| Renewable energy |
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There are various definitions of ‘renewable’ as applied to energy . The UK Renewable Energy Advisory group defines it as “the term used to cover those energy flows that occur naturally and repeatedly in the environment and can be harnessed for human benefit”. They add that the ultimate sources of most of this energy are the sun, gravity and the earth’s rotation. Most of us are aware of electricity being generated from solar power, and from wind and wave power. Electricity generated from such methods does avoid the kinds of environmental damage created by the burning of fossil fuels, but each of these methods has some, at least local, environmental consequences. However they do not release pollutants into the atmosphere. Another example of renewable energy is that sourced from plants – biomass and biogas fuels as they are often termed. Biomass refers to the burning of vegetable matter and biological wastes. Biogas refers to the production of gas as an ‘intermediate fuel’ from biological sources. The sources of all of this energy are broadly inexhaustible and they have the added advantage – in an increasingly geopolitical world – that they cannot be turned off by another power. So – if, they can make a contribution towards future energy needs, and they are financially viable (now or in the near future) – we should be considering them. Solar power The energy landing on the earth from the sun each minute is vast. The problem with solar power is not is availability but the problems with converting it into usable energy. Solar power is used in ‘passive systems’ to heat water and heat spaces (though nature is sometimes helped by using mirrors to concentrate the energy) but more commonly it undergoes some form of conversion process and is turned into electricity. Since it is the sun (and differential warming) that causes air movements, sea currents, rainfall and river flows, solar power is also the underlying source of wind, wave and hydro-electric power. Most people are aware of solar power because they have seen ‘solar panels’ – devices which convert energy from the sun directly into electricity. These are more properly arrays of photovoltaic (PV) cells …. useful devices because they have no moving parts and are thus very reliable. Over the last few decades they have become lighter and cheaper … and perhaps more importantly, more efficient. This increasing cost effectiveness is likely to continue for some time. (As yet, the economics of PV energy production do not make it a viable competitor for current power station processes.) PV cells are particularly useful in developing countries where no electricity infrastructure might exist – to power irrigation and water supplies, refrigerators (especially for medicines) … and lights, radios, TVs, etc.
Wind Energy We have all seen wind turbines … and experienced the controversy about their siting. We are also familiar with its forerunner, the traditional windmill – showing that wind energy has been used for centuries. As with solar power, the technology has been improving steadily over the last few decades to make wind energy cheaper. The power produced by a wind turbine depends on the wind speed and its effective capacity depends also on its reliability – or availability. Modern wind turbines have availability in the 90-95% range (over a year). Because of fluctuating wind speeds, typical capacity is usually inn the range of 25-40% of the theoretical maximum, depending on the prevailing winds at the particular site. This makes wind farms economically viable for electricity generation over a 20 – 25 year period. The controversy about wind farms (as groups of wind turbines are called) stems from the visual impact on the landscape, the noise they produce, the electromagnetic disturbance they create and possible impacts on wildlife. For this reason, offshore wind farms are often regarded as a ‘safer’ location … and there is another advantage in that the different temperatures of land and water create wind – sea breezes.
Wave Power The concept of power from waves and tides has been around for centuries but there has been little practical development, with viable technologies only emerging in the 1970s. However tides are more ‘certain’ than sun or wind 9in the UK) and this form of energy generation has real potential. There is a wide range of technology being developed for different types of location – from deep water generation to surface devices. There are very high capital costs associated with harnessing wave and tidal power but operating costs are low because there are no fuel costs. There is still, however, a long payback period and this seems to dissuade both private organisations and governments. Wave power offers advantages over wind power installations in that the installations are less visually intrusive and they generate little noise (though they can, of course, pose a hazard to shipping). Tidal power does have an effect on the local ecosystem (though effects can be both positive and negative) and this makes a ‘balanced judgement’ necessary but difficult. The economics are not right yet, but wave and tidal power offers a long-term development opportunity as technology brings costs down and scarcity drives up the cost of ‘traditional’ energy sources.
Biomass The earth’s living matter – its biomass – exists in a thin surface layer – the biosphere. It is a store of energy which is being constantly replenished by the sun … so as long as we consume less energy than is replenished in the natural cycle, we have another renewable source. What is more, the biomass is part of a natural cycle that generates heat and carbon dioxide … which (apart from a small fraction which is stored in peat or converted into fossil fuels) is naturally released into the atmosphere. As long as we consume less than the replenishable supply, we should cause no more atmospheric pollution than those natural processes. Remember that earth’s history is a history of biofuels – wood and coal. What earth’s population failed to do was to ensure replacement of the fuels they were using. Some counties are already using the biomass as a major source of energy – using processes from simple direct combustion, to thermochemical processes (such as liquefaction) to biological processing (again often to a liquid fuel). Notice that unlike the other renewable energy sources we have been talking about, biomass is used for direct heat or is concerted into a fuel (more than 4 million Brazilian vehicles run on ethanol derived from sugar cane) … it is rarely used to generate electricity. Summary We are going to see an increasing contribution to our overall energy needs from energy derived from renewable sources. This is a political issue as well as an environmental issue and politicians of all sides are committed to ‘more’ renewable energy. The actual percentage contributed will depend on the economics as well as the politics …. but the economics depends on the politics as governments introduce carbon taxes and carbon trading systems. Some argue that we cannot afford to contribute more than about 20% of total energy needs unless there is a revolution in energy storage. This is because renewable energy is mostly derived from sources which fluctuate in capacity (much more solar power in summer, for example). This ‘storage’ might be in the form of hydrogen – if hydrogen-fuelled cars move beyond their current experimental levels of production. Clearly the balance of sources of energy will differ from country to country depending on their history (and current energy infrastructure), their climate, and their political climate. The energy is there – but it costs money to develop each of these energy sources, and each of them has specific environmental impact. Some of the decisions to be taken are, in effect, global decisions – will future cars run on hydrogen? Others are more local – should we move energy-dependent industries closer to the new energy sources? The UK – like every other nation – has to devise and develop an integrated energy plan to which renewable energy sources will undoubtedly make a significant contribution.
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