CONCERNS OVER CLIMATE change have accelerated the drive to find alternative sources of power that do not affect the Earth’s atmosphere or damage its ecosystems. But ‘green’ power is nothing new. We human beings – inventive creatures that we are – have been harnessing the elements for our own ends for centuries.
More than 5,000 years ago, an observant boatsman somewhere must have realized that by catching the wind he could give his vessel an extra push, and so the sailing ship was born – and, with it, a new form of power that would serve mankind well for many centuries.
The earliest-known large sailing ships, dating from around 3,000 BC, ploughed their way around the Persian Gulf. In the fifth century AD, the Vikings took the technology to new levels and crossed the Atlantic Ocean in their sailing ships. Later, in 1492, Christopher Columbus made it to the New World with his fleet of three sailing ships – including the new-style, speedy ‘Niña’, based on the design of the Arab ‘dhow’. But with the rise of the steamship in the nineteenth century, the great age of sail was over.
Wind provided another early source of green power. The new, high-tech invention of the ancient world – the windmill – automated the job of grinding grain and pumping water, saving people the bother of having to do it by hand. Although there are claims that it was invented in China more than 2,000 years ago, the first-recorded Chinese windmill dates from 1219, while the earliest-known design comes from Persia somewhere between 500 and 900 AD.
The potential of water did not escape people’s notice either. The waterwheel, consisting of paddles mounted around a wheel that is turned by the force of moving water, first made its appearance thousands of years ago. Like the windmill, the water-powered wheel automated such tasks as grinding grain and pumping water for drinking and irrigation. Later, it was pressed into service to drive sawmills and other mechanized processes. In 1769, the invention of the water frame by Richard Arkwright (1732–92) – powered by a waterwheel – revolutionized the cotton industry, turning it from a cottage industry dependent on the spinning wheel to mechanized, factory-based production.
It is ironic that with all our technological advances we are – for the sake of our future and of our planet – turning once more to sources of power that have always existed. The forces of Nature are awesome, as electric storms and hurricanes prove, but how do we harness this free and relatively clean energy, and can it work anywhere in the world? The different forms of green energy have their advantages and disadvantages. Here are some of the options:
An inexhaustible source of power, wind can be used to turn large turbines that generate electricity. A group of turbines together earn the name ‘wind farm’.
• The electricity generated by wind farms is generally no more expensive than conventionally produced electricity.
• Off-shore farms, where the wind is stronger and more consist-ent, cost more to build than on-shore ones – but in a country like the UK, with large stretches of windy coastline, off-shore wind farms could easily meet the nation’s needs, with power left to spare.
• Wind farms are of concern to wildlife conservationists because the rotating blades of the turbines kill thousands of migrating birds each year. But in 2009, a Texas wind farm came up with a solution – NASA-style radar that can detect approaching flocks and shut down the turbines until the birds have passed. However, conservationists still maintain that wind farms should be located away from major migration routes.
This is the big one, at least in terms of the source of power itself – the sun. Solar power works by capturing some of the sun’s energy in panels made up of photovoltaic, or photoelectric, cells. These then use the energy to generate electricity or to heat water.
• The current technology is not advanced enough for solar power to be used on a large scale – and it still remains too expensive. But photovoltaic cells have approximately halved in price over recent years, so this energy source may become more viable for general use in the not-too-distant future.
• For obvious reasons, solar power is best suited to countries with a hot climate and many hours of strong sunshine. It is a less effective choice for regions with cool, changeable, cloudy weather.
• To increase the amount of power the panels can generate, large mirrors can be arranged to reflect more sunlight onto the cells.
The raw force of the sea is another inexhaustible powerhouse of renewable energy. One method of generating electricity from the sea shores up the water in dams or manmade lagoons, to exploit the difference in height between high and low tide. The other, more practical option makes use of the power of tidal currents:
• Tidal power is a more reliable source of energy than solar or wind because the tides are predictable and not subject to changing atmospheric conditions.
• Because it depends on the state of the tides, tidal power is an on-off source of energy, able to provide electricity for only six to twelve hours a day. If these hours do not coincide with peak demand, the electricity generated must be stored and a back-up source of energy must be available for when tidal power is low.
• Tidal power stations are inexpensive to run but expensive to build, so it can take a long time to recoup the initial costs.
Humans have long exploited the force of falling water to turn waterwheels and millers’ grinding stones, but hydroelectric power has gone one step further. By damming up rivers, engineers allow a powerful head of water to build up behind the dam walls; when released, the water rushes out with such force that it turns the turbines that generate electricity.
• Hydroelectric power is not subject to the ups and downs of weather and tides – it can be made available on demand, simply by releasing the pent-up water.
• Hydroelectric plants are cheap and easy to run, but cost a lot to build.
• To achieve a sufficient head of water, whole river systems may need to be dammed and this can interfere with the ecology of the region. Massive flooding on one side of the dam can mean loss of habitat for wildlife and loss of homes for people, as well as submersion of historical sites. Meanwhile, lack of water downstream can be equally disastrous for plants, animals and people.
• Dams in hot countries can be environmental polluters. Here, in the hotter months, the water levels fall and lush vegetation rapidly sprouts from the newly exposed, damp soil. When levels rise once more, the plants are submerged and rot – releasing methane gas into the atmosphere.
The ground on which we stand is, in itself, a reliable source of what’s known as geothermal power. At its core, the temperature of the Earth is around 5,500°C (9,932°F) – that’s as hot as the face of the sun – and the top 3 metres (10 feet) of the planet’s surface remain at a consistent 10–16°C (50–61°F). Some countries have spotted the potential of this free and eco-friendly energy source, and use geothermal power to heat water, to regulate temperature in homes and workplaces in winter and summer, and to generate electricity.
• Unlike wind and solar power, geothermal energy is not dependent on changes in atmospheric conditions – but as a natural resource it is not evenly distributed across the globe. The greatest resources are found in regions where there is volcanic activity and that have natural hot springs, such as Iceland and Japan. Icelanders have been reaping the benefits of clean and inexpensive geothermal power for more than 60 years.