Pumped-storage hydro plants offer the most technologically advanced and readily available facilities for stabilizing the grid as more intermittent renewable energy sources come online worldwide, which is prompting significant development of new plants and expansion work at existing facilities.
What makes pumped-storage hydro so attractive? This 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. Thus, 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, electricity produced using renewables 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, 0 GWh 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 0 GWh from solar;
- Non-OECD Europe produced 49 114 GWh from hydro, 167 GWh from wind, 0 GWh 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, hydro electricity (including pumped storage) is the most widely used renewable generating technology. 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 above (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.
For example, the World Wind Energy Association’s World Wind Energy Report 2010, released in April 2011, indicates that worldwide wind capacity has reached 196 630 MW, with 37 642 MW added in 2010, for a growth rate of 23.6 per cent. The report indicates that all wind turbines installed by the end of 2010 can generate 430 TWh per year, equalling 2.5 per cent of global electricity consumption. In 2010, China became the country with the highest total installed wind capacity, adding 18 928 MW in 2010. Germany has a total wind capacity of 27 215 MW and Spain has 20 676 MW. And Denmark, Portugal and Spain have the highest shares of wind power at 21 per cent, 18 per cent and 16 per cent, respectively.
Electricity produced from solar photovoltaics, the most common form of solar facility, is expected to increase rapidly between now and 2035, with its share of global generation at about 2 per cent in 2035, according to IEA’s World Energy Outlook 2010. The report indicates that, in particular, the Middle East and North Africa hold enormous potential for large-scale development of solar power, but there are many market, technical and political challenges that need to be overcome.
Both wind and solar power pose a significant challenge in terms of supply because of their intermittent nature. When the wind is not blowing or the sun is not shining, no energy is produced, which causes problems for the transmission grid through shortfalls in supply. Effectively integrating these intermittent energy sources into an electric power grid requires energy storage facilities such as pumped-storage hydro.
The IEA’s recently published Harnessing Variable Renewables: A Guide to the Balancing Challenge distinguishes between renewable energy technologies such as biomass, geothermal and reservoir hydropower that present no greater challenge than conventional power technologies in integration terms and “variable renewable technologies”. Resources such as wind, solar, wave and tidal energy fluctuate over the course of the day and from season to season and “represent additional effort in terms of their integration into existing power systems”.
Implementing a significantly increasing amount of wind and solar facilities into the electricity supply system requires balancing strategies and storage options. Many current or under-development technologies are 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. Electricity Energy Storage Technology Options finds “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 (440 MW) and sodium-sulphur batteries (316 MW).
Pumped-storage hydro plants store water in two reservoirs, one upper and one 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. In reality, pumped-storage plants are net consumers of electricity. But these plants can be very economical because of the difference between peak and off-peak electricity prices and through the provision of ancillary services, such as load balancing, energy storage, frequency control and reserve generation. In addition, pumped-storage plants can respond to load changes within seconds.
SNAPSHOTS OF WORLDWIDE ACTIVITY
Below are profiles of current pumped-storage activity in representative countries worldwide. This activity indicates the type of work being undertaken and the potential for this technology to continue to expand and provide valuable services to the electric grid worldwide. This represents only a fraction of the total work under way worldwide.
Pumped-storage activity in this country is strong, with several utilities working on new construction and rehabilitation.
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 modernize existing hydro plants.
Vattenfall Europe Generation AG has awarded a contract to Stelba Hydro to refurbish pump-turbine sets at the 80 MW Wendefurth project in Saxony-Anhalt State. The utility plans to refurbish two 40 MW pump-turbine sets, including modification or refurbishment of turbine parts, corrosion protection, turbine covers, guide vanes, servo-actuators and rotary shaft seals.
Schulchseewerk AG has commissioned a consortium headed by ILF Consulting Engineers to provide design services for the 1400 MW Atdorf plant in Baden-Wuerttemberg. ILF will include tender design, construction design, construction, site supervision and supervision of start-up. The plant, scheduled to begin operating in 2019, is intended to improve the integration of renewable energies into the supply system and contribute to security of supply.
In a unique twist on traditional pumped-storage, the firms 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 power plant will use wind power at times of high wind 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.
Although only one pumped-storage facility is under construction in Indonesia, it is a large one. In May 2011, the World Bank approved a $640 million loan to assist with developing the 1040 MW Upper Cisokan project. Construction on the Cisokan River is set to complete in 2016 at a cost of $800 million. Indonesia’s state-owned electricity company, PLN, will provide the remaining project cost. 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 has significant pumped-storage activity, all being undertaken by the utility Energias de Portugal (EDP).
On the Ocreza River, EDP is working to build and operate the 136 MW Alvito project, for which the company won a concession in 2008. At that time, Alvito was expected to need to invest €268 million ($424 million) in the project, which is part of a plan to boost Portugal’s hydro electric capacity to 7000 MW by 2020, up from 4950 MW in 2008.
EDP also is working to expand the 42 MW Salamonde project through adding a 207 MW Francis reversible pump turbine and related equipment. Installing 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 upgrade 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. This and the other projects discussed above 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 in new and existing hydro plants in Portugal.
Other projects under construction in Portugal include 171 MW Baixo Sabor on the Sabor River. It is 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, to begin operating in 2014.
RusHydro is undertaking work at a couple of 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 a second 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.
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. Other projects being built in Switzerland include the 1000 MW Limmern in Linthal Valley, being 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 to be fully operational by 2017.
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).
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 per cent 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.
Although pumped-storage development work is taking place in the US, the main news in this country involves regulations and financing for work in this sector.
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 organized wholesale electricity markets by generators, including hydropower. FERC says current compensation practices for frequency regulation services in organized wholesale energy markets 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 renewable energy sources 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 departments of Energy and the Interior announced $26.6 million in funding and research for development projects to advance hydropower technology, including pumped storage. A total of $11.88 million is to be awarded over four years. DOE intends to provide technical and financial assistance to accelerate pumped-storage projects already in the pipeline, with preference given to projects that begin construction by 2014 and integrate 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, such as wind and solar. 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 further 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.
Elizabeth Ingram is associate editor of Hydro Review and Hydro Review Worldwide (HRW).
This article was first published in the July–August 2011 issue of Renewable Energy World magazine.