Your choices so far:
1 Electricity; 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) | 1 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 | Local heating (ind. house) |
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. Considering that a normal toaster or a vacuum cleaner requires 5-700 W one will realise that to provide sufficient electricity for a normal household, there will be a need for quite large areas of solar cells.
Though solar cells may well contribute to the electricity supply in a single building they are not likely to play a major role in the European electricity balance.
Solar cells also produce low-voltage direct current and to deliver to the grid an inverter must be placed between the photocell array and the grid to transform the low-voltage DC into 230 V AC if the electricity is used locally, inside the building. Just like with small-scale biogas or wind-power generation may the solar cells be connected “behind” the meter so that the electricity produced in the first instance represents a saving rather than an income. The inverter will introduce a loss into the system, a loss representing 2-5% of the total electricity produced by the solar cells.
Hence, electricity production from solar cells should primarily be seen as a local affair in the individual building rather than as a commercial or large-scale enterprise. This means that solar cell electricity will not generally be considered as the bas supply for any larger industrial applications.