A review of renewable energy in New Zealand with emphasis on wind-power utilization

Abstract

Can enough renewable energy from the sun be "captured" to satisfy the demand for energy in an advanced country like New Zealand? We consume oil, coal, natural gas and electricity at a rate equivalent to about 3. 5 kW of continuous power per person. We rely on oil for about 60 per cent of our primary energy requirements. Last year the generation of electricity per head of population was about 6000 kWh, which is equivalent to a continuous electrical power of nearly 700 W per person. Hydro- electricity (78 per cent) and geothermal- electricity (seven per cent), both regarded as renewable energy sources, supplied about 85 per cent of this electrical power; the remaining 15 per cent was supplied from fossil-fired thermal-electric power stations. About half of the electricity generated flows into the home: our household electricity bills indicate that the annual amount of electrical energy consumed by an average family is about 8000 kWh, half of which flows down the drain in the form of hot water. A 1 kg loaf of white bread contains about 10 MJ of food energy; twice this am·ount of energl may be needed to grow the wheat, mill the flour and bake the bread. By eating 13 MJ of food energy per day we each consume food energy at a rate equivalent to a continuous power of 150 w. A 150 W light bulb consumes electrical energy at the same rate. A 1 kW element of a home heater switched on for an hour will consume 1 kWh of electrical energy and produce the same quantity of heat or thermal energy. If the electricity is produced by thermal means three to four times this amount of energy, in the form of coal, oil or some other fuel needs to be burnt in a thermal- electric power station in order to produce 1 kWh of electrical energy. How then does the solar energy incident on a horizontal surface throughout the year compare with our annual per capita energy consumption, for example 'of electrical energy? Consider a horizontal area at Auckland or Ohakea 'where the annual solar intensity is about 170 W/m² . In a year about 6000 kWh of solar energy will be incident on an area of 4 m². Problems arise if we wish to convert the intermittent and variable supply of incident solar energy to a more convenient form, such as electrical energy on demand. Unless supply and demand are perfectly matched energy storage will be required, furthermore, if the overall efficiency of conversion of solar energy to electrical energy on a land area base is 0. 1 per cent, we will need one thousand times the original horizontal area or about 0. 4 ha. In order to find ways and means of using solar energy we can trace the flow of radiant energy in the biosphere.