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Moisture destroys biomass fuel value twice: it dilutes the dry matter and it consumes 2.443 MJ per kilogram of water evaporated. As-received calorific value is dry value x (1 - moisture) - 2.443 x moisture, so wood at 50% moisture has less than half the usable energy of the same weight at 10%.
As-received calorific value
CV_wet = CV_dry x (1 - moisture) - 2.443 x moisture
Electrical output
MWh = energy (GJ) x conversion efficiency / 3.6
Biomass combustion emits particulates and nitrogen oxides and is subject to air quality permits. Sustainability and carbon accounting rules also apply to fuel sourcing.
Reducing moisture from 50% to 30% raises as-received calorific value by around 55% and improves boiler efficiency and combustion stability. Natural air drying is often nearly free.
25-32% electrical for a dedicated steam plant, which is low because of steam parameter limits from ash and chlorine. Combined heat and power raises total utilisation to 75-85%.