Solar Water Heating

[jonboy]

When there is insufficient heat from the sun to bring the water in the roof tank to the required temperature, the filament is triggered by a thermostat and heats up the water. Does anyone have a feel for the cost of running such a system during the winter or not so months? For example is it 10’s or 100’s euros per month in a cloudy or cold January / February.

JB

[fmm]

WHen my broken solar panel was accidentally turned on by the electrical contractor that was upgrading my electrics, it cost me a few hundred extra euros before we noticed there was a problem.

[EMM]

We only turn on the heater when needed, Its too expensive to leave on and rely on the thermostat.

[maccasa]

The electric heater is typically 2.5 kW, so if it was on for 50% of the day, you would use ~31 kwh - check your EDP bill to see what you are charged /kwh.

There is also a special valve system on modern installations which mixes the hot water (60C+) in the solar tank with incoming cold water to maintain the tap water at typically 40C max. In the winter the incoming water is 16C, in summer 27-29. So the valve should be turned down in the winter as less cold water should come in, and you use more of the solar heated water - obviously if that isnt heated by the sun, it will be heated by the electric heater.

In summer the valve is opened as the normal water needs less of the solar heated water to achieve 40C outlet.

So if you forget to change the setting in the winter to reduce the incoming cold water, you are heating more cold water to achieve the 40C - so the trick is to turn your hot water temperature down in the winter to 35C and therefore reduce the make up heater load. You may find the reduced solar energy input is ok to maintain this lower output temperature.

[EMM]

If you reduce the cold water imput do you not also reduce your water pressure for taps .showers etc.

When used to power showers the lower solar pressure does take some getting used to.

[jonboy]

Thanks ever so much for the replies. It is probably prudent to swicth off the heating element from say March - Oct or whenever the weather becomes settled. The tip of reducing the flow of cold water into the tank is I think a good one.

JB

[maccasa]

If you reduce the cold water imput do you not also reduce your water pressure for taps .showers etc.

When used to power showers the lower solar pressure does take some getting used to.

Didnt notice any difference, probably because you turn the shower down when its hot anyway - but I shall try it when I am out next week as I shall turn up my cold water make up to 50% from approx 25%