A suitably sized solar geyser may not need any electrical help for 8 or 9 months of the year. But in the winter, when the sun is low and weak, almost all solar geysers need some help from electricity or gas to get the water hot enough. If you start extracting heat from the system to warm your house, you will only increase the amount of heat you have to add back into the system.

Systems that have been designed to significantly heat homes are oversized, with several solar panels and large water storage tanks. One I know has 4,000 litres of storage!

I do like your idea of radiators. My great uncle in Colorado heated his home using solar heat in hot water radiators. I think they might be more efficient than underfloor hot water and less expensive to install. But I’ve never seen a hot-water radiator in South Africa.

My list dealt only with conventional heating options. I know of someone in Cape Town who connected hot water to a wood-burning stove, which I think was used for underfloor in other rooms. I know someone else is using gas for hot water underfloor. Solar heated water supplemented by gas would be less polluting.

In colder parts of the world–including the Michigan, USA, house I grew up in–solar panels that blow hot air are the best-known option for solar heat, and I am amazed that they are non-existent in South Africa. (As far as I can tell.) The upside of forced-air panels is that they are much simpler and cheaper to build and install than anything involving liquids. The downside is that it won’t give you heat in the coldest part of the day. The most obvious solution is to insulate your house and allow it to overheat during the day. The more complicated and potentially more effective solution is to use a rock bin to store the heat.

One day I am going to experiment with some kind of forced-air solar panels for my home. In the meantime, I already have a modest variation on that theme. Reversed ceiling extractor fans blow warm air from my roof space into the house. I get a moderate amount of heat from these, but their downfall is that I have a very leaky roof and any wind cools my attic rapidly. I believe that modern roofs are commonly laid with a layer of plastic under the tiles; such a well-sealed attic would be ideal for this system. I based mine on that of a Pretoria engineering professor who heats his house EXCLUSIVELY with warm attic air.

Let me know if you come across a solution that works for you.

Don