The performance ratio (PR) based on IEC 61724 standard is calculated under the influence of seasonal variations and the capability of the system. On the other hand, The National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy proposed the weather-corrected performance ratio (PRcorr). This PRcorr index calculates the performance of the PV system which has taken the weather variations that influence the cell temperature into account. Both techniques were compared with the simulation program to analyze the PR index according to system conditions. The study site is the on-grid PV rooftop at Kasetsart University Chalermphakiat Sakon Nakhon (CSC). The PV panel is oriented to the southwest, 215 degrees azimuth. The angle of the inclination of the panel is 17 degrees. The result shows the trend of monthly PRcorr with little variations. At the same time, the PR value over the year has a lot of variations. The variation of PRcorr and PR is 2.39 and 5.07, respectively. PRcorr has low variability due to the correction of weather factors. The average cell temperature is an important variable. To calculate the average temperature of the panels, one year of data is needed to filter out distorted information. The system available condition is an important factor for the on-grid PV system at low voltage.

Study for investigated the optimum photoperiod from blue LED light for the growth of Chlorella vulgaris in culture tank. Photoperiods from blue LED Light (Light/Dark) were set up at 24:0, 16:8 and 12:12 h. The initial number of C. vulgaris cells was 1.6 x 105 ± 0.12 cells mL-1. Culture medium was using commercially available fertilizers. After 17 days of cultivation, the results showed that the 24:0 h photoperiod had better growth of algae than 16:8 and 12:12 h, with maximum number of cells of 1.64 x 107 ± 0.23 cells mL-1 specific growth rate (SGR) was 0.17 ± 0.05, -0.06 ± 0.11 and -0.19 ± 0.1% day-1 with statistically significant differences (P < 0.05) in day 5 of cultivation. The stationary phase continued up to day 3 of cultivation, between the treatment. The optimum temperature for growth ranged from 35.5–38.5°C. The results showed that blue LED lighting at 24:0 h is the optimum photoperiod for cultivation of C. vulgaris. Keywords: Photobioreactor tank, Photoperiod, Blue LED light, Chlorella vulgaris, Growth rate