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Comment by robertlagrant | Hacker News Reader

I'm not sure where you could use it. At least in the UK:

- water for heating your home is in a closed loop, and you wouldn't want to add this cooling to that closed loop as it would heat up your solar panels on cold days

- water for drinking/washing comes from the same cold feed, and you don't want to heat that up as you can't get cold water then

- bisecting the water supply into hot taps and cold taps, and running the hot one under the PV cells could work, but it would only flow the water when something is pulling water, e.g. running a tap, which might be a hindrance to cooling

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There are solutions in the market for this. The heat recovery system is filled with glycol solution, which means it doesn't freeze over even if left unpowered during sub-zero outside temperature. Then there's a temperature sensor and a control unit that only runs the pump when the fluid in the panels is warmer than the warm water accumulator of the home heating system.

The heat collectors are vacuum insulated, so provided with enough solar radiation, they will work even when it's very cold outside. These systems work okay for example here in Finland. Of course it's a limiting factor that you normally need the heating most when the solar radiation is at the minimum. If you've got a swimming pool or some other use for the hot water during the summer, it's a good deal.

> the warm water accumulator of the home heating system

I'm not sure how this would work in a modern UK heating system - there is no warm water accumulator to my knowledge.

I suppose a modern gas or oil burner doesn't need one. But this sort of solar based heater as well as ground-source heat pumps typically would need it. They are not very expensive however, as they are just heat-insulated tanks of water. Of course space requirements and such might rule out adding one in many cases.

I think it's more - how do you hook it up with the rest of your water?

The gas boiler has a small tank where the radiator circuit's water is heated. Warm water accumulator is analogous to making this tank larger. The radiator connections would be moved to the big tank and the boiler would be made to warm that tank. Perhaps typical combination boiler isn't optimal for this setup, so incorporating other heat sources might be best timed when the boiler is due for replacement anyway.

There are lots of houses in the UK that have hot water tanks. The water in these is heated by effectively a radiator inside the water tank. We have one here and the my tank has a 'secondary loop' designed to be driven by a water-filled solar panel. Typical kind of tank: https://www.screwfix.com/p/heatrae-sadia-megaflo-eco-solar-p...

True, but those are often older. I know some new builds also have them (I lived in one of said new builds a few years ago) but my impression is they are often older heating systems that don't have a combi boiler yet.

From:

> 59% of dwellings in 2019 used their central heating system to provide hot water without a separate cylinder. Around a third (32%) used their central heating system to provide hot water through a separate hot water cylinder, 7% had a hot water cylinder and immersion heater as the primary means of water heating and less than two percent had an instantaneous water heater or dedicated boiler (1% and 0.2%, respectively)

So about 40% have hot water tanks, though I guess the number is falling.

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