Hydropower may be flying under the radar for many in the industry, but it remains a key component of the power mix, and a growing one in many areas of the developing world. Though the basics of hydroelectric generation remain the same, technological advances are making it more flexible, efficient, and environmentally friendly.
Hydropower is booming, but unless you live in China, Latin America, or Africa, you may have missed it.
Global installed capacity of hydroelectric generation has grown by more than 25% over the past decade, according to the World Energy Council. The bulk of that development, especially the largest projects, has taken place in China and the developing world. China alone now operates 26% of worldwide hydro capacity along with 11 of the 25 largest projects in existence. In 2014, more than half of all new capacity—more than 20 GW—came online in China.
Globally, according to the International Energy Agency, future development will continue to be led by non-OECD (Organisation for Economic Co-operation and Development) countries. China will continue to account for about half of future capacity additions, with the bulk of the remainder made up by non-OECD Asia and the Americas.
Though small hydro has become the typical approach for new projects in the U.S. and Europe—the median size for hydro projects under development in the U.S. is less than 10 MW, according to the Department of Energy’s (DOE’s) 2014 Hydropower Market Report —big dams are still the rule elsewhere.
China Leads the Way
China’s plans, as with its overall goals for its power sector, are particularly ambitious. The nation aims to reach 350 GW of installed capacity by 2020, with an additional 70 GW of pumped storage hydropower (PSH). Another 110 GW (conventional and PSH) is planned by 2030, and a further 130 GW by 2050, by which point China’s hydropower potential would be about 80% developed.
Outside China, notable projects include the 11-GW Belo Monte plant in Brazil, the 7.1-GW TaSeng plant in Myanmar, and the 6-GW Grand Renaissance plant in Ethiopia, all of which are slated for operations by 2020. Plans for the long-proposed Grand Inga project in the Democratic Republic of the Congo, which could top 40 GW in size when fully built out, have taken a few steps forward in recent years, with the 4.8-GW first-stage Inga III dam slated to begin construction in 2017, according to the World Bank.
Not surprisingly, increasing technological innovation in hydro is being seen in China. Though a substantial amount of hydropower in China was supplied by foreign firms, the country has worked hard to develop indigenous technology through transfer agreements. Working with domestic Chinese firms, western companies such as Voith and Alstom have installed some of the largest turbine generators in the world, such as the 800-MW Francis units at the 6.4-GW Xiangjiaba plant (Figure 1) and the 770-MW units at the 13.1-GW Xiluodu plant.
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| 1. Mammoth. The 800-MW Alstom turbine generators at the Xiangjiaba plant on the Jinsha River in China are the largest in the world. Courtesy: Alstom |
Automation is a top priority as China’s fleet continues to expand. For example, automation equipment for the left-bank first phase of the giant Three Gorges Dam was supplied by ABB, but Chinese firm Beijing IWHR supplied its H9000 control system for the underground and right-bank phases.
The Chinese company has also supplied controls for the Xiangjiaba and Xiluodu projects. The H9000 system allows the central dispatch center in Chengdu to control generation on the Jinsha River (upper Yangtze) cascade from several hundred kilometers away.
Making Hydro More Fish-Friendly
One long-standing objection to hydropower projects has been their impact on aquatic life, especially migratory species such as salmon. Fish ladders and similar devices to restore fish runs have been in use for decades, but new developments are further reducing fish mortality.
As with other elements of hydropower, automation has made significant inroads in reducing effects on fish migration (see sidebar). Other advances have focused on turbine design to improve survival for fish that are not diverted from intakes.
A project by Alden and Voith Hydro, with funding from the DOE, has developed an innovative turbine employing a slower rotational speed and only three blades, to reduce fish mortality due to blade strike. Intended for small hydro projects, the turbine was designed by Alden and optimized and tested by Voith at its hydraulic laboratory in Pennsylvania. The blades are designed to improve the fish passage environment through the turbines by minimizing shear, pressure change rates, and minimum pressures within the water passage. Fish survival rates are expected to be at least 98%, depending on the species.
Not all aquatic life is welcome at a hydropower plant, however. Invasive species such as mussels, as well as algae and bacteria, can wreak havoc on normal operations. Preventing and correcting the growth of these organisms can consume considerable amounts of time and money. Alstom Hydro announced earlier this year that it is partnering with Israeli firm Atlantium to offer an innovative water treatment solution that uses ultraviolet (UV) light. Atlantium’s technology uses UV radiation in much the same way as it is used for sterilization in the pharmaceutical and chemical industries (Figure 2). The UV radiation, diffused by a lamp embedded in Plexiglas tubes, prevents the invasive species from reproducing. Unlike treatments such as chlorine or ozone, UV radiation is nontoxic to beneficial aquatic life and adds nothing to the aquatic environment. The technology is inexpensive and has low maintenance requirements.
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| 2. Death ray. Israeli firm Atlantium has developed an ultraviolet (UV)-based system to prevent the growth of nuisance aquatic species on hydropower equipment. The technology uses UV radiation to deter algae, mussels, and similar organisms. Courtesy: Alstom |
| Case Study: Adding Power and Automated Fish Migration to Cushman No. 2Many dams in the U.S. were built well before the effects on fish migration became concerns. Washington municipal utility Tacoma Power provides electricity to more than 50% of Tacoma residents, 90% of which comes from its 752 MW of hydroelectric generation at seven dams in western Washington. When Tacoma Power’s license to produce power for the city was up for renewal, one condition was building a fish passage around two of its dams to help preserve the local population of endangered steelhead, sockeye, and salmon.
At the time, the Cushman Dam No. 2 on the North Fork Skokomish River was not equipped with generation. The dam was built in 1929 as part of Lake Cushman, a man-made reservoir. In 1992, Tacoma Power had added two river outlet valves to the base of the dam, allowing water to flow from the lake into the riverbed. However, the flow of water through the valves was too strong for fish migration. The utility needed to slow the outflow, and it saw an opportunity to generate power by building a new powerhouse at the base of the dam. The powerhouse would need to simulate the natural flow of the river to keep the surrounding area safe from flooding and make fish migration manageable. It also needed to be completely automated to eliminate the need for on-site staff. Tacoma Power had been using Allen-Bradley ControlLogix programmable automation controllers (PACs) to automate its other seven powerhouses. Tacoma Power engineers designed a completely automated system using four ControlLogix PACs. Two PACs each control one of two 1.8-MW Francis turbine-generator units, a third controls the balance of the plant (including operation of an existing river outlet valve for flow continuation in the event of a unit trip), and a fourth controls the fish collection equipment and fish hoist system at the base of the dam, just outside of the powerhouse. With the new system, the operator controls the powerhouse using a single flow control setpoint for the plant. The balance-of-plant PAC receives the control setpoint and automatically issues flow instructions to each of the generator units and the river outlet valve to ramp flow at a regulated rate, mimicking seasonal river flows. DNP cards and Modbus cards from ProSoft Technology, a member of the Rockwell Automation PartnerNetwork program, interface with sensors, equipment, and other systems at the North Fork Skokomish Powerhouse to provide seamless Ethernet communication across multiple platforms. If one or both of the generators goes offline, the balance-of-plant controller will immediately open the river outlet valve to make up for the lost flow, keeping water flowing at a uniform rate. For the fish collection facility, Tacoma Power needed to design a hoist that could move adult fish over the dam and smolt down the side of the dam smoothly. As fish swim toward the dam, fully grown fish are captured in a hopper at the fish collection facility and automatically hoisted up the side of the dam on a tram operated by an Allen-Bradley PowerFlex 700 AC drive (Figure 3). The drive helps manage control of the hopper when transferring control between the drive and the tram’s mechanical brake. The hopper lifts the fish to the top of the dam, where they are separated, counted, and transported via trucks to Lake Cushman. On the other end of the fish lifecycle, juvenile fish swimming toward the ocean are placed into the hopper at the top of the dam and are carried down onto a smolt release cart to release them downstream, toward the ocean.
The collection facility has restored the fish migration route for the first time since the 1920s. The new generation was also eligible for renewable energy credits from the State of Washington. The entire project cost around $25 million. Because the powerhouse is completely automated, the company avoided incurring additional operator costs. The system also reduces the risk of violating flow requirements set by the Federal Energy Regulatory Commission. The ability to automatically open the backup river outlet valve in case a unit trips helps the utility company meet those compliance standards more effectively. To further boost the fish population, Tacoma Power is building two new hatcheries at the Cushman River Project. The first will raise 2 million sockeye each year, and a second will raise 425,000 young salmon and steelheads. All will be released into Lake Cushman. |
Pumped Storage Ramps Up
Many observers expect PSH to play an increasingly important role as intermittent renewables like wind and solar grow in installed capacity. China is planning to add around 130 GW of PSH capacity by 2050 to its current total of 23 GW. (For one example of PSH’s role in grid management, see “Ludington Pumped Storage Plant Increases Efficiency to Provide Greater Grid Support” in this issue.)
Adjustable-speed (AS) pump-turbines are the most significant recent advance in PSH because they give a PSH plant the ability to offer frequency regulation services, as well as varying the power consumed in pump mode over a range of outputs and generally increasing overall efficiency. Greater deployment of AS pump-turbines will be key to greater renewable integration. While AS PSH is common in Japan, it is still a small component of the PSH fleet globally, especially in the U.S. A 2014 study by the Argonne National Laboratory estimated that the addition of three proposed AS PSH projects in California would cut potential wind curtailments in 2022 by 20% as well as offering significant financial benefits to the grid.
With many PSH facilities having been in operation for decades, upgrades are necessary to keep them operating efficiently on the modern grid. With smaller plants that use lined reservoirs for storage, one key concern as they age is water exfiltration/infiltration as a result of leaks in the liner. Asphalt-lined reservoirs are a particular concern because of asphalt’s vulnerability to freeze-thaw cycles.
Advances in coating materials now offer easier repair options for leaks and much better long-term durability. Polyurea coatings and liners are increasingly being used because of the material’s flexibility, durability, and low maintenance requirements. Polyurea can be applied directly to the existing substrate and cures in as little as an hour (Figure 4). For areas that experience freezing temperatures during the winter, polyurea is much more “ice friendly” than asphalt or concrete as it is able to release frozen ice without damage.
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| 4. Leak stopper. Polyurea coatings can be added to existing pumped storage reservoirs to greatly reduce leaks and maintenance. This facility in Australia was losing 150 gallons a minute through its asphalt substrate prior to adding the liner. Courtesy: Versaflex |
For internal components at a hydropower plant, hydrophobic coatings can be applied to improve efficiency and reduce corrosion, erosion, and bio-fouling, but existing technologies are not as durable as they need to be. One possibility for the future, according to a presentation by researchers from the Massachusetts Institute of Technology, is rare earth oxides (REOs). Tests have shown that, properly applied, REO coatings can create a highly hydrophobic, highly durable layer on piping and turbine elements.
Hydropower’s Benefits Keep Flowing
Hydropower does not always get the attention that wind and solar do, but its advantages are certain to keep it an important element of the power mix in the future, especially as a resource to back up intermittent generation elsewhere. Large and small, hydro appears to have a bright future.
—Thomas W. Overton, JD is a POWER associate editor.