Energy storage systems have long been used to a solution to balance the demands of consumers of electricity and the capabilities and economics of electricity generating systems. Electricity demand fluctuates on a daily and seasonal basis. A graph typical daily electricity demand for Ireland can be seen in the graph below (source SEMO data). The difference between daytime and night time usage is particularly pronounced in Ireland as less of the overall demand is made up of heavy industrial users which operate 24/7.
To date energy storage solutions have been used as older power stations can be most economically run at a relatively constant output. Excess energy was stored at night when the was low demand and released during peak demand times. In the future storage solutions can be used to level out the natural fluctuations in RE generation methods.
By combining wind and storage solutions Prevailing Wind aims to make clean renewable wind energy a more central role in our energy portfolio.
Current energy storage technologies:
Pumped Hydro Energy Storage (PHES)
PHES is the most mature storage technology available, first used in the 1890's in Switzerland and Italy. It is also provides the greatest storage capabilities. The system works by pumping water from a lower reservoir to an upper reservoir during times of excess generation. Then during times of high demand the water flows back to the lower reservoir generating electricity. The efficiency of the system is between 70% and 85%. Further information and examples are available here.
Compressed Air Energy Storage (CAES)
CAES uses excess electricity to compress air into a sealed underground chamber. The energy is recouped by releasing the air. It can be particularly effective when used in conjunction with gas turbine generators as up to 66% of the gas used is required to compress air at the time of generation. By using wind energy to store compressed air the amount of gas used during generation is greatly reduced.
Battery Energy Storage
Large scale batteries have been used as specific solutions in the electrical industry. They have been modularly combined to provide outputs of up to 40MW.
A review of energy storage in the Irish context is available here.