Optimal Design of a Grid-Interactive Solar-Photovoltaic Energy System: The Ateneo de Davao University Case

AUTHOR/S: Randell U. Espina


KEYWORDS: Solar, Photovoltaic, Optimal, Design, Grid-Interactive


              The study intends to understand the operation, the economic viability and the potential of a solar power technology to satisfy the electricity needs of the future. A 13.44-kW grid-interactive solar-PV energy system was installed at the roof deck of the Finster building of the Ateneo de Davao University, Jacinto Campus, Davao City, Philippines with a GPS location of 7.072 N° and 125.613 E°. For optimal energy production, a tilt angle of 22° and azimuth angle of -4° was used which predicted a high incident solar radiation for the months of March and October valued at 5.43 and 5.44 kWh/m2/day, respectively. The actual collected incident solar radiation reached 138.9 kWh/m2 within a 30-day period wherein a peak value of 7.26 kWh/m2 on a single day was detected.

             Four sub-inverters were used in which sub-inverter 1 (gt1) performed better than the other three sub-inverters. The difference in performance was influenced mainly by the “System Availability” (SA) and “Inverter & Transformer” (IT) parameters. SA is a derating parameter that represents the readiness of the solar-PV system to produce solar electricity at any given time when there is available sunlight and when all components are all functioning. On average, SA was 69.50% with the sub-inverter 1 (gt1) providing the highest availability at 82.70% and sub-inverter 2 (gt2) with the lowest availability at 63.40%. IT is also a derating parameter which reflects the efficiency of the sub-inverters and their corresponding transformers. Sub-inverter 1 (gt1) has the highest efficiency at 92.50% while the other sub-inverters had efficiency around 89.00% each.

             With the observed performance of the sub-inverters, the overall daily energy production was diminishing at a rate of 0.0098. Sub-inverter 1 (gt1) experienced the slightest reduction at 0.0076 and sub-inverter 2 (gt2) experienced the highest slump at 0.0129. Aside from the decline, the predicted average daily energy production was lower by 18.30% in which sub-inverter 1 (gt1) out-performed the other sub-inverters (gt2, gt3, and gt4).

             Using the predicted values, a solar-chart was developed to determine the optimal tilt and azimuth angles that can be used in a particular location. By measuring the intensity of solar radiation at 11:00AM and multiply it with 11.24 and 2/3, the solar radiation on a certain day can be found. With the estimated solar radiation on any day, multiply it by 10 (13.44kW x 74.4%) to obtain the expected energy production. The technique described above will help simplify in designing a solar-PV energy system.

              For optimal design of a grid-interactive solar-PV energy system, aside from sizing and selection of optimal tilt and azimuth angles, it is a requisite to suitably choose the right solar-PV modules and inverter. With the optimized design and increasing efficiency of solar-PV cells, the overall cost will be minimized and harvesting of solar radiation can be maximized. Once the acquired knowledge will be put into practice, solar power technology seemed to be a good source of electricity for Universities and the general electric consumers now and for the future.

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