CHAPTER 17: RENEWABLE ENERGY RESOURCES (Hydro-electric power (wave power,…
CHAPTER 17: RENEWABLE ENERGY RESOURCES
Definition: Those that can last indefinitely without any reduction in their supply.
Energy from the sun.
Inside the sun, nuclear fusion reactions release large amounts of energy. The earth receives about 1/200b of the Sun's energy output.
Cannot be collected at night. Amount of sunlight received varies depending on location, time of day, time of year and weather conditions.
So there have been ongoing improvements in solar energy technology: more efficient harnessing methods are being developed and storage battery technology is improving.
Uses solar energy to heat water.
E.g used to heat water for swimming pools. Often placed on the roof of a house, these collectors are large areas of tubing (of black plastic or synthetic rubber) through which the pool water circulates. Heat from the sun is absorbed by the black tubing and heats up the water moving through it, warming the swimming pool water.
Water can be heaeted up to 100C by flat plate solar collectors.
Used for hot water supply in homes, hospitals, industry and agriculture.
Consist of a black metal absorber plate with a series of tubes bonded to it, enclosed in an insulated box with transparent cover. The absorber plate is heated by the solar radiation and transfers heat to the water flowing through the riser tubes or channels. Cooler waterflows into the bottom of the collector,gains heat and rises to an insulated storage tank. A transparent cover allows solar radiation to pass through yet reduces heat loss by protecting the absorber plate from wind and limiting the re-radiation of thermal energy.
When there is insufficient solar radiation to maintain the water temperature, the storage tank may have a back up energy supply, such as gas, wood or electricity
Water can be raised to higher temperature, up to 200C, by evacuated tube collectors.
Similar to flat plate collectors except that the black absorber plate is held within a vacuum in a glass tube.
This results in very little heat loss, allowing higher temperatures to be reached. Because the temperatures are above the boiling point of water, oil is usually used as a heat transfer fluid. These collectors are used in industrial processes.
Photovoltaic Cells (PVs) /Solar
Using solar energy to convert it into electrivity.
Primarily made from silicon, which is a semiconductor. (Which will conduct electricity only under certain conditions.)
In a PVs, two types of impurities have been incorporated into the silicon to create those conditions.
One type of impurity (often arsenic or phosphorus) provides an excess of electrons over those needed for covalent bonding with the silicon. These extra electrons are free to participate in the conduction of electricity. Semiconductors such as these are called n-type, as they have an excess of electrons, which are negatively charged.
The other form of impurity added to the silicon includes boron or aluminium, which have a shortage of outer, valence electrons. This type is a p-type semiconductor.
When a n-type and p-type silicon are in contact with one another, a p-n junction is formed. When a p-n junction is in the dark, and not exposed to light or solar energy, the excess electrons from the n-type silicon with drfit across the junction and occupy spaces in the p-type silicon where there are electron shortages. This creates positive charges on the n-type side of the junction (because it has lost electrons) and negative charge on the p-type side (because it has gained electron). This produces an electric field across the junction.
When solar energy hits the cell, enough energy is provided to move some of the extra electrons in the p-type silicon across the junction to the n-type silicon. If a wire is connected from the n-type to the p-type side of the junction, a current will flow; this current can be used to drive an external electrical device.
Solar cells are used in locations distant from the mains electric supply. e.g they provide power for remote houses, external lighting, electric fenced, weather stations and railway crossing signals.
The electricity stored in the batteries (potential energy) is made use of during the night or on cloudy days.
Cost to the consumer from PVs is higher compared to the cost of electricity from conventional power stations.
Its operation does not produce any pollution, but their manufacture requires significant amounts of energy and produces pollution.
Sand mining for silicon may have detrimental environmental effects.
The energy efficiency of PVs ranges from 15% to 40% as technology advances so too will the energy efficiency of these products.
Wind is a form of solar energy. Sunlight falls unevenly on the Earth, heating the air unevenly.
The warm air rises and cooler air moves into replace it. This circulation of air from cool areas to warm areas produces winds.
These processes operate at a local level, such as thee cool sea breezes coming in over the land as it heats up.
They also act on a global scale, with hot air rising at the equator and cooler air being drawn from the poles.
This basic pattern is complicated by the Earth's rotation, ocean currents and different land masses.
Only 1% to 2% of solar energy that falls on Earth becomes wind energy.
If we efficienty harnesses all of this wind energy and used it to generate electricity, it could produce ten times more energy than humanity uses each year.
Used for mechanical tasks (e.g pumping water, and to generate electricity)
Come in two forms:
Those with a horizontal axis and those with a vertical acis.
Made up of a propeller that spins when the wind is caught by the blades. The spinning blades drive a shaft connected to a mechanical device such as a water pump or to an electric generator. CONT pg 144
Using wind to produce electricity under current methods is approx 45% efficient in terms of energy
Major limitation with wind energy is the need for a constant stream of air flow to produce energy. more info on pg 145
Hydro-electricity is produced by using water stored in dams. The stored water flows through a turbine that spins a shaft connected to an electric generator to produce electricity. The amount of electricity produced depends on the volume of water flowing through the turbine and the vertical distance the water falls. The gravitational potential energy of the water stored in the dam is converted into kinetic energy upon release and this is converted into electrical energy in the generator.
Hydro-electric plants are used mainly to supplement the electricity supply from other forms of power station as they can be brought in and out of operation relatively quickly and easily
It has a fairly high overall energy efficiency, with an average of 70%
It provides about 19% of the world's electricity production. In Aus, about 10% of the total electricity produced is hydro-electricity.
more info on pg 147
The amount of power a wave can produce is directly related to the hight and period (time between successive wave fronts) of the wave.
One of the devices that has been developed to generate electricity from waves involves a system of floats. These use the movement of the waves to compress air to lift a fluid to dive electricity generators.
These are a number of off shore sites suitable for wave power stations, but the devices can be damaged by salt water corrosion and storms.
The energy in the moving water of tides to produce electricity.
Tidal power stations generate electricity in a similar way to hydroelectric power stations.
A dam wall is built across the entrance to a bay or inlet, and moving water is passed through turbines to produce electricity. They can use the incoming and outgoing (flood and ebb) tides to generate power.
Large volumes of water are needed to generate large amounts of power.
Three major tidal power stations currently operating around the world: La Rance River estuary in France, in Canada's Bay of Fundry, and in Kislaya Guba in Russia
It is unlikely to contribute very much to the world's electricity supply because few sites are suitable and they are expensive to build. They also cause massive disruption to the aquatic ecosystems where the stations are built.
Heat energy that comes from deep within the Earth. High pressures and temperatures deep within the Earth constantly seek to escape to the surface. Areas of the Earth's surface where the crust is thin have high geothermal activity. In these areas, cracks and faults in the outermost layer of the Eerth allow heat within the Earth to come close to the surface.
Water finding its way down these cracks is heated and can re-emerge at the surface as very hot water or steam in springs or geysers.
Heat from these sources can also be used for space heating and industrial processes.
On a local scale, geothermal energy could be considered as non-renewable because the removal of the steam or hot water will deplete the source. On a global scale, the resource is so extensive that it can be considered as renewable.
It is a clean source of energy, but there are some environmental considerations.
One is the local depletion of the resource, with the possibility of land subsidence if too much water is removed.
Building the geothermal projects themselves can damage the ecosystem in the area.
The scarcity of high-graade sources of geothermal energy and the costs associated with their development are likely to limit the use of geothermal energy within Australia.
Biomass refers to the amount of plant or animal material.
Biomass energy is energy derived from material produced by living things. It may include waste from agricultural and forestry products, or industrial, human and animals wastes.
Some forms can be used directly. e.g burning wood for heating. or used to produce fuels (biofuels) for transport or gas (biogas) for heating and generating electricity.
All energy in biomass originally comes from the Sun and the solar energy is converted into biomass through photosynthesis.
is produced from the breakdown of plant and animal waste material in the absence of oxygen. The gas is a mixture of methane and carbon dioxide. It usually contains about 60% methane, which is a useful energy source. Biogas can be burned in power furnaces, heaters and engines and used to generate electricity. The residue from the biogas digesters is useful as a fertiliser.
provides about 30% of the world's population with about 90% of the energy they need for heating and cooking.
One problem: low efficiency of energy transfer from wood to usable heat. E.g 90% of the heat produced in an open fireplace is wasted and the smoke produced can lead to air pollution, especially particulates and polycyclic aromatic hydrocarbons. Slow combustion heaters are more efficient and produce less pollution.
Using wood for energy at unsustainable rates can lead to deforestation, which in turn can lead to soil erosion and soil salting.
Although wood is generally considered a renewable resource, it is non-renewable in some places where it is being harvested at a rate higher than it is being replaced.
is a biofuel and can be made from materials that contain sugars, starch or cellulose. It can be produced from sugar and grain crops by fermentation and distillation. Many countries are already blending ethanol with petrol to reduce their use of petroleum for transport.
Using ethanol may do little to reduce greenhouse gas emissions, depending on production methods. The combustion process of ethanol results in less tropospheric ozone being formed, but increases the emissions of aldehydes. Ethanol is costly and, in some pars of the world, turning land over to produce ehanol can conflict with food production.
Hydrogen gas. more info on page 149
Comparison of Different Energy Sources
The characteristics of renewable and non-renewable energy sources, including biomass, solar, hydro-electric,
wind, tidal, oil, coal, natural and coal seam gas, nuclear, geothermal