Many of my deeper questions in permaculture come down to a question of numbers and science, surprisingly, and those facts are hard to find. Perhaps they simply haven't been discovered yet. For example, in my current climate (25 inches rain Mediterranean CA), many rapid growth trees require irrigation, which I currently provide with a grid-powered well. If I am heating with wood, how can I calculate whether the energy cost (as well as the cash cost!) of irrigated coppice wood is worth the benefit of having the additional irrigation-generated biomass to burn? There seem to be WAY too many variables in this seemingly simple question to come up with a usable answer. For instance, what are the ultimate sources of grid power in this region (coal, gas, nukes, wind, solar, hydro ?) And the carbon footprint of each. The caloric fuel yields of the various species I'm planting, and their response, or lack thereof, to supplemental irrigation. As an aside, there are the possible improvements in home insulation and stove technology, each of which has it's own cost in cash, time, and embodied energy.....It's such a confusing mess that I'm currently throwing up my hands and scrounging firewood wherever I can find it and planting whatever I think of willy-nilly as long as I think it's hardy enough to not be dependent on irrigation after establishment.