single string which will slightly oversize the battery bank of 6783Ah。

TABLE IV。 DEEP-CYCLE LEAD-ACID BATTERY CHARACTERISTICS

Battery Voltage Weight (lbs) Ah @ C/20

Surrette 12 272 357

Hence,  the  batteries should  supply daily load  demand   of

1882。4 Ah/day with a 12V system voltage and 85% inverter efficiency is given by (1)。

TABLE III。 DAYS OF BATTERY STORAGE NEEDED FOR A STAND ALONE SYSTEM WITH 99% AND 95% SYSTEM AVAILABILITY

To size the PV array, the peak-hours of daily insolation approach is used。 From the insolation data for the site, the worst average daily insolation is in November which is 4。757 kWh/m2。 The PV module used is Suntech 140 W with electrical performance of the PV module under Standard Test Condition (STC) is listed in Table V。

TABLE V。 ELECTRICAL CHARACTERISTICS OF SUNTECH 140W PV PANEL

Characteristics Rating

Maximum Power at STC 140 Wp

Open circuit voltage 21 V

Optimum operating voltage 17 V

Short circuit current 9。5 A

Optimum operating current 8。24 A

Operating temperature -40°C to +85°C

Maximum system voltage 1000 V DC

Prior to size the storage system, the critical load must meet 99% availability of 8760 hours in a year but 95% availability is satisfactory to meet less critical load。 However, flexible strategy must be taken into account because sizing battery storage needed to meet the demand of 99% availability can simply triple the cost as compared to storage system needed for 95% availability [4]。 Thus, the idea to reduce 5% load for generator will be an economic strategy for this system。 By applying (2) and (3), 3 days of usable storage are needed as November is the design month due to its lowest insolation。 Table 3 gives an estimate for storage days needed to supply the load using the peak sun hours per day as the design month。

Deep discharge lead-acid batteries of Surrette  12CS11PS as shown in Table IV that can be routinely discharged at 80% is chosen for this system。 Therefore, total usable storage needs about 5271Ah for 2。8 days of storage with nominal battery capacity of 6589Ah at 12 V。 These result 19 batteries in a

By using (4), one string of solar panel will deliver 31。8 Ah/day with 90% coulomb efficiency and 90% de-rating factor。 In the end, 59 numbers of parallel strings of PV modules are required to provide 1882。4 Ah/day with 12 V system voltage。 Fig。 5 shows that the PV system designed can supply the entire load even in the worst month of November and deliver excess energy for the rest of the months。 The load demand is constant throughout the year at 19。2  kWh/day which by using peak-hours of daily insolation approach, the solar power system output can generate at least 19。431 kWh/day for the lowest insolation occurs in November。

Fig。 5。 Stand alone PV-battery system designed to cater the worst month deliver energy more than the demand needed throughout the year。

IV。RESULTS

This section goes through the simulation performed in this paper。 It will cover desalination process mentioned previously for stand-alone power system。 The bases of analysis are on economical and electrical analysis。