Questions 28

READING PASSAGE 3

You should spend about 20 minutes on Questions 28-40, which are based on Reading Passage 3 below.

Green Energy

As energy prices rise and the effects of greenhouse gas emissions become more widespread, people everywhere are becoming increasingly concerned about using fossil fuels. [Crack IELTS with Rob] More and more people are turning to so-called “green technologies” as a way to reduce dependence on nonrenewable fossil fuels. The ideal alternative energy source would be sustainable (the supply will not be exhausted), clean (no emissions), and reliable. The three most popular alternative energy sources are geothermal power, solar power, and wind power.

Since geothermal energy taps heat from the earth, its resources range from water found just below the surface of the earth, to hot water and hot rock found a few miles below the surface, to even deeper rock of extremely high temperatures. [Crack IELTS with Rob] In a process similar to drilling for oil, wells as deep as a mile or more can be drilled into underground reservoirs to tap steam and hot water that are used to run turbines and create energy. Power companies can then transmit this energy over power lines.

Geothermal power on a smaller scale can be used for heating and cooling houses or commercial buildings. Geothermal heat pumps, also known as ground-source heat pumps, rely on the fact that the earth beneath the surface remains at a relatively constant temperature throughout the year. [Crack IELTS with Rob] Like a cave, the ground is warmer than the air above it during the winter and cooler in the summer. The geothermal heat pump transfers the heat stored in the earth into the building during the winter, and transfers it out of the building and into the ground during the summer. The ground, in other words, acts as a heat source in winter and a heat sink in summer. While geothermal heat pumps are an emissions-free and reliable source of energy, the biggest disadvantage is that such systems are expensive to install.

Solar energy has come a long way from the clunky boxes of the 1970s. Today, solar energy is commonly collected by sleek and efficient photovoltaic (PV) panels. The photovoltaic cells convert sunlight directly into electricity and are made of semiconductors such as crystalline silicon or other thin-film materials. [Crack IELTS with Rob] The bene fits of solar power vary according to how much exposure a given building has to the sun. However, one does not need to live in the desert to take advantage of solar power. Cloudy Germany is the worldwide leader in the use of solar power.

Solar power is not as pricey as geothermal power, but having a panel professionally installed can still be costly. Some enterprising homeowners reduce the initial costs by purchasing inexpensive kits and setting up the system on their own. The biggest disadvantage of a solar power system is its dependence on the amount of sunlight collected, but some cutting-edge panels can generate energy even in the rain.

Wind power is created when wind is used to generate mechanical power or electricity. Most wind turbines convert the wind’s kinetic energy into mechanical power. The wind turns the blades, which spin a shaft connected to a generator. A generator then converts this mechanical power into electricity. [Crack IELTS with Rob] A group of wind turbines can produce electricity and feed it into the utility grid, where it is sent through transmission lines to homes and businesses. Like solar and geothermal energy, wind is a renewable resource that produces no emissions.

Small wind energy systems can be used by homes, farms, or communities. Such systems can be connected to the larger electrical grid or used for stand-alone energy generation—a particularly attractive option for anyone living far from power company lines. A grid-connected wind turbine can reduce one’s reliance on the power company for electricity. [Crack IELTS with Rob] If the turbine cannot deliver the needed energy, the power company then makes up the difference. However, in order to take advantage of wind energy, a turbine must be in an area with an average wind speed of at least 10 miles an hour, and such systems can be very expensive.

Whether a given home or business uses wind, solar, or geothermal power depends on a variety of economic and environmental factors. However, experts agree that investing in alternative energy now—whether by individuals or power companies—will pay dividends in the future.