Solar Water Heating has been used for hundreds if not thousands of years to heat water. With advances in technology solar water heating systems have become more and more efficient, with Evacuated Tube.
Solar Water Heating offering efficiencies of well over 90%. That means that more than 90% of the sun’s energy handing on a surface is converted into heat which can be used to heat water. This is also one of the cheapest (fastest payback period) renewable forms of energy which is available abundantly.
Vacuum or Evacuated Tubes are made from glass typically ultra-strong and heat resistant Pyrex with a double wall construction. The glass on the inner tube is coated on its outer surface with an absorbent coating, and on its inner surface with a reflective coating. Inside each tube all air is removed making a vacuum and a copper heat pipe is run through the center of the tubes. Most of the infra-red radiation (i.e heat) form the sun is absorbed by this heat pipe.
The advantage of using evacuated tubes is that they will work even during the coldest winter months unlike old style Flat Plate Solar Collectors. The vacuum insulates the heat tube form being cooled much by the ambient temperature which could be well below freezing.
Winter sun can easily heat water to 50+ degrees even in the depths of the coldest season. Even if it is very cloudy and very cold, enough sunlight gets through to keep the tubes well above freezing and so they will still be pre-heating the water which can then be heated further by a standard immersion heater or gas burner reducing the costs of heating the water.