The earth receives more solar energy in one hour than the entire planet consumes in a year!

Solar power works by taking the energy directly from the sun. Solar energy can be captured by solar panels. There are 2 main types of solar panels which use completely different technologies to make use of the energy from the sun:

• Solar Water Heating collectors: These panels absorbs the energy from the sun and transfer it to heat water.
• Photovoltaic (PV) or solar electric panels: These panels transform the solar radiation directly into electricity.

Benefits of using solar energy include:

• Energy from the Sun is readily available
• By locating solar panels on top of houses, no extra land space is needed
• It is an ideal energy source for the urban environment.
• Power is generated silently, unobtrusively and without movement from the structure of a building, so is reliable and low maintenance.
• The electricity or hot water produced is completely green, not contributing to climate change
• There are no running costs, so once your system is installed the electricity is free

Photovoltaic panels have an increasingly important part to play as a sustainable, carbon free, fuel for the future. If all the 'unused' roofs and walls of buildings were clad with photovoltaics it could contribute to the emerging 'energy gap' where demand for power outstrips acceptable supply.

Some examples of PV applications:

• Domestic burglar alarms fitted with PV panels to charge the battery for the system
• In some areas parking meters are powered by solar panels
• Caravans using PV to power TV’s and lighting
• Simple applications e.g. calculators and watches
• Large PV systems can be integrated into buildings to generate electricity for export to the national grid.

So far, around 4,000 homeowners have installed PV in the UK, but the figure is dwarfed by the take-up in Germany, where a guaranteed energy price using a feed-in tariff has led to around 800,000 properties having the technology installed.

With growing sensitivity to energy prices and the need for carbon reduction the number of purchasers actively looking for energy efficient properties is set to increase. Putting solar panels on homes will improve their energy performance and this will be recognised in the Energy Performance Certificate that forms part of the new Home Information Pack that prospective sellers are required to produce.

Picture: Camborne School of Mines, PV

Technology: Solar PV - Electricity

First identified over 150 years ago, photovoltaics (also known as PV) became known during the 1960's providing power in Space for the NASA programmes.

To produce electricity solar PV cells use the photovoltaic effect to convert sunlight directly into electricity. The PV cell includes one or two layers of semi-conducting material, usually silicon. Solar PV tiles cover the roof of a house and take advantage of the sunlight; they do not require direct sun so produce electricity even in cloudy weather. This light is trapped by the cell and creates an electric field causing electricity to flow. PV offers the ability to generate electricity in a clean, quiet and renewable way.

Picture: Shows the how PV panels produce electricity in the home

In some cases more energy is collected than actually needed so most panels are fitted with a voltage regulator to control the flow of energy. The voltage regulator also prevents damage to the battery by diverting power away once it is fully charged, or switching off any DC appliances when the battery voltage falls dangerously low. Only a very small solar panel does not require a regulator.

Solar panels may be used individually or wired together to provide greater amounts of power. The number and size of panels needed is determined by the available light and the amount of energy required. The power generated by solar cells is determined by the weather and time of day. In the majority of cases, some form of energy storage will be necessary.

Solar water heating systems

Solar powered water heating systems are the most popular form of solar energy used in the UK. The system is connected to the hot water system. Solar water heating systems can provide over half of a household's hot water requirements over the year.

Solar water heating systems fall into two broad categories: evacuated tube collectors and flat plate collectors, both of which can be normally be integrated with existing hot water systems.

Flat plate collector panels consist of pipes passed through a metal absorber plate often coated with low emissivity black paint. Solar radiation is absorbed by the solution passing through the pipes. The heated solution is then passed through a water heating element in the hot water tank. Insulated casing protect the system from weather and reduce heat loss.

Evacuated tube systems tend to occupy a smaller area than flat plate collectors. Evacuated tube collectors comprise of a series of glass tubes containing a heat absorbing liquid kept in a vacuum to minimise heat loss and maintain high system efficiency. As with flat plate collectors the heated liquid is passed through a water heating element in a hot water tank.

Area of panels

Solar panels are usually between 25mm and 50mm thick so they can clad a roof or wall without taking anything away from the building’s appearance.

For a solar water heating system, a typical installation in the UK has a panel of 3m2 to 4m2 with a storage tank of 150- 200L. However, the optimum size will depend on actual hot water use. Space may be needed to locate an additional water cylinder if required for hot water generation.

Cost

Solar PV - Electricity The daylight needed is free, but the cost of equipment can take many years before receiving any payback. However, in remote areas where grid connection is expensive, PV can be the most cost effective power source.

A domestic system producing 1.5-2kWp will cost from around £6000. To help with the costs there is significant government funding available for solar PV systems of all sizes, reducing the financial burden considerably.

PV systems produce no greenhouse gases with each kWp saving approximately 455kg of carbon dioxide emissions per year, adding up to about 11 tonnes over a system's lifetime. It is possible that a typical household could be saving up to 1.1 tonnes of CO2 a year and potentially £150 - £200 off the electricity bill.

Solar water heating

Long-lasting life-spans of the solar water heating systems are high, lasting at least 15 - 20 years. The cost of installing a solar hot water system ranges from approximately £500-£1500 for a DIY system, to £2000-£5000 for a commercially installed system (dependent on the size of the system), with payback times varying from as little as 5 years. Accurate payback figures are dependent upon a wide range of variables and are very different for each system installed.

The average domestic system reduces C02 by around 350kg per year and at least £40 a year off hot water bills, depending on the fuel replaced.

System requirements and set up

Solar PV - Electricity

For maximum efficiency, solar panels should be mounted on a south facing roof at a 30° angle and away from any shadows from trees or surrounding buildings. The electricity is transformed from DC to AC using an inverter and is connected into the home's power supply and the Grid.

The solar panels can weigh so the roof needs to be reasonably sturdy. Some local authorities insist on planning permission, especially in conservation areas or listed buildings.

Solar water heating

Each solar hot water system will be tailored to the individual building, the existing hot water system and hot water needs. The solar water heater will require a solar collector, plumbing to join it to the existing system and a pump to circulate water around the system which can be powered either by mains electricity or solar PV (this saves on mains electricity, reduces CO2 emissions further, and in some systems helps to regulate the temperature of the water produced). The solar water can be stored in a large cylinder along with conventionally heated water, or in its own separate hot water cylinder, a new hot water storage cylinder may be required in come cases.

Systems must have freeze protection - if the water in a system freezes it can damage the solar collector, so this needs to be guarded against.

Evacuated tube systems require more energy to pump the water around then flat plate collectors, and so generally will need a pump run off mains power. This will incur slight running costs and offset the environmental benefits (reducing CO2 abatement by as much as 20% in some systems).

Systems using evacuated tube collectors should also have boil protection to prevent water becoming too hot, as they can heat the water to much higher temperatures.