Solar water cost and ROI

Our panels (a pair of evacuated tube panels) set us back of the order of £9000 in (if I remember correctly) 2004. With hindsight, I think we did this too early - the price of a similar system has now dropped considerably (more like £2500-5000, apparently). We're probably saving £50-80 a year, so the ROI time is... a while yet.

On which topic, it's worth noting that our suppliers went out of business, and were taken to court indirectly over their rather inflated ROI claims, and we did get £4000 back as a result. We're currently using the local Peterborough Boiler Services to maintain our system (not that it needs much!), and are pretty happy with them.

It's also worth noting that there are two government incentive payments for solar hot water, one of which is available now, one to come. The one available now is the Renewable Heat Premium Payment, which is (or pretty much was since the deadline is March 31st) a scheme which pays £300 for any solar water heating install since Aug 1st 2011. The future one is the Renewable Heat Incentive - basically, if you've installed since 15th July 2009 (bother!), you will be eligible for some form of payment similar to the solar PV Feed-In Tariff.

As I said, with hindsight, we should probably have left it a couple of years: I'll get some stats upon a subsequent post for the last few years' gas bills, so you can see how much we've saved. Either that or I'll give Anne posting rights on this blog, and she can!

Our solar water heating system

Our solar water heating consists of a couple of panels on the roof of our outbuildings. They show up very clearly in the Google Maps aerial view, although (as of this post) the Maps view is out of date, as we had them moved in 2010 one 'bay' of the roof closer to the house.

The control unit is mounted on our inner landing next to the airing cupboard. Very usefully, it comes with three temperature sensors, one monitoring the temperature of the panels, the other a pair that measure the temperature at the top and bottom of the hot water tank. Essentially, how it works is that if the temperature of the panels is greater than the bottom of the tank (and less than 60ºC), water is pumped round the panels, heating it up. [The astute will note that this uses electricity. The really astute will note that this uses electricity when the sun is out, and we (as mentioned) have solar PV for that!]

Since we've had it installed, we pretty much don't pay for hot water between mid-March and late October, as the solar heating is generally enough to maintain enough of the tank at 40ºC or better for baths, showers and washing up. Sadly, it's not possible to buy a hot-fill washing machine any more, though, so ours does heat water itself for laundry.

I'd go so far as to suggest that even if you don't get solar water heating installed, sticking a pair of contact temperature sensors on the top and bottom of your hot water tank that you can monitor is incredibly educational. Apart from anything else, it cures you completely of setting the central heating timer to heat your water twice a day for an hour, since:

1. we certainly don't use that much hot water in a day
2. the boiler will heat the top of the tank to 60ºC in about 20 minutes flat (and remember, the top of the tank is where you take water from!)

Sadly, our controller doesn't talk to a PC, so as of yet we don't graph the temperatures or track if the pump is running. As ever, however, watch this space, as I have plans.