Energetica India Magazine nº88 March-April 2020

termine array capacity for a system with PWM based charge con- troller, the array capacity will be substantially undersized. Array derating factors and sub system efficiency must be considered based on the site parameters and system configurations. For ex - ample, efficiency of an inverter is dependent on the actual input power and operating temperature. Therefore, the inverter effi - ciency factor must be estimated based on the efficiency versus load curve of the inverter and operating temperature of the site. It is advisable that the design load should be first multiplied by an oversupply co-efficient to allow for the required increase in array size. Consideration of over supply co-efficient will help in the following ways: • Less impact on the performance of the system due to variable solar resources • System would be able to meet demand due to progressive increase in new loads • Less impact from continuous degradation PV array over a pe- riod of time A minimum value of 1.2 to 1.3 of over supply co-efficient should be considered. Critical loads require a higher value of over sup- ply co-efficient than non-critical loads. Recommended Standards for mini-grid system design: Designers and installers should follow standards that are typi- cally applied in regions (within and outside the country) where solar PV Mini-grid systems are installed. In case there are no country specific standards available, IEC or other equivalent in - ternational standards should be followed considering modifica - tions as needed, to fit local conditions. The standards are often updated and amended so that the latest version is always be applied. The following IEC standards are specifically applicable for designing PV Mini-grid systems: • IEC 62548: Design requirements for Photovoltaic (PV) arrays • IEC 62257- Part 9-1 to Part 9-5 Recommendations for small renewable energy and hybrid systems for rural electrification. SOLAR POWER 38 energetica INDIA- March-April_2020