Renewable energy
From WikiClimate
Renewable Energy is energy taken from a resource that is naturally replenished and cannot run out over time. This contrasts with fossil fuels such as coal, oil or gas and nuclear power, based on uranium, all of which have finite resources. Renewable sources of energy produce fewer greenhouse gases than fossil fuels and so contribute less to global climate change.
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Types of Renewable Energy
The main types of renewable energy include:
- Solar Thermal Energy - most commonly found in the UK as Solar Water Heating, but can also contribute to space heating or be used in sunny countries in a solar concentrator to raise steam for electricity production;
- Solar Electricity - generated from Photovoltaic Cells (PV);
- Solar Energy stored in the earth, water or air, and typically recovered by using a Ground Source Heat Pump;
- Wind Energy;
- Hydro, including large scale HEP from reservoirs and smaller millstream or run of river schemes;
- Wave Energy (either shore-based or offshore);
- Tidal Energy - from barrages or tidal flows or currents;
- Biomass - woody or grass-like plants grown for combustion to generate heat or electricity;
- Biofuels - liquid or gaseous fuels from plants (or more rarely animal sources), generally used in transport.
The following are often included with renewable energy:
- Passive Solar Design - arranging buildings so that they make maximum use of natural daylight and of the sun for winter heating, yet are shaded from the summer sun to prevent seasonal overheating;
- Geothermal Energy - using the earth's own internal energy to produce hot water for heating or electrical generation. (This is not strictly renewable, but is a carbon-free source of almost unlimited energy.)
Advantages of and Problems with Renewable Energy
Advantages
The principal advantage is that most sources are essentially limitless and most are carbon-free or broadly carbon neutral, where emissions at the point of use (eg. from combustion of biomass) are balanced by emissions captured in the growing phase. Most countries have access to a number of different types, so they do not need to be imported and so can contribute to a nation's energy security.
Problems
The main problems are cost and intermittency.
- Most renewables require a significant up-front investment, which is then recovered by the supply of free (or nearly free) energy. The economics of renewables tend to depend crucially on the cost of capital and assumptions over the future price of energy. Compared to conventional sources of energy (especially fossil fuels), renewables may appear to be expensive. However, offsetting this issue is the hidden cost of environmental damage, notably climate change, that is not usually levied on fossil fuel users. Costs for many renewables are falling as demand rises, although biomass and biofuel costs are rising due to competition for land with food products, and rapidly rising demand from externally imposed targets, such as those in the EU's biofuels directive.
- Intermittency is the term used to identify that many renewables are only available for part of the time and not on demand. For example, solar electricity can only be produced during daylight hours, and the output is much higher on sunny days than on overcast ones. Wind is also intermittent, although at a national level it is rare for an entire country to be wind-free (as might occur if under a large anticyclone).
There are several ways of overcoming intermittency, including storage (eg in batteries, or in hydro-electric pumped storage schemes), backup supplies of other energy sources (including biofuels and fossil fuels) and better demand management (DSM).
- Lesser issues with renewables include land take (and competition with food crops), damage to protected environmental landscapes (eg through creations of reservoirs or tidal pools behind a barrage) and visual impacts (especially for wind).
See also
More internal links to follow when constructed
