A DIY solar collector can turn solar energy into thermal
energy and heat.

Thermal energy comes from heat, and should not be confused
with electrical energy that comes from a solar panel. A
solar panel converts the sun's energy into electricity,
whereas a solar collector simply absorbs the sun's
radiation, and uses it to create heat.

A simple do-it-yourself solar collector can be made out of
a typical pressed-steel central heating radiator. This is
inexpensive, and can even be purchased second-hand.

If you use a second-hand radiator panel, be sure that you
remove the paint from the front surface and reapply primer.
Size will not matter, but you should consider keeping it
around one square meter or less. Keep in mind that you'll
be installing the solar collector on your roof, and
anything bigger can result in the difficulty in handling it.

Once you've selected your radiator panel, the next step is
building a case for it. It is recommended that you assemble
the case in its final position, to make your job easier.
Then there will be no need to hoist the entire solar
collector up onto the roof after it's been built.

The case is just a simple box with a front cover glazing,
made out of the 3mm glass which is typically used for
windows. The glass must be purchased after you've assembled
the box. Measure the case, and buy the glass already cut to
size. Be sure to leave at least a 2mm gap around the glass,
to allow for its expansion. The glass cover must hang over
the lower edge of the case, by at least 12mm. This will
keep rain water from seeping onto the panel.

Making your DIY solar collector water-proof and keeping it
dry is not necessarily an easy task. You might prevent rain
water from entering, but over time, internal condensation
can occur. You can prevent this by inserting 5mm breathe
holes along the lower side of your box.

Insulation must be placed behind the collector, because
internal temperatures can reach up to 140 degrees Celsius.
Avoid using the cheap types of insulation, such as
polystyrene, because these tend to shrink or melt. To limit
air movement, ensure there are no gaps between the panel
and the insulation.

This homemade solar collector should be cheaper than others
available on the market. The thermal efficiency of a
central heating radiator is fairly comparable with the
commercial solar collectors. If you're looking for a cheap
way to heat your water supply, this will be one of your
options.