Maximum-power-point tracking control of solar heating system

Abstract

The present study developed a maximum-power point tracking control (MPPT) technology for solar heating system to minimize the pumping power consumption at an optimal heat collection. The net solar energy gain Qnet (=Qs−Wp/ηe) was experimentally found to be the cost function for MPPT with maximum point. The feedback tracking control system was developed to track the optimal Qnet (denoted Qmax). A tracking filter which was derived from the thermal analytical model of the solar heating system was used to determine the instantaneous tracking target Qmax(t). The system transfer-function model of solar heating system was also derived experimentally using a step response test and used in the design of tracking feedback control system. The PI controller was designed for a tracking target Qmax(t) with a quadratic time function. The MPPT control system was implemented using a microprocessor-based controller and the test results show good tracking performance with small tracking errors. It is seen that the average mass flow rate for the specific test periods in five different days is between 18.1 and 22.9kg/min with average pumping power between 77 and 140W, which is greatly reduced as compared to the standard flow rate at 31kg/min and pumping power 450W which is based on the flow rate 0.02kg/sm2 defined in the ANSI/ASHRAE 93-1986 Standard and the total collector area 25.9m2. The average net solar heat collected Qnet is between 8.62 and 14.1kW depending on weather condition. The MPPT control of solar heating system has been verified to be able to minimize the pumping energy consumption with optimal solar heat collection.