Conventional electricity

Existing installations

About 80% of the world's electricity is generated from inefficient thermal power stations, of which the majority are coal fired. Some countries have chosen heavy fuel oil while many modern installations use natural gas. These thermal power stations convert only from 25% to 35% of the chemical energy contained in the fuel into electricity; the rest is lost in the form of heat. They all are large sources of carbon emissions. A higher efficiency is obtainable if a gas turbine is used in a combined power and heat plant but this does not reduce the carbon emissions significantly.

The world demand for electricity is increasing rapidly, probably at a rate approaching 10 per cent per annum. In some countries, this figure is even much higher. It is therefore evident that new power stations have to be built. Unfortunately, this will inevitably lead to increases of greenhouse gas emissions. At the best, sequestration of carbon dioxide emissions is still experimental on a large scale; more pragmatically, it is a pipe dream. We are therefore in a Catch-22 situation: we must have more electricity but we cannot generate it from fossil fuel sources. Renewable sources are just not practical in many countries for a variety of reasons. Nuclear energy is not acceptable in many countries because of either political or popular constraints.

Another problem with fossil fuels is the volatility of their supply and their cost. At the time of writing, we have seen oil prices oscillate from $80 to $150 in the course of a few months. Natural gas prices have also varied, albeit not proportionally to that of oil. On the international market, coal prices have also increased, not just directly, but also because the transport of the fuel requires oil. Then there is the potential problem of "Peak oil" although no one knows when world reserves will be exhausted to the point of decreasing supply. Various dates have been proposed, but it seems probable that it will be within the next two decades, possibly earlier. As oil prices increase, as a result, so natural gas demand will also rise. And it will follow a similar "Peak natural gas" curve much more rapidly than would be foreseen by a natural consumption growth. On the other hand, coal reserves are sufficient for the foreseeable future. In view of this, it may seem foolhardy to plan new gas-fired or oil-fired power stations with amortisation over more than 10 to 20 years. There is a strong risk of the cost of electricity becoming several times higher than what it is today.

New power stations

New power generating capacity must be built. The big question is what type?

Natural gas-fired

This is the obvious and easy method, but there are four serious disadvantages that must be taken into consideration:

natural gas combustion produces carbon dioxide emissions, responsible for climate change. For each kilogram of natural gas burnt, nearly 2Â¾ kilograms of carbon dioxide is emitted.
the supply of natural gas is limited, the bulk coming from politically volatile Middle and Far Eastern countries and Russia: supply is therefore impossible to guarantee and the price is sure to rise drastically as reserves dwindle and as oil becomes scarcer
supply is dependent on special tanker ships, which are limited in number
natural gas is inherently a bad greenhouse gas and emissions from the wellhead to the power station are inevitable

There are two kinds of gas-fired stations: conventional thermal types with a boiler driving a steam turbine and direct-fired gas turbines. The latter has the advantages that they are more efficient and, in the event of a breakdown, a loss of wind or sun, or a sudden increase in demand, they can be brought on line in a very short time: this makes for the ideal back-up method without the need to idle conventional thermal systems.

Oil-fired

It would seem unlikely that many new oil-fired power stations will be built in the near future because of the lack of certainty of supply and rising oil prices. Notwithstanding, some very small diesel powered installations will still be used to supply small isolated communities, with powers up to, say, 500 kW. There may be a few special circumstances, such as the supply of local oil, which may justify larger installations.

Coal-fired

Unfortunately, it would seem probable that many major new power stations burning a fossil fuel will burn coal. I use the word unfortunately, because coal is not only the fuel that produces the most greenhouse gases, it is also the fuel that produces the most general pollution, including heavy metals, such as mercury, and airborne radioactivity. One of the big questions is whether coal burning power stations can be made more efficient. At the moment, this does not seem likely, at least to any great extent.

What must be done is to ban the construction of coal burning power stations without sufficient depollution of the stack gases. Apart from the more or less standard precipitator to capture fly ash, this will involve a complex series of operations to remove heavy metals, radioactive elements, sulfurous gases and other pollutants. Another problem with coal burning power stations is that the coal is pulverised into a fluidised bed. This involves a very dirty grinding operation which also releases quantities of methane. This should be captured and fed into the furnace. Every effort must be made to contain the coal dust, as well. These antipollution measures are very expensive and energy consuming. If, at some time, effective sequestration becomes the norm, it will be anticipated that the cost of electricity will rise considerably.

Conservation

Of course, electricity should not be wasted. If it is, it is costly and polluting. It therefore behoves every user to use this source of energy as economically as possible. There are various ways of doing this:

use low-energy light bulbs
switch off lights when not required for more than 3 minutes
switch off all appliances not in use
keep constant room and water temperatures but switch off at night
set the thermostat of immersion heaters to 50 - 55Â°C
ventilate rooms minimally
ffor electric room heating, use the air conditioner in 'heat' mode to rapidly bring a room up to a comfortable temperature, rather than a fan convector or heater
consider night-storage heaters rather than fan convectors or other heaters (these have the advantage that they 'burn' electricity when the supply is much greater than the demand and the power stations are producing their background levels of emissions; the extra load makes almost no difference to the pollution. The cost of energy is also reduced on Tariff 55.)
consider heat pump central heating.
run irrigation pumps at night (this also conserves water)
use thermostatted electric heating to a maximum of 20Â°C in living rooms and 18Â°C in bedrooms
use thermostatted air-conditioning to 28Â°C in summer for only a minimum time
improve house insulation
purchase low-consumption appliances

Conclusion

All parties, including the public, must take the bull by the horns. Conservation is important, as are renewable supplies, where these are feasible. Decisions must be made as to how this will be done, even if they are unpopular, including the possibility of nuclear energy.

Fossil fuel power stations