Your choices:
1 Sunshine; 2 Comfortable indoor climate; 3 District heating
| 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) | 3 District heating | Electricity |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| 1 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) |
The district heating system will never be based on solar energy but solar energy may well play a significant role.
The quality of a district heating system is determined by
- Its capacity to provide each and every customer with the thermal power they demand at any instant
- Its capacity to provide each and every customer with a sufficiently high temperature so as to guarantee that the sanitary limits can be fulfilled with each and every customer
In case solar energy is a major share of the total input, as it may well be during summer when the sun is shining and the heat demands are low, and because the intensity of solar radiation is rapidly varying, the demand for a rapid top-up capacity to maintain temperature levels becomes crucial. In reasonably large district heating systems, the travelling time for the water in the distribution loop amounts to several hours and it is crucial that the temperature control starts early enough and has sufficient capacity to hinder temperature drops even if the sun suddenly disappears and the temperature drops.