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 | Electricity |
| Biomass (solid) | 2 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) |
Producing electricity as the energy carrier from fermentable biomass is not a very suitable process.
The primary product from fermentation is a dilute alcohol which is in itself not combustible. To make this dilute alcohol a combustible, liquid fuel, it must first be distilled. The result of this is a liquid fuel, > 90% ethanol, which is suitable for internal combustion engines (IC-engines) with spark ignition (i.e. Otto engines).
This opens up for two major routes:
- Either the ethanol can be offered as a gasoline additive and used for transport
- Or the ethanol can be used for CHP production in a stationary IC-engine
The first option is the one most used and the reason for that is that the willingness to pay for transportation fuels is generally higher than the willingness to pay for CHP-fuels. The distillation process becomes rather expensive as expressed per kWh of produced ethanol, so the product needs to be sold on a market where price sensitivity is not too high.
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 a third 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.
Since neither price nor efficiency thus speak for this process route, it cannot be recommended.