Hydropower Technologies
Hydropower, or hydroelectric power, is the most common and least expensive source of renewable electricity in the United States today. According to the Energy Information Administration, more than 6% of the country's electricity was produced from hydropower resources in 2008, and about 70% of all renewable electricity generated in the United States came from hydropower resources.
Hydropower technologies have a long history of use because of their many benefits, including high availability and lack of emissions. Hydropower technologies use flowing water to create energy that can be captured and turned into electricity. Both large and small-scale power producers can use hydropower technologies to produce clean electricity.
Hydropower technologies have a long history of use because of their many benefits, including high availability and lack of emissions. Hydropower technologies use flowing water to create energy that can be captured and turned into electricity. Both large and small-scale power producers can use hydropower technologies to produce clean electricity.
Large-Scale Hydropower
Large-scale hydropower plants are generally developed to produce electricity for government or electric utility projects. These plants are more than 30 MW in size, and there is more than 80,000 MW of installed generation capacity in the United States today.
Most large-scale hydropower projects use a dam and a reservoir to retain water from a river. When the stored water is released, it passes through and rotates turbines, which spin generators to produce electricity. Water stored in a reservoir can be accessed quickly for use during times when the demand for electricity is high.
Dammed hydropower projects can also be built as power storage facilities. During periods of peak electricity demand, these facilities operate much like a traditional hydropower plant—water released from the upper reservoir passes through turbines, which spins generators to produce electricity. However, during periods of low electricity use, electricity from the grid is used to spin the turbines backward, which causes the turbines to pump water from a river or lower reservoir to an upper reservoir, where the water can be stored until the demand for electricity is high again.
A third type of hydropower project, called run of the river, does not require large impoundment dams (although it may require a small, less obtrusive dam). Instead, a portion of a river's water is diverted into a canal or pipe to spin turbines.
Many large-scale dam projects have been criticized for altering wildlife habitats, impeding fish migration, and affecting water quality and flow patterns. As a result of increased environmental regulation, the National Hydropower Association forecasts a decline in large-scale hydropower use through 2020. Research and development efforts have succeeded in reducing many of these environmental impacts through the use of fish ladders (to aid fish migration), fish screens, new turbine designs, and reservoir aeration.
Most large-scale hydropower projects use a dam and a reservoir to retain water from a river. When the stored water is released, it passes through and rotates turbines, which spin generators to produce electricity. Water stored in a reservoir can be accessed quickly for use during times when the demand for electricity is high.
Dammed hydropower projects can also be built as power storage facilities. During periods of peak electricity demand, these facilities operate much like a traditional hydropower plant—water released from the upper reservoir passes through turbines, which spins generators to produce electricity. However, during periods of low electricity use, electricity from the grid is used to spin the turbines backward, which causes the turbines to pump water from a river or lower reservoir to an upper reservoir, where the water can be stored until the demand for electricity is high again.
A third type of hydropower project, called run of the river, does not require large impoundment dams (although it may require a small, less obtrusive dam). Instead, a portion of a river's water is diverted into a canal or pipe to spin turbines.
Many large-scale dam projects have been criticized for altering wildlife habitats, impeding fish migration, and affecting water quality and flow patterns. As a result of increased environmental regulation, the National Hydropower Association forecasts a decline in large-scale hydropower use through 2020. Research and development efforts have succeeded in reducing many of these environmental impacts through the use of fish ladders (to aid fish migration), fish screens, new turbine designs, and reservoir aeration.
Microhydropower
Microhydropower systems are small hydroelectric power systems of less than 100 kW used to produce mechanical energy or electricity for farms, ranches, homes, and villages.
How a Microhydropower System Works All hydropower systems use the energy of flowing water to produce electricity or mechanical energy. Although there are several ways to harness moving water to produce energy, "run-of-the-river systems," which do not require large storage reservoirs, are most 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—a channel, pipeline, or pressurized pipeline (called a 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.
Microhydropower System Components Run-of-the-river microhydropower systems consist of:
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.
Whether a microhydropower system will be grid-connected or stand-alone will determine its final 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. If batteries are used, they should be located as close to the turbine as possible because it is difficult to transmit low-voltage power over long distances.
Dams or diversion structures are rarely used in microhydropower projects. They are an added expense and require professional assistance from a civil engineer. In addition, dams increase the potential for environmental and maintenance problems.
How a Microhydropower System Works All hydropower systems use the energy of flowing water to produce electricity or mechanical energy. Although there are several ways to harness moving water to produce energy, "run-of-the-river systems," which do not require large storage reservoirs, are most 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—a channel, pipeline, or pressurized pipeline (called a 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.
Microhydropower System Components Run-of-the-river microhydropower systems consist of:
- A water conveyance, which is a channel, pipeline, or pressurized pipeline (penstock) that delivers the water
- A turbine, pump, or waterwheel, which transforms the energy of flowing water into rotational energy
- An alternator or generator, which transforms the rotational energy into electricity
- A regulator, which controls the generator
- Wiring, which 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.
Whether a microhydropower system will be grid-connected or stand-alone will determine its final 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. If batteries are used, they should be located as close to the turbine as possible because it is difficult to transmit low-voltage power over long distances.
Dams or diversion structures are rarely used in microhydropower projects. They are an added expense and require professional assistance from a civil engineer. In addition, dams increase the potential for environmental and maintenance problems.
Microhydropower Turbines, Pumps & Waterwheels
A microhydropower system needs a turbine, pump, or waterwheel to transform the energy of flowing water into rotational energy, which is then converted into electricity.
Turbines Turbines are commonly used 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.
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.
The 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.
Pelton wheels, like this one, can be purchased with one or more nozzles. Multi-nozzle systems allow more water to impact the runner, which can increase wheel output.
The Turgo impulse wheel is 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 is also less bulky, needs few or no gears, and has a good reputation for trouble-free operation. The Turgo can operate under low-flow conditions but requires a medium or high head.
Another turbine option is called the Jack Rabbit (sometimes referred to as the Aquair UW Submersible Hydro Generator). The Jack Rabbit is 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 the site.
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 also often used in large-scale hydropower sites.
Because of their complexity and cost, reaction turbines aren't usually used for microhydropower projects. But one exception is the propeller turbine, which comes in many 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 Conventional pumps can be used as substitutes for hydraulic turbines. When the action of a pump is reversed, it operates like a turbine. Because pumps are mass produced, they can be found more readily than turbines. Pumps are also less expensive. For adequate pump performance, however, a microhydropower site must have fairly constant head and flow. Pumps are also less efficient and more prone to damage.
Waterwheels 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.
Content Credit: U.S. Department of Energy - Office of Energy Efficiency & Renewable Energy
Turbines Turbines are commonly used 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.
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.
The 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.
Pelton wheels, like this one, can be purchased with one or more nozzles. Multi-nozzle systems allow more water to impact the runner, which can increase wheel output.
The Turgo impulse wheel is 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 is also less bulky, needs few or no gears, and has a good reputation for trouble-free operation. The Turgo can operate under low-flow conditions but requires a medium or high head.
Another turbine option is called the Jack Rabbit (sometimes referred to as the Aquair UW Submersible Hydro Generator). The Jack Rabbit is 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 the site.
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 also often used in large-scale hydropower sites.
Because of their complexity and cost, reaction turbines aren't usually used for microhydropower projects. But one exception is the propeller turbine, which comes in many 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 Conventional pumps can be used as substitutes for hydraulic turbines. When the action of a pump is reversed, it operates like a turbine. Because pumps are mass produced, they can be found more readily than turbines. Pumps are also less expensive. For adequate pump performance, however, a microhydropower site must have fairly constant head and flow. Pumps are also less efficient and more prone to damage.
Waterwheels 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.
Content Credit: U.S. Department of Energy - Office of Energy Efficiency & Renewable Energy