Your choices:
1 Comfortable indoor climate; 2 Local cooling (ind house); 3 Sunshine
| What is your resource? | What do you want to deliver? | What is the service the customer wants? |
| Biomass (digestible sludge) | District cooling | 1 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) |
| 3 Sunshine | Fuel: Liquid | Process heat (150 - 1000 °C) |
| Water | Fuel: Solid | Process heat (> 1000 °C) |
| Wind | 2 Local cooling (ind. house) | Transport |
| Residual oils/fats etc | Local heating (ind. house) |
Opposed to geothermal heating systems will a solar heating system not automatically provide the opportunity for cooling. Solar-drive absorption heat pumps are available but will usually not be able to defend their own cost in small-scale applications.
Instead, to cool down the indoor air, air-conditioning must be installed. Air-conditioning units for the private market basically consist of compressor heat pumps and to cool away 2-3 kWh of surplus heat from the indoor air they will require the addition of about 1 kWh of electricity.
If situated in a sunny climate – and the cooling needs will always be most pronounced when the sun is shining bright – roof-mounted solar cells may well provide a significant amount of the marginal electricity needed for cooling.
Solar cell electricity production suffers mainly from three limitations:
- First the intensity of solar irradiation is limited and only scarcely exceeds 800 W/m2 as measured on a surface oriented at a right angle to the incoming sunlight.
- Second the sun does not always shine bright and thus the intensity just mentioned is only reached during a limited number of hours.
- Third the actual efficiency with commercial solar cells is today less than 20%.
The net result of this is that only scarcely can more than 160 W of electricity be produced per m2 of solar cell area. But on the other hand, this electricity will be synchronized with the need for cooling purposes. Assuming 6 h at a mean production of 150 W/m2, the total will be 0.9 kWh/m2 which may – provided a large enough array – well be a significant contribution.