Glossary Of Alternative/Eco/Renewable Energy Terms

There are quite a few terms, words, phrases and abbreviations in the realm of alternative/eco/sustainable and renewable energy. Here are some of those you are most likely to come across.

• Alternative Energy
  
  Vertical Axis Wind Turbine
  This widely used term is difficult to define precisely. Loosely it describes energy (power) that is derived from unconventional sources - or sources that are alternative to conventional energy sources. Conventional energy sources are for example coal, oil and nuclear.

  Unconventional sources include bio-diesel, wave energy and solar energy. Most people would class wind energy and hydro-energy as alternative. However these forms of energy have been used for hundreds of years - though not in the same way.

  Both hydro and wind energy were used for powering mines, factories and mills using waterwheels and windmills. The energy was used to directly drive machinery whereas nowadays the equivalent water turbines and wind turbines are usually used to generate electricity which is then used used to drive machinery, provide lighting etc.

  Wind energy has been used for thousands of years to power boats and ships. Solar energy has been used since the beginning of agriculture to dry things such as hay and crops - and, of course, growing crops.

• Eco Energy

  This term is used to describe sources and utitilisation of energy when it is eco-friendly - that is it has no or only a small impact on the local ecology or wider ecology of the world. In general this is very difficult to achieve on a large scale as taking energy out of the environment to use it somewhere else is always going to have some effect on the local environment.

• Geothermal Energy
  
  Geothermal Plant In Iceland

  Geothermal energy is the energy in hot parts of the earth's crust (solid top layer). In some areas - normally those with volcanic activity - these can be relatively close to the earth's surface.

  Energy is usually extracted as steam and can be used to power turbines to produce electricity or used to provide district heating etc.

• PV
  
  Small Array Of Polycrystaline Silicon Solar Cells

  This stands for Photo-Voltaic. A PV material generates a small electrical voltage when illuminated with light (photons).

  Normally a number of PV cells have to be connected together to provide a useful voltage.

  If a number of PV cells is connected to a electrical circuit and the cells are illuminated (normally by sunshine) the generated voltage causes an electrical current to flow. This can be used to charge batteries; power light bulbs etc. If connected to the electricity grid any surplus electricity can be exported to the rest of the country.

• PV Cell

  This is an individual unit made of PV material normally specially prepared silicon. A number of these are normally fitted into a panel and connected electrically together to form a PV solar panel.

• Renewable Energy

  This term is used to describe sources of energy that are naturally renewed, for example solar energy or wind energy.

• Silicon

  Silicon is an element. Ordinary sand is mainly made of silicon dioxide an oxidised form of silicon. Very purified silicon with very small amounts of other elements added is used to make most transistors, integrated electronic circuits including microprocessors and computer cpus etc. It is also used for the production of PV cells.

• Solar Heating Panel
  
  Roof Mounted Solar Heat Collector Using Heat Pipes

  This is a panel that collects the radiant energy from the sun.

  Energy in both the infra red and the visible spectrum lands on the panel collecting surface and warms it up. Usually a fluid (normally water or water with anti-freeze added) is pumped past the collector plate to remove the heat and pass it on to a hot water and/or central heating system via a heat exchanger coil. This is called an indirect system.

  Sometimes a direct system is used to heat water. In this system the water to be heated passes directly through the panels. Some collectors consist of a series of heat collecting tubes instead of a flat plate. With these a heat pipe may be used to transfer the heat energy to the end of each tube where the circulating fluid is then heated indirectly.

• Solar Panel

  This term is used for both solar PV panels and solar heating panels which can sometimes be very confusing as these are very different from each other.

• Sustainable Energy

  This term is used to describe sources of energy that are naturally renewed, or maybe renewed/sustained by human effort. For example the generation of bio-diesel may be considered sustainable (though there are major uncertainities) or the growing and burning of wood such as willow.

• Water Wheel
  
  Overshot Water Wheel
  Waterwheels were used for centuries to provide direct power to grind flower, pump water or run machinery. There is renewed interest in the possibility of using water wheels to generate electricity as turbines are very expensive per unit of electricity capacity when deployed on a small scale with a low head of water (ie where there is only a small drop between the input and output).

  Usually a water wheel is used to extract energy from water falling from a raised channel to a lower one. In this type of water wheel the main energy comes from the potential energy of the mass of the water in the high channel released as it falls in the wheel to the lower channel - very little comes from the energy of the horizontal movement of the water (the kinetic energy).

  However there are some water wheels that just 'dip' into the fast moving stream of a river and effectively extract the kinetic energy from the flow.

  For an excellent introduction to waterwheels see Southampton University Energy Website

• Wave Energy
  
  Overtopping Principles
  A number of ways of extracting energy from waves are being developed. They range from oscillating water column (OWC) systems to articulated floating segments (eg: Pelamis) and overtopping designs. The OWC designs may be shore (eg: Wavegen), near shore based stationary or tethered.
  
  Wave Dragon Prototype
  An example of a tethered overtopping design is the Wave Dragon - see the pictures here.
• Wind Turbine
  
  Wind Turbines
  This is machine that has rotating blades that are powered by the wind. Effectively it is a modern windmill, but one which normally drives an alternator that produces electricity rather than a mill to grind flower, pump water or provide power directly to machinery.