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Will they make any real difference?
Generally, a megawatt hour of wind energy avoids one ton of greenhouse gas emissions.
A typical 2MW wind turbine will reduce greenhouse emissions by about 6000 tons per
year. Worldwide wind energy capacity is roughly 60,000MW, which is the equivalent
of taking 36 million cars off the road each year in terms of greenhouse gas emissions.
Like solar energy, the amount of space that wind generators use in relation to their
outputs is small compared to mining fossil fuels or uranium.
Will wind power put people out of business?
All industrial structures, like coal-based and nuclear power plants, have limited life spans.
Centralized energy plants are being closed down by environmental and health legisla
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tion or obsolescence. Wind power, due to its dispersal, creates jobs in construction
and operation and other benefits to regional communities. It can reduce the social
dislocation that will result from the inevitable closure of conventional plants. The jobs
created are of a higher quality and less dangerous than those associated with coal or
uranium.
What about the up-front costs?
As with other technologies that eventually pay for themselves, performance contract
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ing can be used to cover the initial costs. If the building owner does not have to pay
for the installation, energy service providers can eventually recover their costs from
the energy savings. They could demand a relatively higher profit, as long as the building
owner saves money in the end. Further, there is little evidence that wind power plants
affect property values negatively, and some communities earn additional income by
showing wind farms to tourists.
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Boxes
Box 18 Solar Powering the Future
Keith Lovegrove
We have been led to believe that solar power is too expensive or incapable of supplying all
the needs of society. Not so.
In the more energy intensive societies of the world, such as the US and Australia, fossil fuels are
being consumed at a rate of between 15kg and 20kg per day 365 days per year for every man,
woman and child. This in turn leads to emissions of carbon dioxide of around 50kg per day per
capita. This adds up to a lot of energy, a lot of fossil fuel to provide it and a lot of greenhouse
gas emissions. However, at the personal level, 800MJ/day per person is needed, which is the
amount of energy falling on 40m
2
of the average house roof in Australia. Less sunny parts of
the world, such as Europe, would need twice as much area per person to achieve this from
solar inputs but, of course, they also benefit from good wind, biomass and hydro, or other
renewable energy resources. So powering the future from solar energy is not limited by the
amount of solar energy available, yet Australia has been slow to implement this technology.
There are basically two approaches to producing electricity directly from solar radiation:
1 Turning photons to electricity with photovoltaic cells; or
2 Using the radiation to produce high temperature fluids that turn turbines or other
power cycles in solar thermal power systems.
Photovoltaic (PV) cells are predominantly made from wafers of silicon, the same stuff that
computer chips are made from. In simple terms, individual photons from the sun give individual
electrons a kick to a higher energy place and so create a voltage. Solar cells are typically
dark blue squares 10–20cm a side, assembled into panels about a metre long. Arrays of such
panels can be assembled on house roofs and connected to an inverter. This converts the
DC electricity from the panels to the higher voltage AC electricity that household appliances
run on. Such inverters can connect into the electricity mains so that a house can import or
export electricity to the grid. Houses can run completely autonomously if electric storage
batteries are added to store energy for night and cloudy days. PV systems can be installed in
large arrays as well, for connection to the electricity grid.
Over the last two decades the photovoltaic industry has been booming, with annual growth
rates of over 30 per cent. Worldwide annual sales in 2006 had a capacity to generate electricity
at a rate of approximately 2000MW, equivalent to two large coal power stations. Much of the
growth has been stimulated by favourable policies in some countries, Germany and Japan in
particular. The downside of PV is the high capital cost, considerably higher per unit capacity
than a wind farm, for example. New technologies are currently being commercialized that
achieve the same results with much thinner layers of silicon and so have considerable potential
to bring costs down in the future.
Solar thermal power is best suited to the construction of much larger power systems than the
household scale. But with the world increasingly looking for utility scale renewable energy,
proponents feel its time may have finally come. Solar thermal power systems work using
ordinary glass mirrors to focus radiation onto high temperature receivers, where fluids such
as molten salt, heat transfer oil or steam are heated up to provide the heat input for power
systems. The vast majority of the world’s electricity today is produced from steam turbines
provided with steam from either coal or nuclear boilers. Solar thermal power systems have
the ability to directly substitute for these heat sources and allow power stations to continue
to be built with steam turbines on the same scale. In Southern California, plants with a total
capacity of 354MW (enough to power a small city) have been working successfully for 20
years. In 2006, another 200MW of systems were under construction in the US, Spain and
Australia. Solar thermal systems also offer the potential for large-scale, cost-effective energy
storage through stores of hot fluids or thermo-chemical processes.
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Positive Development
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