A liquid air energy storage system comprises an air liquefier, a storage facility for storing the liquefied air, and a power recovery unit coupled to the storage facility. The air liquefier comprises an air input, an adsorption air purification unit for purifying the input air, and a cold box for liquefying the purified air. The power recovery unit comprises a pump for pressurising the liquefied air from the liquid air storage facility, an evaporator for transforming the high-pressure liquefied air into high-pressure gaseous air, an expansion turbine capable of being driven by the high-pressure gaseous air, a generator for generating electricity from the expansion turbine, and an exhaust for exhausting low-pressure gaseous air from the expansion turbine. The exhaust is coupled to the adsorption air purification unit such that at least a portion of the exhausted low-pressure gaseous air is usable to regenerate the adsorption air purification unit.