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How a Hydro Site Works

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.

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 energy of water flowing from a high point to a low point. The first step to harnessing this energy is to divert a small portion of a stream. In this picture you can see an intake, which is designed to divert the proper amount of flow. 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 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 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 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 picture 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 an nozzle and turbine, enclosed by a powerhouse, at the bottom.

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 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 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.

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!

Joey

2 Responses to How a Hydro Site Works

  1. Zat Winarko October 1, 2013 at 10:04 am #

    Nice info Joey.
    Can you explain how to design penstock and nozzle in my case below?
    In my final project I have value of “rate of flow is 20 m/s3″ and “head 60 m”.
    So I devide “rate of flow” into 3 part (absolutely with 3 turbines).
    I choose Francis turbine…
    Thanx…

    • Joey Anthony January 27, 2014 at 3:17 am #

      Hi Zat,
      The flow rate, head and nozzle diameter are all interconnected. So when you know two of the values, the third is automatically set. The relationship is described by the mechanical energy equation (http://www.engineeringtoolbox.com/mechanical-energy-equation-d_614.html).
      You also will want to look at the manual for the turbine that you choose. It will probably list different power outputs based on head and nozzle diameter. Also, it will probably come with nozzles of certain sizes. You may have to use one of there predetermined sizes, and then the flow rate would change based on that. You may need to send some water through an overflow because the nozzle will not allow any more water through.
      As for designing the penstock, the maximum static pressure will be P=density*gravity*height. That will be the maximum pressure if you have a shutoff valve that shuts very slowly. If the valve stops water flow quickly, then you will have to consider water hammer effects (http://en.wikipedia.org/wiki/Water_hammer). I hope that helps! Good luck with your project.

      Joey

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