Renewable energy sources
Renewable energy is fuel that comes from a source that can be replenished in a short amount of time. This includes solar, wind, water, geothermal power and bioenergy. While renewable energy sources may not always be available – for example, if there is no wind to drive wind turbines, or cloudy days that reduce solar energy – they play an important part in reducing the use of non-renewable resources. Furthermore, many of these resources do not emit greenhouse gases directly into the atmosphere.
In the broadest sense, solar power supports all life on Earth and is the original source for all other energy resources we use. Solar energy is the Sun’s rays (solar radiation) that reach the Earth. Having produced solar radiation for millions of years through nuclear fusion, this powerhouse produces so much energy that the amount of sunlight that reaches the Earth in a single hour could meet the energy demands of the whole world for an entire year! Outside Earth's atmosphere, the Sun's energy contains about 1,300 watts per square metre. About one-third of this light is reflected back into space, and some is absorbed by our atmosphere. Solar energy can be used directly to heat water or spaces (a greenhouse, for example). In this process, the energy in the form of solar radiation is converted into thermal or heat energy. Solar energy can also be transformed into electricity through photovoltaics or solar power plants.
With such an amazing power source that produces no air pollution, you may be asking yourself why we do not utilise it more. The problem lies in our ability to harness the Sun’s power efficiently. At the moment, solar panels that capture sunlight and turn it into energy are expensive to produce and inefficient, but technology is improving. New Zealand does not yet have any solar-powered power stations.
People have been using wind for hundreds of years to transform the wind’s kinetic energy into mechanical energy that drives machines, mills grain and pumps water. Modern technology wind mills use the wind to drive blades that turn generators that produce electricity. Wind power is hailed as a ‘green’ technology as it produces no air pollution. However, wind farms need a lot of wind turbines to be efficient, opponents complain about the noise, some people think they are eyesores, and there are fears that large wind turbines could be endangering wild bird populations. New Zealand has some areas with consistent and strong wind levels, for example, in the Manawatu. This provides prime conditions for wind farming – indeed, New Zealand already has a number of wind farms supplying our electricity.
Hydro (water) power
Like wind power, hydro power has been used to generate power for a long time – the Egyptians were using hydro power 2,000 years ago to mill grain. Hydro power is the most common form of renewable energy to generate electricity. It is estimated that around 70–80 percent of New Zealand’s electricity supply is generated through hydro power.
The movement of water on Earth that fills the rivers and subsequently drives hydro power is due to the water cycle. To use the power of water, it is often stored in dams and then channelled through pipes that drive the turbines of a generator.
The benefits of storing water in dams for hydro power include areas for water sports and recreation. However, the modification of rivers can damage the ecology of an area, for example, interfering with fish migration. Now, any proposed hydro power schemes must take into account the ecological and local impacts they might have.
Geothermal energy is derived from heat retained inside the Earth. To use this heat, we need a fluid that transports the heat (steam or water). The fluid needs to be able to move through pores and cracks in the Earth’s crust. When a source of heated fluid is close enough to the Earth’s surface, wells can be drilled into the ground to transport the geothermal fluid up. In New Zealand, there are several low and high temperature geothermal fields, the most famous area being the Taupo Volcanic Zone where the geothermal reservoir reaches temperatures between 200–340°C. There are a few technologies used. Most commonly, the water or steam is heating a secondary fluid in a power station, which drives generators to produce electrical power.
Side effects of geothermal power are mostly related to what is being done with the water or steam after it has been removed from the ground. Geothermal power plants generate CO2 – but far less than fossil fuelled plants.
Bioenergy means converting biomass to produce a form of energy like heat, light, electrical power or transport fuel. Burning wood in a fire, for example, is using bioenergy. Natural materials that are used as energy sources can be wood, plants and even bacteria. With rising oil prices and concerns about how long fossil fuels will be available, bioenergy has received a lot of attention in recent years as people search for alternatives like using the by-products from sawmills, re-using cooking oils and planting fast growing plants that can be converted into a usable fuel. While these resources are renewable, they produce greenhouse gases.
A map showing all the wind farms in New Zealand.
New Zealand’s water cycle, on Te Ara Encyclopedia of New Zealand.