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Heat on the cheap

‘Who says you can’t get owt for nowt’. Phil Gomersall, an experienced allotmenteer from Leeds, proved otherwise when he made his own solar soil heating system from an ice cream tub and an old radiator!

The Victorians used straw and manure to heat their raised beds, I fancied something a bit more up to date to heat mine in an attempt to extend the growing season in my polytunnel.

If you have lots of money you can use electric or LPG or fossil fuels but being a true allotmenteer I wanted to make do and mend and get heat on the cheap.

I’ve had an interest in solar thermal heating for some time and as I had a few bits and pieces kicking about I decided to create my own under-soil heating system. I had an old flat panel radiator and some 15mm copper tube (not ideal due to internal surface resistances but I thought I’d give it a go anyway) and a second-hand double-glazed unit.

Creating the solar collector
The solar collector was knocked up from some old boards and plywood, lined inside at the back and sides with old polystyrene packaging, the flat panel radiator was painted matt black and placed in the box unit. To cut down the double-glazed unit was a bit tricky but I managed with a glass cutter, sharp knife, pliers and some sealant to reseal it afterwards. Solar collector complete.

Under the soil in the raised bed I split the piping into two runs (more would have been ideal and with some medium such as stone chippings to hold the heat would have been even better) neither I had, so I didn’t use. The feed pipe was fitted with an uphill gradient to allow the heated water to rise and flow by gravity. At the high point a feed and expansion tank was fitted. In my haste to experiment and get the system up and running I used a plastic Wall’s ice cream tub (not ideal); a catering-sized bean tin would be a lot better.

The big day came all coupled up and raring to go. Would it work? Or leak? Would the sun ever come out? Eventually it did and wow! The feed pipe got amazingly hot in a short time and it did flow around the system when the sun was shining in a clear sky in February. Success!

The flow rate was however limited in hazy sunshine. A solar pump could be fitted but that would mean expenditure and defeat my aims. If ever I do it again, next time I will do what I already knew and fit a 22mm or larger pipe on the feed and have a much more efficient system.

But what the heck it works and sunshine costs nothing!

For more see this month's issue, available to buy online!

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