The American media also loves the “homes” analogy for what a power plant can power.

Obviously it is possible to calculate a home’s avergae usage in kilowatts (take kilowatt-hours for any period, divide by the hours in the period).

Our media particularly loves to use it in misleading ways. They take the nameplate capacity of a wind turbine or solar system (which is max rated power, not average), disregard the capacity factor (sometimes there is little or no wind, or it is dark or cloudy), and assume the plant always outputs max. power and powers a representative number of homes. Typically, these issues will limit “renewables” plants to about 20-30% of their nameplate capacity, which is fine if the implications are correctly thought out.

Also ignored is the home’s load factor. You don’t use “average” 24/7. Household usage has peaks and valleys. Some average out, but typically everybody has a peak around dinnertime (just as the sun goes down and the wind calms). Much more serious analysis is required to assess what the plant can really power.

The publication is available free from the Wellcome Trust
see: http://www.wellcome.ac.uk/bigpicture/order and freepost address in the UK
Big Picture series,
Wellcome Trust, FREEPOST RSHU-ZJKL-LCZK, Feltham, TW14 0RN

However, for estimating how long it will take to drive somewhere, kilometers per hour is quite useful. For estimating impact on your electric bill, watts times hours makes a certain amount of sense too. The kilowatt hour is deeply seated in the electric industry; we may have to settle for it there and strive to prevent its expansion.

The metric system unit for measuring energy is the joule.

Prior to the selection of the unit, joule, by the British Association for the Advancement of Science (BAAS) in 1889 there were many varied, randomly generated and poorly defined words associated with measuring energy.

For example, there were multiple British Thermal Units and multiple calories that arose because of the many definitions used for these words. These definitions vary wildly according to the whimsy of the definition creators. For example 1 Calorie is 1000 times larger than 1 calorie according to whether the initial letter is an upper C or a lower case c. British Thermal Units and calories also vary with temperature – a calorie at 20 °C is not the same as a calorie at 37 °C for example.

Many of the old energy words are still in use. I made a collection from news media over a 12 month period. Previous words used in the context of energy measurement included:

Atomic energy unit, barrel oil equivalent, bboe, billion electron volts, Board of Trade unit, BOE, BOT, brake horsepower-hour, British thermal unit, British thermal unit (16 °C), British thermal unit (4 °C), British thermal unit (international), British thermal unit (ISO), British thermal unit (IT), British thermal unit (mean), British thermal unit (thermal), British thermal unit (thermochemical), British thermal unit-39, British thermal unit-59, British thermal unit-60, British thermal unit-IT, British thermal unit-mean, British thermal unit-th, BThU, BThU-39, BThU-59, BThU-60, BThUIT, BThU-mean, BThU-th, Btu, Btu-39, Btu-59, Btu-60, Btu-IT, Btu-mean, Btu-th, cal, cal-15, cal-20, cal-mean, calorie,Calorie, calorie (16 °C), calorie (20 °C), calorie (4 °C), calorie (diet kilocalorie), calorie (int.), calorie (IT) (International Steam Table), calorie (mean), calorie (thermochemical), calorie-15, Calorie-15, calorie-20, Calorie-20, calorie-IT, Calorie-IT, calorie-mean, Calorie-mean,
calorie-th, Calorie-th, cal-th, Celsius heat unit, Celsius heat unit (int.), Celsius heat unit-IT, Celsius heat unit-mean, Celsius heat unit-th, centigrade heat unit, centigrade heat unit-mean, centigrade heat unit-th, Chu, Chu-IT, Chu-mean, Chu-th, coulomb volt, cubic centimetre atmospheres, cubic foot atmospheres, cubic metre atmospheres, double Rydberg, duty, dutys, dyne centimetres, E-h, electron mass energy equivalent, electron volt, equivalent volt, erg, eV, foot grains, foot pound, foot pound force, foot poundal, ft-lb, ft-lbf, ft-pdl, gigaelectronvolt, gram calorie, gram calorie-15, gram calorie-20, gram calorie-IT, gram calorie-mean, gram calories (mean), gram calorie-th, grand calorie, grand calorie-15, grand calorie-20, grand calorie-IT, grand calorie mean, grand calorie-th, hartree, Hartree energy, horsepower hours, horsepower hours (metric), inch pound force, Kayser, kcal, kcal-15, kcal-20, kcal-mean, kcal-th, kgfm, kilocalorie, kilocalorie (16 °C), kilocalorie (4 °C), kilocalorie (int.), kilocalorie-15, kilocalorie-20, kilocalorie-IT, kilocalorie-mean, kilocalorie-th, kiloelectronvolt, kilogram calorie, kilogram calorie-15, kilogram calorie-20, kilogram calorie-IT, kilogram calorie-mean, kilogram calories (int.), kilogram calorie-th, kilogram force metre, kiloton TNT equivalent, kilowatt hour, kilowatt minute, kilowatt second, kWh, large calorie, large calorie-15, large calorie-20, large calorie-IT, large calorie (mean), large calorie-th, Latm, latm, litre atmosphere, major calorie, major calorie-15, major calorie-20, major calorie-IT, major calorie-mean, major calorie-th, megaelectronvolt, megaton TNT equivalent, megawatt hours, metric ton oil, metric ton TNT, metric ton coal, micri-erg, natural unit of energy, newton metre, petit calorie, petit calorie-15, petit calorie-20, petit calorie-IT, petit calorie-mean, petit calorieth, Q unit, quad, quadrillion, Rydberg, small calorie, small calorie-15, small calorie-20, small calorie-IT, small caloriemean, small calorie-th, therm, therm (EC), therm (EU), therm (UK), therm (US), thermie (16 °C), ton coal equivalent, ton oil equivalent, ton TNT equivalent, tonne coal equivalent, tonne oil equivalent, tonne TNT equivalent, watt hour, watt minute, and watt second.

Note that for a journalist or a politician to comprehend all of these 199 old energy words 39 402 conversion factors are needed.

Cheers,

Pat Naughtin

Geelong, Australia