Here is a very simple and viable way to produce charcoal in bulk. All this requires is a 55 gallon drum with lid. No modifications other than figuiring out how to lean it over for the process. This is the method most are using on the DOW forum now. There is no limit to how many of these you can run at a time. You could get like four of these drums off craiglist cheap. Then spend an afternoon and make like 200 gallons of fuel in one session. That is a lot of charocal and would last most at least a week and that is running everyday. If for solar back up thats probably a months worth of fuel.
https://www.youtube.com/watch?v=bNOiVCpRWXw&t=2s&pp=ygUPd2l0bG94IGNoYXJjb2Fs