The first uses the temperature difference between the surface and bottom waters to create a hydraulic head that drives a conventional water turbine. The advantages of this proposal include the absence of heat exchangers. Consider a hemispherical canister as depicted in the Figure 5a. A long pipe admits cold water, while a short one admits warm water. The canister is evacuated so that, in the ideal case, only lowpressure water vapor occupies the volume above the liquid surface. In practice, gases dissolved in the ocean would also share this volume and must be removed. This configuration was proposed by Beck (1978). At a temperature of 15° C, the pressure inside the canister is about 15 kPa (0.017 atmospheres). At this pressure, warm water at 25°C will boil, and the resulting vapor will condense on the parts of the dome refrigerated by the cold water. The condensate runs off into the ocean, establishing a continuous flow of warm water into the canister.