Your choices so far:
1 Biomass (solid); 2 Comfortable indoor climate
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| Biomass (digestible sludge) | District cooling | 2 Comfortable indoor climate |
| Biomass (fermentable sludge) | District heating | Electricity |
| 1 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) |
In case the supply of a comfortable indoor climate is the main purpose of the energy supply system and the source is solid biomass, there will be two major system solutions to choose between:
- The first alternative is to equip each individual building with its own, complete, energy production system and then see to that fuel can be distributed to the individual houses.
- The second alternative is to set up a central energy production unit and then see to that the energy required for climate control can be distributed to the individual houses.
The first system – fuel distribution and de-centralised energy production – is still very common even in densely populated areas like city centres and is sometimes motivated by the accessibility of natural gas. The advantage by this type of system is that the individual building is completely independent and that any energy- or fuel-saving initiatives taken in the individual building will immediately reflect on the fuel bill. The disadvantage is that the individual boiler units will, by necessity, be small. The individual boilers will have no flue gas cleaning, they will have a rather simple combustion control system and their efficiency will not be the highest. In the case of pellet firing in the individual buildings, this may well lead to air pollution problems and this will be even more pronounced in the case of wood-log firing. Finally, each building will have to assign the responsibility for the indoor climate to someone, someone who is usually not a professional energy engineer.
The second system solution – centralised energy production followed by energy distribution – has the advantage that the central energy production unit becomes large and may carry the cost for professional personnel, advanced combustion control and sophisticated flue-gas cleaning. With a large production unit (10-15 MW thermal or larger) there will also be the option to co-produce district heat, district cooling and electricity in the same plant. Finally, a large-scale boiler unit will have a certain flexibility with respect to fuel so that it can make use of cheap or seasonal fuels in a way that a system based on the distribution of one specific fuel quality has not. The disadvantage is that the individual building will be "hooked" onto a communal energy distribution network, the rate of which will to a great extent be fixed because of the distribution network so that energy saving measures in the individual house will only reflect to a minor degree on the monthly bill.
For systems based on solid biofuel, the second option is always the preferred one in densely populated areas while modern pellet or wood-log heating systems may be accepted in countryside areas.