Gasification of woody biomass waste streams (walnut shells, wood chips, corn stover, bigasse) is quite renewable, and can be run 24/7 regardless of weather. The CO2 emmitted comes from the atmosphere and therefore is cyclical in nature (thus sustainable). If you take biochar into account the carbon generation is actually negative, as you have carbon left over that can be used for other things or put back into the soil in a form that is stable for thousands of years and beneficial to the soil quality for life.