Types of energy

A resource is defined as any aspect of the environment that can be used to meet human needs. Energy resources can either be classed as either renewable or non-renewable.

• Non-renewable energy resources - (also known as finite, stock, or captial resources) are those that have been built up, or have evolved, over time. They cannot be used without depleting the stock because their rate of formation is so slowthat it is meaningless in terms of human lifespan. There is no theroetical limit on the rate of use of non-renewable resources - but it depends on the capacity of society to exploit them. Non renewable energy resources are primarily fossil fuels (oil, nautral gas, coal) but they also include nuclear energy.
• Renewable energy resources - (also known as flow or income resources) have a natural rate of availability. They yeild a continous flow that can be consumed in any given period of time without endangering future consumption, as long as current use does not exceed net-renewal during the same period. Renewable energy resources include: solar power, hydroelectric power, geothermal energy, wave and tidal power, wind power and biomass sources. Renewable resources can be subdivided into:
• critical - sustainable energy resources from forests, plants and animal waste, which require prudent management
• non-critical - everlasting resources such as tides, waves, running water and solar power.

Renewability may not be automatic and certain resources may be depleted by heavy use or misuse. In such cases the life cycle of the resource is curtailed. Resource management is the control of the exploitation and use of resources in relation to the associated economic and environmental costs. A key element of this is the concept of sustainable development. This involves a carefully controlled system of resource management to ensure that the current level of exploitation does not compromise the ability of future generations to meet their own needs.

A reserve is the proportion of a resource that can be exploited under existing economic conditions and with the available technology. Reserves can be classified as recoverable or speculative.

• Recoverable reserves - are the amounts of a mineral likely to be extracted for commercial use within a certain time period and at a certain level of technology. They: are known to exist, can be estimated on the basis of information and judgement, and are in unexplored areas near established areas of production.
• Spectulative reserves - are deposits that may exist in a geological basin or terrain where no exploration has yet taken place. They occur where the geological makeup of the Earth's crust is similar to regions that have yeilded comparable deposits.

Primary energy resources - are raw materials used for power in thier natural form such as coal, oil, wood and uranium. They can be converted into secondary energy sources such as petrol or diesel and used to run vehicles, or into electricity and use to power domestic, industrial and commercial premises. In more developed countries energy sources such as oil, natural gas, coal, hydroelectric pwoer and uranium provide the main sources of power. A continual supply of this energy is necessary for the survival of such advanced technological nations. In contrast, most less developed countries rely on sources of energy such as wood, peat and animal waste.

Demand for and consumption of energy has grown dramatically worldwide over the last 200 years due to:

• rapid population growth, initally in the more developed countries but in the last 50 years more markedly in less developed countries.
• economic development and wealth - in more developed countries that rate of demand for energy has outstripped population growth. With increased wealth comes increased personal mobility and the demand for more goods, services and labour-saving devices in the home.
• technoligical change, initially as a result of the developement of the steam engine fuelled by coal during the Industrial Reveloution of the 19th century. In the 20th century demand for oil outstripped that of coal as combustion and jet engines were developed.

Until recently the UK was self-sufficient in terms of primary energy resources, producing considerable quantities of its own coal, oil and nautral gas. Although there are still significant coal reserves, there are not considered to be economically viable at present. In addition, clean air leglislation has led to the increase in demand for clearer sources of fuel. The coal industry was privatised in the 1990s and since then alomost all pits in the UK have closed down.

Non-renewable sources

Natural gas and oil dominate UK primary energy supply in the first decade of the 21st century, with over 70% if the total coming from these two non renewable sources of fuel. The share of nautral gas has increased significantly in recent years, with a total increase of around 85% since 1990. Coal has decreased in importance by 40% since 1990 and although renewable resources have increased thier share they still provide only a small proportion (2%) of the total primary energy supply. The share of nuclear power has not changed much in the recent past, although the government is considering the expansion to reduce dependence on potentially shrinking supplies of fossil fuels.

Although the UK is still the largest producer of oil and natural gas in the EU (with proven oil reserves of 4 billion barrels and natural gas reserves of 0.53 trillion meters cubed at the end of 2005), the depletion of these reserves coupled with the decrease in domestic coal production has led to a growing dependence on imported energy. In 2004 the UK became a net energy importer for the first time since 1993, although it is still a net exporter of oil and maintains on of the lowest import dependencies in the EU. Natural gas is now overtaking coal as the primary fuel for Britains power stations. In the future it is likely that increasing amounts of natural gas will need to be imported. At the present Norway is a signifcant source of imported natural gas but Russia is likely to become increasingly important.

In 2005, approximately 76% of the UKs energy was generated from fossil-fuel sources, just over 19% from nuclear sources, and just over 4.5% from renewable sources. As part of its goal to reduce carbon dioxide emissions, the UK government has set a target for the generation of electricity from renewable resources. By 2010, 10% of the UKs electricity should come from renewable sources, and the aim is to double this by 2020. To reach this target, approximatley 10,000MW of energy will need to be created from renewable resources, which equates to between 3000 and 5000 wind turbines, or 200 biomass power stations generating 50MW each.

Until recently hydroelectric power was the most important source of renewable energy in the UK. By 2000 this had been overtaken by biofuel. Most HEP stations are large-scale schemes in the Scottish highlands. Oppertunites to increase the numbers of large plants are limited as most commercially attractive and environmentally acceptable sites have already been used, although many smaller-scale schemes are feasible. If small-scale HEP from all the streams and rivers in the UK could be tapped, it would be possible to produce just over 3% of total energy needs.

In 2006, biomass used for both heat and electricity generation accounted for 82% of renewable energy sources in the UK. Most of this energy was generated from landfill gas and waste combustion (47%) with smaller amounts from sewage waste, domestic wood and industrial wood. Biomass has the potential to make a significant contribution to the UKs energy needs in the future.

Wind is the 3rd largest contributor of renewable energy in the UK and in 2007 there were 1769 wind turbines in operation at 137 sites, producing enough energy to supply electricity to around 400,000 households. By 2010 it is expected that wind power will make the main contribution towards the governments 10% renewable energy target, with more offshore wind farms.

Energy consumption in the UK has remained fairly constant over recent years. Transport consumes over 30% of the total energy supply and has shown the largest growth in demand over the past 20 years. Although domestic consumption has also increased during this period, this has been balanced by a decrease in deamand from the industrial sector. Most of the energy used by transport, domestic and industrial consumers is secondary in nature. Within the energy industry, losses during conversion to secondary fuels and during distribution accounted for just over 30% of the total energy consumption in 2005. In future improved methods of conversion could result in better effiency and less overall waste.