The drive to turn them can be reasonably direct for example in the form of water and air turbines or indirect via a heat engine with the heat being produced for example by gas, oil, coal or nuclear energy.
While there is a mechanical loss in converting the available potential energy of the water or wind energy into electrical power, as there is no production of CO2 involved in the process these are considered to be very ‘green’. With heat engines in addition to mechanical losses there are thermodynamic considerations which further limit quite substantially the conversion of available energy in the heating material, to the electrical output. With regard gas, oil and coal in producing heat considerable quantities of CO2 are produced so the process is not very ‘green’ and there are also losses in the burning process to produce heat. With nuclear energy providing the heat, while there is no CO2 produced the by-products of the nuclear process are very difficult to handle and dispose of because of their toxic nature which puts their ‘green’ credentials in some considerable doubt.
To try and explain simply why producing electrical energy from a heat driven machine (car and aircraft engines included ) the general idea of the processes involved need to be considered. A so called working fluid (water/steam in the case of electrical steam turbines and air in engines including gas turbines) needs to be heated to cause it to expand and be able to push the turbine or engine around. Once it has done the work of turning the device this hot (water/steam) or hot gas needs to be removed to make way for the next lot. While engines and gas turbines discard the mixture of hot air and combustion products, the steam turbine needs to condense the discarded steam to return it to the boiler as water using devices such as cooling towers. Hence it can be seen that in addition to heat losses in the boiler itself a lot of heat is simply discarded into the atmosphere.
Equipment does employ heat saving procedures to reduce this waste but particularly with isolated power stations more use of the heat which is lost in the cooling process cannot be made. For instance if the power station were located close to a town use could be made of the heat wasted to provide hot water at a temperature useful for domestic purpose. So called total heat system are used in factory type situations.
Further losses are encountered with electrical energy in distributing it around the country. To try and reduce these losses very high voltages are used which lead to the wires distributing the power not getting so hot and wasting power but they do mean large pylons in the countryside.
It is hoped that this explains to some extent why electrical energy is more expensive to buy than other forms. If you only want heat energy then it is cheaper to just burn the fuel as efficiently as possible. However if you require mechanical work (vacuum cleaner and other motor driven tools) or convenience products such as lighting, TV, microwave etc. then electrical energy is required. To use electrical energy for heating (except for items like heat pumps) is particularly wasteful on CO2 production and money as in effect you waste quite a lot of heat to the atmosphere that was originally available in the gas, oil or coal.
Article by a site contributor called David, thanks, David!