questions about solar powered circulator pump for solar hot water system

Jerry,

I've been using an El Cid to circulate water here in the Cayman Islands for over a year and it works great. I pump using PV power only, and in my case I have found that it works best to use only the 10 watt panel that is matched to the pump. When the sun is shining bright and the water is hottest then the pump is operating at max throughput, and on cloudy days when the panel gets shaded and the water not so hot, the pump circulates the water much slower.

I haven't purchased any yet, but in your case I would recommend a couple of sensors and a temperature differential switch to prevent the water from circulating early in the morning before it has heated up, and again late in the evening after the sun has stopped heating the water but is still light enough for the PV to operate the pump.

John

Jerry,

I use a single 3' x 7' AET flat panel. Evacuated tubes are more efficient (and expensive!), but when you live in the tropics there is not a great deal of need for hot water. Other than the washing machine and dishwasher we could easily get by without it.

I have a single pressure/temperature relief valve installed at one end of the AET solar collector. When I first installed my system I got some air in the lines and the El Cid pump was just spinning and not actually pumping the water. After a short while the temperature reached 210F and the valve opened up spraying hot water everywhere. Luckily nobody was near it. This also cleared the air out of the lines and it has not given a single problem since the day that I installed it.

You might want to run a piece of hose from the pressure/temperature relief valve into a gutter to avoid a similar problem.

The El Cid pump is very quiet and you almost have to put your ear next to it to hear it running, although it does have small led lights to indicate that it is on. If you can hear the pump (as I now know!) then it has air in it and you are probably looking at the situation described above.

My system just circulates water from the hot water storage tank through the collector so it is a very simple setup, whereas you will probably need some sort of heat exchanger and also have to take freezing temperatures into consideration.