A new opportunity for hydro: Using air turbines for generating electricity

A concept that uses hydropower to compress air could increase the number of locations where hydro is economically and environmentally feasible. The idea is being tested in a demonstration project in the northeastern U.S. The hydroelectric industry could experience substantial growth in low-head hydro facilities if a concept now being developed proves successful. This concept aims to enable power developers to generate electricity economically at sites currently not feasible for hydropower because water heads are too low. Many areas of North America are studded with low-head dams that could provide considerable hydro capacity if low-head generation were economically feasible. The six New England states in the US, for example, contain approximately 15,000 dams that have never been used to generate electric power because they impound water with heads ranging from 3 to 13 feet. Conventional facilities are not economically practical for generating electricity at these low heads. However, a promising alternative approach is to use water at these low-head dams to compress air, and then to use the air to power an air turbine-generator that produces electricity. The concept, called hydropneumatic generation, can be visualized by imagining a container, such as a large teacup, inverted and submerged in tidal waters.more » As the tide rises, the water compresses the air trapped inside the container. When the tide ebbs, the pressure decreases, putting the air into a partial vacuum. If a vent pipe were installed from the container to the atmosphere, air would flow out of the container as the water depth increased, and flow back in as the water depth decreased. Hydropneumatic energy is generated by installing an air-powered turbine to harness the energy of this airflow through the vent pipe. The turbine can be installed to rotate in the same direction at all times, even though the airflow reverses direction.« less