I realized as I was writing a post about civil works construction that it might be good to refresh the readers on the technical workings of our hydro systems. To briefly explain, we have two pico hydro sites in Banda, Rwanda and one in Rugote, Rwanda, each of which generate under 1kW of continuous electrical power to charge batteries. The power is generated by diverting some water from a steam on top of a hill and sending that water, at high velocity, through a turbine at the bottom of the hill. Here are some pictures and captions to help explain each component of the system in more detail:
This diagram from the DOE provides a good overview of the components that I’m about to describe. Please note a few differences in terminology. What they call Canal, I call Channel and what they call Forebay, I call Settling Tank. Also note that our systems charge batteries and do not transmit power through power lines like on this diagram.
Step 1, Intake: Hydo sites generate electricity by harnessing the potential energy of water at the top of a hill. The first step to harnessing this energy is to divert a small portion of a stream. In this picture you can see our intake, which is designed to divert the proper amount of flow from the stream. In this case, we are doing construction on the system, so water is not flowing through the intake, but normally, about 10% of the water enters the cement intake in the photo and continues on to the channel.
Step 2, Channel: Once the proper amount of flow is diverted from the stream, it must be transported to a suitable spot on the hillside so that the settling tank, penstock and powerhouse can be constructed. The channel is just a gentling sloping, man-made stream that transports the water.
Step 3, Settling Tank: At the end of the channel, the settling tank separates out sediment from the water that is about to be sent to the turbine. Large sediments can damage the turbine. The settling tank is essentially just a big tub where sediments fall to the bottom, and clean water enters the penstock.
Step 4, Penstock: The penstock is a pipe that transports water from the settling tank down the hillside and to a nozzle that shoots high speed water into the turbine blades. Unlike the channel, the penstock is steep and totally closed by high-pressure piping. It is difficult to get a photo of an installed penstock since they are normally underground, but this picture of us installing an overflow pipe is almost exactly what a penstock installation would look like. Imagine a settling tank at the top of the pipe and a nozzle and turbine, enclosed by a powerhouse, at the bottom.
Step 5, Nozzle and Turbine: At the bottom of the penstock, high pressure water is shot into the turbine blades to spin the turbine. You can see the end of the penstock coming through the powerhouse walls and into the turbine. Unfortunately the turbine casing keeps the nozzle and turbine blades hidden.
Step 6, Electricals: The electrical system takes mechanical energy of a spinning turbine and turns it into electrical energy stored in batteries. Maybe a more electrically inclined traveller can post a review of the electrical system at some point!
Step 7, Powerhouse: The powerhouse is just a place to put the turbine and the electrical system.
I hope that this was educational! Please comment with any questions that you have!