Renewable Energy Sources
We are familiar with the use of renewable energy from the sun. The domestic application of photovoltaic cells and of wind power is discussed under Lifestyle. Both of these sources of renewable energy are currently in service domestically and commercially.
Alternative Energy Supply - Solar Power
At a cost of several thousands of dollars, it is possible to install a solar-powered domestic power source, using silicon photovoltaic cells. Government subsidies are available in Australia to householders who install solar power systems, and this is commendable. The system can draw upon the normal mains supply for power when there is insufficient sunlight to meet demand. Larger, more expensive systems can return surplus power to the public supply and the householder can receive a rebate on the electricity account. Alternatively, and more cost effectively, if storage batteries are installed, surplus energy may be used to charge the batteries for overnight electricity supply and to heat water - the system need not be connected to the "grid".
(It is estimated that, in Australia, as much as 30% of generated power is consumed by households. If all households were "Off The Grid", then international protocols for greenhouse gas emissions would readily be met.)
The owners of supermarkets, and of other buildings with large flat roofs, should be encouraged to install solar photovoltaic power generators. During the daylight hours they may be self-sufficient in power supply for lighting, for airconditioning and for freezer cabinets. Surplus power may be returned to the grid and the rebate will assist in meeting the system costs.
Any commercial solar power generator must incorporate a mechanical system to track the sun, so that the maximum amount of power will be generated by the photovoltaic cells or heat absorbers. This machinery inevitably introduces additional maintenance costs.
In remote areas, where connection to the mains power grid is not available, backup is provided by storage batteries, by wind power, and by diesel generators for higher power systems. Since installing solar power, the owners of such systems are benefiting from very significant savings in the costs of maintenance and of diesel fuel.
In Australia, the C.S.I.R.O. and others are constructing experimental solar power generators for connection to the electricity grid.
Alternative designs include a large array of steerable phototelectric solar panels, another uses an array of steerable mirrors to concentrate heat energy upon a steam boiler which will feed a conventional turbine generator. Other examples use parabolic trough collectors to concentrate the solar thermal energy.
Such a large scale solar thermal power station, a "Solar Tower" was, in May, 2007, demonstrated in Spain and has a maximum power output of the order of 130 MW. It has been announced that a 330MW plant will be constructed in a desert area in northern India, and will use natural gas to generate power during the night.
While quite large power outputs may be produced by huge solar generators, they cannot produce base load power unless they have some form of energy storage. They may provide a useful peak load capacity during daylight hours, e.g. for such purposes as hydrogen production, metal smelting, water desalination etc.
The cost of photovoltaic solar power generators is uneconomic, except in small scale installations. Wind power generators offer competitive generating costs. Both types are emission free, except during the construction phase, so that they do not contribute to greenhouse gases. Because the sun and the wind are intermittent, neither will satisfy requirements for base power.
Recent design improvements to silicon photovoltaic solar panels (e.g. sliver cells) are lowering manufacturing costs and increasing efficiency. New types of photovoltaic cell, e.g. using organic materials, offer reduced cost.
Alternative Energy Supply - Wind Power
Rural property owners with sufficient space may use a wind generator to supply power needs, with battery or diesel generator backup for periods of low wind speed. In future, the diesel generator may be replaced by fuel cells and a gas storage tank for methane or hydrogen gas.
Larger "wind farms" which feed into a local grid are already operating in several areas of Australia. These have an estimated operational life of the order of 25 years. Individual turbines may have a maximum output power of the order of 25kW - 1.5MW. Grid connection over a large region will reduce the effect of periods of "no wind" for the system. Unlike solar power, wind power is available throughout the day and night. A new design of "gearless" wind generator, patented by Isis Technologies, of Oxford University in the U.K., offers a quieter machine, operating at lower wind velocity.
In the 1950s, when microwave and coaxial cable repeaters were installed throughout Australia to provide long distance communications, the Postmaster General's Department conducted exhaustive wind speed surveys, to assist in the selection of suitable locations for wind-powered generators. This valuable information is still available.
Land-based wind farms can generate power at competitive rates. Offshore wind farms are of interest in the absence of space for land installations, but have a significantly higher capital cost.
Another type of wind generator uses a large concrete tower, which looks rather like a power station cooling tower, to absorb solar thermal energy. The hot air inside the tower produces an updraft by convection to drive a turbine power generator. Unlike the photovoltaic generator, this type of wind generator may have sufficient stored energy to operate throughout day and night.
The eventual installed capacity for solar and windpower is unlikely to exceed 20% of total global power demand.
When all costs have been included, it is now calculated that large wind power installations and nuclear energy have a clear cost advantage over all other energy sources. This situation may change, as a result of new technological developments such as, for example, organic photovoltaic films.
Hydroelectric Power
In Australia, power is generated by hydroelectric schemes in the Snowy Mountains, and in Tasmania. The feasibility of hydroelectric power generation in other areas, such as the Kimberleys, should be investigated.
It has been suggested that significant amounts of power may be generated by harnessing wave motion, or tides. These renewable energy sources should also be investigated.
Hydrogen Gas
The combustion of hydrogen gas produces no carbon dioxide. The water which is produced is a valuable resource. Hydrogen is a suitable source for both fixed and mobile power generation installations of any practicable size.
Future domestic electricity supplies could well be powered by piped hydrogen gas, using fuel cell generators, and supplemented by rooftop solar photovoltaic generators.
A hydrogen gas pipeline, as a future energy distribution method, may be a viable alternative to an electricity grid. Surplus off-peak electricity from renewable energy sources, such as wind power or solar photovoltaic generators, may be used to produce hydrogen by the electrolysis of water. The hydrogen may be added to existing natural gas pipelines.
Hydrogen may be produced directly in high-temperature nuclear reactors, but these are less likely to be used in the future because of their additional safety and maintenance requirements. New catalysing electrodes, which will offer improved efficiency in the electrolytic production of hydrogen, are under development.
Hydrogen gas may also be produced from solar radiation and water by photosynthesis using algae. At present, the best available conversion efficiency is less than 10%, so that large-area hydroponic installations, constructed from inexpensive plastic film, are necessary. It is hoped that genetic engineering of the algae may result in a viable system for countries like Australia, which have large areas of unused land and plentiful access to solar energy. Large algal systems have also been suggested for oceanic installations.
Bio-Fuel
Oil seeds, palm oil, waste cooking oils, animal fats, waste lubricating oil etc, may be converted into a suitable fuel for diesel engines. In common with other combustible fuels, they contain carbon, and so when burned they contribute to the carbon dioxide load. However, because of the hydrogen content, they produce more heat energy than equivalent amounts of coal and so are marginally less polluting.
However, there is a danger that the diversion of food crops to the production of bio-fuel, as is the case in Brazil, may result in famine.  
Methane
Methane gas is produced by the breakdown of organic wastes in composting, in garbage landfills, and in sewage treatment. It may be used in i.c. gas engines or fuel cells for power generation, or for space heating, e.g. in piggeries.
Ethanol
Up to 15% ethanol (ethyl alcohol) may be added to gasoline for automobile engines, without concern for damage to engine components, such as rubber seals. In the U.S.A. and Brazil up to 85% ethanol is added to gasoline for use in specially designed i.c. engines.
Ethanol may used directly in fuel cells to generate electricity.
Ethanol is the major source of energy in Brazil, which also exports ethanol to the United States. About 50% of the Brazilian sugar crop is used for ethanol production.
Ethanol is produced by hydrolysis of di-saccharides and starch (malting), then by the yeast fermentation of sugars, followed by extraction of pure alcohol. Major sources are sugar cane, maize, and other grains. Presumably sugar beet could be used to produce ethanol.
Wood Chips
Wood chips are primarily used for paper production, but may also be used as fuel, to produce methanol (methyl alcohol) or to manuacture building products such as particleboard, mdf (medium density fibreboard) or osb (orientated strand board).
The growing trees produce cellulose by photosynthesis, sequestering carbon dioxide, so reducing the burden of greenhouse gases. The carbon will remain captive until the timber product is broken down, or burned. For this reason, the establishment of new timber plantations and the re-planting of clear-felled forest areas is essential for the reduction of global warming.
Plantation areas effectively reduce water run-off and prevent erosion. They provide habitat for wild life. However, unless carefully planned and managed, plantations may be subject to disastrous fires resulting from lightning strikes.
Adequate and reliable sources of water are essential for a successful plantation industry. The plants to be grown must be suitable for the anticipated future climatic conditions. Some Australian trees and shrubs, such as macadamia, may produce a viable source of income as an alternative to wood chips, especially if the area is drought-proofed by "manufactured" irrigation water. Many long-living species of tree are able to survive in areas of low rainfall, and with a minimum of maintenance, and offer attractive landscaping, e.g. californian oaks.