Hydropower technologies generate power by using the elevation difference from a dam or diversion structure to the powerhouse location, commonly referred to as ”head”. The amount of power generated is a combination of the project’s head and the amount of water available (flow). The Department of Energy's Energy 101: Hydropower video explains how hydropower works, and highlights some of the research and development efforts of the Water Power Technologies Office in this area.
Operations
There are three primary types of hydropower facilities, and not all involve dams:
Impoundment. Image courtesy of Energy.gov.
Diversion. Image courtesy of Energy.gov.
Conventional hydropower is the most common type of hydropower generation. These projects utilize a dam or diversion to direct water to a powerhouse located at the base of the dam or further downstream. Conventional projects are designed as Impoundment, Diversion, or a blend of both designs.
An impoundment project utilizes a dam that creates a reservoir and water is then diverted through penstocks to the powerhouse at the base of the dam.
A diversion project utilizes a smaller dam where the water is diverted from the riverbed and conveyed through tunnels, canals, and/or pipelines to the powerhouse located further downstream. It is not unusual for a diversion project to also contain an impoundment since a dam is still needed to divert the water from the riverbed but the reservoir is usually much smaller than that of an impoundment project.
There are two forms of generation:
Run-of-river operations take place when the reservoir lacks sufficient storage capacity and the project generates power from the available streamflow on a real time basis.
Peaking / load following is an attractive power producing feature of conventional hydropower generation that can be utilized variably during the day to provide power flexibly, such as in the morning or evening during cold months and during summertime days when air conditioners are called upon. This type of operation requires storage capacity in the reservoir that is sufficient to meet the operational needs.
Projects may be designed to operate using a blend of run-of-river and peaking/load following generation.
Pumped Storage works as a form of energy storage – basically, a giant battery. Water is pumped from a reservoir at a lower elevation to a reservoir at a higher elevation using lower cost electricity during periods of low energy demand. When the demand for electricity increases, the water is released back down to the lower reservoir, spinning a turbine, and generating electricity to meet the increased demand. Depending on the project, this cycle can repeat daily or even multiple times per day.
Unlike conventional hydropower, pumped storage does not create “new” electricity as it requires more energy to pump the water uphill than is generated during the downhill part of the process. The benefit of pumped storage is the ability to shift generation to meet varying demands. The economics of pumped storage can be challenging as the differential between low and high demand pricing needs to be sufficient to cover the cost of the project and its operating expenses.
Pumped storage has varying levels of impacts depending on the design of the system (open loop or closed loop), water availability and consumption, and location.
This technology produces renewable electricity by harnessing the kinetic energy of a body of water, the energy that results from its motion. Since water is hundreds of times denser than air, tides, waves, ocean currents, and free-flowing rivers represent a concentrated energy resource. This technology is new, and projects in the U.S. are largely experimental.
Economics, power prices, and markets
Today’s power market is evolving due to the advent of low-cost renewable energy generation (wind and solar); the desire for low to carbon-free power; the retirement of large capacity thermal plants (coal, oil, and nuclear); and the effects of climate change. While the hydropower industry has shared the benefits of hydropower as a low-carbon renewable energy source, a growing body of evidence shows that, under certain conditions, hydropower reservoirs can produce significant amounts of greenhouse gases.
Historically, baseload power was supplied by large thermal plants and large-scale hydropower generation. In recent years, many of these large thermal plants have been decommissioned due to their high operating costs and the owners desire to reduce carbon emissions. Hydropower is still recognized for benefits that include that it is a cleaner and more cost-effective source of electricity than some other forms of energy production. Hydropower can also serve as a flexible form of power generation to help balance the variable nature of wind and solar generation.
Due to the tremendous growth of renewable power from wind and solar facilities, pricing in today’s highly competitive energy market can vary significantly throughout the day, season, and geographical area. While hydropower facility costs in terms of maintenance, operations, and fuel can be relatively low throughout a project’s lifetime, a projects’ ability to provide flexible generation at competitive rates compared to baseload generation vary. Understanding project economics is critical to both understanding project viability and evaluating tradeoffs between streamflows and power generation.
