Solar To Stop External Cold Water Tank Freezing In Winter ?

Q: Despite living in the South of Spain, we still encounter some cold winters (including -8c a couple of years ago). I was wondering what everyone's thoughts are regarding the use of a solar panel hooked up to a small portable heating element (similar to the small 12v water boilers used in car cigarette lighter sockets) into my cold water deposit tank (located on the roof of the house), not to provide hot water, but so as to keep it at a temperature just sufficient to prevent freezing during the winter months. Obviously I could add a battery solution to ensure that the heating element could continue to work during the coldest hours of the night. Any thoughts on whether or not this is a practical idea ?

A: Using PV to run a resistance heater is a big waste of money (if that's what you meant by 'solar panel hooked up to a small portable heating element) If you're trying to prevent freezing, use some insulation to lower the heat losses. Maybe just a 'cold frame' type collector against the sun-facing side so it collects a bit of solar *thermal* energy during the day. Insulation to limit the losses at night. The piping would be more at risk than the tank. Piping leading into/away from the tank would need good insulation. Even in cold climates, outdoor water towers aren't insulated or heated. Some ice forms, but the tank doesn't freeze solid. The piping leading to them has constantly moving water so it doesn't freeze. In your case, the piping will have stagnant water much of the time, so freezing *there* would be hazard. Not cost-efficient. Better to insulate the whole outside of anything wet, and maybe use a solar thermal collector if that's not enough. Like, maybe with a closed loop of anti-freeze mix through collector and exchanger inside tank. Photosensor controlling low-power circ pump a/r. Much better to reduce waste than boost supply. Some good suggestions here but maybe all you need is insulation plus a closed loop that goes inside your house which you are heating anyway. If you have a furnace in an uninsulated basement, you could run a piece of pipe next to that or some part of the heating system. That way you are not removing heat from the living space itself.

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