Comparative capacities of residential solar thermal systems versus F-chart model predictions and economic potential in an equatorial-latitude country

Abstract

One popular simulation tool for predicting solar thermal (ST) performance is the F-chart model, which has not been validated for the conditions in equatorial-climate countries. In this work, the performance of two ST systems (evacuated tube collectors (ETCs) and flat plate collectors (FPCs), widely used for supplying domestic hot water (DHW) was assessed and compared with F-chart simulation results. The energy demands were simulated by scheduling hot water discharges and measuring the backup energy requirements to fulfil DHW needs. Then, the difference between the calculated solar fraction using the F-chart model and the measured solar fraction was obtained. Both the measurements and simulations showed that the ETC systems performed better than the FPC systems in a city located on the Ecuadorian highlands with distinct climate conditions. The results showed that ETC systems are, on average, up to 18.5% more efficient than FPC systems. A comparative economic analysis was carried out considering that domestic water heating systems are backed up with liquified petroleum gas (LPG) or electricity, both with and without state subsidies. However, due to the higher cost of ETC technology compared to FPC technology, and despite ETC’s higher efficiency than FPC’s, only US$0.34 per month can be saved on average because of the impact of energy subsidies. Thus, the FPC technology seems more profitable, under the mentioned conditions, because of its lower capital costs. With backup systems powered by unsubsidized energy, the two technologies are nearly comparable. The ETC technology appears suitable only under the unsubsidized electricity scenario. The novelty of this research is that real ST systems installed under similar conditions are integrated, the operation of ST technologies for DWH is simulated, and the different inclinations and orientations of solar collectors are considered. The results are compared with simulations from the F-chart model, and each system is economically assessed.