A thesis submitted in partial fulfillment of the requirements for the Degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1989

For sizing a photovoltaic system to supply a specified load in a region, knowledge in predicting the future radiation profile is necessary. Oversizing can always be an easy solution but neither the manufacturer nor the user can financially survive by this. Hence, radiation prediction with an acceptable level of accuracy becomes essential in sizing to prevent undersizing as well as oversizing. Two models have been developed and proposed for the prediction of required radiation and available radiation. The first model computes the minimum daily average radiation required for the system to survive without failure, given the load and the consecutive days-of-run. The component ratings of the system, PV panel size and battery size are observed to have great influence on the necessary radiation. The second model calculates the probable mini mum radiations in the future, given the number of consecutive run-days and the percentage probability with which the values are to be minimized. The five-year radiation data for Bangkok (1983 1987) were obtained from the climatological division, Bangkok, and were statistically processed-for the use of the model as raw data. Computer programs are written for the models, and the output of the two models, when superimposed on each other, gives a clear idea about the system performance and about the optimum sizing. In the experimental part, a photovoltaic hybrid system was designed and set up in the AIT energy park. A special study by the author previously revealed that a photovoltaic hybrid system (PV + a back-up source) would be the most economical choice than either constituent chosen alone. A de power source (12- 18V, 7A max.) was designed and used as back-up. Electronic circuits to start the back-up source automatically when the solar energy is insufficient, and to stop it automatically when there is enough solar energy, are designed and fabricated. The whole control over the loads and the collection of necessary data is taken care of by an APPLE-II microcomputer, using a control program in APPLESOFT -BASIC. The system operated successfully and several load profiles were executed in the system and the results are analyzed.