Your choices:
1 Electricity; 2 Process heat; 3 Water
| 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 | 2 Process cooling (< 0 °C) |
| Geothermal | Fuel: Gaseous | 2 Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | 2 Process heat (150 - 1000 °C) |
| 3 Water | Fuel: Solid | 2 Process heat (> 1000 °C) |
| Wind | Local cooling (ind. house) | Transport |
| Residual oils/fats etc | Local heating (ind. house) |
The energy found in moving water is mainly exergy and since this is also the form of energy in electricity, water shall be used to produce electricity and basically nothing else. The most efficient way to do this is by the use of a dam and then to have a completely enclosed channel including the turbine itself, letting the water out again downstream the dam. This is the most efficient way to produce electricity with total efficiencies often exceeding 95%. No other technology comes even close to this.
The dam may in itself cause a severe environmental impact depending on the local conditions but it may also be turned into a positive thing if only proper care is taken to install fish ladders and the water level in the dam is closely controlled. Examples can be found where the dam itself has successfully been marketed as a fishing lake and where tourism flourishes around a hydropower station. Also, micro-power stations – ranging only a few hundred kW or up – can often be integrated in old water-mills and hence also contribute to the maintenance of cultural heritage.
The turbine types preferred for this type of plants will range from Francis turbines in the smallest installations where the flow rate is low (say less than 1 m3/s) and the height difference is small (a few meters). When the flow rate exceeds some 5 m3/s, fixed or variable pitch propeller turbines are the main alternative as long as the height difference (the head) is not too big.
If possible – and to avoid interfering with the landscape – old installations should be restored into production order but it must be remembered that an old dam was designed for the flow and precipitation conditions once it was designed at that these conditions are rapidly changing because of the climate change. Therefore, the restoration of old hydropower stations may well also require a reinforcement of the dam.
In specific locations may submerged generators be of interest.
The grid operator will usually have no objections to the connection of a hydropower station since this is a relatively stable source of electricity.