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THE POWER OF OUR SUN
Our Sun represents an inexhaustible source of power. In fact, it
is already our main source of power, albeit the prehistoric Sun.
Millions of years ago forests captures it's energy, died, became
compacted over time and eventually turned into the coal, oil and
natural gas that we now use. But using these fossil fuels has
two major drawbacks: they are only available in limited amounts
and they require burning to release their energy - and this
isn't too environmentally friendly.
The world turns and the Sun shines. What methods are
available to us to capture and utilise that sunshine? Well,
basically there are three ways to use direct sunlight:
"passive", "active" and
Passive solar collection means collecting and storing the
Sun's energy in physical masses, such as
large, thick concrete walls. The wall is heated up during
daylight hours and slowly releases that energy during the night
time. There is no mechanical apparatus involved in this method
and such structures may be incorporated into new buildings
to efficiently regulate the temperature. Having lived in a large
Victorian building with very thick stone walls in Cornwall some
years ago I know that the internal temperature of the house was
a lot more stable than a modern brick built house, being
relatively cool inside during a hot summer and warm during the
Solar energy can also be collected to heat water, either
directly or indirectly. The most basic configuration is to place
black pipes in a flat box with a glass cover facing the sun. If
the pipes are filled with water it will heat up as the sun's
energy is absorbed. If there is enough capacity in the pipes
then a household's hot water can be supplied (or at least
supplemented) in this way. Because hot water rises relative to
cold water, if the pipes are connected in a circuit then a
natural circulation will occur with warm water slowly exiting
the box at the top being replaced with cold water at the bottom.
This can be further enhanced by pumping the water around the
circuit, ensuring that the coolest water is always in the pipes;
this is an example of "active" solar power
In addition, the water may be replaced with a heat- transfer
fluid, which can be pumped around and remotely heat water or
any schoolboy knows, if you take a magnifying glass on a sunny day
and focus the sunlight onto a piece of paper enough heat is
generated to generate a flame and set light to the paper.
Unfortunately, it is not practical to place vast magnifying
glasses around the world to concentrate the Sun's power. However,
the same concentrating effect can be produced using mirrors. At
it's very simplest, if you take two mirrors on a sunny day and
reflect the light from both onto the same area of a surface then
you will double the heating effect on that surface; take a third
mirror and you will triple the energy on the surface and so on.
Use enough mirrors and you'll create an enormous "hot
spot". You can boil water and cook food in this way. Small
problem: the Sun moves and, therefore, so does the point where the
reflections fall, so you need to constantly adjust the angle of
all of those mirrors. The answer is to use a large concave mirror,
known as a parabolic reflector. (A parabolic reflector is shaped
to that all of the Sun's rays falling on its surface are focused
onto a single point.) Now your only problem is to adjust the
single mirror to track the sun, a task that can be achieved by use
of a small motor and some gears.
There are some very big arrays
around the World which use this concentrating power of mirrors to
focus the Sun's energy onto a steam generator and the resulting
steam is used to generate electricity. In Barstow, California
there is a Solar Two, an experimental array of more than 1800
mirrors (known as "heliostats"), focused onto a
"power tower" where it heated molten salts to generate
electrical power via a steam generator (if you click on the
picture above left you'll open a window with a couple of photos of
this incredible experiment). France, Spain, Italy, Switzerland,
Israel, Germany, Japan and Russia are working on these
"central collector" systems.
So, considering sunlight
is free, why don't we see more of these fantastic generators.
Well, the best explanation I have found was on an American solar
energy FAQ. I
"The field of mirrors in a
concentrating solar power plant delivers the thermal energy that
is provided by fossil fuels in a conventional power plant. Since
the sunlight is free, the initial capital expenditure for the
collectors is equivalent to buying a lifetime supply of fuel. To
recover this high first cost, plant operators need to be able to
sign long-term power purchase agreements. However, the current
environment favors low first-cost, gas-powered plants, with
ratepayers bearing the risk of escalating fuel costs. Other
factors, including risks associated with building new
technologies, tax equity with conventional technologies, and cost
reductions needed from technology advances and economies of scale,
are also important."
(PV) is something different. The previous methods rely
on heating something using the Sun's energy and, perhaps, using that heated
substance to drive something mechanically to generate electricity.
Photovoltaics convert the solar energy directly into electrical
energy, without any mechanical intermediary, using semi-conductors
to convert between 7% and 22% of the solar energy falling on them.
Materials in use include silicon, cadmium telluride and something
called copper indium gallium diselenide (CIGS).
been around since 1950 (although the first solar-cell seems to
have been made by Charles Fritts of New York in 1883) and many people will be familiar with them
powering battery-less calculators (the small dark grey window
somewhere on the front of the calculator). PV devices, in the form
of solar panels made up of many solar cells, are very
cost-effective because their fuel is free, they have no moving
parts and are low-maintenance, so require very little upkeep apart
from occasional surface cleaning. Once
purchased they should have a life of at least twenty years.
WIND POWER - BEING UPDATED
Our Planet's weather systems are incredibly complex, arising and
developing as a result of the Sun's warming of the oceans, land
masses and atmosphere and the motions of the Earth and Moon. As
a result, our atmosphere is in constant motion, moving vast
amounts of air around the globe. The phenomenon is familiar to
us all when we feel the wind blowing on our faces.
In former times, our ancestors recognised the power of the
wind and harnessed it in the form of sails to move their boats
across oceans; then in the form of windmills, used to grind
grain to make flour and to pump water. The earliest references
to windmills in England date back to the 11th century, although
windmills seem to have been developed in 6th century Persia. It
was the rise of steam power, fuelled by coal, which signaled the
demise of the windmills.
But in recent years wind-power has
become a steadily rising force in energy production, with rotor
blades mounted on a tower, turned by the wind being coupled to an
electrical generator. Now-days
"wind farms" of many of these towers can be seen in
all parts of the world.
The technology and efficiency of wind generators has improved
greatly over the past twenty years, as the following table
|Maximum rotor diameter (m)
|Generating capability (kW)
|Power output (MWh)
Wind farms are best placed in areas of high average wind
speeds, as the power generated is a cube of the wind speed. In
other words, if the wind speed doubles then the power it
generates is eight times higher.
Unfortunately, the wind doesn't blow steadily at the same
rate at all times, so wind farms have a variable output. Wind
power, therefore has a valuable potential to play a major part
in supplying the World with it's energy requirements, but it
isn't the only answer.
In the UK, the latest wind-farm was
launched at Bein an Tuirc, Argyll, Scotland in July 2002. The
farm consists of 46 wind turbines, which will generate 30
megawatts of electricity, enough to power 25,000 homes, making
it the biggest in the Britain. Scottish Power, in answer to
concerns voiced by the Royal Society for the Protection of Birds
(RSPB) regarding disruption to local breeding pairs of Golden
Eagles, has said that it will clear 450 hectares of conifer
plantation and replace it with natural heather moorland, a
breeding ground for red and black grouse, providing the Eagles
with a new hunting ground.
WATER POWER - BEING UPDATED
Water moves. When it moves it can be with incredible force. When
rivers flood and break their banks they can sweep everything
away in their path. The incredible power of a tidal wave can raze
entire coastal towns. The rivers and oceans of our World possess
an unbelievable amount of energy, either in terms of potential
energy because of its height or kinetic energy as a result of
Man has long tried to harness this source of energy and, just as in the case of wind, our forefathers utilised water
power in water-mills to grind grain and saw timber. One project,
launched 24 June 2002, is a water wheel used for generating
power to manufacture cloth and steel 100 years ago which has
been restored to power 50 homes in Ludlow, Shropshire, as part
of a £100,000 UK national 3 year pilot project into alternative
Hydro-electric power generation, or hydro-power as it becoming known, currently produces one
fifth of all the world's electricity. In the USA it is
responsible for 10% of all power generation. Emerging economies
generate up to one third of their electricity from water
sources. A modern hydro-turbine generator set can convert better
than 90% of the energy in the available water into electricity.
This is more efficient than any other form of generation.
Although hydro-power can be used to store vast amounts of
potential electricity the result is often a flooded area which
wrecks the local environment.