grammatical number - How to add a plural to a lower case abbreviation?

The average Arizona home uses 1,129 kWh of electricity a month or
13,548 kWh a year.

kWh is an abbreviation for kilowatt hour. How do I express kilowatt hours? Maybe kWh(s)? It would look strange as kWhs.

Also,

The average retail price for residential electricity in Arizona is
11.90 cents per kWh.

Do I need the "per" kWh? Is the word per already assumed?

Answer

Technically, "kWh" is an initialism for both "kilowatt hour" and "kilowatt hours". The one that applies depends on whether you're referring to more than one, e.g.

1 kWh = 1 kilowatt hour; and
2 kWh = 2 kilowatt hours.

the "per" is not assumed, but you can replace it with a "/", e.g.

10c per kWh; or

10c/kWh.

edit: for what it's worth, I found a similar question in the physics forum of the stackexchange site.

https://physics.stackexchange.com/questions/172039/usage-of-singular-or-plural-si-base-units-when-written-in-both-symbol-as-well-as