Published by Australian Academy of Science
Glossary | Australia’s low emission energy future

biomass. A general term for material from living things such as plants, animals, fungi, bacteria and food waste. Taken together, the Earth's biomass represents an enormous store of energy. Since biomass can be regrown, it is a potentially renewable resource. For more information see Biomass – the growing energy resource (Nova: Science in the news).

combined cycle. Power plants that use a combined cycle burn gas to generate electricity, then use the waste heat produced to generate more electricity via a steam turbine. For more information see Energy sources: gas (Ergon Energy).

electromagnetic induction.The production of electrical current in a conductor due to a changing magnetic field (moving magnet) or to the movement of a conductor through a magnetic field. For more information see Faraday's magnetic field induction experiment (Florida State University, USA).

fuel cell. A cell that converts energy from chemical reactions directly into electrical energy. A simple fuel cell 'burns' hydrogen in a flameless chemical reaction with oxygen to produce electricity. For more information see Fuelling the 21st century (Nova: Science in the news).

geosequestration. The capture and long-term underground storage of carbon dioxide. Carbon dioxide produced by coal-fired electricity stations and other industrial sources is compressed to form a liquid and injected into deep underground geological formations. Possible storage sites include saline aquifers, coal seams, and used oil and gas reservoirs. For more information see About geosequestration? (Cooperative Research Centre for Greenhouse Gas Technologies).

Kyoto protocol. An international agreement associated with the UN Framework Convention on Climate Change that commits participating countries to reduce their greenhouse gas emissions relative to 1990 levels over the period 2008-2012. The Kyoto Protocol was adopted in Kyoto, Japan, in 1997.

life-cycle emissions. Emissions of greenhouse gases throughout the full life-cycle of the generating system. Emissions are not only from the generation of electricity, but also from the production of the energy and materials needed to build, maintain and operate the plant, as well as from disposal of wastes and decommissioning.

low emission fossil fuel technologies. Technologies aimed at reducing the environmental impact of burning fossil fuels for power generation. These technologies have recently focused on reducing carbon dioxide emissions. However, they can also include measures to reduce other pollutants, such as sulfur dioxide and particulate matter, as well as more efficient technologies. For more information see Clean technologies for fossil fuels (Nova: Science in the news).

photovoltaic cells. Also known as solar cells. A photovoltaic cell is made of thin wafers of two slightly different types of silicon. One, containing tiny quantities of boron, is called P-type (P for positive) and contains positively charged 'holes', which are missing electrons. (Electrons are negatively charged particles that orbit the nuclei of atoms.) The other type of silicon has small amounts of phosphorus and is called N-type (N for negative). It contains extra electrons. Putting these two thin P and N materials together produces a junction which, when exposed to light, will produce a movement of electrons – and that constitutes an electric current. Photovoltaic cells thus convert light energy into electrical energy.

renewable energy. Used to describe energy sources that are replenished fast enough that they can be used by humans more or less indefinitely, provided the rate of use is not too great. Examples include biomass, wood, wind, falling water and sunlight. Compare non-renewable.

solar thermal. Describes an energy system that harnesses solar energy to produce heat energy. Small flat plate systems are often used to heat water for household or commercial use. Larger high-temperature systems use reflective mirrors or dishes to focus the energy. The heat may then be used to convert a liquid into a vapour, which turns a turbine to produce electricity.