Sukatani revisited: on the performance of nine-year-old solar home systems and street lighting systems in Indonesia

In 1988, 86 solar home systems, SHS, and 15 street lighting systems, SLS, were installed in the village of Sukatani in the province of West Java of Indonesia. The systems have a PV array of 80 Wp. In this paper we analyse the performance of these systems. For this purpose we use monitoring data and data from field surveys recorded in the period 1988-1993 and data collected in a field survey in 1997. This survey comprised both technical measurements on 62 solar home systems and interviews with 22 users of these systems. We found that, although the failure rate of street lighting systems is high, the villagers have a positive opinion about these systems. Further, we found that technically the solar home systems performed well. The users are satisfied about the performance. However, in the course of time the configuration of the SHS has changed: villagers have replaced most of the strip lights with cheap home-made candescent lamps and have replaced the initially-installed 100 Ah capacity solar batteries with cheaper locally produced 70 Ah capacity car batteries. From an analysis of monitoring data we found that the average irradiation in Sukatani is 4.2 kW/m2/day, which is a common value for Indonesia, but more than expected in 1988 when the systems were installed (3.5 kWh/m2/day). Furthermore, we found that daily electricity consumption per SHS can be as high as 25 Ah/day. Average values, however, range from 8.8 to 14.8 Ah/day, which is 15-50% below the daily load used in the design calculations (17.4 Ah/day). However, the average daily electricity consumption is close to the recommended value on the instruction sheets given to the users of the SHS. Because of the low demand of electricity the average performance ratio is 49%. By means of an energy loss analysis of the PV systems we found that 15% of the theoretically available energy from the array cannot be fed in the battery because it is fully charged. The replacement of 100 Ah batteries by 70 Ah batteries was justified on the grounds of the low electricity consumption of the SHS users in the period 1988-1993. On the basis of field surveys we found that the average lifetime of the 100 Ah and 70 Ah batteries is 4 and 3.5 years, respectively. The realized battery lifetime is rather long compared with other SHS projects in the world. While the average battery size in Sukatani decreased in course of time, we found on the basis of interviews with users of SHS that the average daily electricity consumption increased. We found a value of 18 Ah/day in 1997. Furthermore, the spread in the demand of electricity in 1997 and the use of other than initially-installed appliances, such as small incandesent bulbs and intercoms, indicates the need for a broad offer of system sizes and low power appliances. By means of design calculations we found that PV arrays in the range of 35-130 Wp are needed to satisfy different demand patterns. We conclude that monitoring by means of data loggers is a useful approach to allow the analysis of the long-term system performance. To increase the statistical reliability of results, monitoring should be supplemented by field measurements and interviews with users. However, due to the deviation between real and narrated experiences, interviews alone may not be sufficient to assess an SHS project.