Optimal sizing and control strategy of low temperature solar thermal utility systems

This work describes the development of an integrated method for the design of networks of flat plate solar collectors and a temperature control strategy. The main stages of this methodology include the optimization of single collector geometry, size and structure of the network, energy storage system, and design of a temperature control system. Solar network inlet temperature and flow rate are maintained at its optimal value and outlet temperature is conditioned to meet the process specifications. Comparison with common temperature control based on the manipulation of network inlet flow rate is presented. A case study to supply 480 l/min of water at 70 °C is analysed. Results shows that the network operates efficiently throughout the year using the alternative control strategy. In terms of the solar network design, the results indicate a reduction of 52.3% in payback time compared to networks that use commercial collectors, reduction of 21.4% in payback compared to the purchase and installation of a natural gas boiler, and reduction in CO₂ equivalent gas emissions of 759.6 t/y. In terms of the operation, the results show a reduction in pumping costs of about 24,584 USD/y, compared to the control strategy based on flow rate manipulation.