Centre for Sustainable Energy Systems

RENEWABLE ENERGY AND THE GREENHOUSE EFFECT

The enhanced greenhouse effect

There is now a consensus among climate scientists that the burning of fossil fuels is causing an enhanced greenhouse effect. Consequences over the next 50 years are likely to include:

significant temperature rises (particularly at high latitudes)
rising sea levels and temperatures (causing flooding, coastal erosion, loss of coral reefs etc)
more frequent extreme weather events (such as storms, drought and floods)
the need to move agricultural activities and infrastructure to different locations
an expanded range for tropical diseases
loss of biodiversity

It is possible that there will be catastrophes such as destruction of the Amazon rainforest due to reductions in rainfall and loss of the Gulf Stream due to changes in the circulation of the Atlantic Ocean.

Energy options

There are three large-scale commercially traded energy forms, namely nuclear energy, fossil fuels and solar energy. Nuclear energy from fission has severe problems relating to waste disposal, reactor accidents, nuclear weapons proliferation and nuclear terrorism. Nuclear fusion is still many decades away from commercial utilisation. Fossil fuels are the principal cause of the enhanced greenhouse effect and are subject to resource depletion, in addition to other problems. Solar energy (which includes both direct radiation and indirect forms such as biomass, wind, hydro, ocean thermal and waves) is available on a massive scale, and collection and conversion methods usually (but not always) entail few environmental or social problems.

In addition to these three large sources of energy there is tidal and geothermal energy. These are available on a relatively small scale at a limited number of sites. In the case of tidal energy there is usually a major environmental impact associated with the construction of what amounts to a coastal hydro scheme.

Fossil and nuclear fuels are used primarily for electricity production, transport, low temperature heat (eg space heating and water heating) and high temperature heat (eg steel production). In addition, fossil fuels are used in the manufacture of plastics and other materials. Solar energy can completely replace fossil and nuclear fuels over the next 50 years. Some applications of solar energy are more advanced than others.

Low temperature solar heat

Solar water heaters are directly competitive with electricity or gas in most parts of the world. Good building design and insulation minimises the requirement for space heating. Direct and indirect solar energy together with the use of heat from the ground can eliminate the need for additional space heating.

Solar electricity

Photovoltaics (solar cells), solar thermal electricity and wind energy (http://www.windpower.dk) are the only renewable energy technologies in sight that can provide very large quantities of sustainable electricity with a reasonable (>10 per cent) overall efficiency in order to limit land use requirements. Wave, ocean thermal and hydro sources are geographically limited. Biomass energy has a very low overall efficiency (<1 per cent) and ultimately competes with food and timber production or with habitat preservation when used on a large scale.

Electricity production from photovoltaics and wind energy has been increasing at a rate of about 25% per year over the past decade, which is far in excess of the growth rate in energy consumption. Wind energy is likely to generate 10% of the world's electricity by 2020, and is now regarded as a conventional energy source. Photovoltaics and solar thermal electricity still occupy niche markets. However, rapid growth in production is causing steady reductions in cost, which will eventually lead to a true mass-market developing.

Solar energy for transport

Oil and gas used to power vehicles will be relatively difficult to displace with solar energy. A first step will be the displacement of the private car by public transport, which can be electrically powered. Freight can be shifted to electrically powered trains. Lightweight electric cars will be much more efficient than current automobiles. In addition, solar electricity can be used to create hydrogen and methanol can be manufactured from biomass. Biomass can replace fossil fuels in the production of plastics and other materials.

High temperature solar heat

Concentrated solar energy can achieve the same temperatures as fossil and nuclear fuels, either directly or through the use of electricity. One problem for high temperature solar heat is that heavy industry is currently located in regions that are relatively poorly endowed with solar energy. Given sufficient political will, it will be possible to move heavy industry to solar-rich regions over the next 50 years.

More information about solar energy can be found on the web site of The Australian and New Zealand Solar Energy Society (ANZSES). You can also send your specific solar inqiries to: anzses@unsw.edu.au