Your choices:
1 Biomass (solid); 2 Electricity; 3 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 |
| Biomass (fermentable sludge) | District heating | 2 Electricity |
| 1 Biomass (solid) | 3 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) |
In the case that your customers want to buy electricity and that the sale of electricity is also your prime business idea – you should not use solid biomass as the resource for the production.
Producing electricity from solid fuel using today's technology will result in the main part of the fuel energy input to be converted into heat while only a minor part of the energy input will actually be converted into electricity. Thus, your business idea should be based on selling the heat and then to maximise the electricity production based on the heat production. So the size of the heat sink will be the determining factor for the size of the plant – and only if the heat sink is large enough will the co-production of electricity be economically feasible.
To maximize the electricity production based on a certain heat sink, you may want to look at more advanced technologies such as BIGCC. This technology, thermal gasification, integrated in a large-scale CHP or tri-production (heat, electricity and district cooling) plant opens up for an increase in the total electricity efficiency. The reason is that if the fuel is first gasified and the gas is then cleaned from ash components (the gas cleaning is still the bottleneck in this process concept), then a so-called "combined cycle" can be used for the electricity production.
A combined cycle power production process first releases the fuel energy in a gas turbine, then makes use of the hot flue gases from the gas turbine to produce steam, uses the steam in a steam turbine and may finally produce district heating from the steam turbine outlet.
The drawback is that gas turbines are very sensitive to deposition on and to erosion of the turbine blades and in the case of a gas turbine the blades are directly exposed to the flue gases from combustion. The fuel must therefore be free from ash and from such impurities that can form corrosive gases. Solid biomass, as well as sorted waste fractions or indeed any solid fuel are thus effectively excluded as gas-turbine fuels while clean converted fuels such as bio-methane, bioethanol or clean gasifier gas can well be used.
Though the gasification process in itself will induce energy losses and though the gas cleaning necessary to protect the gas turbine will also induce energy losses, the whole process may still be advantageous from an electricity efficiency point of view. However, to be feasible, this is only viable in large scale (more than about 100 MW thermal) and has, so far (2013), not been demonstrated in commercial applications.