A cost-benefit analysis for reconfigurable PV modules under shading

Highlights

• Reconfiguration of solar cells is used to improve energy production of PV modules.

• Performance of reconfigurable Snake PV modules under shading are examined.

• Additional cost of reconfigurable Snake PV modules are taken into account.

• Cost-Energy analysis to compare reconfigurable Snake PV modules to conventional.

• Profitability of reconfigurable PV modules over 20 years of operation demonstrated.

Abstract

Non-uniform conditions within a PV module lead to significant energy losses in conventional topologies. Some of the energy lost due to partial shading can be recovered by installing reconfigurable modules. In order to explore the potential benefits of reconfigurable topologies in installations where non-uniform conditions are dominant, three shading scenarios are simulated throughout the year, both for reconfigurable and conventional modules. This allows the evaluation of the performance of each topology and estimation of the long-term gains. Using a cost function, which includes the additional investment cost, the energy gain can be translated to financial terms. Through this, locations where reconfigurable topologies can be beneficial, both in energy and financial terms, can be identified. The methodology is applied to the case of reconfigurable PV modules with a snake-like configuration. Simulation results show that these PV modules allow for higher energy production compared to conventional modules under all the simulated shading scenarios. However, they remain economically profitable over 20 years only in locations where partial shading is expected to occur daily, either throughout the full year or at least in the period of the year where energy generation is high.

Introduction

In recent years, the Photovoltaic (PV) market has expanded and PV arrays are installed in locations which are considered far from ideal. Building-Integrated PhotoVoltaics (BIPV), Building-Applied Photovoltaics (BAPV) and solar vehicles are increasing, leading to a plethora of PV plants which are operating under non-uniform conditions (Kumar et al., 2018, LIGHTYEAR, 2018, Salfiti, 2018).

Such non-uniformity can happen at different levels and can be due to different causes. For instance, installation of PV modules on different facades of a building, as well as on different parts of a vehicle, leads to non-uniformity between the PV modules. Furthermore, objects belonging to or surrounding a given building (e.g. chimneys or trees) can cast shades onto only a part of a PV module, thus moving the non-uniformity to a sub-module level (Shukla et al., 2016, Biyik et al., 2017). This can be even worse for solar vehicles, where the casted shade continuously changes while the vehicle is moving depending on the environment (usually urban) and the direction of the vehicle motion. Partial shading can be either dynamic or static. Dynamic shading can be caused by static objects (trees, chimneys) or by moving objects (clouds). Static shading is caused mainly due to soiling, but also bird dropping as well as localized degradation of PV modules creates static shading (Wohlgemuth et al., 2013). Operation under non-uniform conditions causes poor performance of standard series connected conventional modules (Teo et al., 2018).

A possible approach to mitigate the effects of partial shading and non-uniform conditions within the module is by allowing reconfiguration within the module and enabling control in the submodule level. The benefits of reconfigurable module topologies for static shading patterns have been discussed in Baka et al., 2014, Baka et al., 2016. It is shown that reconfigurable modules can recover lost power during conditions of partial shading, but produce less energy than conventional topologies under uniform operating conditions. Clearly, reconfigurable modules can be beneficial when non-uniform conditions are sufficiently present. However, this earlier work does not allow yet to quantitatively identify under what conditions gains extend beyond costs. To illustrate the potential long-term benefits of reconfigurable topologies, the performance of PV modules needs to be evaluated in realistic and dynamic shading scenarios over a longer period of time, thus a detailed simulation is required which includes time-varying effects. Ideally, one full year should be simulated, in order to account for variability of both overall irradiance and shading pattern. Results of a full year simulation can be extended to the following years by considering typical degradation rate of solar panels and power converters. Also, the cost introduced by extra components of reconfigurable modules should be taken into account.

To address this gap, in this work, an energy vs cost analysis is performed for the reconfigurable modules with a snake-like configuration previously introduced in Baka et al., 2014, Baka et al., 2016. Realistic shading scenarios are considered and the recovered energy is compared to the expected cost. It is worth to note that, although the discussion will focus on reconfigurable PV modules with a snake-like configuration, the methodology can be applied for any other module topology. This paper is organized as follows. In Section 2, works which focus on the mitigation of non-uniform conditions in the PV array are presented. The cost aspects which are considered for the design of reconfigurable modules are discussed in Section 3, where both design-time and run-time instantiations of reconfigurable modules which are considered in this work are presented too. The simulation framework, the shading scenarios and the simulation results in terms of energy are shown in Sections 4 Simulation framework, 5 Simulation results. The investment cost of these topologies is discussed in Section 6, and an estimation of the financial gain is made in Section 7. Conclusion ends the paper.