Micro Hydro Intake

[Marylouise Colleen]

Debrisand coarse sediment wreck havoc on micro hydro systems. The smaller orifices in these turbines can easily become plugged and the jets, which direct water to a pelton wheel or impeller, eroded and worn by any sediment in the water.

Our micro hydro diversion screens can help protect your investment, reduce maintenance costs, and insure continuous turbine operation. If you have ever walked up the hill to take leaves, pine needles and trash off an inferior intake screen, you have an appreciation, and need, for a self-cleaning intake screen from Hydroscreen.

Beyond debris and sediment, regulations often require that all diverted water be screened to exclude the passage of fish into the penstock and through the turbines. Our screens will exclude all fish from your diverted water, guaranteed. Their effectiveness in this regard has been shown by numerous case studies (references will be furnished upon request).

Hydroscreen has furnished micro hydro diversion screens to a number of leading pelton turbine manufacturers such as Canyon Industries of Deming, Washington. From the smallest to the largest pelton turbines, the removal of damage causing debris and sediments is a prime design consideration for Hydroscreen.

Submerged Intake Structures, as the name suggests, are fully submerged in an upstream lake or impoundment. They need a certain water depth (depending on intake size) to ensure the penstock will not pull in air, which could negatively affect system operation and efficiency. Submerged intakes are less prone to freezing of the lake as water flow remains constant underneath potential ice layers on top of the lake. They also are less prone to clogging, as much of the debris floats closer to the water surface than deep below. Submerged intake structures allow efficient flow regulation into the micro-hydropower system as well as down the waterfall. They are usually located at a deep location within the lake, making installation and repairs complex.

Exposed Intake Structures are located closer to the edge of the lake (or impoundment) or at least upstream of the waterfall within the stream bed. Size, shape, and location depend on the site-specific requirements but are mostly concrete boxes with openings towards the center of the lake. Trash racks and screens prevent floating debris and fish from entering the penstock sized for the site-specific requirements. Freezing can cause intake blockage. Maintenance staff will perform regular cleaning and clearing of the trash rack to ensure efficient water flow.

Exposed intake structures can be installed in combination with a partial dam removal or dam breach. The remainder of the old dam structure can help direct a larger amount of flow towards the intake structure while creating a free-flowing stream environment that is not preventing fish migration. Nuisance and high-priority dams can be removed without giving up the potential to generate renewable energy.

Collecting Intake Structures can be installed at an upper location on the waterfall, or above the waterfall in the stream. Designed correctly, they are mostly self-cleaning and low maintenance.

The penstock connects the intake structure with the turbine system. For micro-hydropower installations, the preferred material is HDPE (high-density polyethylene), a plastic that is durable, cost-effective, and light-weight. Even pipes of up to 18 inches (interior diameter) can be cut and installed manually without heavy construction equipment. This ease-of-use is important in uneven terrain near the waterfall as it limits costs and minimizes the environmental impact of system installation.

Besides its conveyance function, the penstock can also act as a water reservoir for smaller turbines, which helps minimize losses within the system as losses are proportional to the water velocity within the pipe: a larger pipe reduces the water velocity and thus friction losses. Instead of running a small diameter pipe all the way, the diameter should be reduced close to the turbine. The higher the elevation change, the higher the necessary pressure rating of the penstock. Piping manufacturers offer different wall thicknesses and coupler mechanism to address increasing pressure requirements. Standard lengths of pipe sections are 20, 40, or 50 feet but can vary by manufacturer.

The local site parameters (head, flow, space) and the goals of the site owner dictate the turbine technology. The microhydrony.org-website offers additional guidance with a decision-making framework of how to choose the right turbine technology for your site.

Interconnection refers to the connection of the micro-hydropower system to the public utility grid. The interconnection allows excess energy from the hydropower system to flow to the local power grid. In turn, the interconnection enables the grid to provide electricity to the site owner if local energy consumption exceeds generation output.

But if the potential energy generation from the hydropower system in conjunction with other local renewable energy sources is either under or over the local energy consumption, it makes sense to interconnect with the utility grid. Smaller systems can be added to an existing grid-connected meter. Larger systems (above 30 kW capacity) might need upgrades to the existing utility line or meter. More information about the possible ways of selling hydroelectricity in New York State is found under Financial Models.

In the natural setting of waterfall, picking the best location for the intake and outlet is key: In a dam-free scenario, the design team will locate the outlet location somewhere near the bottom of the waterfall. But the intake location could be at any elevation along the waterfall, depending on the site-specific parameters. The intake should be located as high as possible to maximize power output, but, depending on the local topography, the shape of the waterfall and the flow direction, might require the design team to locate the intake further downstream. In general we are looking for a minimum head of about 13 feet, even though there are turbine technologies that can work with less.

Hydro engineers use a flow duration curve (FDC) to estimate flow availability over the course of a year. To create a flow duration curve, they use daily flow data from previous years, sort the data points from large to small, and then display the result as a percentage on a time axis. These percentages identify expected minimum flows, e.g., a flow of X or more occurs 50% of the time (at the 50%-mark). In other words, the FDC allows the reader to see the frequency of occurrence of the average flow exceedance value / the minimum expected flow availability.

Adequate flow estimates are only the first step, as in a natural setting, not all of the available flow is necessarily usable in a dam-free microhydro scheme. Depending on the design of the intake structure and the topography of the stream near the intake location, the actual usable flow might be significantly less than the available stream flow. This is a challenge that does not exist in the dam-setting, since the relationship between usable flow and available flow can be regulated using a simple valve or gate.

While sufficient head and flow are the obvious two requirements for a micro-hydropower system, other site-specific requirements need attention: the site needs allowance for intake structure installation, it needs space for a penstock and/or stilling chamber (forebay), a location for the turbine, a generator, and electrical equipment. Some sites might require a powerhouse enclosure as well.

These requirements might limit the usable head of the site because either intake or outlet need to be located at energetically less favorable locations. They might also limit the amount of flow that can be used for energy generation by restricting the intake structure. In the worst-case scenario they might prevent the installation of a dam-free micro-hydropower system all together.

So if one wanted to define the ideal topographic setting for a dam-free micro-hydropower project, it would be a steep waterfall with a natural lake at the top as well as at the bottom of it. The lake at the top side is providing penstock inlet submergence similar to the dam/impoundment setting; the lake at the bottom allows bypassing the waterfall most directly, without creating a bypass reach or aesthetic visual impacts (visible intake structure, penstock). Such a setting also guaranteed enough space for intake and outlet structure on either end of the penstock, while the system can be located closer to a possible interconnection point with the utility grid.

But if you want to design your own dam-free micro-hydropower system or at least get a sense of the overall feasibility at your waterfall, you will have to know a bit more about the design and key aspects of the necessary components of a dam-free micro-hydropower system. So read on: Part 2, Design Components .

Micro-hydro power is one of the most reliable and consistent sources of renewable energy available. A good water resource with a year-round flow and several feet of elevation drop can provide years of continuous power.

This introductory publication discusses the steps necessary to develop the potential power in a water resource. It does not, however, provide answers to the technical questions you may have about developing a micro-hydro power project. You will want to refer to a more technical do-it-yourself ATTRA publication, Micro-Hydro Power: A Beginners Guide to Design and Installation, if you are planning to install your own micro-hydro system.

Head is usually defined as the vertical distance between the point where you will collect water (the intake) and the point where you will install a turbine. There are usually only a few possible locations near the water resource for the turbine and generator, while there may be several possible locations upstream for the intake.

Flow is the volume of water that can be temporarily diverted to the hydro turbine. It is usually measured in gallons per minute (gpm) or cubic feet per minute (cfm). Keep in mind that it is best to take as little water as possible from the source.

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