The traditional approach to supply hot water in the UK, it to heat it using a gas boiler or an electric 'immersion' heater. In many UK homes it is possible to add solar water heating, which adds the ability to solely use the sun's energy to heat the water in the summer months and to provide some energy input on cloudy days and during winter months. Typically this involves mounting solar collectors on a South facing roof but, they can absorb sun from quite wide angles.
In the British summer it is quite easy to generate more hot water than you can use, so consideration needs to be given to how best to utilise it. This should include things like washing machines that will use this solar heated water.
Solar Water Heating
When the energy from the sun radiates on to a dark material (a solar collector), it heats up and this heat can be transferred into water, which can then be transferred to and stored in a hot water tank. If the solar collector is a highly insulated array of evacuated glass tubes, temperatures in excess of 80°C can reached. This is a photo of the glass tubes installed on my parent's house.
There are other types of solar collectors and we have built and tested a few ourselves but the evacuated glass tubes tend to be the most efficient.
This water is stored in an insulated tank, to keep it hot. An electronic controller regulates the system, pumping water through the solar collectors, when it will increase the temperature of the water stored in the tank.
The design of the tank may also support other energy sources being used to heat up the water such as a gas boiler of an electric heating element. This ensures a hot water supply on days when they is not enough energy from the sun to heat up the required volume of water to the temperature required.
DIY Solar Water Heating
Solar water heating installers don't want people to know this but, installing systems like these is not hugely complex or difficult. Quality kits of components are available at very reasonable prices on sites like eBay.
This is an interesting web site documenting a DIY solar water heater installation: Solar Friend. Despite using a relatively inefficient, home made solar collector, he is making significant savings in gas usage.
Ground Source Heat Pump
A ground source heat pump uses the earth as a heat source (in the winter) or a heat sink (in the summer). Depending on latitude, the temperature beneath the upper 6 metres (20 ft) of Earth's surface maintains a nearly constant temperature between 10 and 16ºC.
Air Source Heat Pump
An air source heat pump works in much the same way as a ground source heat pump but transfers heat to/from the surrounding air. These tend to be less efficient and very much so below about 5ºC, which makes them less popular in the UK. The main advantage is that it is much easier to install.