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 Heatings offering efficiencies of well over 90%.
That means that more than 90% of the sun's energy landing on a surface is converted into heat which can be used to heat water. This is also one of the cheapest renewables, with costs starting from pennies per Watt required comparing to pounds per Watt for PV Solar and Wind Turbine power generation.
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 absorbant 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 located through the centre of the tubes. Most of the infra-red radiation (i.e heat) from the sun is absorbed by this sealed heat pipe which contains an anti-freeze type liquid.