Abstract:
This thesis describes a 200 kW Battery Energy Storage (BES) System owned and operated by The Electricity Generating Authority of Thailand (EGAT) at Fang district Chiengmai Province since 1997. This system derives electricity from the near by Geothermal Power Plant to store in a 2600 ampere -hour 600 volt Lead -Acid battery bank during off peak (10 PM. to 9 AM.) and despatchs the stored energy via a 200 kW inverter back to grid to help shaving peak demand from 5 PM. to 9 PM.. During the first phase of operation battery was discharged at 10% capacity continuously for 10 hour and was found to perform according to the battery specification. The evaluation result of this system reveals that BES can help shaving peak demand of the district by about 2.2 %. The system efficiency was reduced from 74 % in 1997 to 63 % in 2001 due to inappropriate operation and maintenance of the battery while the inverter can still maintain its 92.5 % efficiency. Following the June 2001's experiment ,it was found that the battery was undercharged because the charging voltage drops to 2.23 volt / cell and the specific gravity of the acid solution drops to 1.24whgrch is not appropriate. From the economic evaluation of the BES system, its benefit is less than its cost even if the Time Of Use (TOU) rate is applied. It is observed that the cost is quite sensitive to its loan interest rate. Should a 50 % subsidy is made available it would become economically feasible if the interest rate does not exceed 5.5 % ,provided that a proper charging scheme (Step Charging) is applied. Since the present Daily Depth of Discharged (DDOD) always exceeds the manufacturer's specification ,which resulted in a shorter usable life of battery ,it would be interesting to consider other types of battery such as Nickel -Cadmium or Vanadium ,which is claimed to be suitable for a high cyclic application such as a BES.