Enter your cost of coal and the typical NCV in GJ as well as the biomass you are looking at. This calculator takes into account the NCV difference and uses 100kg of CO2 produced per GJ of coal. So, assume 2.5 tonnes of CO2 on a coal with 25GJ.

This does not take into account any local taxes or emissions duties.

This takes the cost of coal and its associated emission factor for CO2, using the December EU EUA

DDP/CPT cost of coal + (emission factor * EUA) = total cost of coal.

Take this total and normalise the costs given the NCV difference. For example: 22GJ coal and 17 GJ biomass.

 Breakeven = Total Cost of Coal  * 17/22

All things being equal, this should be the centre of the indifference curve.