Sunday, 07 August 2022

Using the sun to heat your water

Using the sun to heat your water

WHAT do you look forward to in July? As a child, I loved those long warm days of school summer holidays which seemed to stretch on forever. Maybe you’ll be taking a relaxing holiday on the beach, or a welcome break from work? Me, I look forward to free hot water.

Some years ago we installed a solar thermal panel on our roof. Unlike a solar photovoltaic panel, these do not generate electricity but it warms water directly for your hot water tank. Sunlight warms the panel on the roof, which contains loops full of a glycol/water mix. The sun warms the fluid in the loops which in turn heat cold water from your tank and automatically pump it back down.

Our experience has been that when the weather is sunny, the panels produce all of the hot water we need for a family of four. Even when the weather is cooler, the panels will heat the water a little and our boiler can then complete the process. Only in the winter do we get nothing at all.

Solar thermal panels are a simple technology and there is little to go wrong. But, recently, our panels which we have had for more than 10 years blew a fuse and stopped working. Happily, I found that Henley Heating and Plumbing was able to mend them for me. So, it seemed like a good time to find out how popular solar thermal is and whether it’s worth investing in.

A typical system for a domestic home costs about £4,000 plus VAT, including installation. If you need scaffolding to get the panels on to your roof, this will add an extra £1,000 or so to the cost. So the price is not inconsiderable. At current costs for gas and electricity and using standard industry figures, a solar thermal system will save you about £257 a year if you currently use gas to heat your water, £599 a year if you use electricity.

So, if you have a gas boiler that’s a payback time of about 17 years, if you use electricity it’s about eight years. Of course, with the current frightening increases in gas and electricity prices, these will come down but don’t compare particularly favourably with solar photovoltaic when you will usually get your money back in about eight years for panels that will last on average for 25 years.

So is it worth it? Dave Parfitt and Adam Wheeler, of Henley Heating and Plumbing, told me that it depends on your roof. If you have a roof that is low enough not to need scaffolding installation costs will be significantly less.

Thermal panels are quite small in comparison to photovoltaic so will fit on a smaller piece of roof. But technology has moved on since I installed my panels and a better solution today would be to install photovoltaic panels and a battery to store any excess electricity generated and then use this stored electricity to heat your hot water. Dave and Adam did tell me that solar thermal is good for heating swimming pools — not a problem that most of us will have.

So, here are my conclusions. Solar thermal still has a place. It is a simple technology that will fit on to most roofs and is well worth it if you currently use electricity to heat your water. But you may be better off taking advantage of the huge fall in price of photovoltaic panels and batteries to store your own excess electricity and use that instead for water heating.

And, lastly, it’s very encouraging to see greener technology becoming cheaper and better.

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