Designing a Microhydro System

Intermediate

Inside this Article

Nice stream
This looks like a great stream with microhydro potential.
ES&D Stream Engine
An Energy Systems & Design Stream Engine
HiPower turbine
This 1,200-watt HiPower induction turbine is mounted in a plastic barrel bottom. If there’s a water resource at your site, hydro can be one of the most inexpensive and reliable renewable energy options.
There are as many possible intake designs as there are varieties in flow rate, stream topography, streambed geology, and debris loads.
Another HydroScreen intake
There are as many possible intake designs as there are varieties in flow rate, stream topography, streambed geology, and debris loads.
Another HydroScreen intake
When planning your intake, consider seasonal variation in flow and debris, both for the protection of the turbine, runner, and penstock, and for the intake itself.
Measuring pipeline length
The penstock may or may not follow the path of the stream. Measuring vertical drop is an independent process necessitating a sight level, or accurate GPS or topo map.
Measuring flow
Flow can be measured by the time it takes to fill a container of known volume. Some streams require calculating flow based on the stream’s cross-sectional area and speed of current.
Microhydro overview illo
Microhydro system overview
Welding poly pipe
High-density polyethylene pipe for penstocks can be welded, reducing the cost and friction loss of using couplers or other connectors.
Flume and hydro
A low-head system may use a flume for a penstock, especially in a location where all of the drop occurs in a short horizontal distance.
Pipeline thrust block
A thrust block at the bottom of the penstock keeps the heavy water-filled pipe from sliding downhill.
Tailrace with runner
At the end of the line—a Pelton runner turbine is tilted up to show the “tailrace,” where waste water falls away from the spinning runner to prevent interference with incoming water. Commonly, water is returned to the stream.
Harris Hydro
A four-nozzle Harris Hydro turbine, with Pelton runner.
ES&D impulse turbine
The ES&D Water Buddy impulse turbine is designed for low-flow applications, and has a 2-inch-diameter runner and 200-watt maximum power output.
PowerSpout turbine
A reaction turbine like this PowerSpout LH places the runner within a falling column of water, perfect for low-head applications.
Reaction turbine runner
Reaction runners come in various styles like this propeller type.
Crossflow turbine runner
This impulse machine is a crossflow runner.
OutBack hydro BOS equipment
Unloaded, hydro turbines can be damaged by overspinning. Off-grid hydro systems may use battery-based inverters and diversion-capable charge controllers to shunt extra energy to dump loads—usually air or water resistance heaters.
AC hydro power plant
AC-direct hydro units like this HiPower unit often employ induction alternators to match AC waveform with the grid.
Hydro control system
Off-grid AC-direct hydro systems require specific electronic controls to variable dump loads to ensure that all of the generated electricity has a place to go.
Dump load
An Alternative Power & Machine air resistance heater (dump load) with protective cover.
Meter on a hydro system.
Various types of analog and digital metering can tell you a lot about how your hydro system is functioning—if you know how to interpret the readings.
Pressure gauge on penstock
Various types of analog and digital metering can tell you a lot about how your hydro system is functioning—if you know how to interpret the readings.
ES&D meter
Various types of analog and digital metering can tell you a lot about how your hydro system is functioning—if you know how to interpret the readings.
Huge & tiny Pelton wheels
Hydro is a scalable technology, dependent only on the size of the resource: Coauthor Ian Woofenden sits on a couple of large Pelton runners at Canyon Industries, while holding a small one in his hands.
Nice stream
ES&D Stream Engine
HiPower turbine
Another HydroScreen intake
Another HydroScreen intake
Measuring pipeline length
Measuring flow
Microhydro overview illo
Welding poly pipe
Flume and hydro
Pipeline thrust block
Tailrace with runner
Harris Hydro
ES&D impulse turbine
PowerSpout turbine
Reaction turbine runner
Crossflow turbine runner
OutBack hydro BOS equipment
AC hydro power plant
Hydro control system
Dump load
Meter on a hydro system.
Pressure gauge on penstock
ES&D meter
Huge & tiny Pelton wheels

The energy in falling water can be a reliable and economical source of electricity for homes and businesses. This natural and recurring energy is a form of solar energy, since it’s the sun that drives the hydrological cycle, evaporating water, which condenses in the clouds and rains back down on us. While much of the potential energy is lost as the rain falls miles from the clouds to the land, there is still plenty to use as it makes its way down the mountains and hills to the oceans.

Basic Principles

Hydropower is a combination of vertical drop (“head”) and flow. There must be energy in the water that powers a hydro machine. The water has to be flowing downhill or at least moving—there is no energy in still water. These two parts of hydropower equally influence how much energy we can get.

To make significant energy:

  • If the water source doesn’t have much head, it will need a lot of flow
  • If the source doesn’t have much flow, it will need a lot of head

Unlike wind and solar energy, water power is limited by the source. You can always add more solar-electric modules or wind generators if you have a good site for these technologies. But at a hydro site, once you are using most of the available flow and head, you cannot add more collectors to reap more energy. Solar and wind systems are limited primarily by space available for the collectors, and the homeowner’s budget. While budget is always an issue, home hydro projects are most often limited by the actual resource (head and flow) on site.

For a typical small system, a useful formula for estimating available power is:

Head (in feet) × flow (in gallons per minute) ÷ 10 = power (watts).

This formula assumes an output efficiency of 53%, which is typical for small systems. For example, a system with 120 feet of head and 55 gpm of flow could yield about 660 watts of output. Multiplying by 24 hours means 15.8 kilowatt-hours (kWh) per day of potential production. This amount of electricity can provide an energy-efficient home with plenty of modern conveniences.

Sizing a system requires knowing how much energy you are using now and how much you’ll use in the future. Load analysis is a key part of any renewable energy system design process, and a hydro system is no exception. Calculating your current energy use, making a detailed load list of planned future energy use, and accurately determining the number of kWh needed per day will help you make a good plan for your hydro system.

Once you have a good load estimate, work a little harder to see if you can reduce it through conservation and efficiency measures. While some hydro systems produce a surplus of energy, it still makes sense to whittle your usage before you start. That may allow you to pare down all the system components—pipeline, turbine, transmission, storage, and electronics—which will shrink the purchase and maintenance costs. There’s usually no better money and time spent on an energy system than figuring out how to use less energy.

It’s also worth considering whether your hydro system will power your home completely, or if it will be supplemented by the utility grid, another renewable source, or even an engine-generator. Many hydro sites are limited—there is only so much water, and that might disappear in the summer or other dry times. Then, solar energy can be useful, since the dry periods usually coincide with the sunny times. If you’re off-grid, this makes for a rain-or-shine system. If you’re on-grid, you don’t need to make all your own energy, and this could affect your design choices as well.

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