Your choices so far:
1 Biomass (fermentable sludge); 2 Electricity
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| Biomass (digestible sludge) | District cooling | Comfortable indoor climate |
| 1 Biomass (fermentable sludge) | District heating | 2 Electricity |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | Process heat (150 - 1000 °C) |
| Water | Fuel: Solid | Process heat (> 1000 °C) |
| Wind | Local cooling (ind. house) | Transport |
| Residual oils/fats etc | Local heating (ind. house) |
Fermentable biomass sludge does not lend itself well for electricity production, since the primary product becomes a dilute alcohol that has to be distilled to become a viable fuel. Due to the cost for the distillation, the final fuel, ethanol, will be relatively expensive and therefore it should be used exclusively in such processes where the total efficiency is high or where the price sensitivity with the end-user is low.
The efficiency from fuel energy to mechanical energy (i.e. to exergy) in an Otto engine is about 35% and this is the maximum amount of electricity that can be produced from ethanol in case this route is used.
Theoretically there will be another route, and that would be to burn or to co-combust the ethanol with oil, gas or some other fuel in a steam boiler and then to use a steam cycle to produce electricity. Again the efficiency throughout this route will be low.
In case ethanol is produced for – say – transportation fuel, a certain buffer volume might be set aside for use in a local, stationary IC (internal combustion) engine to be used for local CHP production in emergency cases, but a constant electricity production based on locally produced ethanol is likely to be non-profitable.
The prime energy carrier from fermentable biomass, ethanol, is not well-suited for local electricity production so a customer requiring the unique properties of electricity would not be likely to buy ethanol to supply their need.