In today's issue we are going over the basics of hydroelectricity, a form of renewable energy that creates electricity by harnessing the power of moving water (aka hydropower). Humans have been utilizing hydropower since the first grain mills were placed along river banks, making it one of the oldest renewable energy sources. Hydroelectricity became an energy commodity in 1882 with the opening of the first hydroelectric energy plant selling electricity in Appleton, Wisconsin. According to the U.S. Energy Information Administration, “In 2020, total U.S. conventional hydroelectricity generation was about 291 billion kilowatt-hours (kWh), equal to about 7.3% of total U.S. utility-scale electricity generation,” (Where Hydropower Is Generated - U.S. Energy Information Administration (EIA)). At just over 7%, hydropower is one of the most used renewable sources, right below wind energy, which produces about 8% (“Renewable Energy”).
The amount of power that can be harnessed by a hydroelectric plant is dependent on two major factors: the volume of water that is moving through the plant, as well as the elevation change of the water before and after entering the plant (“How Hydropower Works”). While many of us associate hydroelectricity with dams, there are actually three different forms of hydroelectric power plants; impoundment, diversion, and pumped storage plants.
Impoundment plants are the most common type of hydroelectric power plant in the United States. By using a dam to store river water in a reservoir, the plant will release this water that it flows through a turbine which powers a generator to produce electricity (“Types of Hydropower Plants”). Because the water is held in a reservoir, it can be released selectively to accommodate electricity needs (which is not possible with wind or solar) or to respond to environmental pressures (like flooding or wildlife passage). Power lines connected to the generator connect this electricity to the power grid and distribute it to our homes and businesses (Hydroelectric Power: How It Works)!
A diversion plant diverts a river from its natural course to channel it toward a generator producing electricity (Society). A diversion plant does not require a dam, but instead utilizes a “penstock”, which is a pipe that moves the water down a natural decline in a river bed towards the generator (“Types of Hydropower Plants”). Once the water has moved through the generator, it is able to rejoin the natural flow of the river.
Pumped Storage Plants:
Pumped storage plants can best be thought of as a water battery (cool, right?). During off-peak times in the grid, excess power can be used to pump water uphill from a lower reservoir to a higher one. This is generally in the middle of the night when energy demand (and cost) is at its lowest. While there is some loss in the process from pump inefficiencies (as well as a small amount of evaporation), essentially all the power that was used to pump the water uphill is “stored” in the upper reservoir via the potential energy of the now elevated water. During peak hours when a supplement of power is needed, the higher reservoir can be opened up, and all the water will run back downhill through a turbine generator, thus adding all the power back into the system! This form of power production is amazing for short term, high load periods - think middle of a hot summer day in Georgia when everybody needs their A/C. However, the energy used to pump the water back uphill is taken from the energy grid, meaning that there is no guarantee that this power is renewable in and of itself. (Hydroelectric Power: How It Works)
While it may not be the first thing you think about when the topic of renewable energy comes up, hydropower is one of the most versatile and long standing forms of power generation in the modern world. Renewable energy isn’t perfect, and hydropower is no exception. But with high efficiencies and existing infrastructure, hydropower can be some of the cleanest renewable energy we can get today. However, interrupting the natural flow of water has always been a point of controversy, especially as we start to experience worse and worse drought conditions each year. Check back next issue as we dive into what makes hydropower so controversial!
Hydroelectric Power: How It Works. https://www.usgs.gov/special-topic/water-science-school/science/hydroelectric-power-how-it-works?qt-science_center_objects=0#qt-science_center_objects. Accessed 31 Oct. 2021.