The thermal store in the loft is already up and running, and has a solar coil in the bottom. A 2m x 1m solar panel will be mounted vertically on the house wall, below the tank level, and will work by gravity thermosyphon. To reduce the chance of occasional boiling and generation of steam in summer, I want to pressurise the circuit up to 1 bar (raising the boiling point by 18-20 degC), using something like an automotive coolant header tank near the thermal store. Does anyone have experience of such a system, please? Any advice and recommendations for sourcing a tank will be welcome. Thanks.
Thanks, Stoneyboy. I take your point, and I have considered an off-the-shelf expansion vessel - the entire solar circuit is only about 10 litres. But the advantages of a header tank from, say, a truck are that it would be translucent, so it's easy to fill, vent and top up; it's flat so it will mount to the loft wall easily; and any overspill from the pressure cap would be collected and drawn back into the system on cooling down. Under normal operating conditions there's no need for the system to be pressurised. But your comment reminds me there is little need to provide for topping up - maybe once every five years to drain and replace the antifreeze - so I'll give it more thought. (I am a steam engineer, so I am comfortable working with low-pressure systems.)
My father-in-law was sold a commercial DHW solar panel system, we asked how it was, and was full of praises, then he had a smart meter fitted and no more DHW, so then I went to look at it.
It turned out the meter fitter had not re-lit the boiler pilot light, however it was summer so should have had DHW from solar panels, since the fitters had used the immersion heater supply, it seemed likely my father-in-law had turned off the switch marked immersion heater in the kitchen, so we had a firm come and bleed the system and recommission it.
However even on a sunny day in summer, it would only just take the chill off the water in about the most North East point of Wales.
The solar heating my daughter has in Turkey works well, no lagging so need to have shower in afternoon as it cools down over night, but it does work.
There was many years ago a display in the Alternative technology centre, and they also found most systems simply did not work, the best it seems was a home made which was a radiator behind a double glazed window, but that is Mid Wales.
At what point one is south enough for them to work I don't know.