Your choices so far:
1 Sunshine; 2 District heating
| 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) | 2 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) |
District heating is distributed by the aid of hot water or, in some cases, steam. Most common is the distribution of hot water. District heating systems can accommodate a large number of different energy sources – including solar energy.
With a solar panel, collection efficiencies well in excess of 90% are common and supposing then that the panels are oriented at a right angle to the sun and that the incident radiation is 800 W/m2 one may collect a bit more than 700 W/m2. Further assuming that the district heating system needs 7 MW we find that 10 000 m2 of solar collectors will be needed to produce the thermal power decided.
Solar heating systems for district heat applications thus tend to become quite big. Their production capacity will also be unpredictable since weather conditions tend to play a major role with respect to incident sunshine. Thus solar heating systems cannot be trusted for baseline production in district heating systems but may only serve as a complement to easily controllable, preferably fuel-fired, heating.
The main advantage with solar heat production is – besides its obvious environmental advantage – the low operational costs. To increase the total annual production, the panels should be mobile so that they follow the sun but doing that will increase the complexity and the maintenance costs and is only scarcely worthwhile.