4 – Woodwork in Šumava and the Bavarian Forest

Hydroelectric power is a form of renewable energy, meaning it has the ability to either partly or wholly renew itself. Apart from hydropower, renewable energy includes solar, wind, or biomass power. Hydropower is sourced by taking advantage of the permanent water cycle on Earth. Hydroelectric power stations use both the water’s potential energy, which is dependent on the difference in height through which the water falls, as well as its kinetic energy, which depends on the speed of the water flow. The water coming into the power station gives this energy to the turbine, which begins turning the generator connected to it via a shaft. With the use of electromagnetic energy, the mechanical energy of the generator’s rotor then turns into electricity.
The turbine’s output is mainly influenced by the fall gradient, the flow rate, and the turbine’s efficiency. The most important part of the turbine is the runner. A number of types of turbines were developed over the years. Here in Dlouhá Ves, they use a Francis turbine, a type of pressured turbine where the water enters horizontally in a spiral case wrapped around the runner. It is the longest used modern turbine. Other types include the Kaplan, Pelton, or the cross-flow turbine. Depending on their output, we differentiate between small hydropower stations such as this one (output to 10 MW), medium stations (100 MW) and large stations (over 100 MW). The local power station can also be classed as a low-pressure one, given its small fall gradient (up to 20 metres). Another attribute which classifies the power station is the way it uses the water course. The Dlouhá Ves power station is run-of-the-river (ROR) and derivational, meaning that the used fall gradient is created by a shortening of the riverbed with a canal.
By the end of 2017, Czech Republic had 1457 small hydropower stations, over 1000 of which were added after 1989. The combined output of these plants is 351 MW. On the 112 km long Otava river alone, 22 hydropower stations with the combined output of 3,6 MW have so far been built. With an installed output of 334 kW (real output 270 kW), the Dlouhá Ves power station is the second most efficient and has the highest yearly output (2,166 GWh).
Other parts of a small hydropower station include a feeding canal which leads the water to the turbine, a trash rack which prevents debris and mechanical impurities from entering the turbine, and an output canal returning water back into the riverbed.
The weir, which lifts the surface of the Otava river and thus diverts the necessary amount of water into the feeding canal, is largely made out of a water-filled rubber cylinder. At its beginning stands a floodgate, which regulates the inflow of water and protects the power station from floods. The feeding canal itself is 970 meters long and the water in it flows at a speed of over 3 m/s. The height difference between the surface of the canal and the surface of the Otava river is almost nine meters. Before the feeding canal enters the power station, a slant pillar diverts ice or floating debris away from the station. Another barrier preventing the inflow of unwanted materials into the turbine is formed by coarse screens, which are cleaned out with rakes. The former engine room was equipped with a synchronous generator, but the current one has an asynchronous one. Next to the engine room is the power station’s control centre, which, among other things, supplies electricity to the neighbouring factory.