by several research teams as a storage media, it would be attractive to use it to also carry the heat from the collector field to the central storage site. The major drawback for this role is the liquid-solid phase change at 142°C. This would cause severe problems since the fluid would freeze each night. All night circulation from storage, draining the system each night or resistance heating are all approaches to avoid freezing. But the problems of operation and plant reliability are felt to eliminate Hitec as an energy transport medium. Except for the high temperature NaK and helium systems, the optimized heat leaks are kept in the 5% to 10% range. The heat leak as well as pumping power is accounted for by increasing the collector field accordingly. The heat leak also causes a loss in temperature in the transported fluid. This has only a small effect on a liquid system. For example, consider a liquid where there is a 100°C rise through the collector field. It would lose only 5°C in the delivered temperature even if all of a 5% heat leak were removed from the outlet lines. This is not the case for superheated steam where all the leaked energy is removed from superheat. If the same 5% heat leak existed in a steam system that went from 250°C water to 510°C (950°F) 1500 psi steam in the collector field,the delivered temperature would drop 43°C and arrive at the turbine at 467°C (873°F). A 10% heat leak would cause an 85°C temperature drop in the delivered steam. This will reduce the turbine efficiency. This effect will be considered in Section 3.3.2 and 4.2. 3.2.1.4 Initial Energy Investment. The four heat transport subsystems which operate above ambient temperature require an initial energy investment (IEI) to heat the fluid and pipe walls to the operating temperature before the transport subsystem is able to deliver heat to the power plant at the design conditions. In addition, night heat losses from hot insulated lines must be replaced prior to any useful system output. The IEI, collection heat rate and thermal heat loss
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