Hydro

Hydro power systems use running water to turn a turbine and generate electricity. Micro hydro plants generate less than 100 kW and can produce a sufficient reliable source even from a small stream. Although costs can be high, this can be a good option in areas where grid connection would be a problem. The amount of energy produced will depend on the water's flow rate and the height that the water falls. Output will depend on how efficiently it converts the water's power into electricity and is likely to be about 60-80%.

Hydro systems can be stand-alone or connected to the main electricity grid but the source must be fairly close to the grid connection/point where the power will be used. In stand alone systems, electricity can be supplied directly to the devices to be powered or to a battery bank and inverter. Costs are site specific and relate to energy output but could be about £25,000.

Wind

Wind turbines use the wind's lift forces to rotate aerodynamic blades that turn a rotor to create electricity. In the UK, we have 40% of Europe's wind energy, which is a clean renewable form of energy that produces no carbon emissions or waste products - and once the equipment is installed, the energy costs nothing.

Turbines can be connected to the national grid or can be stand-alone. Most systems generate DC electricity and they require an inverter to convert the DC to AC mains electricity. Stand-alone systems also require battery storage. They can be mast mounted or roof mounted and could vary in size and power from a few hundred watts to two or three mega watts. A typical domestic system would be 1-6 kW.

Ideal locations are smooth topped kills, with clear exposure, free from turbulence and obstructions and with wind speeds of more than 6 m/s. Turbines are best located on masts or towers where the height leads to increased wind speeds.

The amount of electricity generated depends on the speed and direction of the wind and before proceeding; you should undertake a professional assessment of the wind speed for a year, at the exact location of the intended turbine. Planning permission will be required for a wind turbine - check with the planning authority before you consider having a system installed. You should use an accredited installer.

Costs can vary from £1,500 for small roof mounted installations to £10,000 - £25,000 for 2.5kW to 6 kW turbines but both the costs and energy production depends on the location, size and type of system.

Ground source heat pumps

Heat pumps do not require any external fuel and they heat the whole building. A buried ground loop transfers heat from the ground to the building, in order to provide heating or to pre-heat domestic hot water. You could save £400 - £800 on energy bills and 2-8 tonnes CO2 a year using these systems. Lengths of pipe filled with a mixture of water and anti-freeze are buried in the ground, and can be vertical in a borehole or horizontal or coiled in a trench. The mixture is pumped through the pipes, absorbing heat from the ground and transferring the heat to underfloor heating, radiators or hot water systems.

Sufficient space is needed outside the building for the ground loop and there needs to be sufficient depth to bury it adequately. The type of heat distribution system needs to be considered: underfloor heating will be more effective, as this operates at a lower temperature, whereas radiators would need to be much larger than with conventional boiler systems.

Solar PV

Photovoltaic panels convert energy from the sun to create electricity to run lighting, appliances etc. This is the technology that is commonly used nowadays on temporary road signs, in phone kiosks and bus shelters. In the leisure industry, it is used in boats, caravans and garden lighting. These systems produce no greenhouse gases and each KWp can save about 455 kg carbon dioxide emissions a year, adding up to 11 tonnes over a system's lifetime. PV requires only daylight, not direct sunlight, to generate electricity, so it can still generate power on a cloudy day.

PV cells, consisting of one or two layers of a semi-conducting material, usually silicon, convert sunlight to electricity. When light shines on the cell it creates an electric field across the layers causing electricity to flow. The greater the intensity of light, the greater the flow of electricity.

PV systems can be used on buildings that have a roof or wall that faces within 90 degrees of south and that are not overshadowed by other buildings, trees etc. The roof must be strong enough to support the structure, which nowadays comes in a variety of shapes and colours, from grey solar tiles that look like roof tiles to transparent cells that can be used on glass and in conservatories. Check with the planning authority before you have any system installed.

PV panels are especially useful where grid connections are a problem and, particularly if combined with a micro wind turbine, they could produce a very reliable source of electricity - harnessing the increased wind in winter when the sun is weaker and vice versa. You can also add together groups of PV panels to provide increased levels of power.

Prices depend on the size of the system installed, the type of cell used and the nature of the building on which the cell is to be mounted. The average domestic system could cost upwards of £5-8,000 per KWp installed. Solar tiles are more expensive than conventional panels and those that are integrated into the roof cost more than those that sit on top. Every year, you could save £150 to £200 off your electricity bill and up to 1.1 tonnes of CO2. Grid connected systems require little maintenance other than cleaning and ensuring that the panels are not shaded. Electrical components should be checked regularly by qualified professionals and systems that aren't connected to the grid will need battery checks etc.

Solar Water Heating

These systems use heat from the sun to work alongside your conventional water heater. Domestic solar hot water systems have solar panels or collectors fitted to the roof and collect heat from the sun's radiation. These can be flat plate systems that have an absorber plate with a transparent cover, or evacuated tube systems that have a row of glass tubes, with each containing an absorber plate feeding into a manifold that transports the heated fluid. A heat transfer system uses the collected heat to heat household water and a hot water cylinder stores the hot water that is heated during the day and supplies it for use later on.

These systems can only contribute to part of your heating energy requirements, as the sun is weakest (in winter) when your heating requirements are highest. However, if the system is sized correctly, it can provide you with at least 40 - 60% of your hot water needs throughout the year. The average domestic system reduces CO2 emissions by about 350 kg per year, and about £40 a year of your hot water bills, depending on the system it replaces.

Solar systems require three to four square metres of south east to south west facing roof, receiving direct sunlight for the main part of the day and a boiler that is suitable for use with a solar system. An accredited installer should be used as this system requires specialist expertise to size, install and balance effectively. An experienced professional will be able to discuss with you, the best system to meet your specific needs. Typical costs range from £3,200 to £4,500, although evacuated tube systems may be more costly. The energy savings that result mean that for the average household, the cost of purchase and installation will be covered in 7 - 15 years. Little maintenance is required apart from a quick annual check by the householder and a detailed check by a professional every three to five years.

Information source: Energy Saving Trust and The Renewable Energy Centre. Further details can be found on the Energy Saving Trust website or contact ALIenergy for more information by phoning 01631 565183 or E mailing us at