Your choices so far:
1 Electricity; 2 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 | Process cooling (< 0 °C) |
| Geothermal | Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | Process heat (150 - 1000 °C) |
| 2 Water | Fuel: Solid | 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 traditional hydropower station where a dam blocks, partly or completely, a river flow so as to provide a water reservoir with a sufficient volume and maintain a constant height (head) so that there is a height difference across the turbines. It is the most efficient way to produce electricity with total efficiencies often exceeding 95%. No other technology comes even close to this. 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.
Hydropower – together with solid biomass – are dominant when it comes to the use of renewable energy sources worldwide as well as in the European energy balance. There are also a large number of abandoned and closed-down micro-power stations all around Europe that can again be restored and brought into operation. Though the resource is already used to a great extent – it is thus not yet exhausted.
One main characteristic for hydropower electricity production using the traditional technique, with a dam, is that it is fast and simple to control. The flow of water through the turbines may be controlled within seconds or minutes and therefore hydropower stations are used to balance the electricity grid.
Pumped hydropower stations work so, that water is pumped from low level to a high level reservoir during the part of the day when the demand for electricity is low. As the demand then peaks, the water is again allowed to flow down from the reservoir through the pumps – which then act as turbines – and electricity is produced.
It is obvious that since there will be losses of energy during the pumping and since there will again be losses during the electricity generation process, a pumped hydropower station will always be an energy loss. However, since it makes use of "surplus" electricity and then supplies power during peak periods, it may s till defend its place in in an optimised energy system. A possible role for pumped hydropower is for example to store "surplus" electricity from intermittent sources such as photoelectric or wind electricity.
Pumped hydroelectricity power stations have so far not been realised in any commercial scale worth mentioning.