What is Renewable Energy?

Renewable energy is energy generated from natural resources - such as sunlight, wind, biomass, rain, tides and heat from the earth - which are naturally replenished and therefore essentially inexhaustible, unlike fossil fuels, of which there is a finite supply.

Why is it necessary to develop renewables?

Fossil fuels such as coal, oil and gas produce carbon dioxide when they are burned to the produce heat and power (electricity). Carbon dioxide is a major greenhouse gas. An increase in the level of greenhouse gases in the atmosphere since the Industrial Revolution is causing climate change. In Britain this could lead to wetter winters and drier summers making it more difficult for farmers to grow the food that we need. Low lying areas of the world are likely to flood as sea levels rise.

When renewable energy sources are used to produce heat and power they produce little or no carbon dioxide. For this reason they are often referred to as being 'zero carbon'. Using biomass to produce heat and power does result in the release of carbon dioxide but this is usually only a little more than the tree or plant absorbed when it was growing. What is left is the carbon dioxide released as a result of the energy that is used to process the biomass (e.g. to chip wood) and to transport it to where it is going to be used. This is usually a very small amount compared to that produced by fossil fuels for the same level of energy production.

Until a few years ago the UK exported gas and oil. Now we are reliant on imports from Norway, the Middle East and Africa to meet the shortfall in our energy requirements. Making use of local, renewable energy supplies gives the UK better security of supply - our energy supplies are less likely to be interrupted by foreign disputes. Making use of a variety of energy sources also gives the UK greater security as we are not so reliant on one source meaning that there are less likely to be interruptions in supply and wide fluctuations in prices.

A final reason to develop renewable energy is because fossil fuels will eventually run out - although when this will happen is much disputed.

What are the main types of renewable energy?

Renewable Energy for the National Grid

The main types of renewable energy for the production of electricity in the UK are wind, hydro and the co-firing of biomass in conventional coal power stations. There are also a number of smaller stations linked to the grid including ones burning chicken litter and biomass in combined heat and power units.

Most of the renewable energy generated in the UK comes from large hydropower schemes Hydropower generates electricity from the moving power of water as it falls under gravity from a higher to a lower level. On a large scale this is done by building dams with turbines inside them. Most of the sites suitable for the development of large hydropower schemes in the UK have been used.

Biomass, mostly in the form of woodchip, can be used for the production of electricity in a dedicated biomass power plant. Biomass can also be used in a coal fired power station in a process known as 'co-firing' where the biomass and coal are pulverised before being burned together in the plant. Biomass materials include sustainable wood-based products, including special crops such as willow, poplar, switchgrass and elephant grass, as well as forestry residues and residual agricultural products, such as sunflower seed husks and peanut husks.

Energy from wind comes from large on and off-shore wind farms. RenewableUK report that there are currently over 250 wind farms in the UK, generating enough electricity for 2.3 million homes (around 11TWh annually). This includes 9 large offshore wind farms that already generate around one-sixth of the electricity from wind. The wind turbines which are used for the production of electricity on this scale are fairly large structures with a mast in the region of 100 to 150m tall - the largest ones being found offshore.

Over the next decade it is expected that an increasing proportion of the UK's electricity will be generated offshore - and not just from wind. There are already commercial scale tidal stream plants off the coast of Northern Ireland and Eastern England, and several wave power schemes are being developed, working both at the shoreline and using deep water waves, with many of the projects off the coast of Scotland.

Electricity generators are required to produce a certain proportion of their electricity from renewable sources by the Renewables Obligation. In 2010 10.4% of electricity generation should come from renewable sources, although the actual figure is likely to be lower than this as the figure for production of electricity from renewable sources was 5% in 2008.

Renewable Energy on the Community Scale

As well as large-scale generation of electricity, renewable energy can also be produced on a smaller scale, at home, on farms and by businesses. Small scale generation can produce heat or electricity. Heat is most commonly generated from the sun (usually by solar water heating panels), from biomass - including logs, woodchip and pellets, or through heat pumps, which extract heat from their surroundings. Biomass can either be burnt directly in a stove, or used to heat water in a boiler serving a conventional central heating system.

Most heat pumps in the UK capture energy from the ground or air to heat water in a central heating system. Ground source heat pumps use a collector loop laid either in trenches or boreholes to capture energy stored year round in the ground. (They work in a slightly different way from higher temperature geothermal plants, which rely on hot underground rocks to raise steam for electricity generation.)

Small-scale electricity is most commonly generated from solar electric panels (known as photovoltaic or PV) or from small wind turbines or hydro schemes. However it can also be produced from smaller combined heat and power plants using biomass as the fuel source. PV panels are usually fixed to South facing roofs of buildings, where they can generate electricity silently. Small hydro schemes do not always need a dam; they sometimes take water from the run of a river, or are fitted onto old millstreams or millponds.

Some tariffs certified under the Green Energy Supply Certification Scheme invest in small-scale renewable energy at a community scale, supporting projects such as biomass or ground source heating systems and photovoltaic electricity.

Are there problems with renewables, and how do they compare with other low or zero carbon fuels?

Although renewables are a clean and plentiful source of energy, they are often more expensive to develop than conventional sources of energy, even though they also often have lower ongoing costs. It's important then that we should not waste scarce renewable energy, and make sure we have done everything we can on energy efficiency to reduce demand before relying on renewables.

At present, Britain grows enough biomass to meet most of its needs. However, as demand for low carbon heating and electricity grows, new plantations will be needed using crops such as short rotation willow if the country is to avoid importing supplies. In either case, land used for growing crops for fuel may start to compete with land used for food, and will need careful management to maintain high standards of sustainability and biodiversity.

Some renewable energy technologies, such as wind, wave and tidal power are described as intermittent. This means that they do not produce electricity all of the time, as they can only do so, for example, when the wind is blowing. The demand for electricity from customers is also variable. In order to ensure that electricity supplies always meet demand the national grid has to have reserves - power stations that can be called upon to produce extra electricity at short notice. However the output from most renewables can be reasonably accurately forecast at least a day in advance, with hydro and biomass plants able to be controlled independent of weather and tides.

Once more than 20% of our peak electricity demand is met from intermittent sources such as wind, there may need to be a strengthening of the grid to cope with fluctuations, and the UK is planning to work with other countries around the North Sea to share supplies and meet peak demand.

According to RenewableUK (formerly the British Wind Energy Association) wind turbines generate electricity for 70-85% of the time, but not always at full output: they produce about 30% of their potential capacity a year. This compares to 65 to 85% for a nuclear or conventional coal fired power plant.

Nuclear power is another zero carbon source of electricity, but it is not a source of renewable energy as there are finite resources of the uranium and plutonium that are used as the fuel. Although the UK Government supports the use of nuclear energy on the basis that it is zero carbon, many people are concerned about the safety of nuclear power plant and about how and where the spent fuel can be disposed of. Nuclear power stations are also expensive to build and decommission.

In summary, although clean and renewable power provides new challenges for the UK, they can be solved using current technologies at a cost that will be acceptable to consumers of energy.