105 Alternative and Sustainable Energy Used via the Grid

There is no reason at all why alternative sustainable forms of energy such as solar, wind, hydro, tidal, wave, biomass, waste and energy taken from under sea currents should not be used to provide energy to electric vehicles via the grid. In some ways this is a much better option than powering electric vehicles directly from small wind generators and solar panels, where the energy is wasted when the vehicle is not directly charging. With the grid the energy can be transferred from one use to another. When electricity is not being supplied to one consumer it will be supplied to another. When there is ample electricity from alternative sources it will be used, fossil-fuelled generators being switched off to save fuel. When there is less alternative energy the fossil-fuelled generators will be used, the customer not experiencing any break in supply during periods of little sun, wind or tide. Also, the grid allows electric vehicles to be supplied with energy from all available energy sources including hydro, tidal, wave and under sea currents.

Although most electricity is currently obtained from burning fossil fuels at power stations, there is a positive effort being made to introduce alternative sustainable forms of energy. These could be used to provide electricity for rechargeable battery cars and also to provide and process fuels for metal air batteries and fuel cells.

Using alternative forms of power to energise electric vehicles would make a real impact on the environment, totally eliminating emissions and pollutants from motor vehicles. Perhaps society should make a concerted effort, not only to introduce electric vehicles, but at the same time to install sufficient sustainable energy to power these vehicles. It is therefore appropriate to examine the various alternatives to see how they can be used.

10.5.1 Solar energy

Solar energy was discussed briefly in Chapter 3 in relation to small scale use with electric vehicles. On a large scale it can be used to supply electricity to the grid or to use it to electrolyse hydrogen for use in fuel cell vehicles. The maximum efficiency for commercial solar cells is currently about 16.5%, which drops to around 14% when encapsulated. Given the current drive to maximise the performance of solar photovoltaic cells this is likely to increase. The maximum power of solar radiation on the earth's surface is 1000 Wm-2, but is normally less due to cloud and dust in the atmosphere.

The actual cost per peak kilowatt of solar cells is around $4500, the installed cost will be higher. In order to convert the direct current electricity from the solar panels to AC electricity for the grid, an inverter is required. This will also need to synchronise the frequency with the grid frequency, and deal with a multitude of safety issues relating to this type of equipment.

Solar panels for production of electricity can be mounted on the ground or alternatively on buildings. Interestingly, the amount of solar energy falling on all buildings in the UK is about 1600 TWh per year, as compared to fossil fuel use of about 1500 TWh per year. Although efficiencies of conversion must be accounted for, this is still a substantial amount.

10.5.2 Wind energy

Wind energy, as with solar, is a rapidly developing technology. Growth of wind energy production has averaged at 40% per annum and it is likely to go on expanding at this rate. In the early 1980s the largest commercially available wind turbine was 50 kW. By the end of the 20th century 1.7 MW machines were commercially available. The total wind power installed in Europe is 20 447 MW and the British Isles 655 MW. This equates to around 60 000 000 MWh per annum in Europe and around 2 000 000 MWh in Britain. To produce this amount of energy by burning oil at a power station with an overall efficiency of 0.33 would require 18 million tonnes of oil in Europe and 600000 tonnes of oil in Britain compared to 41 000 000 tonnes of oil used for road transport in Britain. Wind energy currently available in Britain could possibly provide 1.5% of the energy needed for transport if it were used to charge electric vehicles. Although this is a relatively low figure the UK is only capturing 0.5% of the wind energy available. It would therefore be possible, in theory at least, to provide most if not all of the energy needed for transport by wind energy if required.

Large wind farms can now be found all over the world, many producing up to 40 MW of electrical power. An example large (750 kw) wind turbine is shown in Figure 10.6. This is from the wind farm in El Perello, Spain, 'Parc Eolic de Colladeres'. This park has 54 large turbines giving a total maximum power of 36.63 MW. These typically produce 97.5 million kWh per annum. Again, if this energy were produced in a conventional fossil fuel burning power station of efficiency 33% it would require 30000 tonnes of oil.

10.5.3 Hydro energy

Hydro energy has been used successfully for several thousand years, initially in the form of water wheels to drive mills. The principle of hydro power is essentially simple, running water used to drive a turbine. In large hydro schemes a valley in a hill or mountain is dammed and a lake formed. Outlet pipes from the dam direct water through a water turbine. The water flow is controlled to give power on demand.

The surprisingly high figure of 6% of world electricity generation is currently obtained from hydro power. In the UK 2% of power is obtained, compared to Canada where the figure is 60%. There is potential to increase the amount of hydro electricity, current thinking encouraging a multiple of smaller hydro schemes.

10.5.4 Tidal energy

Tidal energy on a small scale has been used for centuries on the coasts of Britain and France. Proposals for a major barrage in Britain were published as early as 1849. Probably the best known tidal scheme is the Rance power station in France. In this scheme the tidal energy is captured by damming the estuary and forcing the tidal waters through axial flow nf

Figure 10.6 750 kW wind turbine from the Parc Eolic de Colladeres, Spain

turbines. The scheme typically produces about 500 GWh of electricity per year; 150 000 tonnes of oil per year would need to be burnt in a conventional power station to produce this amount of electricity.

10.5.5 Biomass energy

Energy can be obtained from plants, which are in effect a form of stored solar energy, the solar radiation being used to form chemical energy. There are two main ways of using biomass. The first is to grow plants such as sugar cane, extract the sugar and turn this into ethanol, which can be used as a fuel for IC engines. This could either be used to run IC engine vehicles directly, as has been done in Brazil for several years, or could be used as a fuel at suitable power stations. The second is to grow fast-growing trees, which are coppiced annually. The wood is then used as fuel in a wood burning power station to generate electricity. Typically 10 to 20 tonnes per hectare of wood fuel can be produced per annum from wood plantations.

10.5.6 Geothermal energy

Geothermal energy is produced by taking heat from underground rocks and running this through a heat engine and generator to produce electricity. Normally water is pumped underground via a pipe and returns to the surface via a second pipe. Provided too much heat is not taken away when the rocks become chilled, this method is sustainable. Such energy is only usable in a few locations, Iceland being a case in point. Interestingly, they are actively working on conversion of this energy to chemical energy in the form of hydrogen, for use in fuel cells.

10.5.7 Nuclear energy

There are two types of nuclear energy, nuclear fission and nuclear fusion. Conventional nuclear power stations use nuclear fission and are currently in service providing electricity. The nuclear lobby point out that nuclear power stations do not give off gaseous pollutants or carbon dioxide. However, there is concern about the nuclear waste and in many countries the nuclear program is gradually being phased out.

Nuclear fusion creates energy by fusing hydrogen into helium. The principle is used in the hydrogen bomb, but the energy release is uncontrollable. Recently nuclear fusion research has been carried out in the JET project at Culham, UK. Although there is a long way to go before nuclear fusion becomes a commercial reality, it still holds out great hope for the future.

10.5.8 Marine current energy

A considerable amount of energy can be captured from undersea currents; certainly this is the opinion of companies working in the field, such as Marine Current Turbines Ltd. The company plan to install up to 300 MW in the next decade. Up to 20 to 30% of the UK's electricity needs could be provided from this source alone. Up to 48 TWh per year could be produced from 106 sites around Europe, the majority being in the UK.

Around 48 TWh of electricity would require the burning or 15 million tonnes of oil (assuming an efficiency of conversion of 33%), which in theory could power one-third of the UK's transport energy requirements. The marine currents are more predictable than wind and solar.

10.5.9 Wave energy

Another method of obtaining sustainable energy is by tapping the power in waves. There are several systems under trial but as yet none has been commercialised. None the less, this is another strong contender for providing energy supply in the future.

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