Electricity is consumed predominantly as it is produced. Electricity generation relies increasingly on new renewable energy (RE) sources, mainly sun and wind. These are intermittent and not always available when needed, so electrical energy storage (EES) becomes essential in integrating them successfully into the energy mix. Pumped storage is by far the largest-capacity form of EES available, representing around 95% of the total available globally, according to the US Department of Energy Global Energy Storage Database.
Balancing needs, ensuring grid stability
To balance increasing levels of intermittent RE generation from wind and solar systems and help improve grid stability and flexibility, EES solutions are needed to use and store energy efficiently.
The IEC strongly supports EES. The IEC Market Strategy Board (MSB) has published two White Papers, the first on EES, the second analysing the role of large-capacity EES systems that integrate large-capacity RE sources. Both White Papers stress the crucial importance of EES in future installations. There are a number of utility-scale storage solutions that can be classified under the following headings: electromechanical, electrochemical, thermal, hydrogen, liquid/compressed air energy storage and pumped storage.
Mature but still valid
EES is not recent: some storage solutions have been around for well over a century.
Pumped-storage hydropower was first used in Italy and Switzerland in the 1890s.
IEC Technical Committee (TC) 4: Hydraulic turbines, develops International Standards for “hydraulic rotating machinery and associated equipment allied with hydropower development”. This includes conventional hydraulic turbines and pumped-storage equipment.
In pumped storage installations, energy generated at low-demand periods is stored by pumping water into a higher reservoir. It can then be released at peak time to produce electricity. Since electricity is used to pump water into the higher reservoir, the overall efficiency of pumped hydro installations varies, but is lower (around 80-87%) than that of large modern hydraulic turbine installations (95%).
Pumped storage installations are very useful for balancing load within the overall power system. They prove particularly valuable when used together with RE sources: excess electricity produced by wind or sun can be used to pump water into the higher reservoir. The limitation of pumped storage is that it can only be installed in places where water can be pumped into a higher reservoir.
Last year, 6,4 GW of pumped storage was installed. This is nearly twice the installed figure for the previous year.
IEC experts meet at Swiss Laboratory for Hydraulic Machines
Experts from IEC TC 4/Working Group (WG) 36, which “prepares documents on transient calculations of hydraulic transients in hydropower turbine-generator units”, met in mid-June at EPFL-LMH, the Laboratory for Hydraulic Machines at the Swiss Federal Institute of Technology in Lausanne (EPFL).
The meeting was supported by IEC TC 4 Secretary Robert Arseneault, who was awarded the 2016 IEC Thomas A. Edison Award, that “recognizes exceptional current achievements of technical committee/subcommittee (TC/SC) and conformity assessment officers”.
The experts, and e-tech, seized the opportunity to visit the recently-upgraded Veytaux underground pumped storage power station near Montreux, on the shores of Lake Geneva.
The operation of the new installation was studied in the machine hall of the EPFL-LMH on a 1:30 scale model.
Visiting the new expanded pump storage installation
The Veytaux power plant first entered in service in 1971, with four Pelton hydroelectric turbines, each with a capacity of 60 MW (total capacity 240 MW), and four pumps.
The turbines generate electricity by processing water from the Lake Hongrin reservoir, 880 metres higher (altitude 1255 m) at a rate of up to 32 m3/sec. When demand for electricity is low, the pumps can send water in the opposite direction, from Lake Geneva up to Lake Hongrin at a rate of 24 m3/sec.
To meet the increasing demand for balancing energy, prompted by the rapid development of new RE sources that generate electricity in an intermittent and fluctuating manner, the operator, Alpiq’s group Forces Motrices Hongrin-Leman (FMHL), decided to double the station’s generating capacity. It started work in 2011 to fit two new groups of 120 MW pump turbines (each consisting of two Pelton turbines and two pumps) in an underground cavern measuring 100 x 25 x 56m. The work cost some CHF 330 million (USD 337 million) and the new system was inaugurated in May 2017, 10 years after the first feasibility study was initiated.
The upgraded Veytaux facilities have a total installed capacity of 480 MW. 420 MW is used for operations and the rest is held in reserve. Veytaux is now the second most powerful pumped storage power station in Switzerland.
After visiting the 1971 installation, TC 4 experts were given a comprehensive tour of the new group of pump turbines by an FMHL official. The contrast between the two is striking: the first group of turbines is fully visible while the new pump turbines are ensconced in large enclosures with only the pumps at the lower end of the enclosures visible.
Speaking at the inauguration of the new installation, the chairman of the FMHL board of directors said: “the new FMHL power station will make a significant contribution towards meeting our country’s future power supply challenges and is perfectly in line with the [Swiss] Energy Strategy 2050”.
Switzerland, in common with many other countries, will see the share of electricity it generates from new RE sources grow steadily. As a result, EES facilities like the Veytaux pumped storage installation will play a major role in ensuring grid stability and flexibility.
Originally published as an e-tech article by Morand Fachot here.