Hydropower Technology
Hydropower draws its power from the gravitational forces that make water flow downhill. All water in motion carries kinetic energy, and flowing water carries much more energy than the moving air used in wind power because water is much denser than air. From a practical perspective, this means that even slow-moving water can be an economical source of energy.
Developing Hydropower Technology
Mankind has transformed the kinetic energy of streams, rivers, and other flowing waters into mechanical energy for thousands of years. Since the 19th century, hydro facilities have been used to produce electricity in applications ranging from utility-scale projects to residential-scale installations.
Modern hydroelectric technology is basically the same regardless of generating capacity. The kinetic energy of flowing water spins a turbine, producing mechanical energy that is converted into electricity by a generator. Additional components include dams, foundations, or other structures, as well as the power electronics, instrumentation, control, and cabling systems associated with all renewable generation facilities.
Hydropower Dams
Conventional hydro turbines are typically installed either within or adjacent to dams and diversion structures. Hydro dams, also known as impoundment facilities, create a barrier between upstream and downstream waters, inundating terrestrial habitats and irrevocably altering aquatic habitats and natural flow regimes. Their engineering function is to increase the elevation (head) between water surfaces and thus the amount of kinetic energy that can be converted into electricity as water flows or cascades through the turbines. Releases of water stored in the reservoir behind a dam can be timed to boost hydro generation during periods of high demand.
Hydro Diversion Structures
Hydro diversion structures, or run-of-river facilities, redirect or channel a portion of the flow to take advantage of natural elevation changes. This enables kinetic energy to be harnessed without completely changing the character of the aquatic environment.
Pumped Storage Hydro
Pumped-storage hydro plants integrate one or more reservoirs with a diversion structure. Electricity is consumed to pump water upwards, through the diversion structure, for storage. During high-demand periods, the stored water is released to generate electricity. If the pumping load is carried by wind power, these storage facilities represent an option for addressing intermittency challenges associated with this renewable resource.
The adverse impacts of dams and diversion structures on upstream and downstream habitats, fish populations, water quality, recreation, aesthetics, and other issues are well documented. These impacts, combined with public opposition, make new installations of conventional hydro technology in Massachusetts very unlikely. Upgrading and relicensing of existing facilities and reactivation of dormant facilities also present regulatory and permitting challenges.
To address these challenges, advanced operating strategies, high-energy turbine designs, and wildlife protection technologies are being developed and applied to enhance facility performance while reducing adverse environmental and social impacts. Large- and small-scale facilities that apply measures like these may even be able to secure certification from the Low Impact Hydropower Institute, an organization dedicated to reducing negative effects from hydro generation.
Free Flow/Low Head Hydro
Free-flow (low-head) hydro technology is being developed for river and stream applications as well as for tidal waters and other marine areas with persistent currents. It represents a promising option for tapping hydropower without disrupting aquatic environments and harming wildlife populations. The generating units may be anchored by an underwater foundation, or they may be attached to tethered floats. In either instance, the energy conversion system is located in-but it does not impede or direct-the flow of water. Some designs are similar in form to modern, three-blade wind turbines, while others rely on more elaborate blade and device configurations.
Free-flow systems may be deployed individually or in multi-unit arrays. Pre-commercial installations are operating elsewhere in the United States and around the world, and a demonstration project is planned for Massachusetts.
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