Visitors to the Cabinet Office website will see that this branch of the Government is measuring its energy use in “kilowatt-hours per hour”. It is a sad reflection on the quality of civil service support given to this crucial part of the Government machine that such an incongruous and scientifically illiterate measure should be published.
If you go to the homepage of the website of the Cabinet Office (aka “Number 10”), http://www.cabinetoffice.gov.uk/, you will see in the right hand column an animated display headed “real time energy use”. This oscillates between kg of CO2 per hour, £ per hour and (yes!) “kWh per hour”. See extract below (or click on it for a clearer image):
As the website invites feedback (and promises a response), I wrote on 27 December as follows:
“I wonder if you realise that the measure of energy used in your webpage http://www.carbonculture.net/orgs/cabinet-office/70-whitehall/ (kWh per hour) is in fact nonsense.
The SI unit of energy is the joule (J). The rate at which energy is used is power, for which the SI unit is the watt. Thus 1 W = 1 J/s (joule per second). Although it is in widespread use by energy companies, the kilowatt-hour is a somewhat unsatisfactory unit since it is energy divided by time multiplied by time. (In fact as there are 3600 seconds in an hour, a kWh is 3600 kJ (or 3.6 MJ)).
Your website then compounds the problem by dividing the unit again. So we have energy divided by time multiplied by time divided by time!
Since what you are trying to convey is the rate at which energy is used (= power), the correct unit to use is the watt – or in this case the kilowatt. Thus the clumsy expression “Average 289 kWh per hour” should be simply 289 kW. This should be meaningful to readers as they will be familiar with electrical appliances such as kettles (which consume, say, 2 kW of power) and the output of power stations measured in megawatts (MW).
I would suggest that you amend your website to give more meaningful and scientifically correct information.
(BTW you should also leave a space between the number and the unit of measurement)”
As at 4 January no response had been received (but I will of course publish it if one does eventually appear).
The website does attempt to deal with the question of measurement units as follows:
“Why are you using these units and what do they mean?
We provide three different measures of the energy used: the amount of energy, its monetary cost, and the carbon impact of the energy used.
Energy use is measured in kilowatt hours (kWh), which are the standard units of a home energy bill (1kWh is the amount of electricity used by ten 100W light bulbs in one hour).
For electricity this number represents the amount of energy that flows into a building through the meter, and excludes distribution losses. For gas it is the amount of energy that is theoretically available by burning all the gas in an imaginary burner. For district heating it reflects a flow of temperature [sic] into the building over time (after the heat produced by burning the fuel has been transported to the meter, which involves other losses). So these numbers, while all being measured in kWh, mean very different things. This is one reason that we prefer to use ‘units per hour’ when combining them. In some ways it would be better not to combine them at all, because it implies that the measures are comparable. This is a global challenge though, and conventions have become established around combining kWh. So we’ll have to fix it another day…”
Comment: It is true (unfortunately) that energy companies measure energy in “kilowatt-hours” rather than joules, but there is no need for a Government Department to implicitly endorse this practice. In any case, it does not excuse the obvious error of multiplying by a unit and then dividing by the same unit. Even the most scientifically-challenged should be able to see that. Perhaps it is just an untypical error by a junior civil servant (I hope so), but one wonders why it wasn’t spotted by a scientifically aware colleague.