Operation of Hybrid Wind-Turbine Compressed-Air System for Connection to Electric Grid Networks and Cogeneration

Abstract

This paper describes a storage system that uses wind energy to compress air in a series of high-pressure storage tanks. When needed, the compressed air is expanded through a turbo-expander to generate electricity. The system is designed for the storage of wind energy and utilises above-ground compressed-air storage with 8,278 kPa (1,200-psia) tanks. It is applicable in the operational power region between (1) electrical storage batteries for relatively small peak power and (2) large pressurized underground salt caverns for large peak power. Therefore, it is most economic for between 0.5 and 100 Megawatt electric power systems. The key advantages over these other storage methods are that there is no need to either purchase, maintain and dispose of waste chemicals, or locate large underground caverns. In addition to supplying electrical power, the by-product heat may be utilised as cogeneration. For instance, the multi-stage compressor coolant may heat domestic water and the cooled exhaust air from the turbo-expander may benefit air-conditioning. Accounting 5% benefit from the hot water and 20% from the refrigerated air, the $0.076/kWh cost of delivered electricity decreases to $0.057/kWh. Reducing or eliminating high-pressure tanks and high-voltage power lines by using the volumetrically equivalent of long high-pressure transfer lines, further reduces the unit cost. This is particularly applicable for offshore windfarms.