Watch your units!

When I was doing GCSE science and A level chemistry, I was always taught to be careful about units of measurement, especially when I was doing calculations. This is a lesson that would not be lost on the odd science journalist. Today's Guardian has an article on a photovoltaic solar farm in Portugal. According to the article, the farm is "expected to supply 45MW of electricity each year, enough to power 30,000 homes”.

A megawatt (MW) is a unit of power, equivalent to 1,000,000 watts. 1 watt is equivalent to one joule per second. So it doesn't make sense to say that the farm will supply 45MW "each year".

Pedantic, I know, but you'd expect a national newspaper to get that sort of thing right.