Batteries store energy by electrochemical reactions. Battery technology has advanced rapidly in recent years. Newer technologies, such as lithium ion, have high energy densities meaning they can store more energy in a given size. The life expectancy as determined by the number of cycles by which batteries can be charged and discharged before losing their effectiveness has also increased substantially. However, the cost of advanced batteries is very high.
Older technologies such as lead/acid or nickel/cadmium are also options, but their lower cost has to be weighed against their lower energy densities and shorter life expectancies.
Pumped storage is an option where wind turbines are located close to hydroelectric facilities. When the electricity from the wind turbine is not needed in the electrical system, it is used to pump water into the reservoir. When the wind is not available (or electricity costs are more attractive), the water can be released from the reservoir through the hydroelectric generator to produce electricity.
Similar to the pumped storage concept, electricity from wind turbines could be used to run air compressors that compress air into large underground chambers. When we want to produce power at a later time, the compressed air can be released through air-driven generators.
Hydrogen or ammonia can be produced from electricity from wind turbines. These gases can be stored in pressurized vessels. Both gases can be used directly as fuels to run engines. Hydrogen can also be supplied to a fuel cell to produce electricity at a later time.
Electricity from wind turbines could be used to heat or cool a large thermal mass, which could be used for space heating or cooling at a later time.
It has been proposed to use the electricity to spin up large fly wheels, which could later be used to power generators.
Capacitors in electrical circuits store small charges. Research is underway to develop super-capacitors to store large amounts of electricity for later use.
The "Smart Grid" would help in integrating the intermittent power from wind turbines into the electrical system. The concept is a computerized electrical distribution system that has the ability to control the demand on the electrical system as well as the supply. For example, it could route excess power from wind turbines to idle, parked electric cars that are connected to charging stations. Alternately, when there is a temporary shortage on the system, the same cars could supply a short-term boost.