Your choices:
1 Local heating (ind. house); Comfortable indoor climate; 2 Sunshine
| 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 | Electricity |
| Biomass (solid) | Electricity | Process cooling (< 0 °C) |
| Geothermal | Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| 2 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 | 1 Local heating (ind. house) |
Systems for the use of solar energy for heat are commonly separated into two different types:
- Passive systems: These are usually systems for low-temperature house heating where there are no special collectors for the solar energy but where the building architecture in itself provides the heating. Windows, extended roofs and – in some cases – massive building elements to store heat may be parts of such a system. But passive solar heating is not only to plan for solar energy to enter the building – it is also to hinder it when it is excessive and to maintain it in the building to the extent that is desired. The energy service is to provide a comfortable indoor climate – not to accumulate the most solar energy.
- Active systems: Active solar heating involves concentrating the irradiation by aid of mirrors, lenses or specially designed collectors to provide higher temperatures. But these systems will usually still be designed for space or tap-water heating. Also heat pumps may be used to achieve higher temperatures and such systems would also be classified as active.
The first and foremost way to use solar energy to provide space heating in individual buildings will be through passive heating. Making use of passive heating in a building is a question of the building architecture and of the general layout of the building.
As a complement to passive heating, solar collectors for hot-water production may be placed on the rooftop to provide space heating and tap water. Using the simplest, and cheapest, flat-plate, glazed, collectors may provide water at 30-35 °C during sunny winter days while the temperature may reach 80 °C during summer. For tap-water production, where temperatures must exceed 50 °C for sanitary reasons, the winter temperature is obviously not enough while during summer the temperature may well exceed the safety limit for scalding.
With the more advanced vacuum-tube solar collectors you will reach higher but more stable temperatures, but the price paid is that they are significantly more expensive.
The third and most advanced option is to use a low-temperature solar energy collector, such as a water-tube immersed 30-50 cm under-ground or in a pond, and then to make use of a heat pump to raise the temperature to the desired level for tap-water production and for space heating.
With the two first system solutions, the area for the solar collectors is usually restricted to the roof area of the house and with multi-storey buildings this will usually not be sufficient for the energy needs in the building. With a one-storey, single-family house, though, may solar heating well provide the main part of the annual energy needs for heating.