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Editor's Note: CR4 would like to thank Del the Cat for writing this story and
sharing photographs of his DIY solar hot water panels. Cheers, Del!
Thinking of building your own solar panels? My main advice
is simple: go for it! For this DIY project, the most expensive items were the
copper pipe, glass, and aluminum sheets. If you can find any of these for free (or at a good price) and in vaguely the right size, then get them. But don't make the panels
too big, for they will be heavy. (Mind you, it would be interesting to try
polycarbonate sheet instead of glass.)
With regard to performance and setup, I moved the thermostat
for the gas hot water slightly higher on the tank. In the summer, I turn it
down a tad so that on dull or wet days (like all of June and July last year),
the gas boiler kicks in to provide hot water. On a sunny day, the water gets up
above 60-degrees Celsius by about 10:30 and stays hot enough for showers the
next morning.
Here are three pictures, each with some commentary.
My solar panels are installed on a flat roof. The U of pipe
between the two panels dips below the middle window. The push-fit connectors
are inverted to drain the system in winter. You can see the insulation on the
poly pipe and the steel straps retaining it to the wall. The panels are held to
the wall by two straps at the top. The bottom edges rest on wooden blocks which
sit on two layers of EPDM sheet. This allows for expansion and wind movement,
and prevents chafing.
The panels were built largely from scrap material, and
according to information from this web site. If I was to build them
again, I'd hand-paint the panels because spray paint is both wasteful and
expensive. I used 25-m of 10-mm copper pipe, but this was a bit of a mistake as
there are 9 zigzags of tube in 1 panel and 13 in the other. Whoops! Masochists
may wish to check out the Solar Hot Water Panels: Newsletter Challenge (95/22/07).
This may look odd to European or U.S.
standards, but the indirect cylinder is typical of older properties in the U.K.
The water in the central heating system also goes through the panels. Ideally,
I'd like a separate coil and header tank for the solar panels so that they
could run all year with antifreeze; however, this would add a lot of cost (new
twin-coil cylinder, etc.). Filling the whole system with antifreeze would also
be expensive. The compromise is to shut-off and drain down the panel from
November to March or April.
The hot water circulates through the coil from bottom to top – an
unconventional method. There are several reasons for this, with convenience of
pipe runs being one. Originally, the pump for the solar panels was positioned
to "pull" the water through the panels. This didn't work, however, and the water
wouldn't circulate. Changing it to "push" the water through the panels solved
the problem. The pump is controlled by a microcontroller-based sensor circuit
which uses two temperature sensors: one on the output end1 of the
solar panels, and one on the hot water tank. A difference of about 10 degrees
will turn the pump on.
1When I reversed the flow to make the system pump, the output end
became the input end. This led to unnecessary pump-hunting, as the input to the
panels was cooled by the return water. Moving the sensor back to the output
cured this.
This picture shows the rather messy pipe work and a hole in the garage
ceiling. It also shows a repro' crossbow and bending level. The
annotations were made with my new graphics tablet.
It is so nice on a summer's morning to stroll into the garage and see if the
friendly red LED is glowing brightly to show the pump is on and I'm getting
free hot water. It feels so much nicer than the stuff you pay for.
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