I recently spotted an error in an advertisement for EDF - Energie de France, erstwhile our old friend London Electricity, and one of Britain's (and France's) largest energy suppliers - and wrote to their Chief Executive to point it out.

I expressed my alarm that EDF did not know the correct units in which to measure its prime product. The unit is the kilowatt-hour (kWh), the product of power in
kilowatts and time in hours for which supplied. These are the units totted up on your electricity meter and for which your supplier charges you 20 pence
or so, depending on your tariff.

The units measured on your gas meter are quite different - they measure the volume of gas supplied. This is converted to heat value in kWh in the calculation of your bill. If your meter measures in cubic feet of gas each such unit recorded on the meter delivers about 31 kWh to your home, not necessarily to your hearth or hot water. Burning gas is not 100% efficient -some of the energy is lost via the flue. But unit costs of gas are, despite recent increases, generally much cheaper than electricity. With electricity, on the other hand, what you pay for is what you get – the wastage takes place at the power station and a long the transmission lines.

Whatever the fuel, the kilowatt-hour is a valid unit of measurement and is the much bigger brother of the International System unit known as the joule, after a pioneering scientist Robert Joule. Energy is so precious I like to think of these units as "jewels". It takes 3,600,000 of these jewels to make one kWh. I would also rename "fossil" fuels, such as coal, gas and oil as "heritage" fuels, because that is how I think of them. When we burn them we burn our, and our children’s, heritage. Yes, they are renewable but only in the very long term. To replenish the stock we have already used we’d have to desist from use for millions of years. I just can’t wait!

Meanwhile EDF has placed a similar ad, this time carefully avoiding any statement involving numbers or units of measurement!