Renewable Energy Technologies

Renewable Energy Technologies

Renewable energy uses natural resources such as sunlight, wind, tides and geothermal heat which are naturally replenished. Most forms of renewable energy are cheap to operate, but relatively expensive to install, as they have to take quite dispersed energy and concentrate it into a useful form.

Until the industrial revolution almost all energy came from renewable sources, but much of it was used inefficiently. Modern technology can capture a lot more of this naturally occurring energy and convert it into electricity or useful heat.

Solar thermal - solar water heating collectors

The heat from solar energy can be captured by solar thermal panels. These panels absorb the energy from the sun and transfer it to heat water. Solar water heating systems are the most popular form of solar energy used in the UK. Solar water heating systems can typically provide over half of a household's hot water requirements over the year, but do not contribute towards central heating.

There are two types of solar water heating collector: flat plate and evacuated tubes. There are other active forms of solar heating, including ones designed to pre-heat air through sun spaces or solar walls. However, most are either still at an experimental stage or not widely available in the UK, so will not be considered in detail on this website.

Solar electricity - photovoltaic (PV) panels

Solar energy can also be captured by solar PV panels. Photovoltaic (PV - also sometimes called solar electric panels) transform the solar radiation directly into electricity. PV panels generate electricity in a clean, quiet and renewable way. Although initially photovoltaic (PV) cells were used in simple applications such as calculators and watches, they are now very widely used for domestic and larger applications. Large PV systems integrated into buildings use inverters to convert the low voltage direct electric current from the panels into alternating current that can be used in the building on which they are mounted or exported to the national grid.

Biomass - fuel from wood or other plants

Biomass is a term used for solid fuels derived from plant materials, such as wood or specially grown crops. In order not to increase the amount of carbon dioxide in the atmosphere it is important that the wood burned as a fuel comes from sustainable sources. This means that as trees are felled to be use as a fuel, more trees should be planted. That way, the carbon released during the combustion of the wood is reabsorbed by the new trees growing and the process is carbon neutral. Biomass can be used as logs, wood chip and wood pellets in wood or pellet burning stoves, or in boilers for space and water heating. Biomass can be bought in quite small quantities bagged, but can also be purcahsed in bulk, typically supplied ij a tanker that will then blow the fuel into a stoarge container. Biomass can also used in bulk to generate electricity in power stations, either burning straw, specially grown crops, or as processed wood products.

Some biomass power stations also capture waste heat in the combustion process to heat nearby homes or factories; this is known as biomass combined heat & power (CHP). Plants can also be processed to create liquid fuels (such as bioethanol or biodiesel) for use by motor vehicles or gaseous fuels that can be injected into mains gas. Waste plant materials can be precessed in an anaerobic digester to produce such biogas. These are not covered in detail by this website, although some liquid biofuels have been tested in domestic oil central heating systems in a blend known as B30K.

Heat from the sun - ground source heat pumps

When the sun shines on the ground its heat energy is absorbed. Ground source heat pumps extract this energy, to use for space heating. So, strictly speaking, the energy source that is used for ground source heat pumps is the sun and not the heat from the earth. In contrast, deep geothermal energy (which includes tapping hot water aquifers or access hot dry rocks) can be used for both district heating schemes and contribute to generating electricity through steam turbines, although this is usually only done in geothermally active countries such as Iceland or Japan. 

Heat from the sun - air source heat pumps

Air source heat pumps also use the sun's energy indirectly, as they extract residual warmth from the air and pass it through a heat exchanger to provide useful heat for buildings. In the UK, this heat is most commonly transferred into a wet central heating system. 

Wind - wind turbines

The power of wind has been used for many years to produce mechanical power for milling grain and pumping water. In recent times wind turbines harness wind to generate electricity. The electricity is then exported either to the grid for use locally or to power a standalone application. This renewable source of energy has great potential in both onshore and offshore wind farms and may also be used at a smaller scale on farms. Wind power is one of the cleanest and safest of all the renewable commercial methods of generating electricity.

Hydro - water turbines

The energy potential of moving water has been harnessed for thousands of years, originally using water wheels to drive mills and machinery. However, over the past century it has instead been been used to turn turbines that generate electricity. Hydropower currently produces 2% of the UK electricity needs; while most of this comes from large dam projects installed many years ago, there is still an untapped small hydro potential in certain parts of the UK.

There are several other ways of capturing energy from water offshore, including from tides and waves, but they are outside the scope of this website which focused on technologies that can be applied directly to, or nearby, buildings.

Complete the Energy Saving Trust's online Renewable Selector to find out which renewable systems might be suitable for you and your home.