely follow the daylight hours and cloud cover. From about March to mid-September I managed, by rationing and timing usage to sunny conditions, to switch off the ‘mains’ hot water completely. The solar hot water on its own was enough. I can’t say how much money – or gas – we saved yet. I haven’t lived here long enough to tell our seasonal usage and cost patterns. But the summer quarterly gas bill was quite low (about 30 GBP). Of course the central heating was off too during that period.

I’d say the cash saving seems modest at present. With regular price rises though, the benefit may increase in future… ‘Carbon’ still has only the weakest of roles in our economy as well. Were that situation to change the financial aspect might get stronger too.

Fourth, we’ve now reached a time of year – and temperatures – that the solar hot water will struggle with. The roof-mounted panel temperatures are getting so low that the system will not feed the solar system’s liquid into the flow. So for about half the year, in our climate, the system will be effectively dormant.

Overall though I’m impressed with the system. The feeling of having ‘free’ hot water is great – though there are pumping costs involved (you can hear it going when it’s working). The cash saving appears modest, and the system is only going to be usable – in this part of the world – for about half the year. Still I’m glad the system came pre-fitted on the house, as I think my experience makes a fairly weak case for a retrofit cost-benefit analysis so far…

In sunnier climes though, first-hand experience of a system like this does make me feel that it’s insanity not to have solar hot water installed as standard, by law.

I spent several weeks last month in two far sunnier places than the UK – Rome (Italy) and Atlanta (Georgia, USA). (Hence the lack of posts these past 6-8 weeks!) With long hours of daylight and strong, warm sun, I expect you could switch off your ‘mains’ hot water for about 9-10 months in a year – even with fairly heavy demands on a system. Solar hot water systems are still a rare sight in the UK, it’s true. But sadly I saw no evidence of any during my trips abroad – in spite of the benefits they’d likely bring.

Well, here’s hoping for some positive change in this direction. After having lived with the results for a little while now, I can say I think it’d be worth it!

Duncan Thomas


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