The sizing of the inverter in comparison to the rated capacity of the photovoltaic generator is investigated for high-concentrator photovoltaic (HCPV) systems. An HCPV module of typical characteristics is modelled and parameterized, taking into account direct normal irradiance (DNI), ambient temperature, air mass and aerosol optical depth as atmospheric inputs, while the DC losses of the HCPV generator are allowed to vary in the ranges reported in the literature. A set of 80 commercial inverters are analysed to obtain the typical efficiency curves of state-of-the-art low-, medium-, and high-efficiency inverters. Four locations worldwide with high annual DNI levels and different average values of the weather variables influencing HCPV performance are studied. Results show that the inverter can be sized between 84% and 112% of the rated capacity of the HCPV generator at Concentrator Standard Test Conditions depending on the scenario considered for maximizing the final energy yield of the system. The proposed methodology uses analytical equations, all the model parameters are provided and justified and atmospheric inputs are obtained from meteorological databases in order to make the application easy regarding its use in other locations where the climate data is available.

Introduction

The basic concept of the concentrator photovoltaic (CPV) technology consists in the use of optical devices to concentrate the sunlight onto photovoltaic (PV) cells. These systems incorporate different elements such as CPV modules, sun trackers and grid-connected inverters, with many possible different configurations (Muñoz et al., 2015). The present work focuses on high-concentrator photovoltaic (HCPV) systems, characterized by a geometric concentration ratio in the range between 100 and 2000 suns (Pérez-Higueras et al., 2011; Shanks et al., 2016). In HCPV systems, the HCPV modules are mounted on two-axis sun trackers because the optical elements must be always pointing to the sun in order to concentrate the sunlight on a very small area, where the solar cells (usually multi-junction III-V solar cells) are placed. In this way, HCPV systems only exploit the direct component of the solar radiation and are appropriate in locations with high annual levels of direct normal irradiance (DNI). HCPV technology is of big interest nowadays as an emerging renewable energy technology, which began the commercialization stage recently and has greater presence in the market than the rest of CPV technologies (Philipps et al., 2016). These systems have demonstrated the highest conversion efficiencies of terrestrial PV applications and the forecast of HCPV installed capacity for 2020 is above 1 GWp (Global Data, 2015). However, at present, the cost per generated kWh of electricity is higher for HCPV systems than for conventional PV systems (Talavera et al., 2016). This implies that a careful selection of all the system components must be carried out in the design of HCPV facilities in order to optimise the energetic and economic performance of the projects. One of the aspects to be considered is finding an adequate matching between the inverter nominal power and the PV array peak power. This allows the average annual inverter efficiency and, thus, the final energy yield of the system to be maximized. Even when many studies in the literature analyse the sizing of inverters for conventional PV systems, as shown in Section 2, and taking into account that all of these studies could be taken into consideration as a reference for adequate choosing the size of inverters in HCPV systems, it is important to highlight that the sizing task in HCPV is inherently different than the sizing in conventional PV systems. This is because of two main reasons: first, the main input regarding atmospheric variables in HCPV is the DNI, instead of the plane-of-array global irradiance considered in conventional PV systems.