Hydropower Resources


History of Hydro Electric Power

Hydropower has been around the world for more than 2,000 years. The first documentation of hydropower being used was around 100 B.C. when Greeks and Romans used this form of energy for numerous tasks. Back around 100 B.C., Greeks and Romans used a waterwheel to grind corn and also grind wheat into flour. The waterwheel would be placed in a stream or river, and as the water would run down the stream or river, the waterwheel would in turn rotate. The rotating wheel would then turn, therefore turning the gears that would grind the grains. The waterwheel was not only used to grind grains, they were also used to saw wood, power textile mills, and manufacture plants.


As the waterwheel began to spread across the world, people started to expand on new ideas on how to make the waterwheel better and more efficient. One of the most important improvements was the orientation of the wheel. Since the idea had been thought of, the wheel had always been placed in a river or stream vertically, turning from top to bottom. People had the idea of putting the wheel into the water horizontally, turning from left to right. The horizontal orientation was proved to be more efficient. Two other break through thoughts that were proved to be more efficient were curved paddles and the breasted position (where the center of the wheel lies on the water surface). The waterwheel served people for thousands of years and as technology advanced, the turbine was created and replaced the waterwheel.

How Does Hydropower Work?

Hydropower is not a complicated concept and is the most widely used renewable energy. When it was discovered that hydropower could produce electricity, it was a very big innovation. The thought of generating electricity from simply running water through a turbine was once a dream to most scientist and people.

Hydroelectric power comes from water at work, water in motion. Most people do not think about the initial stages of hydroelectric power. The first step of hydropower is the powers the hydrologic cycle which in turns gives the earth its water. In the hydrologic cycle, atmospheric water reaches the earth’s surface as precipitation. Some of the water evaporates, but most of the water is absorbed by the ground and becomes surface runoff. Water from rain and melting snow eventually reaches ponds, lakes, reservoirs, and oceans where evaporation is constantly occurring. This cycle is a never ending cycle and nature ensures that water is a renewable resource.


The second step is to generate the electricity. To generate electricity, water must be in motion. When water is in motion, the energy generated is kinetic energy. When flowing water turns blades in a turbine, the form is changed to mechanical energy. The turbine turns the generator rotor which then converts this mechanical energy into another energy form — electricity. Since water is the initial source of energy, we call this hydroelectric power or hydropower for short.

At hydroelectric power plants, hydropower is generated. Some power plants are located right on a river or canals but for the plants to work at optimum efficiency with a reliable water supply, dams are needed. Dams are used to store water and later release it for purposes such as irrigation, domestic and industrial use, and power generation. The reservoirs are like rechargeable batteries. The water is stored and when power is needed, water is released to generate power. The reservoir is then filled back up with rain and runoff.


The dam creates a “head” or height from which water flows. A pipe (penstock) carries the water from the reservoir to the turbine. The fast-moving water pushes the turbine blades, something like a pinwheel in the wind. The waters force on the turbine blades turns the rotor, the moving part of the electric generator. When coils of wire on the rotor sweep past the generator=s stationary coil (stator), electricity is produced. The turbine is probably the most important part of the hydropower process next to the actual water.

In the previous paragraph, “head” was mentioned. Head and flow are two very important factors when building a hydro plant. Head is how far the water drops. It is the distance from the highest level of the dammed water to the point where it goes through the power-producing turbine. Flow is how much water moves through the system—the more water that moves through a system, the higher the flow. Generally, a high-head plant needs less water flow than a low-head plant to produce the same amount of electricity. For example, the higher the head, the more water that is in the reservoir. If there is more water in the reservoir, that means that there is more weight pushing on the penstock. If there is a high weight pushing on the penstock, that means that the harder and faster the water is flowing thought the turbine. Some hydro plants use pumped storage systems. A pumped storage system operates much as a public fountain does. The same water is used again and again.


At a pumped storage hydro plant, flowing water is used to make electricity and then stored in a lower pool. Depending on how much electricity is needed, the water may be pumped back to an upper pool. Pumping water to the upper pool requires electricity so hydro plants usually use pumped storage systems only when there is peak demand for electricity.
Pumped hydro is the most reliable energy storage system used by American electric utilities. Coal and nuclear power plants have no energy storage systems. They must turn to gas and oil-fired generators when people demand lots of electricity. They also have no way to store any extra energy they might produce during normal generating periods.

Once the electricity is produced, it must be delivered to where it is needed — our homes, schools, offices, factories, etc. Dams are often in remote locations and power must be transmitted over some distance to its users. Vast networks of transmission lines and facilities are used to bring electricity to us in a form we can use. All the electricity made at a powerplant comes first through transformers which raise the voltage so it can travel long distances through powerlines. At local substations, transformers reduce the voltage so electricity can be divided up and directed throughout an area.

Levelized Costs and Government Subsidization

Hydroelectric power plants have been a source of energy for the U.S. and world for many years now. Today, these power plants generally range from several hundred kilowatts to several hundred megawatts. However, in the instance that a hydroelectric power plant is providing electricity to millions of people, it can reach capacities of tens of thousand megawatts. Today, the world’s hydroelectric plants have a total capacity of 675,000 megawatts that produce over 2.3 trillion kilowatt-hours of energy per year. This is providing roughly one quarter of the world’s electricity. Many countries outside of North America have the majority of their electricity coming from hydroelectric power plants. For instance, nearly a decade ago, 99% of Norway’s electricity was provided via hydroelectric power plants.


The United States produced about 159.74 gigawatts in 2010 according to the Energy Information Agency, and that is approximately 6.67% of total U.S. production

Hydropower is the cheapest way to generate electricity. On average it costs about seven cents per kilowatt-hour to produce electricity from a hydroelectric plant. Modern hydroelectric turbines can convert as much as 90% of the available energy into electricity. In comparison, the best fossil fuel plants are only about 50% efficient. The seven cent per kilowatt hour that hydroelectric power costs is about one-third the cost of using Petroleum or nuclear and one-sixth the cost of using natural gas. This is true as long as the cost for removing the dam and repairs for silt build up are not included. Efficiency of these power plants could be further increased by refurbishing hydroelectric equipment. An improvement of only 1% would supply electricity to an additional 300,000 households.

This power and the costs associated are subsidized. Hydroelectric power receives its main federal subsidies through government ownership. The ownership and distribution of electricity is owned by various power marketing administrations. The role of these administrations is to market hydroelectric power at the lowest possible rates to consumers while adhering to sound business principles. These administrations are the Bonneville Power Administration, Southeastern Power Administration, Southwestern Power Administration, and the Western Area Power Administration.

The Bonneville Power Administration is a part of the U.S. Department of Energy, however, it is self funding and is able to take care of its costs by selling its products and services at cost. They receive no tax revenues or appropriations. The customer’s electricity bill is what is paying for their costs. Roughly one third of the electrical power utilized in the Northwest is provided by the Bonneville Power Administration. The Columbia River Basin is BPA’s main area of operation. It markets energy provided by 31 federal hydro projects that are operated by the U.S. Army Corps of Engineers and the Bureau of Reclamation. About 1.2 million jobs depend on power supplied by the Bonneville Power Administration.

Since 1977, the Southeastern Power Administration has been apart of the U.S. Department of Energy. Similar to BPA, the Southeastern Power Administration deals with federal hydro projects, and their main mission is to market the hydroelectric power at the lowest cost to its customers. Unlike BPA however, they do not have their own transmission lines and must cooperate with other utilities or “wheeling” services to get the electricity to its customers.

Similar to the Southeastern Power Administration, the Southwest Power Administration was established by the secretary of interior in the 1940’s and operates within the Department of Energy. The U.S. Army Corps of Engineers also maintains and operates a series of about 24 dams in the Southwest U.S. Rural electric cooperatives and municipal utilities is where most of the power generated is marketed and delivered to. Similar to Southeast, Southwest markets to what they call “preference” customers that in turn distribute electricity to millions of end users. Southwest does operate its own transmission lines, communication lines, and substations. This is where we Oklahomans get our power.

The last of the four main power administrations is the Western Area Power Administration. They too deliver cost-based electricity within a 15 state region. They too are apart of the Department of Energy and have their own transmission system. One difference is that in addition to the U.S. Army Corp of Engineers and the Bureau of Reclamation, they are also operated by the International boundary and water commission.

The two main reasons that these power administrations are able to sell electricity at such lower costs is due to the fact that there are no real fuel costs to speak of and their original financing for construction was set at rates of the 1930’s and 40’s. These administrations have been able to pay interest rates below the market even for the very few new construction or upgrades that take place nowadays. The U.S. treasury creates the subsidy by paying long term rates higher than what the administration is required to pay. The list for hydroelectric subsidies for the fiscal year 2007 can be observed in the Federal Financial Interventions and Subsidies in Energy Markets Report.

This information was taken from a California draft report from September 2nd 2009. For simplicity, overnight costs do not include interest or inflation and assume the project was constructed overnight. The hydroelectric power plant is a Renewable Portfolio Standard eligible plant. The project characteristics of the plant in this table are:
Technical and Economic Requirements for Generic RPS Eligible Hydroelectric Installation

Technical and Economic Requirements for Generic RPS Eligible Hydroelectric Installation
Plant Capacity (MW) 10
Unit Life (yrs) 30
Availability Factor 90%
Capacity Factor 50%
MWh/year 43,800
Capital Cost ($/kW) $3,500
Fixed Operating and Maintenance ($/kWh - year) $15
Non-fuel Variable Operating and Maintenance $5
Capital Replacements ($/kW) $100

The capital and financing assumptions are as follows:

Capital and Financing Assumptions (for profit)
Capital and Financing Assumptions (for profit)
% Debt (avg) 50
% Equity (avg) 50
Cost of Debt 7%
Cost of Equity 12%
Debt Term (yrs) 20
~ Capital and Financing Assumptions (not for profit)
% Debt 100
% Equity 0
Cost of Debt 5%
Debt Term (yrs) 20

Different types of technology cost different amounts of capital and they output a different amount of power. Levelized costs represent the present value of the total cost of building and operating a generating plant over its financial life, converted to equal annual payments and amortized over expected annual generation from an assumed duty cycle. Technologies such as solar energy typically have high levelized costs due to the necessary high capital costs to build the technology and the relatively low output of electricity. The levelized cost of hydroelectric however is relatively low due to the amount of electricity that the technology produces relative to the capital costs. Here is a comparison of the differences in types of renewable energy in regards to levelized cost:

flickr:5185327469describe link

Current Hydroelectric Power Output and Capacity in the United States and the World

The history of the evolution of hydroelectric power to where it is today, along with the mechanical technology involved in producing hydroelectric power has been discussed. Levelized costs have been calculated to show how the costs of the generation of hydropower compare to other forms of energy. The following is a look at the current energy output throughout the world and in the United States by way of hydroelectric power generation.

Currently hydropower is the overwhelming leader in energy production by a renewable source other than nuclear energy in both the United States and throughout the world. Hydroelectricity is accounting for around twenty four percent of the world’s electricity generation at three thousand TWh’s supplied per year. Its share of the renewable energy production throughout the world is around sixty to seventy percent (see pie chart below).


In countries, such as Norway, the Democratic Republic of Congo and Brazil, hydroelectric plants account for over ninety percent of the country’s total power generation.

The United States currently has more than two thousand hydroelectric power plants which account for more than half of the country’s renewable energy sources. China, Canada and Brazil are the only countries producing more hydroelectric power than the United States. Despite being a leader in hydroelectric power generation, proportionally the United States hydroelectric power only accounts for nearly six percent of the total electrical power generated within the borders.


In comparison Canadian hydroelectric energy production accounts for over sixty percent of total electrical power generated throughout the country. The following table shows how the net generation of hydroelectric power through August of 2010 compares to net generation through August of 2009. The Pacific coast makes up for half of the hydroelectric power generation in the United States.

Hydroelectric power plants can range in size from micro (six kilowatts to a hundred kilowatts) to small (a hundred kilowatts to thirty megawatts) to large (a few hundred megawatts to over ten gig watts). There are three hydroelectric power plants that have capacities over ten gig watts. These include Guri Dam at 10.2 GW, Itaipu Dam at 14 GW and the largest Three Gorges Dam at 22.5 GW located in China. The largest hydroelectric power plant inside the United States is the Grand Coulee Dam located on the Columbia River in the state of Washington which has a capacity of 6.8 GW.

Hydroelectric power plants do not normally operate at full capacity during a complete year. Therefore the annual hydroelectric production is not a true representation of what the producing plant or country is capable of. In order to include excess capacity, the sum of all generator nameplate power ratings (installed capacity) must be multiplied times the total time period and compared against the actual annual power generated. This ratio, known as the capacity factor, can be used to rank hydroelectric capacity when annual hydroelectric production is not descriptive enough. These characteristics are shown in the table below for the top seven hydroelectric producers as of 2009.
Seven of the largest hydroelectric producers as of 2009

Seven of the largest hydroelectric producers as of 2009
Country Annual hydroelectric production (TWh) Installed capacity (GW) Capacity Factor % of Total Capacity
China 652.05 196.79 0.37 22.25
Canada 369.5 88.974 0.59 61.12
Brazil 363.8 69.080 0.56 85.56
United States 250.6 79.511 0.42 5.74
Russia 167.0 45 0.42 17.64
Norway 140.5 27.528 0.49 98.25
India 115.6 33.600 0.43 15.80

As you can see hydroelectric power serves as an important part of the world and United State’s energy portfolio. Some countries such as Norway, the Democratic Republic of Congo and Brazil are very dependent upon their hydroelectric power. Hydro power and nuclear energy are leading the way for the implementation of renewable energy as a future energy source. While other renewable sources of energy continue to grow with increased technology, hydro power will continue to be very influential into the future. Currently there are large amounts of energy coming from hydropower plants and it seems that the hydroelectricity production will only continue to grow since there is excess capacity available.

Hydroelectric Power Potential in the United States

Not only is there available unused capacity in hydroelectric power plants, there is also a wealth of power potential that has yet to be developed. The Idaho National Laboratory (INL) did extensive research that led to the issuance of a very informative report. The report titled, Feasibility Assessment of the Water Energy Resources of the United States for New Low Power and Small Hydro Classes of Hydroelectric Plants, was issued in 2006 detailing the availability of opportunities across the United States to increase hydroelectric power generation dramatically.

For its study, the INL used a run-of-river model, which employs a penstock to direct water through a powerhouse and then back into streams without any impoundment of water. For the addition of powerhouses to existing dams and for adding capacity to existing hydropower operations, the INL considered an assortment of current turbine technologies.
The INL evaluated the likelihood of development based on land use and environmental sensitivities, prior development, site access, and load and transmission proximity, and only included those sites in its estimate that met all of the criteria. For new sites, only streams that demonstrated power greater than 10 akW and were within one mile of a road and transmission lines, a power plant or substation — or were within a distance of population centers comparable to other power plants of the same power class in the area — were included. Funding of potential projects, however, was not addressed in the report.

INL found that of the approximately 300,000 MWa of total, gross power potential of U.S. natural stream water energy resources, only about 10 percent has been developed. About 30 percent are located in zones where development is unlikely. The remaining 60 percent of over 170,000 MWa have not been developed and are not restricted from development based on information sources used in the assessment. Of this potential, it was found that nearly 100,000 MWa of gross power potential could feasibly be developed. This feasible potential corresponds to nearly 130,000 potential low-power and small hydro projects. Estimation of the hydropower potential of these sites indicates 30,000 MWa of new power supply could feasibly be developed in the United States. The West is home to nearly 20,000 MW of these undeveloped, prime hydropower opportunities. Moreover, the sum of feasibly developable hydropower in the Western states roughly equals the region's developed hydropower, in terms of potential average megawatts.

The majority of the identified feasible hydropower potential could be harnessed without constructing new dams and by using existing techniques and technologies developed over the long and extensive history of installing small hydroelectric plants in the U.S. In fact, 84 percent of the identified hydropower potential could be developed using existing

While solar energy may possess the greatest amount of potential energy, it has been demonstrated by the Idaho National Laboratory that hydropower also has great potential that has yet to be developed. One concept to keep in mind is that with the emergence of new technology there may be advances in tidal hydropower derived from tides, waves and ocean currents. Currently many large hydroelectric power plants are under construction and it seems that many more will come.

The Future of HydroElectric Power

The future of hydroelectric power in the US, as well as worldwide, is complicated. As we know, the capabilities of hydroelectric power have been maxed out here in the United States, however this is not the case in most other countries. There are a range of large scale hydro electric construction projects in the works in the developing industrial nations. The true future of hydroelectric power worldwide depends on the abilities of scientists to make technological breakthroughs.

Current Projects

There are currently fourteen large scale hydroelectric facilities in production and numerous smaller ones. These projects are scheduled to be completed over the course of 2012 to 2022 and are located in China, India, Venezuela and Berma, with the majority located in China.

China has ten major projects schedule to be complete between 2012 and 2017. These projects are the Xiluodu Dam, Xiangjiaba Dam, Nuozhadu Dam, Jinping 2 Hydropower Station, Jinping 1 Hydropower Station, Guanyinyan Dam, Lianghekou Dam, Dagangshan, Guandi Dam, and the Ludila Dam. The largest of these projects is the Xiouodu Dam, with an estimated maximum capacity of 12,600 MW. The dam is scheduled to be complete in 2015, but construction has been temporarily halted due to a lack of studies detailing the environmental impact.

The total additional estimated capacity added by these dams to the Chinese energy supply totals 46,350 MW. This is no surprise considering China is already the largest producer of hydroelectric power in the world, with an annual production of 652.05 TWh annually, as of 2009.

One of the most advanced forms of hydroelectric power employed today is known as pumped-storage hydroelectricity. Power plants use this for load balancing, which refers the ability of the plants to store excess electrical power during low demand periods for use in the periods of high demand. The method of pumped storage hydroelectricity stores energy in the form of the water itself. During the periods of low cost off peak electricity consumption, electricity is used to run pumps that pump water from a low elevation reservoir to a higher elevation. When electrical demand rises during the peak hours of consumption, the water is released. The released water flows downward, through turbines, producing electricity. The process is displayed below;


The process however is not as environmentally efficient as standard forms of hydroelectric energy. The pumping process requires a substantial amount of energy, more infact than is generated by the production process. The process is actually a net consumer of energy, the benefit is that the system increases revenues for the facility by producing and selling its energy during the peak periods. The following chart displays energy consumed and produced at a pumped-storage plant facility during an average 24 hour period.


An analysis of the type of data displayed in this chart calculates that approximately 70% to 80% of the energy used to used in the pumping process to elevate the water is regained during the generation process. Unlike other forms of energy such as wind and solar, that struggle with energy storage, pumped-storage is an effective means of storing energy for later use.

A new use of this technique applies the pro’s of applied storage to the con’s of alternative energies such as wind and solar. One of the main difficulties with these forms of energy is the variability in their production, or intermittent energy production. Pumped storage allows for the energy produced by intermittent sources that falls in times of high output but low demand to run the pumps that elevate the water for hydroelectric production, essentially storing the energy for peak consumption periods.

Alternative and Cutting Edge Technologies

Scientists are no ambitiously looking to new sources for generating hydroelectric power. When looking for a new form of hydroelectric, it makes sense to look towards the largest supplies of water on the planet, our oceans. Scientists are looking to harness the energy contained within the tides and the waves of our oceans. These forms of energy are known as tidal power and wave power.

Tidal power is a viable mean of generating electricity, although not widely used, the first plant had been online since 1966. The difficulties with tidal energy are the same as with most forms of alternative energy, there is a relatively high cost associated with generating the energy, and there are only a few states with enough shoreline that has high enough tidal activity. It is believed however that new advances in the design of tidal hydroelectric plants coupled with advances in turbine technology could allow tidal power to one day become a cost effective energy source.

Tidal energy, as mentioned, is extracted from the changes of water level within the earth’s oceans. These fluctuations are caused mainly by the gravitational relationship between the earth and the moon, as well as the earth and the sun. There are three main categories of factors that weigh in on the strength of the tide and any given location at any point in time, these are;

• The relative positions of the Moon and Sun
Earths rotational pattern
The geography of the sea floor and coast line

The charts displayed demonstrate the fluctuations in the tide over the course of a twenty four hour period. Three distinct types of tides are displayed; the semidiurnal tide, mixed tide, and diurnal tide. Each varies in its tidal period, length, and variance in amplitude of water levels. All graphs are displayed with time on the x-axis (24 hours), and variance in total height (measured in feet) from the standard level on the y-axis.


Tidal power can be divided into three methods of generating; tidal stream generation, tidal barrage, and dynamic tidal power.

A tidal stream generator is a machine, often much like a wind turbine, that extracts energy from the movement of the tide as the water flows past it. Of the three main forms of tidal generation, tidal stream generator machines are the least damaging the natural environment as well as the cheapest. The three main types of turbines are displayed below, with the “Modern HAWT” being the most widely used.


These underwater turbines are not yet widely used so there is little information available on their environmental impacts, economic viability, rate of return, or energy output.

A tidal barrage, unlike the turbine systems of tidal stream generation, is a structure similar to that of a dam. The function of a tidal barrage is to capture the energy of the water flowing in or out of a bay or river. A conventional dam dams the water on one side, and then allows it to flow through turbines generating electricity. A tidal barrage allows the water to flow through during the periods of high tide, and then traps it. During the periods of low tide the water is released. This allows energy to be generated during both halves of the flow process, when the water flows through turbines during high tide, and when the water flows through turbines during the low tide release.


The third technique is dynamic tidal power. This also uses a structure similar to that of a dam, one that extends from the shore directly into the ocean, with a perpendicular barrier on the tip. This forms a large “T” structure that is meant to interfere with the oscillating waves of the tides in order to create hydraulic currents. These “dams” are usually 30 to 60 km long. They are large enough to exert force the horizontal tide movement, creating a head the flows over both sides of the dam. The head can then be used to power standard turbines housed throughout the top of the dam. No dynamic tidal power dam has ever been built, although all the data and technologies are available. This image displays the effect of a dynamic tidal power dam on the oceans tides.


Wave power is the harnessing of energy transported in the surface waves of the ocean. Wave technology is not widely employed in the world today, although some attempts have been made. Wave power technologies are categorized by either their location, or their power take-off system. The location categories are shoreline, nearshore, and offshore. There are six types of power take-off systems including; hydraulic ram, elastomeric hose pump, pump-to-shore, hydroelectric turbine, air turbine, and linear electrical generator. One of the difficulties experienced with wave power is the same encountered with wind power, power must be carried from the source directly to the point of use through transmission power cables, because there is no way to store the energy. This can be extremely expensive causing the energy to be produced at a net loss. The image below is of a near shore wave power device known as “Pelamis.” It is the world’s first attempt to commercially harness wave energy and add that energy to the grid. Pelamis’s first use was in an offshore wave facility located off of Portugal, officially opened it 2008.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License