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Balancing the Grid with Pumped Storage

What makes pumped-storage hydro so attractive? Recent development and expansion can primarily be attributed to the fact that pumped-storage hydro is the predominant renewable energy source available to balance intermittent resources, such as wind and solar. Pumped-storage facilities can enable countries to meet targets for reducing greenhouse gas emissions and build clean renewable energy capacity. In addition, these plants can provide many stabilizing features to the grid, further enhancing their value.

WHY PUMPED STORAGE?

Renewable power sources have become important contributors to the energy portfolio in many countries. However, according to the International Energy Agency (IEA), renewable electricity varies widely by region. For example, in 2008 (the most recent data available):

  • Africa produced 98,153 GWh from hydro (including pumped storage), 1307 GWh from wind, 1193 GWh from geothermal, 746 GWh from biomass and 26 GWh from solar photovoltaic (PV);
  • Asia (excluding China) produced 252,091 GWh from hydro, 14,443 GWh from wind, 19,022 GWh from geothermal, 7333 GWh from biomass and 45 GWh from solar PV;
  • China produced 585,187 GWh from hydro, 13,079 GWh from wind, nothing from geothermal, 2359 GWh from biomass and 172 GWh from solar PV;
  • Latin America produced 673,862 GWh from hydro, 1025 GWh from wind, 2972 GWh from geothermal, 29,996 GWh from biomass and nothing from solar;
  • Non-OECD Europe produced 49,114 GWh from hydro, 167 GWh from wind, nothing from geothermal, 345 GWh from biomass and 4 GWh from solar PV;
  • OECD Europe produced 554,211 GWh from hydro, 120,067 GWh from wind, 9932 GWh from geothermal, 79,132 GWh from biomass and 7479 GWh from solar PV and solar thermal; and
  • OECD North America produced 703,753 GWh from hydro, 59,784 GWh from wind, 24,070 GWh from geothermal, 59,299 GWh from biomass and 2492 GWh from solar PV and solar thermal.

As this data shows, hydroelectricity (including pumped storage) is the most widely used renewable generating technology today. The second most predominant source varies by region, with wind being second in Africa, China, OECD Europe and OECD North America; geothermal being second in Asia; and biomass being second in Latin America and non-OECD Europe.

Of the generating technologies mentioned (excluding hydro), wind and solar are the fastest-growing and most technologically advanced renewable energy sources in the world, with many countries turning to them to meet mandates for increased generation using renewables.

But both wind and solar power pose a significant challenge in terms of supply because of their intermittent nature. Simply put, when the wind is not blowing or the sun is not shining, no energy is being produced. This causes problems for the transmission grid because there may be shortfalls in supply. To effectively integrate these intermittent energy sources into an electric power grid, facilities must be available to allow storage of energy, such as pumped-storage hydro.

The IEA recently published Harnessing Variable Renewables: A Guide to the Balancing Challenge, to address the need to actively manage power systems to maintain a steady balance between supply and demand. As the report indicates, "Some renewable energy technologies (for example biomass, geothermal and reservoir hydropower) present no greater challenge than conventional power technologies in integration terms. In contrast, another group of renewables - including wind, solar, wave and tidal energy - are based on resources that fluctuate over the course of the day and from season to season. Collectively known as variable renewable energy technologies, these represent additional effort in terms of their integration into existing power systems."

Integrating a significantly increasing amount of wind and solar facilities into the electricity supply system requires balancing strategies and storage options. There are many technologies currently available or under development that are or will be capable of providing this balancing and storage, including pumped-storage hydro, according to a recent white paper by the Electric Power Research Institute in the US. Entitled Electricity Energy Storage Technology Options, this paper says that "While many forms of energy storage have been installed, pumped hydro systems are by far the most widely used, with more than 127,000 MW installed worldwide." The next closest options are compressed air energy storage, with just 440 MW, and sodium-sulphur batteries at 316 MW.

Pumped-storage hydro plants store water in two reservoirs, upper and lower. During periods of peak demand, when electricity prices are high, water from the upper reservoir is used to run the pump-turbines and then discharged into the lower reservoir. When demand and prices are low, the water is pumped back to the upper reservoir. Pumped storage systems are also effective when excess renewable capacity is used to pump water to the upper reservoir for later use when variable renewable ourput falls. In reality, though, pumped-storage plants are net consumers of electricity.

However, these plants can be very efficient economically because of the difference between peak and off-peak electricity prices and the provision of ancillary services, such as load balancing, energy storage, frequency control and reserve generation. Pumped-storage plants can also respond to load changes within seconds.

SNAPSHOTS OF WORLDWIDE ACTIVITY

Profiles of current pumped-storage activity in representative countries worldwide indicate the type of work being undertaken and the potential for this technology to continue to expand. The following represents only a fraction of the total work under way worldwide.

GERMANY

Pumped-storage activity is strong, with several utilities working on new construction and rehabilitation projects.

German utility EnBW Kraftwerke AG is advancing construction of the 270-MW Forbach project at Schwarzenbach Dam. The utility plans to expand the century-old 70-MW Rudolf Fettweis project by adding an upper reservoir of 1.8 million m3 above the existing Schwarzenbach Reservoir of 14 million m3, adding an underground lower reservoir, and installing two powerhouses. This work is part of a multi-year programme by EnBW to expand and modernise existing hydro plants.

Meanwhile Vattenfall Europe Generation AG awarded a contract to Stellba Hydro to refurbish pump-turbine sets at the 80-MW Wendefurth project in Saxony-Anhalt State. The utility plans to refurbish two 40-MW units, including modification or repair of turbine parts.

In other activity, Schulchseewerk AG commissioned a consortium headed by ILF Consulting Engineers to provide design services for the 1400-MW Atdorf plant in Baden-Wurttemberg. ILF will include tender design, construction design, construction, site supervision and supervision of start-up. The plant, scheduled to begin operating in 2019, is meant to help improve the integration of renewable energies into the energy supply system and contribute to the future security of supply.

In a unique twist on traditional pumped storage, RWE and RAG signed a letter of intent in December 2010 to co-develop integrated pumped-storage hydro and wind projects at RAG's coal slag heap sites. The concept would integrate intermittent wind output with the flexible response of pumped-storage hydro to provide steady, dependable power. The planned combined plant will use wind power at times of high output to pump water to a reservoir on top of the waste heap, some 50 metres higher up. A pilot project at RAG's waste dump at Halde is proposed.

INDONESIA

Although only one pumped-storage facility is under construction in Indonesia, it is a large one. In May 2011, the World Bank approved a US$640 million loan to assist with the development of the 1040-MW Upper Cisokan project. Construction of the project on the Cisokan River is expected to be completed in 2016 at a total cost of $800 million. Indonesia's state-owned electricity company, PLN, will provide the remaining investment. The project is to have four 260-MW reversible Francis pump-turbines in an underground powerhouse, two roller-compacted-concrete dams impounding upper and lower reservoirs, and transmission lines connecting with the Java-Bali power system.

PORTUGAL

Portgual is another country with significant pumped-storage activity, but it is unique in that one utility, Energias de Portugal (EDP), is undertaking all the work listed below.

For example, EDP is working to build and operate the 136 MW Alvito project, on the Ocreza River. The company won a concession for this project in 2008. At that time, Alvito was anticipated to require an investment of €268 million. The project is part of a plan by Portugal to boost hydroelectric capacity to 7000 MW by 2020, from 4950 MW in 2008.

EDP also is working to expand the 42-MW Salamonde project through the addition of a 207-MW Francis reversible pump turbine and related equipment. Installation of this unit will more than quadruple power output at the project. Salamonde's two existing units were installed in the 1950s, and the generators were retrofitted during the 1980s. Alstom is supplying and installing the entire new unit under the terms of a contract worth more than €55 million. This unit is scheduled to be commissioned in 2015.

In addition, in February 2011, the European Investment Bank approved a €300 million loan to EDP for ugprade work on the Alqueva and Venda Nova plants. The loan will be used to increase installed capacity at Alqueva, on the Guadiana River, to 496 MW from 240 MW and at Venda Nova, on the Cavado River, to 1017 MW from 281 MW. These projects are in line with the national strategy on renewable energies decided by the Portuguese government in 2007 and forms part of EDP's investment programme for the coming decade.

Other projects under construction include the 171-MW Baixo Sabor on the Sabor River, scheduled to begin operating in early 2013. And, EDP is undertaking a repowering project at its existing Venda Nova Dam on the Rabagao River. The dam was completed in the early 1950s, and the original 90-MW powerhouse at this site has been decommissioned. The repowering will involve building a new 435-MW powerhouse, due to begin operating in 2014.

RUSSIA

RusHydro is undertaking work at several pumped-storage facilities. First, the company has begun construction on the 840 MW Zagorsk 2 project about 150 km east of Moscow. The project is on the left bank of the Kunya River. Second, construction of an unnamed facility with a capacity of 1560 MW is scheduled to begin between September and November 2011. This plant, about 100 km from St. Petersburg, is expected to produce 2900 GWh annually.

SWITZERLAND

Forces Motrices Hongrin-Leman has begun work to double the capacity of its Veytaux project. This 240-MW facility will grow by 240 MW with the construction of a new underground cavern containing two additional pump-turbine groups. This expansion is scheduled to be complete by the end of 2014. The company plans to use the existing 420 MW of this capacity for operations, and hold the rest in reserve.

Other projects being built include the 1000-MW Limmern in Linthal Valley, developed by Kraftwerke Linth-Limmern AG. The first of the four units is expected to begin operating in 2015. And, the 600-MW Nant de Drance, being developed by Nant de Drance SA, is expected to begin operating in 2015 and be fully operational by 2017.

UKRAINE

The first unit at the 2268-MW Dnister project in Ukraine began operating in January 2010, and the second is scheduled for operation in 2012. When completed, the station will have seven identical units. The overall cost of the project, being developed by UkrHydro Open Joint Stock Company on the Dnister River, is anticipated to be UAH5.8 billion ($720 million).

UNITED KINGDOM

Even very small pumped-storage facilities are making economic sense. In the Channel Islands, tidal energy developer Alderney Renewable Energy is planning a 3-MW project that, uniquely, would pump sea water into a land-based reservoir before releasing the water through at least one turbine. This development, which will use tidal power devices, should be able to supply about 90 percent of the power demands on the island of Alderney. The developer has begun an environmental impact assessment to obtain marine consent from the Alderney Commission for Renewable Energy. The project could be completed by 2012.

UNITED STATES

Although pumped-storage development work is taking place in the US, the main news in this country involves regulations and financing.

For example, the Federal Energy Regulatory Commission (FERC) has issued proposed rules intended to ensure just and reasonable rates for frequency regulation service provided to organised wholesale electricity markets by generators, including hydropower. FERC says current compensation practices might not acknowledge the benefits of faster ramping resources, which might improve operational and economic efficiency and reduce costs to consumers. FERC has been examining such ancillary services, partly to ease barriers to integrating variable renewables into the grid. The Commission proposes a two-part market-based compensation method under which resources would receive a uniform capacity payment for standing ready to provide frequency regulation service and a market-based performance payment for each megawatt provided in response to a system operator's dispatch signal.

In addition, in April 2011, the US Department of Energy and the Interior announced $26.6 million in funding and research for development projects to advance hydropower technology, including pumped storage. DOE intends to provide technical and financial assistance to accelerate projects already in the pipeline, with preference given if construction begins by 2014 and integrates wind and/or solar. DOE will also support analyses that calculate the economic value of pumped-storage hydro in dynamically responding to the grid and in providing other ancillary services.

Pumped-storage hydroelectric facilities are the most technologically advanced, widely available resources to provide balancing and integration of variable renewable technologies. In addition to the benefits provided by peak power production, pumped storage can generate when the wind is not blowing or the sun is not shining. Further policy work around the world can contribute to the development of these valuable facilities, as can assigning an actual value to the ancillary services and response time pumped-storage plants provide.

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