Do you have an old washer?
most of the now don't use that much energy.
I can't see washing them on hot cost much more than taking a hot shower. And you do that 7 times a week at least.
I never noticed my power bill going up by washing diapers.
Just wash them on cold and see for yourself if you like them. That's the best way to find out if it will work for you.
Wanted to add, you would be spending at least $15 to $20 a month on sposies anyway, so you still...