Your choices so far:
1 Sunshine; 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 |
| 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) |
A comfortable indoor climate is maybe the most common energy service and is one of the most important ones.
Apart from illumination – which is one component of indoor climate – solar energy is mainly used for space heating and for tap water production.
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 the summer 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.
In case the interior climate control in a building is based on air conditioning using compressor heat pumps (the most common) and in case the building is equipped with solar cells and in case the solar cell array is equipped with an inverter so that the solar cell electricity is fed into the internal 230 V electricity net, then will the electricity produced by the solar cells contribute to maintain a comfortable indoor climate – when the sun shines. However, and due to the low efficiency with commercial solar cells and to the "dilute" nature of solar radiation – except special conditions – the electricity produced from solar cell arrays is usually not near the demands for indoor climate control.
A solar cell array may also be used for an immersion heater in the tap-water heating system. Such immersion heaters are also available for DC/24 V. The advantage, as compared to a solar panel water heater, will be the ease of installation – the disadvantage will be the price and the low efficiency.