New or revised pages:
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20 December 2009
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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 generating capacity must be built.
The big question is what type?
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 2¾ 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.
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 - 55°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 20°C in living rooms and 18°C in bedrooms
-
use thermostatted
air-conditioning to 28°C in summer for only a minimum time
-
improve
house insulation
-
purchase low-consumption
appliances
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.
The following three references are
EU publications, impartially putting forth the advantages and disadvantages
of nuclear power:
Nuclear energy: the benefits of an unpopular sector
Nuclear energy: there are risks and risks
Nuclear energy: waste management, a crucial matter
The following summarises the
problems and solutions for an "environmentally-friendly" supply of
electricity:
The salient points
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