Environment & Energy

...recognized by the International Bureau of Weights and Measures.

These units are based on the metric system using seven basis units from which all others can be derived. These are time, length, mass, quantity of pure substances, (the mole) and temperature, Kelvin, luminosity, and electric current.

How one derives other SI units is by unit analysis carrying them through calculation.

The formular for energy for instance I'd E = 1/2mv². It follows that the unit of energy can be written as kg-m²/sec² which is for convenience defined as the Joule.

Watt-hours are widely used but are informal. As a scientist, I prefer formal. The derrived unit for power is the Watt, which is defined as Joules/sec. This can be converted to the non-standard Kilowatt-hour by multiplying 1000 Watts by 3600 seconds. A Kilowatt-hour is 3,600,000 Joules. The International Bureau of Weights and Measures has defined prefixes such a kilogram, mega, and exa, to represent powers of ten connected to groups of three digits.

One can take a course in physics at a community college or a good high school and understand these formalities.

There are a lot of informal units used by the general public especially in the United States and in popular literature. Whenever I encounter these I convert them to SI units. For many years, the IEA used to report quantities of energy in an absurd unit, MTOE, million tons oil equivalent. I had to deal with this annoying practice by putting the numbers in a spreadsheet and convert them to Exajoules. Happily in recent years they've reverted to SI units in their tables