Solar Water Heaters and Solar Generated Electricity

This page has been produced to provide information on solar energy, it will be improved to provide option for people wanting to choose a solar system for their home or business

For more details : contact me Robin Thomson

The Radiation from the sun is used in 2 main ways - Heating and Generating electricity

Heating - Solar water heaters (SWHs)- 70% efficiency - 1.5m2 panel would supply a 100 litre hot water system

SWHs are household products that are installed on roofs of houses to absorb solar radiation and use it to heat water. A SWH consist of two parts; the solar collector, which is the area of material that absorbs and transfers the sun’s heat to water, and an insulated water storage cylinder that stores the heated water. SWHs sizes are measured in the stored volume of water (litres) and they range in size from 70 litres to 300 litres. The size appropriate to each household is dependent on the amount of hot water that the household uses daily.

The solar collector size is measured in square metres (m²) of area of solar collector. There are two main types of solar collectors, glazed flat plate collectors and evacuated tube collectors. The sizing of solar collectors depends on the volume of the storage cylinder, the type of collector and the geographical situation of the SWH installation. Some areas of the globe receive more solar radiation than others, and therefore would need smaller collector areas to heat the water. The energy saved by using SWHs is measured in megawatts (MW) and calculated over one year’s usage. Solar energy is free, and savings are calculated on the equivalent cost of electricity or other fossil fuels that would otherwise have been used.

Cape Town receives sufficient solar radiation to allow SWHs to supply a large renewable energy supply to heat water for households. It has had a SWH manufacturing industry for over 30 years, yet SWHs have not penetrated the market to a level of even 1%. The main means of households heating water are electricity and paraffin. Electricity and paraffin are subject to economic inflationary effects, whereas solar energy is free and not subject to inflation.

Lwandle: more than 300 large SWH systems which were installed for communal showers in Lwandle by the former Helderberg Sub-structure

Biggest users - China - which has less solar energy than Cape Town and a low income population. SWHs are widely available and there are over 1000 local manufacturers.

Typical systems used in China -evacuated tubes, gravity fed

South Africa mainly uses flat plate collectors

Over the life of a hot water system, you have 2 costs - the purchase price and the running costs. If the running costs are electricity, we can expect them to rise by about 5% per year. If the main heating method is solar, then the running costs are greatly reduced. This graph shows that for 2 systems of 150 litres that last 10 years, you will pay nearly R6000 more for the electric geyser. This was at 2005 rates. By the time we get final electricity the value of the savings will be even greater.

Generating electricity - 15% efficiency - a panel in Cape Town would provide 500 - 700 Wh/m2

Solar panels use the energy available in sun light and convert it into direct current electricity.

A 100W panel in South Africa currently costs R5615.