Your choices so far:
1 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) | Electricity | Process cooling (< 0 °C) |
| Geothermal | Fuel: Gaseous | Process heat/steam (50 - 150 °C) |
| Sunshine | Fuel: Liquid | Process heat (150 - 1000 °C) |
| 1 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 basically exergy and since this is also the form of energy in electricity, water shall be used to produce electricity and basically nothing else.
The energy in moving water can take different forms:
- Wave energy. Along the European west coast, to the Atlantic, several places are suitable for wave energy power stations. The prerequisite is that the normal wave height is big enough, ate least 1-2 m. However, in this material we will not mention this kind of installations.
- Tidal energy. With tidal energy, the most common way is to allow the tide to fill a reservoir and then empty it again through a set of turbines. Also during filling may the water be directed through the turbines. For this to be feasible the tidal range must at least be a few meters and this is the case only in few places along the European coastlines. Again, this type of installations will not be mentioned any further.
- Pumped hydropower stations. With these, 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 through 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 still 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. The requirement for a pumped hydropower station is basically that the landscape provides a large enough and high enough hill or mountain to host a sufficient reservoir at its top and that the height is enough for a power station to be feasible. There must also be a recipient river in the vicinity.
- Power stations with a dam. This is the "traditional" hydropower station where a dam blocks, partly or completely, a river flow so as to (1) provide a water reservoir with a sufficient volume and (2) maintain a constant height (head) so that there is a height difference across the turbines. The total efficiency in this type of hydropower installations – i.e. the ratio of produced electricity to latent energy in the water – often exceeds 95%.
- Submerged power stations. This type of hydropower stations can be described a as a chubby submarine anchored at a river bed. Just like the common wind power stations, these make use of the flowing water in the river and may be virtually invisible. Like with common wind turbines, these will suffer from the limitation known as "the Betz limit" and the theoretical maximum electricity output amounts to approximately 60% of the total energy in the flowing water.
The 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.
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.
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.