Thermoeconomic analysis in solar collector fields: a focus on constant flowrate and variable flowrate models

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In this study, the operation models with constant flowrate and variable flowrate of a flat-plate solar collector field are analysed. The model that achieves greater energy utilization and lower operating costs was determined under two conditions: when scaling fouling occurs in the collector tubes and when a clean operation (without fouling) is considered. The case study involves a pasteurization plant operating at temperatures above 85°C. The operational scenarios are as follows: 1) Variable flowrate: the flowrate is adjusted based on environmental conditions to maintain a constant outlet temperature, and 2) Constant flowrate: the flowrate remains constant, resulting in varying collector outlet temperatures depending on weather conditions. The results show that under clean conditions, operating with variable flowrate yields a lower cost per kWh of captured energy ($0.048/kWh). In the presence of fouling, the cost of operating with variable flowrate significantly increases to $0.15/kWh, while constant flowrate results in the lowest cost ($0.077/kWh).