Baldurs_Underdark
Hero
Oof. You propose to fuel the heavy industries with plant-based fuels? Maybe with a lot of druids that go around casting Plant Growth it might be possible to at least grow enough plants. In our real world, we don't even have nearly enough surface to grow all the plants on. We'd need another earth just to grow all the fuels we use. But Plant Growth doesn't solve the other challenges of biobased fuels, such as the huge need for fertilizers, and all the effort needed for harvesting and converting.Lamp oil was made from olives for rather a long time before petroleum was refined in an industrial process. No reason to think plant-based fuels like lamp oil, fruit-based sugar alcohol, etc, wouldn’t be developed at an accelerated rate in a world with no mineral fuel sources.
It's probably just as realistic to use charcoal, in terms of yields per hectare, the effort needed to make it and the applicability for heavy industry. But I consider charcoal part of the medieval fantasy setting.