Several electricity storage methods are under development, including electric batteries and synthetic fuels, which may provide some much-needed flexibility for the clean energy system of the future.
The importance of electricity storage will increase as the energy system heads towards carbon-neutrality. According to Jero Ahola, a professor of energy efficiency in electrically driven systems at LUT University, hydroelectric power will continue to be an important source of balancing power in the future, although new methods will be developed alongside it.
Ahola says that the electric batteries currently available are best suited to storage for approximately one day.
"Lithium-ion battery systems current cost EUR 200-300 per kilowatt-hour. Because they are so expensive, they should be put to maximum use. The advantages of electric batteries in terms of the security of energy supply are their speed and efficiency when they are charged and discharged. The question of which applications will see widespread battery use is largely one of politics."
According to Ahola, the availability of raw materials for batteries should not pose a problem, at least in the near future.
"The production of electric vehicles is driving battery capacities higher. At the same time, the energy density and efficiency of batteries is increasing while prices decrease. In the future, electric vehicles may be grouped to form energy stores. Decommissioned batteries from vehicles could be used in network-level battery systems or to store energy for individual buildings."
Ahola says that the technologies competing with electric batteries for short-term energy storage include flywheels and various technologies that store potential energy. There is no shortage of ideas, but, as a mass product, electric battery technology is hard to beat.
Week-long heat storage and seasonal storage of synthetic fuel
Ahola considers heat stores to be an important method of storing energy for a week or more. One method involves storing thermal energy using heat pumps operating on wind power. The heat store can then reduce the need for heat to be generated using electricity when demand rises.
"Hydrogen or synthetic fuel produced using electricity could be used for seasonal storage. At present, the most promising alternative is to use electricity, hydrogen and carbon dioxide to produce synthetic fuels such as methanol and methane. These could be produced in a country like Morocco, which has good wind and solar conditions, and then shipped to Finland.
Carbon dioxide and hydrogen can also be refined to create fuels such as gasoline, diesel and kerosene. However, Ahola says that synthetic fuels are less efficient than electric batteries.
"Roughly half of the electricity consumed for production can be stored in the fuel as chemical energy, and a quarter of it is released as electricity."
