Can you do DIY solar thermal?

The short answer is yes, and you can choose your level of involvement from constructing your own collectors to assembling a kit of parts – the choice is yours!

It's perfectly possible to construct your own flat plate collector, places such as the centre for alternative technology in Machynlleth, Wales still run courses on the subject I believe. Home made collectors are usually sheet copper with a serpentine arrangement of 10mm copper pipe sandwiched between insulation and a double glazed panel. Some of these panels built over 40 years ago are still in use!!!

Of course if you don't want to build your own collector there are plenty of mass produced options available such as flat plate,or evacuated tube types. To connect the collector to where the heat is needed (generally a hot water cylinder) some heat resistant metal pipe of some sort will be required. You could use standard 15mm or 22mm copper for this,but remember to use compression joints and not solder (this is because under fault conditions the collector may produce enough heat to soften or melt solder!). Also available is stainless steel 'flexi pipe'. This makes installation much easier but remember to order any connections you might need in plenty of time as few plumbers merchants will stock them!

In order to get your collector on the roof you'll need scaffolding and all the usual safety precautions when working at height. To get the pipes through the roof and still keep things weather tight you'll need a 'flashing kit'. This is a lead or aluminium sheet with a silicone gland for the pipes to pass through. You'll also need a roof mounting kit for the collector itself – the last thing you want is any movement during period sof high wind.

Most (though not all – see 'drain back') solar thermal systems use a 'sealed system' containing some form of antifreeze. As the fluid in the sealed system expands with a rise in temperature you must include a solar rated expansion vessel in the plumbing circuit. If the system overheats the expansion vessel may not be able to cope with the extra volume, so a pressure release valve is required. Some form of heat proof catchment vessel will be needed to accommodate the excess solar fluid. An air trap somewhere in the system will help you when you first fill the system up,and a pressure gauge allows you to check that system has enough fluid in.

To move the thermal energy from the collector to the cylinder a Solar rated pump is needed, this can be a 'mains' pump or one designed to run at a lower voltage. Using a pre fabricated pumpstation really simplifies things as it includes air trap,pressure gauge, pressure relief valve, flowmeter and pump all in one'box'.

The last part of the system is the hot water cylinder. This should be an indirect twin coil type and there are plenty to choose from. If you are using an unvented cylinder remember that this needs to be fitted by a professional plumber who can notify building control after installation.

So there you have it!

You can do DIY solar thermal and there are plenty of kits available. Just remember that any parts used must be 'solar rated'.