Renewable energy
The renewable energy sector has experienced explosive growth in recent years as the need to find sustainable alternatives to fossil fuels becomes more urgent. Global energy consumption is increasing at the same time as the availability of fossil fuels is falling. Growing concern about climate change and the need to generate power from sources which emit no, or less, greenhouse gases is also driving the growth in the renewable energy industry.
Renewable energy comes from sustainable sources which do not rely on fossil fuels such as coal, oil and gas which will eventually run out. The main sources of renewable energy in the UK are:
- Hydroelectric
- Wind
- Wave
- Tidal stream
- Biomass
- Hydrogen and fuel cell
- Solar
- Geothermal energy
Hydroelectric
The use of flowing water to produce electrical energy both on a small scale (river) and large scale (dam).
Wind
Kinetic energy present in wind motion can be converted to mechanical energy for driving pumps, mills, and electric power generators.
Modern turbines for commercial power generation are increasingly of a magnitude of 1MW+ with larger turbines exceeding 4MW with hub heights in excess of 100m.
Wave
Energy produced from the motion of waves which are, in turn, generated by the motion of wind across water.
Tidal stream
Tidal and current stream energy systems use the natural ebb and flow of tides and currents to power turbines.
Biomass
The term ‘biomass’ means any plant-derived organic matter available on a renewable basis, including:
- dedicated energy crops and trees;
- agricultural food and feed crops;
- agricultural crop wastes and residues;
- wood wastes and residues;
- aquatic plants; and
- animal wastes.
Converting biomass for electrical generation is often called ‘bio-energy’, although different organisations and countries interchange the terms biomass and bio-energy.
Today, biomass usually involves large-scale uses and aims to substitute for conventional fossil fuel energy sources. It includes forest wood and agricultural residues, urban wastes and biogas and energy crops.
Worldwide, wood and charcoal are still valuable fuels because they are the cheapest and most readily-available form of energy in many developing countries.
Only around 300,000 tonnes of wood is used for fuel each year in the UK and most of this goes into domestic open fires, boilers and wood-burning stoves. Charcoal is barely used as a fuel, and most of the 5000 tonnes we consume each year ends up in barbecues.
Hydrogen and fuel cell
The principle of the fuel cell was discovered in the mid 19th century but it was not until the 1950s that it gained more widespread recognition when developed by NASA for manned space program. Today's focus on global warming and the need to develop carbon-free sources of energy has accelerated the development and application of fuel cell technology.
A fuel cell is a device which converts chemical energy contained in fuels into electrical energy with heat and water generated as by-products. A fuel cell converts fuels directly into energy via an electrochemical process and does not require combustion which converts kinetic energy to electricity. Consequently electricity is generated more efficiently in a fuel cell than in an engine.
There are a variety of fuel cell types operating at different temperatures and different fuels, for example
Polymer Electrolyte Membrane fuel cell operate at 80 degrees Centigrade. They are fuelled by pure hydrogen or hydrogen generated from reformed hydrocarbon fuel. They are primarily used in transportation, power back-up and portable power applications
Solid Oxide fuel cell operate at 700-1000 degrees Centigrade. They are fuelled by many different hydrocarbon fuels. This type is more suited to combined heat and power in residential applications or primary power applications.
Find out more about this sector at The Scottish Hydrogen and Fuel Cell Association website
Solar
Energy radiated by the sun as electromagnetic waves (electromagnetic radiation) that is converted into electricity using solar (photovoltaic) cells or concentrating (focusing) collectors.
Geothermal
Hot water or steam extracted from geothermal reservoirs in the earth's crust can be used for geothermal heat pumps to heat water or to generate electricity.