Only One Planet





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 "photovoltaic".

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 winter.

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 collection. In addition, the water may be replaced with a heat- transfer fluid, which can be pumped around and remotely heat water or air.

The solar collecting system, Solar Two - Picture credit: Hugh Reilly - Sandia National LaboratoriesSolar test facility at MSFC (20' x 24') focuses 10 kW of solar energy - picture courtesy of NASAAs 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 quote: 

"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."

Photovoltaic cells in use. Source: Solar Cells, Inc. 1996Photovoltaics (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).

Photo-cells have 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.

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 demonstrates:

1981 1985 1990 1996 1999 2000
Maximum rotor diameter (m) 10 17 27 40 50 71
Generating capability (kW) 25 100 225 550 750 1,650
Power output (MWh) 45 220 550 1,480 2,200 5,600

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 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 its movement.

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 energy.

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.


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This page last updated: 20 July 2002