Energy storage helps power world ahead

Balancing power generation and demand requires the right storage solutions

By Morand Fachot

To balance increasing levels of intermittent RE generation from wind and solar systems, EES (Electrical Energy Storage) solutions are needed that use and store energy efficiently and help improve grid stability and flexibility. The IEC MSB (Market Strategy Board) 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.

Reversible pump turbine in the Goldisthal pumped-storage station (Photo: Hydroprojekt Ingenieur GmbH)
Reversible pump turbine in the Goldisthal pumped-storage station (Photo: Hydroprojekt Ingenieur GmbH)

Multiple systems

EES solutions are the key to addressing the energy challenge that’s why the IEC decided in 2012 to create TC 120: EES (Electrical Energy Storage) Systems, to accelerate the integration of RE and to enable a more reliable and efficient supply of electrical energy. This TC oversees the development of International Standards that address all different types of EES technologies taking a systems-based approach rather than focusing on individual energy storage devices.

EES systems are usually classified according to the form of energy they use, i.e. mechanical, electrochemical / chemical, electrical and thermal. A number of IEC TCs are involved in standardization work for several of these.

Mechanical energy storage

EES is not recent; some storage solutions have been around for well over a century.

Pumped-storage hydropower, first introduced in the 1890s, stores energy generated at low-demand periods, when its price is lower, by pumping water into a reservoir that is located on higher ground. It can then be released at peak time to produce electricity. This technology currently represents the largest and most flexible EES solution, accounting for more than 99% of installed storage capacity for electrical energy. IEC TC 4: Hydraulic turbines, created in 1913, prepares International Standards for hydraulic rotating machinery and associated equipment associated with hydro-power development, including pumped storage, for which reversible pump turbines have been in use since the 1930s.

Compressed air energy systems predate electricity and were initially installed in the late 19th century to deliver [compressed air] power to factories and homes. CAES (compressed air energy storage) was first used for utility-scale electricity storage in the late 1970s. Its use is similar to that of pumped storage. Air is compressed and stored in an underground reservoir during periods of excess power. It is then released, heated and expanded in an expansion turbine driving a generator to produce electricity at peak time. IEC TCs involved in standardization work for components and systems used in CAES, include, among others: TC 2: Rotating machinery, for motor and generators, TC 5: Steam turbines, and TC 61: Safety of household and similar electrical appliances, for pumps and motor-compressors.

Flywheels are another type of mechanical EES system. They were used in mechanical systems long before electricity was introduced. Flywheels store electrical energy in the form of kinetic energy in a low-friction spinning mass that is driven by a motor. When electricity is needed, the spinning mass drives a generator to produce electricity. TC 2 prepares International Standards for motor and generators.

Chemistry to the rescue

Electrochemical storage, which uses secondary (rechargeable) batteries, is a well-established and mature technology. Various types of chemistry are used in batteries. Lead acid is the most widely used and has been commercially deployed since the 1890s. Nickel-based NiCad (nickel cadmium) and NiMH (nickel metal hydride), as well as Li-ion (lithium ion) and NaS (sodium sulphur) batteries are the main other types used for storage from RE sources. New chemistries and production methods have greatly improved the efficiency of secondary batteries. IEC TC 21: Secondary cells and batteries, prepares International Standards for all secondary cells and batteries, including flow batteries, another fairly recent electrochemical storage system, which can be recharged almost instantaneously by replacing the electrolyte liquid.

Beside electrochemical solutions, chemical storage, in the form of hydrogen or SNG (synthetic natural gas) produced from excess electricity, is another form of storage. Both hydrogen and SNG can subsequently be used to produce electricity at peak time or for other applications such as transport.

IEC standardization will be central to future EES needs

EES systems will become essential technologies in achieving RE integration and Smart Grid expansion as well as achieving a more efficient and reliable electricity supply. IEC International Standards will be central to realizing these goals.

Gallery
Reversible pump turbine in the Goldisthal pumped-storage station (Photo: Hydroprojekt Ingenieur GmbH) Reversible pump turbine in the Goldisthal pumped-storage station (Photo: Hydroprojekt Ingenieur GmbH)
Beacon Power 20 MW flywheel frequency regulation plant (Photo: US DOE) Beacon Power 20 MW flywheel frequency regulation plant (Photo: US DOE)
8 MW Li-ion battery grid storage system in New York State (Photo: AES Corporation) 8 MW Li-ion battery grid storage system in New York State (Photo: AES Corporation)