Technical NoteOptimal sizing of a grid-connected PV system for various PV module technologies and inclinations, inverter efficiency characteristics and locations
Introduction
The purpose of this work is to calculate the optimal sizing of a grid-connected PV system under a wide variety of weather conditions and for four photovoltaic module technologies. The kWh produced by a grid-connected PV system is calculated as the sum of hourly production all over the year. This hourly production depends on many parameters such as [1]:
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PV array peak power Ppv,peak;
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solar irradiation on PV module plane Gβ;
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PV module temperature θcell;
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inverter efficiency and size Pinv,rated;
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maximum power point tracking losses; and
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other losses.
In a first part, the hourly production for various PV module technologies are estimated using a model elaborated by Durish et al. [2] in optimal conditions (maximal power point conditions) because the PV array is supposed connected to an inverter integrating a MPPT. Then, the efficiency of the inverter is studied and the various losses introduced. The optimal configuration is determined i.e. the sizing between PV array and its associated inverter with the aim of the highest production of the total PV system. Several parameters are taken into account:
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PV module technology;
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inverter type;
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PV module inclination; and
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location of the PV system.
In a second part, the monthly PV system performances are analysed in optimal configurations with various PV technologies, inverter types and photovoltaic modules’ inclinations.
Section snippets
Some models of PV efficiency and maximum power
The ambient temperature θa and the solar irradiance Gβ on the PV module tilted from β° have high effects on the PV efficiency. The most known model to describe the PV module efficiency, in MPP conditions, ηpv is given by:with θcell the PV cell temperature, ηref the reference module efficiency at a PV cell temperature θcell,ref(25 °C) and for a solar irradiance Gβ onto the module (1000 W m−2). γ and β′ are the solar irradiance and temperature
Grid-connected inverters
The inverter efficiency ηinvdepends on the DC/AC converter output power Pout. Electrical losses Ploss are described in a good approximation by a constant load-independent part called p0 (%) and a second one which includes all load-dependent losses [22], [23]:Pinv,rated is the rated inverter power; p0 and k are calculated from η10 and η100 efficiencies at 10% and 100% of the nominal power:Pin is the
Solar radiation estimation on tilted PV modules
The influence of the photovoltaic modules inclination on the optimal configuration is studied. The most available solar irradiation data are the horizontal solar global irradiation. As hourly tilted solar irradiations are used for the optimization procedure, the measured hourly solar global solar irradiations must be converted in irradiation on tilted plane. This objective has been reached in a previous paper [28] where many combinations of models have been tested. A combination of two models
Sizing optimization methodology
Optimum PV/inverter sizing ratios for grid-connected PV systems were determined in terms of total system output; the influences of inverter characteristics, PV modules inclination and technology (m-Si, p-Si, a-Si and CIS) and sites are studied. The optimum output of a grid-connected PV system depends on the relative size of PV and inverter. Numerous studies [26], [27], [32], [33], [34], [35], [36], [37] have been performed to determine the optimal sizing ratio (Rs) defined as the ratio of the
Optimization results
Successively, the following influences are studied:
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inverter type: type 1 to 3;
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PV modules inclination: horizontal plane (reference) and from 20° to 70° (by 5° step)
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PV modules technology type: m-Si, p-Si, a-Si, CIS; and
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locations: five Corsican and seven Bulgarian sites.
Monthly variation of the PV efficiency
The monthly mean value of the PV efficiency is calculated according to the PV technology for the 13 studied locations. In Fig. 10, the results are shown for Ajaccio and Sofia.
For m-Si and p-Si the variation is quite similar according to the month, the maximum is reached during winter (low temperature) and the minimum during summer due to the negative impact of the temperature on the PV efficiency. For CIS, the monthly variation is less sensitive. Concerning the a-Si technology, the monthly
Conclusions
The main results concerning the optimal sizing of a grid-connected PV system are:
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the parameter that most affects the relative size of the inverter and the PV array is the efficiency curve of the chosen inverter; for the same PV module technology and the same site, the PV array must be oversized by 30% or undersized 30% compared to rated inverter capacity depending on the chosen inverter;
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the influence of the PV module technology seems less important excepted for amorphous photovoltaic modules:
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