Harmonise efficiencies for biomass combustion

[millingermarkus]

@toniseibold:

For medium temperature heat the biomass route has an efficiency=costs.at["direct firing solid fuels", "efficiency"] which equals 1. The low temperature heat biomass route has an efficiency=costs.at["solid biomass boiler steam", "efficiency"] which equals 0.89. This would mean that biomass to low temperature heat is less efficient than biomass to medium temperature heat.

This stems from DEA technology data and appears to be inconsistent in this case. There is an option for a condensing steam boiler, but that would not apply to the bulk of steam usage which is at higher temperatures. Other data could possibly be found from a UFZ/DBFZ database on biomass applications.