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Alternative Energy Sources

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Renewable Energy

 

Main final use form: electricity (some heat and motor fuel)

In the long term (assuming the unlikelihood of producing nuclear fusion), renewable energy sources are the only hope for mankind. They are the only forms which will not run out and are therefore less likely to lead to resource wars. Unfortunately the costs of manufacture and the length of time needed to fully develop are major obstacles, as well as the inability of most of the forms to replace oil and gas for transport and agriculture.

The "Present" and "Potential" figures are from information in "Energy: a Guidebook" by Janet Ramage 1997. Values show present (1997) contribution and maximum realistic potential in exajoules per year. For comparison, oil contributed 135 EJ per year (1997), gas 79, coal 91 and nuclear 8. They are shown graphically in chart E4.

Unit cost is also from "Energy: a Guidebook" and was in pence per kilowatt-hour (1997 figures). Since the actual numbers are of limited value, they have been changed to an index with small-scale hydro (2.9 p/kWh) as 1. To see the original data from which the index was calculated, click here.

   

 biomass icon Biomass

Main final use form: motor fuel and electricity.
Present: 52 EJ/y   Potential: 100 EJ/y
Unit cost index: 2.1
EPR: 0.7–1.8 (ethanol)

Biomass is the oldest of all fuel systems in the sense that we have been burning wood for thousands of years. Biomass is defined as power generated from recently produced animal and plant matter, unlike the fossil fuels which were living matter millions of years ago. To be truly renewable, the plant or animal matter has to be regrown or it becomes as finite as coal or oil. There are two main uses for biomass: burnt to create energy directly and converted to a fuel for transportation (biodiesel).

Bioenergy

There are many ways to use biomass to create energy, depending on the original plant or animal material. The oldest method is direct burning of material grown specifically for that use such as wood and bagasse (crushed sugar cane). Another technique is to burn waste material rather than leave it in landfill sites (or, alternatively, recycle it). This includes material such as urban refuse, industrial waste, agricultural and animal residues, wood chips, and sewage sludge.
Whatever ends up being incinerated, the end result can be used for heating or generating electricity or both (CHP - combined heat and power). The biggest problems with bioenergy is the danger of air pollution from the toxic substances often released upon burning, and the loss of the material from other areas; the cow dung that is burnt for cooking in India deprives the soil of valuable nutrients.

Biofuels

The other option with biomass is to convert it to a fuel to run machinery and transportation. As the other renewables are limited to electricity and heat, this is clearly an important benefit. The diesel engine, after all, was originally designed to be used for a variety of fuels and can be used for biofuels with little or no adjustment. Biodiesel is a chemically altered vegetable oil while another common fuel, ethanol, is a fuel-grade form of alcohol produced from grain fermentation. The waste oil from chip fat is commonly used to power vehicles, a good use for an otherwise useless waste material.

The biggest problem with bioenergy and biofuels, especially where they are grown specifically, can be seen in the Agriculture page. Modern farming is an intensive business and makes large use of fossil fuels for powering machinery and making fertilisers and pesticides. If we are not careful, we could end up using the fossil fuels that the biomass is supposed to be replacing. Using oil to grow crops to turn into oil seems bizarre to say the least and there is a danger that we use more energy growing the crops that we get out of them. Also, as oil and gas decline, we will be forced to move towards more organic means of growing food. This could result in a competition for arable land: do we grow food or grow energy?

The grain required to fill the petrol tank of a Range Rover with ethanol is sufficient to feed one person per year. Assuming the petrol tank is refilled every two weeks, the amount of grain required would feed a hungry African village for a year.

As well as this, the irresponsible use of biocrops can do tremendous harm. The rise in the growth of palm oil for biodiesel could turn out to be catastrophic, threatening to put more carbon dioxide into the atmosphere than it could save. This is because countries like Malaysia are cutting down vast areas of rainforest to grow the crop, endangering not only the flora and fauna that live there, but releasing all of the vast amounts of carbon dioxide locked up in the trees.

Growing maize [used to create ethanol in the USA] appears to use 30% more energy than the finished fuel produces, and leaves eroded soils and polluted waters behind.

Biodiesel should not be looked upon as a replacement for oil but, at most, as a temporary source to tide us over to a more sustainable future. In the end, we need to travel far less than we do if we are to solve the twin demons of climate change and peak oil. (The low energy output of most biomass fuels can be seen in chart  E2.

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 hydroelectric icon Hydroelectricity

Main final use form: electricity.
Present: 8 EJ/y   Potential: 70 EJ/y
Unit cost index: 1 to 1.5 (small to large scale plant)
EPR: 11.2

Large-Scale

Flowing water has been used to generate electricity since the 1880s and has been used to create mechanical power for centuries before. It is the most advanced and important renewable source at the moment, contributing about 19% of the world's electricity supply with the potential of something like five times that, including areas such as Asia and Africa. If it a very efficient conversion of energy and, although expensive to construct, is very cheap to maintain. It is also able to store the energy and release it very quickly on demand, something few other energy sources can. The largest power station today is the Itaipu plant between Brazil and Paraguay which has a capacity of 12 GW, ten times that of a coal or nuclear station.

It is, however, not all good news. The damming of rivers can create many serious environmental problems and destroy valuable farmland which is often found in valleys. Existing inhabitants are often forced to move and the collapse of a dam would be catastrophic for those living downriver. Also, the best hydroelectric sites are often found in mountainous areas, far from the areas of demand.

Small-Scale

Small-scale hydroelectricity, relying on small turbines to generate power for houses or small towns, has less potential than other renewables like wind and solar. A reliable and strong flowing source is obviously needed, and the installation must not cause other problems such as reduced flow or obstructions. There is also the danger that it can cause problems with water supply which is often an endangered resource in itself.

Pumped Storage

Pumped storage generators like Dinorwig in Wales are not really power stations but electricity storage schemes. Water is pumped up to the reservoir when power demand is low and released to generate electricity when demand is high. Like all forms of energy conversion, it loses something in the process and the energy that is generated is about 70-80% of that used to pump the water up. However, pumped storage has uses in sporadic energy generation such as wind and solar in that it can use electricity generated when there is surplus capacity and store it for when demand exceeds supply.

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 wind icon Wind Power

Main final use form: electricity.
Present: 0.02 EJ/y   Potential: 180 EJ/y
Unit cost index: 2.4
EPR: 0.03–2

Large-Scale

Wind power has the largest growth of any energy source in recent years. A single wind turbine can now be built with an output of up to 3 MW. A recently built single turbine in Reading, Berkshire, has a capacity of 2 MW and generates 4.5 kWh, enough electricity for 1,500 homes.

There are many advantages to wind power. Most countries have large areas where the wind blows fairly reliably and stronger winds can usually be found simply by building higher. They do not take up much space as the land beneath the turbines can be used for farming or storage (although they cannot be built too close to homes or workspaces because of noise and TV interference). Although the wind, of course, does not blow all the time, it tends to blow strongest during the winter and during the day, the periods when demand is highest. The fuel for the turbine is free and the environmental effects limited as long as they are not placed in areas prone to high bird use. Visually, their appearance is subjective - some find them ugly while many find them attractive, not something that is often said about coal or nuclear power stations. But even this can be offset by building them offshore.

With a typical modern wind turbine, electricity would begin to be generated at a cut-in point of maybe 3.5 m/s and power output would increase with wind speed until it reach a maximum, for example, 225 kW at 13 m/s. Any increase in the wind after that would not produce any greater output. Finally, there would be a cut-off speed when the turbine would have to be feathered to stop it spinning dangerously fast. This might be at about 25 m/s but these high speeds are rarely reached as long as the designers choose the best sites. In the UK, a wind turbine on average will generate power for 80-85% of the time.

The problems of low wind speed can be reduced by building farms over different areas of the country. In all but the smallest countries, it would be very rare for all of the land and sea area to be affected by low wind speeds. A similar condition is met with wind speeds that are too high: if the wind in north Scotland is too strong, it is highly unlikely that the south west of England would be similarly effected.

Small-Scale

Small-scale use of wind power is not a new thing: look in any marina and you will see dozens of yachts with little turbines spinning away on the stern. Of course, a yacht's demands are far less than a house but then a house has a larger area on which to attach turbines and they can be fitted higher up. At present, it is quite expensive to fit a wind turbine to most houses (unless they are far from the normal electricity grid) but, with the increase in prices likely to come from decreasing oil and gas, it will become more economical. If governments subsidise the turbines or they are fitted when a new house is built, they could well become commonplace.

A typical house would look for a turbine/s generating 1.5-3 kW while something like a public building would use 5-6 kW. The turbines could last for 20 years but, if the power is stored rather than supplied to the national grid, batteries would have to be replaced every 6-10 years.

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 waves icon Sea Power tidal icon

Main final use form: electricity.
Present: 0.002 EJ/y   Potential: 1 EJ/y (tidal)
Unit cost index: 2.8 (tidal), 5.2 (wave)
EPR: 15 (tidal)

Wave Power

The UK once held the one of the largest government-funded research programs in the world on wave energy. Tragically, this was greatly reduced in the 1980s and decades of potential development were lost. So we are still much in the R&D stage although several ideas exist.

The potential for wave power is vast: it is estimated that it could meet up to a quarter of Britain's electricity demand although, like wind and solar, the times when suitable waves are available is unpredictable and variable.

There are many ideas of how to harness the power of waves. One involves creating a sort of reservoir on land which is filled by waves lapping over the wall as they are forced into a narrow channel. This water is then released through a normal turbine. Another idea is the oscillating water column. A hollow cylinder is built with the sea entering through the bottom. As the sea rises and falls in the column, it pushes and sucks air in and out, which drives a turbine.

Sea-based ideas involve inflatable bags which are squashed by the waves, creating a flow of air inside to again drive turbines, and cam-like floating devices which bob up and down with the water, extracting energy from the rotation. None of these ideas has yet caught the imagination like wind turbines and wave power still remains a source with potential rather than being exploited.

Tidal Power

The rise and fall of the tides is caused mainly by the moon and partially by the sun. Unlike most renewables, there is a certain guarantee with tidal power in that we can predict well in advance both when the tides will occur and at what strength. The disadvantage with this is that the tides only occur twice a day (in most areas) and power can only be generated when the tide is flowing (about 10 hours a day). But as we can be sure that it will happen, that combined with some form of storage makes it a valuable resource in renewables.

Harnessing the tides involves first finding a suitable area and these are limited. You cannot just put a barrier across any old bay or river. Many areas like the Mediterranean have small tidal ranges and sometimes, building a barrage can affect the tide itself, reducing its strength. A barrier is then constructed across the estuary or bay rather like a dam in which turbines are constructed. Either these are turned directly by the water or the water compresses air which turns the blades.

One method of using the tide is to trap the water at high tide and not release it until low tide: this creates the largest head of water and therefore the greatest power output. Unfortunately this creates two short but powerful output periods while, for the rest of the time, the turbines are sitting idle. An alternative is to produce power most of the time that the tide is ebbing. The output is less but is spread over a longer period of time. Combining the two, you could divide the bay/estuary into two basins, one of which is kept full until low tide while the other gradually empties.

In suitable areas, there is certainly potential for tidal power. If all reasonably exploitable estuaries were utilised, annual generation of electricity from tidal power plants would be equivalent to about 15% of current UK electricity consumption. The Severn Barrage alone could generate up to 15GW, the equivalent of at least 10 nuclear power stations. Unfortunately, there is one big disadvantage – placing a large barrier across an estuary or bay can create enormous problems, greater than most other renewables. For humans, there is the problem of ships and boats moving past the barrier, especially if it is the sort which needs to retain the water until low tide, and the restrictions on sewage flow. The problems for wildlife can be devastating as the natural flooding and drying of the area is altered. So it is likely that limited sites and these problems will restrict the use of tidal power in the future unless we can consider the possibilities of offshore turbines which are rather like underwater wind turbines. The environmental problems associated with these would be much less significant.

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 eothermal icon Geothermal

Main final use form: heat and electricity.
Present: 0.3 EJ/y   Potential: 1.5 EJ/y
EPR: 1.9–13

Large-Scale

The interior of the Earth is incredibly hot and this heat is constantly flowing towards the surface of the earth. In some areas of the world, that heat reaches close to the surface or even breaks through in the form of geysers or hot springs. That is the principal of geothermal energy, making use of that hot water to either warm buildings directly or spin turbines to generate electricity. Unfortunately it is extremely localised, often close to the edges of tectonic plates (where volcanoes and earthquakes also dominate) which makes it of limited use except where it coincides with established habitation.

There is also the possibility that geothermal energy may not be renewable as believed. Using hot water to generate electricity can involve depleting the water source (although this is estimated to take 40–100 years).

Small-Scale

There is a form of small-scale geothermal energy (although it is strictly speaking solar energy) which could contribute a little to energy needs, known as ground source. In the UK, the earth a few meters down remains at a pretty constant temperature of 11-12°C throughout the year. The high thermal mass of the earth stores the sun's heat through the summer and this heat can be pumped into a building to provide space heating and sometimes used to pre-heat domestic hot water. The EPR from the electricity needed to operate the pump is good at about 3-4. It is not suitable for every building though as a certain amount of space is needed for the piping.

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 solar icon Solar Energy

Main final use form: heat and electricity.
Present: 0.005 EJ/y (1997 electricity generation)
Unit cost index: 13.1 (PV)
EPR: 1.6–1.9 (water heat), 4.2 (power tower), 1.7–10 (PV)

Solar energy is the acquisition of heat or power directly from the rays of the sun (unlike, for example, biomass and ground source heating which use the sun indirectly). The amount of sunlight falling on any area of ground obviously depends on its location and the time of year. In Britain, for example, a square meter will absorb about 900 kWh over a year. As the average household uses 20,000 kWh of power annually, you can see that it is unlikely that you could supply all of your energy use from solar alone, even if all your south-facing roofs were covered in collectors. As the sun does not shine at all at night, and much weaker in the winter (1/6 of the summer energy) when demand is higher, massive batteries would be needed. Nevertheless solar can contribute much to reducing energy needs and should not be overlooked.

There are three ways in which we can use solar energy: passive and active solar heating, and photovoltaic (PV).

Passive

Passive solar heating is the simplest method and has been in use in many countries for centuries. It involves designing buildings to gain the maximum benefit from the sun's rays. (In hot countries, this design principle is often turned around to lessen the heat from the sun). Examples include installing large windows on south facing walls (in the Northern Hemisphere, of course) and smaller windows on north walls. Heavy absorbent materials can be used in walls which release heat slowly and those walls could be painted in dark colours. Trees should be carefully planted so that they do not obstruct the sun and a conservatory could be built on the south side to act as a heat capture. These systems cost little if any money if included in the design process, not retrospectively, and yet are so rarely found. Governments, who control the building regulations, must implement these rules as soon as possible to prevent unnecessary waste energy.

Active

Active solar heating involves creating a mechanism to capture the sun's heat. This usually involves piping water through insulated boxes which have glass covers and black-painted insides. These act like 'mini-greenhouses', heating water as it is pumped through the box (known as a 'collector'). This water is then used either directly or transfers its heat to the domestic supply. The heat generated is not likely to do away with the need to use other fuels to heat water, especially as there would be no solar input during the night and some of the daytime. Nevertheless, it could be used to pre-heat domestic water to a temperature of 35ºC or so, thereby reducing the overall fuel bill.

On a larger scale, it is possible to use this principle to create a solar power station. This would involve positioning hundreds of mirrors to reflect their radiation onto a boiler at the top of a tower. The liquid in here is heated enough to generate steam and turn turbines to generate electricity. Another option is to create a tall hollow tower in the centre of a vast greenhouse. As the air is warmed by the sun, it rises and turns turbines again.

These large-scale power stations are still a rare thing as they suffer from the same problems of no sun in the night and little in the winter. But, in sunnier climates like Australia or California, they are likely to be more useful.

Photovoltaics (PV)

PV, known to everybody from solar cells in calculators, turn the light of the sun directly into electricity rather than via heat. However, a calculator uses very little power and generating enough electricity to make a significant difference to a house or office is another thing.

Initial solar cells were only 4.5% efficient. They grew to about 15% in the 1960s and are about 30% efficient now. A square meter on a sunny day would keep a 100W light bulb going. At the moment, PV electricity is one of the most expensive of the renewables. No doubt it will become cheaper as production increases and new cells are developed, but it remains to be seen how important this energy source will become.

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The Future

Renewable sources suffer from some of the problems of nuclear power in that they will take enormous amounts of money and energy to develop into serious replacements, and that they only produce heat and energy, and not (apart from biomass) liquid fuel, plastics or fertilisers. Given enough time and will, we might be able to develop wind, wave, solar and geothermal systems to replace hydrocarbon electricity generation. Time, of course, is one thing we are desperately short of.

Nevertheless, renewables are the only long term future for our energy needs. If the human population does collapse and we revert to smaller, more independent communities, the use of small term renewables such as wind generators, solar heaters and biomass might be the best we could hope for. A two-pronged strategy of increased energy efficiency and intense research and development of renewables is likely the only hope for our energy intensive society.

 

Remember there is a table of disadvantages on the Alternative Energy Sources page.

 

Unconventional Oils : Natural Gas : Coal : Nuclear : Renewables : Hydrogen

 

Contents

Biomass

Hydroelectric

Wind power

Sea power

Geothermal

Solar

The future

 

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