Thesis Defence: Evaluating Series-Connected and Sub-Array Solar Panel Configurations Under Mismatch Conditions Including Partial Shading and Manufacturing Variation

Simon Faber, supervised by Dr. Thomas Johnson, will defend their dissertation titled “Evaluating Series-Connected and Sub-Array Solar Panel Configurations Under Mismatch Conditions Including Partial Shading and Manufacturing Variation” in partial fulfillment of the requirements for the degree of Master of Applied Science in Electrical Engineering.

An abstract for Simon’s thesis is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person defence.

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ABSTRACT

Industry-standard construction of solar panels involves connecting solar cells in series or parallel configurations with bypass diodes. This configuration of panels causes a reduction in efficiency when the intensity of light and temperature varies between cells due to series-connected strings being limited by the cell with the lowest current generation in the circuit. In this work, an alternative panel configuration is proposed where individual sub-arrays of series-connected cells are load-matched to minimize the losses due to mismatch from partial shading and variation of cell parameters due to manufacturer process variation. To evaluate and compare the performance of series-connected and sub-array panels, a mathematical expression for “Utilization Factor” (UF) is expressed as a ratio of the output power of a series-connected string over the maximum power available (MPA) from each cell in the string. The UF of a variety of panel and string configurations are determined using a solar simulator and an experimental testbed. These results are verified using an equivalent circuit model simulated in LTSpice and simulation error is established. The loss of power due to manufacturing process variation is ultimately deemed negligible for the cells used in experimentation, because the variation between cell parameters is less than the variation introduced in experimentation. The losses due to partial shading are demonstrated as significant for any shading scenario and intensity. Ultimately, the potential use of load-matched sub-arrays to reduce the effect of cell mismatch and therefore reduce power lost due to partial shading conditions is evaluated through UF. These alternative configurations are demonstrated to provide a significant increase in efficiency compared to traditional configurations such as bypass diode-protected strings. However, these increases are highly dependent on cell variance due to partial shading conditions and manufacturing process variation. Therefore, practical use of alternative panel configurations is recommended when the user or manufacturer has prior knowledge of the panel’s operating environment. This allows for the calculation of efficiency lost due to additional hardware compared to the efficiency gained from alternative panel configurations to determine if an alternative configuration is beneficial to power output over time.