Renewable energy is energy which is self replenishing. Many people would say that it is also sustainable energy, which implies that in accordance with many definitions of sustainability it should be self replenishing within a generation, so that the present generation does not rob energy resources from future generations.
Renewable energy takes many forms but starts out being either stored in the earth’s crust and deep magma, or nuclear; the vast majority of which is from the sun.
Geothermal energy is not totally renewable, because when we use geothermal energy it is removed from the earth’s crust. However, the proportion we could conceivably use is so tiny that it would take billions of years for man to use up all the earth’s geothermal energy. Therefore, geothermal energy is classed as renewable.
Burning wood is thought of as renewable, but it is only really renewed once the forest it was cut from has grown again. As long as the woodland is replanted though, most people would consider burning it to be renewable since it will regrow in temperate regions within a generation. In contrast, burning fossil fuel is clearly not renewable because it takes millions of years for new coal, oil, or natural gas to form. That’s a lot longer than one generation!
There is an interesting form of renewable energy which often renews itself in a year or less, and if it isn’t used it simply is wasted: That is biogas, which is made from the anaerobic digestion process, which uses ancient microorganisms which have existed since there has been life on earth, to make it.
Renewable (sustainable) biogas energy works like this. A crop, or better still an organic waste left over from the growth of a crop (for example supermarket food waste), is fermented in a biogas digester, a gas (biogas) bubbles off, and that gas is used instead of natural gas. This is a fabulous renewable energy, because it burns clean – which wood certainly doesn’t. It can be used for anything natural gas can be used for, including as CNG (compressed natural gas) for vehicle fuel. It is also quickly replenished (much more quickly than wood) by using the material remaining afterwards as a fertilizer, to grow the next year’s crop.
A few years ago many governments saw oil prices rising along with all other fossil fuel prices rising and decided that to make bio-fuel and in particular bio-diesel would save their bations spending a lot of money which would leave their countries to pay for imported oil used to make diesel fuel. They saw uding biogas as a wonderful way to make bio-diesel, and started to subsidize the production of biogas. But, they encouraged farmers to divert their food crops like maize to making bio-diesel. When, simultaneously food prices started rising faster then inflation there was a public outcry against the subsidies. The result was that governments (such as Germany and Brazil) got a lot of bad publicity for encouraging farmers to stop supplying food. The result has been that most of those subsidies have now been stopped.
However, it did not have to be like that because there are many sources of organic feedstock materials for running anaerobic digestion plants and making biogas. In recent years there has been a realisation that it is much better to use manure, and all sorts of types of organic waste, which otherwise get dumped in landfills and cause big pollution hazards.
This is big news. In the UK biogas from wastes could, if all the waste produced were digested, heat half the homes in the UK. Don’t take our word for it that there is scope for large numbers of anaerobic digestion plants. It is a fact recognised by the US Depatment of Agriculture in their Renewable Energy Roadmap which sets out be get 11,000 biogas (energy from waste) plants built solely on large US dairy farms, by 2020.