Hydroelectric power is the largest source of renewable energy currently used in the world. In this video, we will summarize some of its most important characteristics. The picture here is of the 22.5 gigawatt dam on the Yangtze River in China, currently the largest dam in the world. The availability of hydro-power arises from the naturally occurring hydrologic weather cycle. Water evaporates from oceans, lakes, and rivers, clouds of water vapor form, and water precipitates from clouds as rain or snow, which replenishes ocean, lakes, and rivers. The potential energy of water held above sea level is equal to the product of its mass, the gravitational constant, and its height above the sea level. This schematic of a hypothetical hydroelectric dam illustrates its principal components. The reservoir or forebay is the lake or body of water held behind the dam. The intake permits water from the forebay to flow into the dam. The penstock conveys water to the dam's turbine. Water flowing through the turbine causes it to turn a shaft, which powers a generator to create electricity. Finally, the water exits the dam into an afterbay or tail-water. The head of a dam is the depth of water from the surface of the forebay down to the location of the turbine. Low-head dams are defined as dams less than 30 meters high. These dams often use a Kaplan propeller type turbine. Medium-head dams are between 30-250 meters; it's a lot of meters. The dams often use an inward flowing Francis turbine for the greatest deficiency. High-head dams are greater than 250 meters. These are often run off the river type projects, where water at a high altitude is piped down to generating station. The dams often use a Pelton turbine or high pressure jets of water, spin cups on a wheel. General calculations for hydroelectric power and energy are straightforward. The electrical power obtained from a dam is calculated as the product of the head height of the dam, H the gravitational constant of Earth, g, the mass flow rate of water through the dam, F, and the efficiency of that dam, Greek letter Eta, which depends on several factors, including the efficiency of the turbine and generator, and friction in the piping. The efficiency of a dam typically is about 90 percent, meaning that 90 percent of the potential energy of water in the forebay is converted to electricity. Note that flow rates can be calculated using liters, cubic meters, kilograms of water, or metric tons. Annual energy production is calculated as a product of the capacity utilization of the dam, its rated power times 8,760 hours in a year. The capacity utilization of dams average about 45 percent depending on the downtime for maintenance and varying water flow rates throughout the year. An example of dam calculations is the 49 megawatt run of river high-head dam at Rutherford Creek in British Columbia, Canada. A nine kilometer long penstock of 2.5 meter diameter pipe whose laid between an upstream uptake to the downstream generating station. The head height of the dam is 325 meters with a maximum flow rate of 17.2 tones per second. Efficiency of the dam is about 90 percent with a capacity utilization of about 42 percent. Graded power is therefore calculated is about 49.4 megawatts. Annual energy production is estimated at about 182 gigawatt hours annually, enough to power more than 25,000 households. These charts show some important economic and performance statistics for global hydropower. The left chart shows that the installed cost of hydropower is $1,500 per kilowatt of power. The middle chart shows that the utilization factor for hydropower capacity is about 47 percent on average, and the levelized cost of hydropower is about five cents per kilowatt hour and it's slowly trending up. Regarding hydroelectric adoption trends, this first chart shows that China is far and away the largest producer of hydropower energy in the world, followed by Canada, Brazil, the United States, Russia, and then the rest of the world. The second chart shows the forecasts for hydropower capacity to 2050, which is expected to grow about 40 percent from the present. Summarizing, hydropower has many advantages as a source of renewable energy. It's mature, widely used technology. It's scalable from 10 kilowatts to 20 gigawatts. It's dispatchable, meaning it's available on very short notice. It's highly efficient, greater than 80 percent, with an average efficiency approaching 90 percent. Hydropower is clean with few operating emissions, and has low operations and maintenance expenses. However, hydropower is not without its challenges. Hydropower projects have large initial capital costs with long lead times due to required environmental approvals and extended construction timelines. Water resources may be variable and uncertain due to droughts and water diversion. Hydropower projects increasingly raise environmental concerns such as loss of forests and grasslands, destruction of riparian wetlands, impacts on fish and wildlife, loss of canyonlands and valleys, and impacts on indigenous populations. For example, the controversial 11.2 gigawatt Belo Monte mega Dam in the Amazon River Basin in Brazil is claimed to have caused significant environmental harm to the Xingu River and to the indigenous and traditional people living nearby. Hydroelectric power currently remains the largest source of renewable energy. In the next video, we will review another large source of renewable energy, biomass. I will see you there.
