‘Going Around Your Elbow to Get to Your Thumb’ in Solar Water Heaters
Every once in a while someone will ask me if it makes sense to collect solar energy with photovoltaic panels and then use that electricity to heat water. The answer is a rather emphatic NO.
The reason is very simple. Photovoltaic (PV) systems have efficiencies in the 10-15% range and solar thermal systems have efficiencies in the 40-60% range.
It makes no sense to utilize only 15% of the available solar energy to heat water, when you could be using 50%.
So, It doesn’t take much thought to realize that trying to heat water with a PV system is like “going around your elbow to get to your thumb”. Heating water directly with sunlight is much smarter. Actually about 3-4 times smarter.
Of course, PV has its uses. You can’t run a TV with hot water. If you need electricity, use PV. If you need heat (space heating, cloths washing, dish washing, car washing, bathing, …) use hot water.