Microhydropower

hydropowere_rev

 

Microhydropower

(source: energy.gov)

If you have water flowing through your property, you might consider building a small hydropower system to generate electricity. Microhydropower systems usually generate up to 100 kilowatts of electricity. Most of the hydropower systems used by homeowners and small business owners, including farmers and ranchers, would qualify as microhydropower systems. But a 10-kilowatt microhydropower system generally can provide enough power for a large home, a small resort, or a hobby farm.
96-inch-pelton-runner
A microhydropower system needs a turbine, pump, or waterwheel to transform the energy of flowing water into rotational energy, which is converted into electricity.

The Department of Energy’s page on planning a microhydropower system has more information.

How a Microhydropower System Works

Hydropower systems use the energy in flowing water to produce electricity or mechanical energy. Although there are several ways to harness the moving water to produce energy, run-of-the-river systems, which do not require large storage reservoirs, are often used for microhydropower systems.

For run-of-the-river microhydropower systems, a portion of a river’s water is diverted to a water conveyance — channel, pipeline, or pressurized pipeline (penstock) — that delivers it to a turbine or waterwheel. The moving water rotates the wheel or turbine, which spins a shaft. The motion of the shaft can be used for mechanical processes, such as pumping water, or it can be used to power an alternator or generator to generate electricity.

A microhydropower system can be connected to an electric distribution system (grid-connected), or it can stand alone (off-grid).
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Microhydropower System Components

Run-of-the-river microhydropower systems consist of these basic components:

  • Water conveyance — channel, pipeline, or pressurized pipeline (penstock) that delivers the water
  • Turbine, pump, or waterwheel — transforms the energy of flowing water into rotational energy
  • Alternator or generator — transforms the rotational energy into electricity
  • Regulator — controls the generator
  • Wiring — delivers the electricity.

Commercially available turbines and generators are usually sold as a package. Do-it-yourself systems require careful matching of a generator with the turbine horsepower and speed.

Many systems also use an inverter to convert the low-voltage direct current (DC) electricity produced by the system into 120 or 240 volts of alternating current (AC) electricity. (Alternatively, you can buy household appliances that run on DC electricity.)

Whether a microhydropower system will be grid-connected or stand-alone will determine many of its balance of system components.

For example, some stand-alone systems use batteries to store the electricity generated by the system. However, because hydropower resources tend to be more seasonal in nature than wind or solar resources, batteries may not always be practical for microhydropower systems. If you do use batteries, they should be located as close to the turbine as possible because it is difficult to transmit low-voltage power over long distances.

Microhydropower System Turbines

Turbines are commonly used today to power microhydropower systems. The moving water strikes the turbine blades, much like a waterwheel, to spin a shaft. But turbines are more compact in relation to their energy output than waterwheels. They also have fewer gears and require less material for construction.

Only a few companies make microhydropower turbines, and most are high-head turbines. Low-head, low-flow turbines may be difficult to find, and may have to be custom-made.

There are two general types of turbines: impulse and reaction.

Impulse Turbines

Impulse turbines, which have the least complex design, are most commonly used for high-head microhydro systems. They rely on the velocity of water to move the turbine wheel, which is called the runner. The most common types of impulse turbines include the Pelton wheel and the Turgo wheel.

  • Pelton wheel — uses the concept of jet force to create energy. Water is funneled into a pressurized pipeline with a narrow nozzle at one end. The water sprays out of the nozzle in a jet, striking the double-cupped buckets attached to the wheel. The impact of the jet spray on the curved buckets creates a force that rotates the wheel at high efficiency rates of 70–90%. Pelton wheel turbines are available in various sizes and operate best under low-flow and high-head conditions.
  • Turgo impulse wheel — an upgraded version of the Pelton. It uses the same jet spray concept, but the Turgo jet, which is half the size of the Pelton, is angled so that the spray hits three buckets at once. As a result, the Turgo wheel moves twice as fast. It’s also less bulky, needs few or no gears, and has a good reputation for trouble-free operations. The Turgo can operate under low-flow conditions but requires a medium or high head.
  • Jack Rabbit turbine — a drop-in-the-creek turbine that can generate power from a stream with as little as 13 inches of water and no head. Output from the Jack Rabbit is a maximum of 100 Watts, so daily output averages 1.5–2.4 kilowatt-hours, depending on your site. Sometimes referred to as the Aquair UW Submersible Hydro Generator.

Reaction Turbines

Reaction turbines, which are highly efficient, depend on pressure rather than velocity to produce energy. All blades of the reaction turbine maintain constant contact with the water. These turbines are often used in large-scale hydropower sites.

Because of their complexity and high cost, reaction turbines aren’t usually used for microhydropower projects. An exception is the propeller turbine, which comes in many different designs and works much like a boat’s propeller.

Propeller turbines have three to six usually fixed blades set at different angles aligned on the runner. The bulb, tubular, and Kaplan tubular are variations of the propeller turbine. The Kaplan turbine, which is a highly adaptable propeller system, can be used for microhydro sites.

Pumps and Waterwheels

Conventional pumps can be used as substitutes for hydraulic turbines. When the action of a pump is reversed, it operates like a turbine. Since pumps are mass produced, you’ll find them more readily than turbines. Pumps are also less expensive. For adequate pump performance, however, your microhydropower site must have fairly constant head and flow. Pumps are also less efficient and more prone to damage.

The waterwheel is the oldest hydropower system component. Waterwheels are still available, but they aren’t very practical for generating electricity because of their slow speed and bulky structure.

Accessibility to the Land

Although most project developers own the land on which the project will be located, others must those rights from landowners. The system intake may have to be located on land owned by a state or federal agency or by another private party. In other cases, both intake and powerhouse may sit on the project developer’s land, but the penstock that connects them might cross another person’s property.

The feasibility of an entire project should be determined before any purchase or lease agreements are arranged. Also, if it is known that the property in question is not available under any circumstance, alternate plans should be considered.

Determining Site Potential

In order to determine the hydro potential of a site, information regarding amount and variation of streamflow is essential. You should find out if streamflow records have been kept for the stream at any time. A good place to begin inquiries is with the U.S. Geological Survey (USGS) Water Data Discovery, where you’ll find real time streamflow data and historical streamflow data, including lists of active and discontinued stations.

If historic flow records are not available, you should immediately begin monitoring the streamflow at the site: the feasibility of constructing a small power plant is dependent on exactly how much power your stream will put out. The two most important factors to consider are flow and head.

Flow is the quantity of water flowing past a point at any given time. This amount varies both seasonally and annually, so it is important to collect accurate data for each season of a full year. These data should then be compared to USGS information from your area to decide if it was a dry year or a wet year. You can obtain snow pack information for your area at the U.S. Department of Agriculture Natural Resources Conservation Service.

Minimum flow rates are necessary to accurately assess the minimum continuous power output you can expect from your hydro unit. Also, maximum flow estimate is needed to ensure that your structure will withstand peak flooding.

Head is the vertical distance in feet from the surface of the supply water to where the water leaves the turbine. The head exerts pressure that can be turned into usable power, so the greater distance the water falls, the more energy is available.

Low head is considered to be less than 60 feet; high head is 60 feet or more. Although there are exceptions, 10 feet of head is usually the minimum necessary to generate power.

Once you have determined the net head and the average flow rate for your site, you can calculate the power output from your stream.

Determining Energy Needs

A central question to project feasibility is whether or not the site will produce enough power to meet your energy needs. Two types of energy estimates should be evaluated – peak demand and total consumption. Peak demand is the maximum power needed at any one time. In household use peak demand occurs when all electric loads are on at once. Total consumption is the number of kilowatt-hours used in a given period. Utility companies usually use the measure kilowatt-hours per month.

A system capable of meeting total consumption will not necessarily cover peak power needs; consumption or power needs may have to be adjusted. If your power needs are greater than your potential energy source, you may consider storing electricity in batteries or buying extra electricity from a utility to supply peak demand needs. Contact your nearest utility to seek assistance early in the process.

Water wheels and water turbines are two basic types of hydropower machines. Water wheels are the traditional devices used to convert the energy in flowing and falling water into mechanical power. They are used in grinding grain, and operating saws, lathes, drill presses, and pumps. Usually large in diameter and slow turning, water wheels work well in streams with large variations in stream flow. Trash racks and screens are usually not needed because sticks, stones, and dirt will flow over the wheel in the stream of water. Water wheels can be used to produce electricity, although the large diameter and slow rotation requires the rotational shaft to be geared up to a much higher RPM.

Because water wheels operate at slow speeds, they are considerably less efficient than water turbines in producing electricity. Water wheels are also bulky and in harsher climates have to be housed in large structures to avoid ice buildup in the winter.

Water turbines spin at high speeds, are used for electrical generation and can be as high as 70 percent – 80 percent efficient in producing mechanical or electrical energy. While water wheels use water carried in an open flume or channel, turbines receive their energy from water carried in pressure conduits. Water turbines are complicated pieces of equipment and must be carefully installed.

Also, debris such as rocks, sticks and sand can interfere with the blades, so a trash rack or screen is required to prevent this material from going through the turbine.

System Components

A typical micro-hydro system consists of several components. An intake structure controls the flow of diversion water to be used. A penstock, or flume, carries the water from the intake structure to the turbine. The powerhouse contains the water turbine, generator and controls.

Calculating Costs

Once the head, flow and system output are known, you can contact equipment suppliers to get accurate cost data. There is no point in contacting these people before the site details are known, as costs of equipment would vary considerably with different sites.

Costs vary widely with each site and size of system.

Environmental Considerations

Water wheels and water turbines alone have a negligible effect on the environment. Most hydro systems, however, require a dam to ensure a continuous source of water. Damming a river or stream can have a long-term effect on the environment surrounding the site. Streamflow is changed, and the water table is usually raised behind the dam and lowered downstream from the structure. You are creating a pond or lake where a stream ecosystem used to exist, so silt may accumulate and you may have constructed an ideal breeding ground for mosquitoes.

Fish movement may be blocked if a fish ladder isn’t used. Access roads may contribute to erosion and disrupt the landscape. In general, the larger the dam, the greater the impact on the environment. If you foresee the ecological impact of installing a hydroplant, you can keep stream disruption to an absolute minimum. Keep in mind that you may have to radically change your design to work with your local ecosystem or, in some cases, abandon the hydropower project completely.

Permitting and Licensing

Before you do any construction on your stream, you should be aware of the regulatory conflicts you may face. A variety of institutional and legal barriers exist and your project will go much smoother if these potential problems are identified early in the schedule so you can take the required actions.

Although numerous agencies have potential permitting or review authority, small hydropower projects are likely to require only a few permits. Nevertheless, the time required for obtaining all permits and licenses may be a major part of the project duration, so it is important for you to begin the permitting process in the early stages of developing your site.

Local Permitting Requirements

First of all, you should contact local government offices to determine local permit requirements. The local city and county planning and public works departments can tell you which permits are needed. All local permits or requirements must be satisfied before federal hydropower licenses will be issued. Generating facilities affecting only the developer’s property should encounter few problems.

State Permitting Requirements

A hydropower developer will have to obtain a number of permits. The best source for information on those permits is your state Department of Environmental Quality’s Environmental Permitting Dept. and Water Quality Info.