I am installing an all new plumbing system in a renovation project and want to run a combination gas boiler for hot water and central heating. I wouldnt have a hot water storage tank. I have a large sunny flat roof above the bathroom where the boiler will be. My idea is to make large solar panels out of old radiators or similar inside frames (black & insulated) with double glazed glass, and run the cold feed that would normally go straight into the boiler, through these first. Therefore the boiler would be heating pre heated water thus saving boiler 'on' time (or at least not at so high a heat) so in theory saving gas. Has anyone done this and can it be done? Obviously there is the winter freeze issue and I propose to deal with this by good insulation and having a Bypass valve and drain-down system for the worst frosts of winter. Any help or advice welcome.
Never heard of it being done by using old radiators etc. Have you ever emptied a heating system and saw all the black sludge and crap built up, if you were to run water directly through the radiators to the cold water inlet of the boiler the radiators will have to be in pristine condition and you will still get discoloured water, so I wouldn't advise it. Boiler parts may become blocked.
Normally for hot water solar panels are used to heat a cold water storage tank in the loft which then feeds the boiler. This takes the chill off the water so the boiler doesn't have to work as hard to heat the water.
I think the main problem of not using a storage cylinder is that when there is no heat from the sun, i.e. at night you will have no pre-heat for your boiler
Having a cylinder will even out the fluctuation in energy available. Also using radiators, I have seen experimental projects like that before but it does sound a bit "Heath Robinson", good as an experiment but I would not want to use it long term. There is a much better integrated system which I can tell you about if you want to know.