The joule is the standard unit of energy in electronics and general scientific applications. One joule is defined as the amount of energy exerted when a force of one newton is applied over a displacement of one metre. One joule is the equivalent of one watt of power radiated or dissipated for one second. In some applications, the British thermal unit (Btu) is used to express energy. One Btu is equivalent to approximately 1055 joules. [Whatis.com]

Short for one kilogramme (1,000 grammes). Also a prefix meaning 1,000 times. Examples: 1 Kilowatt (Kw) is 1,000 watts; 1 Kilotonne (Kt) is 1,000 tonnes.

One kilowatt, written as 1kW, is 1,000 joules per second. The measure of speed is incorporated. So one kilowatt-hour, written as 1kWH = 3.6 million joules. A kwH, however, does not have to be delivered in one hour - it could be delivered in a day, so the associated power would be 41.7 joules per second, or 41.7 watts. A 2MW (2,000kW) wind turbine at full rated power would be delivering 2 million joules per second, or 2 million watts.

Sometimes known as capacity factor, in the context of energy use this means 'production as a proportion of rated output'. For example, a wind turbine may have a rated capacity of 100 MW (Megawatts) but due to not enough or too much wind, repair downtime or other factors, it will produce less than its rated capacity at certain times.

A prefix meaning one million (1,000,000) times. Examples: 1 Megawatt (Mw) is 1,000,000 watts (or 1,000 Kw); 1 Megatonne (Mt) is 1,000,000 tonnes (or 1,000 Kt).

The natural increase of a population during a year is the number of births minus the number of deaths.

The newton is the Standard International (SI) unit of force. In physics and engineering documentation, the term newton is usually abbreviated to N. One Newton is the force required to cause a mass of one kilogram (kg) to accelerate at a rate of one metre per second squared in the absence of other force-producing effects. In general, force (F) in newtons, mass (m) in kilograms, and acceleration (a) in metres per second squared are related by a formula well known in physics: F=ma. [Whatis.com]

1 watt (W) = 1 joule/second. 1 horsepower (hp) = 0.746 kilowatts (kW).
Renewable energy is most usefully considered in terms of the energy that can be gathered over a year. This can be conveniently expressed in terms of Gigajoules per year (GJ/yr). However, since there is a time element in this, 1Gj/yr can be changed into the power that this represents, and 1 Gj over a year represents a mean power output of 1 x 10⁹J/(24 x 365 x 60 x 60) = 31.71 joules per second or 31.71 watts. Thus 1 kW is equal to 1000/31.71 = 31.54 Gj/yr. Without striving for too much accuracy, it is therefore OK to equate a power of 1kW with a rate of energy use of 31.5 Gj/yr. Note that energy doyen Vaclav Smil, in particular, refers to the amount of energy captured, per unit of area, as energy density (both for renewable and other forms of energy), using units of watts per square metre (W/m²). [Andrew Ferguson, OPT]

Unit of mass equivalent to 1,000 kilos (Kg). Equal to 2,204.6 lb. Formerly known as a metric ton.

One thousand billion (1,000,000,000,000 or 10 to the power of 12).

The total surface area of the United Kingdom (England, Wales, Scotland and Northern Ireland) was 24,418,000 hectares at the end of 2001 (population 58.8 million April 2001). This comprises 24,093,000 ha of land area and 325,000 ha of inland water. The land area comprises 19% crops and bare fallow land; 51% grasses and rough grazing land; 4% set aside and other land on agricultural holdings; 11% forest and woodland; and 16% urban land and land not otherwise specified (101% due to rounding up). [Digest of Environmental Statistics, published June 2003, Department for Environment, Food and Rural Affairs. Web: www.defra.gov.uk/environment/statistics/des/index.htm]. The UK is therefore slightly smaller than Oregon (population 3.4 million April 2001), a single state of the USA, whose surface area is 25,166,396 hectares, of which only 2% is developed.[US Department of Agriculture Natural Resources Conservation Service: Surface Area Findings, State of Oregon, December 2000]

The watt-hour (Wh) is a unit of energy equivalent to one watt (1 W) of power expended for one hour (1 h) of time. The watt-hour is not a standard unit in any formal system, but it is commonly used in electrical applications. An energy expenditure of 1 Wh represents 3600 joules . To obtain joules when watt-hours are known, multiply by 3.600 x 10 to the power of 3. To obtain watt-hours when joules are known, multiply by 2.778 x 10 to the power of 4. In general, energy (E) is equivalent to power (P) multiplied by time (t). To determine E in watt-hours, P must be expressed in watts and t must be expressed in hours. IF a 60-W bulb burns for 3 h, then P=60 and t=3, so the energy E in watt-hours is: E=Pt = 60 x 3 = 180 Wh. The watt-hour is rarely used to express energy in any form other than electrical.[Whatis.com].

In eco-footprinting, a factor which describes the extent to which a land-use category of a given country (e.g. Peruvian cropland) is more (or less) productive than the world average in that same category (i.e. world average cropland). Each country has its own set of yield factors. The yield factor is used to relate the yield from a local hectare of biological productivity to the worldwide average, to establish a worldwide hectare (wwha) of productivity. See Hectare, local above.

By Andrew Ferguson and Edmund Davey, and from other sources

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