Solar water heating for pools
please note these are guidance, not specifications

Concerning sizing there are two very useful rule of thumb approaches. One is based on pool size and the other one, the peak capacity of the existing heater. Both these rules of thumb overlap, which can be useful. Full heat loss modeling and panel specification formulae programs are available free on Canadian government websites.

In terms of pool size, in UK we recommend around 30% - 60% (or more) of the pool area should be repeated as panels (each of which has an aperture - heat absorber - area of 2.8 sq metres). This rule of thumb means 1-2 Solartwins per 10 sqm of pool area, with the lower end for taking the chill off outdoor or seasonal pools, the upper end for indoor or all year pools.

In terms of the existing heater, since this usually reflects a heat demand calculation, we suggest around one panel per 2 kW of the pool’s existing heater’s peak capacity. This is only very general measure and is not as useful as the area assessment.

As for plumbing in, and pumping options, there are 3 main options, the first 2 using solar pumping, the last using the filter pump.

1/ for small pools using say 3 or fewer panels, just use Standard Solartwin PV pumps, one per panel. A plumbing diagram is suggested below. Good for remote locations and small summer pools with occasional filtration.

2/ With solar pumping options using 4 or more panels, we suggest larger pumps, one or more, depending on the number of panels. We can supply these. Reducing the number of pumps has little bearing on the cost per unit since the area of the photovoltaic panel and the cost of the pump increases almost proportionately. PV pumping is particularly good for remote locations.

3/ For larger pools, where the filter pump is on all day, we suggest using panels only, without our pumps. Instead of PV pumps, when there is any heat to be gained from the panels, we divert some water downstream of the filter pump to collect it from them by using a motorised valve. We control the valve using a conventional solar “differential temperature controller” so that when panel temp exceeds pool temp the valve opens.

As for plumbing outlet and inlet arrangements, provided the filter and its pump do not obstruct the flow by a head of more than 300 mm of water (for a flow rate of 3 litres per minute, per panel and exceeding this is unlikely) it is best to provide a draw off tee using a 22mm conventional plastic pipe downstream of the existing filter in such a way that the water is gently drawn through the filter and not backwards through the pool recirculating exits. Preventing such backflow usually requires the installation of a valve downstream of the draw off point to prevent this. Concerning the entry of the water to the pool, the solar warmed water is best injected at a low level into the pool either via existing vent point(s) or via new one(s). It should not be injected near the surface since the warmer water would then stratify (float) over the cool water rather than be encouraged to mix as it rises.

We provide special polypropylene connectors (instead of brass reducers / pipe inserts) for pool systems - to minimise corrosion in pool water.

Notes on general pool energy efficiency and related green issues:

Remember every pool is different so please call 0845 1300 137 to discuss your specific requirements.

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