I should write about the plan of the man who wanted to supply heat but not much light.
We had had reservations about his system from early on. During discussions about the chances of actually receiving the NEDO grant, I asked their boss and the builder's boss whether they would cover the grant amount in the event that we didn't get it because they hadn't built our house within the deadline. I think they thought this was funny. Evidently there was no concept of a penalty for not meeting a deadline. The Supplier of Heat but Not much Light suggested a place where I could get a loan to cover the cost.
The radical part of it was a solar thermal system, providing hot water in the summer, and heating in the winter.
Most people assume the problem with a solar thermal system is what to do on days when there isn't enough sun, but in fact that is a fairly simple problem. You need a back-up heating system. There are any number of ways to heat water from gas or oil burners, to a heating element from a kettle in the boiler. You don't see them so often but it's certainly possible to have an electrical heating element at the tap. A low-tech solution would be an electrical shower unit, which may be expensive to use but if you only need it a few days every year, then the total cost would not be so much.
The biggest problem with solar thermal systems is failure in the face of too much solar heat going in and not enough hot water going out.
My simple question about the system was, what if the refrigerant boiled? This seemed likely to happen sooner or later. The behaviour of liquids heating up is quite predictable. As the liquid gets warmer it expands slightly. Then it starts to boil. The amount of gas steadily increases, with the pressure rising. When all the liquid in the solar collector turns to gas it will probably stop circulating and the system will stagnate. Gas tends to have a low thermal capacity so it won't take much more heat, and low conductivity so very little heat will get into the rest of the system, and the liquid in the circuit beyond the solar collector will not start boiling. The gas will reach some temperature at which there is an equilibrium between the solar heat getting in and heat radiating out.
If the system survives this high pressure and high temperature, the next challenge is what to do as it cools down.
The gas will start to condense into liquid, and the collector must fill up again, so that it can continue to flow and get heat where it is needed.
A robust system should probably be able to cope with this. The Victorians were using steam systems for heating, so the pressure should not be a problem.
In the plan of the man providing heat but little light, the solar elements used vacuum tubes, with a refrigerant pumped through them all the time. The pump was served by a dedicated solar panel, ensuring that the refrigerant would not stop, which would lead to disaster. This was his answer: it's not going to happen.
That was one worry about the system.
In discussions around the same time as I found that penalties for not meeting deadlines were from an alien world, I asked what kind of guarantee they had on the solar thermal system, having heard that many solar thermal systems fail within about five years. He could only offer a one-year guarantee. This did not reduce my worry.
Another minor worry, which I would have lived with, was that the back-up heating system used paraffin oil. Having spent too many winters lugging tanks of the stuff to my house, syphoning it into the small tanks and ferrying them to the heaters inside, and spilling several litres of it in the process, I really didn't want the stuff anywhere near my house.
I know that in terms of environmental impact directly using fossil fuels is less wasteful than getting electricity off the grid that has come from gas-fired power stations, but given a choice I didn't want to build a house that took any fossil fuels.
