A system with large thermal capacity may be unaffected by short-term effects of insolation variation due to occasional cloud passage since the hot pipes may provide sufficient heat for a short time to maintain a near constant thermal output. But this advantage is likely to be less important compared to the above discussed liabilities. A compact fluid storage tank is a more efficient thermal flywheel than the transport subsystem itself. The best energy transport subsystem considered in this study is the chemical transport network (system 5). Figure 12 indicates that the direct installed cost is approximately $30/kWt, or less than half the cost of the other considered best candidates. It is nearly independent of network size. The only transport losses are pumping losses since the system operates at ambient temperature also obviating the necessity of expansion loops and insulation. There is no initial energy investment requirement nor overnight heat loss. Since pressure drop and pumping power of a fluid through a pipeline are both inversely proportional to the fifth power of the internal diameter, it is possible and simple to size the lines on a cost optimum basis. The chemical fluid used, methane (CH^) and water (H20) are inexpensive, available and easy to handle. The low temperature and non-corrosive nature of the products and reactants make possible the use of inexpensive carbon steel pipe. Since the heat of chemical reaction is high, only a small flowrate through each line is required. Since the system can be operated at high pressures, the density is relatively high so small pipe diameters will be possible. Because the gases are at ambient temperature, their density is higher than hot gases, which is a system bonus. Another positive feature not considered in this cost comparison study is the possibility of energy storage without heat leaks at ambient temperature. The chemical energy transport subsystem deserves a critical, indepth, analysis and may prove to be attractive compared to optical
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