Alternative Energy Sources
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 mation 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
Main final use form: motor fuel and
Present: 52 EJ/y Potential: 100
Unit cost index: 2.1
EPR: 0.71.8 (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).
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.
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
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.
Main final use form: electricity.
Present: 8 EJ/y Potential: 70
Unit cost index: 1 to 1.5 (small to 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 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 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.
Main final use form: electricity.
Present: 0.02 EJ/y Potential: 180
Unit cost index: 2.4
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 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.
Main final use form: electricity.
Present: 0.002 EJ/y Potential: 1
Unit cost index: 2.8 (tidal), 5.2
EPR: 15 (tidal)
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
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
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
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.
Main final use form: heat and electricity.
Present: 0.3 EJ/y Potential: 1.5
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).
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.
Main final use form: heat and electricity.
Present: 0.005 EJ/y (1997 electricity generation)
Unit cost index: 13.1 (PV)
EPR: 1.61.9 (water heat), 4.2
(power tower), 1.710 (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 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
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
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.
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.
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
Oils : Natural Gas : Coal
: Nuclear :