While an increasing amount of electricity entering the grid is being generated from renewable sources, much of it is wasted on tasks such as heating water that would be best performed by solar hot water systems installed directly on homes. In India, some cities have made it mandatory for new buildings to install solar water heating systems before they can be occupied.
According to researchers in India and reported in the International Journal of Global Energy Issues, a solar water heating system has a payback period of just two years.
The researchers from the Dr Panjabrao Deshmukh Agricultural University in Maharashtra, India, compared solar hot water production per litre with electrical energy approaches and found that solar heating provides 57 percent of the internal rate of return. Their study was based on a 1000-liter system operating at a university hostel.
The team estimates that a solar hot water system will effectively pay for itself five times over, given an estimated working life of about twenty years, however the new solar hot water rebate system now in operation in Australia means that Australians may get an even better return on their investment.
In Australia, electric and gas hot water systems accounting for approximately 20% of a household’s greenhouse gas emissions. By installing a solar water system, householders can significantly reduce these emissions and also save up to 75% of water heating costs.
The two most common types of collectors used in a solar hot water system are flat plate and evacuated tube. Flat plate collectors contain copper piping running through a glass covered collector, often connected to a water storage tank on the roof. The hot water can then thermo-siphon itself in and out of the tank.
Evacuated tube systems use glass vacuum tubes with copper piping running through the centre. The copper pipes are all connected to a common manifold that is in turn connected to a slow flow circulation pump. This pumps water to a storage tank below and the hot water can be used at night or the next day due to the insulation of the tank.
