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To: Haim R. Branisteanu who wrote (38292)	9/15/2003 5:45:45 PM
From: Haim R. Branisteanu	Respond to of 74559

Electric Power from Saline Solar Ponds The basic idea involves a pond of saline water, about 2 m. in depth, which is artificially maintained so that the degree of its salinity (and consequent density) is higher at the bottom than at the surface. Absorption of solar radiation by the floor of the pond heats the lower depths of water which are prevented from rising by their high density relative to the upper layers. In such a situation the temperature of water at the bottom of the pond continues to rise and is found to attain temperatures close to 100oC. Furthermore, since the ponds are very large - one demonstration pond, at Beit Ha'aravah, is 250,000 sq.m. in area - this represents a huge amount of stored energy. The Ormat Corporation who pioneered such ponds developed a special low-temperature turbine which enables the hot pond water to convert an organic fluid to vapor and thus produce electricity. For the Beit Ha'aravah pond, a 5 MW turbine was built. The thermodynamic efficiency of such a comparatively low-temperature power-producing system is of needs small, approximately 1% at best. Accordingly, one would expect such a pond to produce, on average, only about 570 kW of electrical power. A 5 MW turbine would therefore, at first glance, appear to be hopelessly optimistic. However, the unique feature of solar ponds, compared with all other solar technologies, is their built-in storage capacity. It takes several weeks until the pond temperature achieves a steady state at its lower depths, after which, provided one does not withdraw energy at an average rate that exceeds the nominal 570 kW on an annual basis, one can in fact achieve vastly greater power outputs for a few hours each day - typically during the morning and evening peak load periods. In effect one allows the pond to absorb solar energy during the day but only operates the turbine in the early morning and late afternoon hours. Ormat's organic fluid turbine has turned out to have such a long life-time, partly because it is a totally sealed unit, that such devices are to be found all over the world in situations where low-temperature heat sources are available and electric power is required. members.optusnet.com.au