In order to keep the total power consumption low, high efficiency LED Lamps were used. Each lamp comprised of 3 Luxeon Star 3 watts LEDs driven by a constant current circuit at 400mA. The lamps were operating at 12Vdc. The lamps housing is IP44 comformance, meant for outdoor use. It is important in Cambodia because at night, there are alot of flies attracted to the light and they will try and enter the lamp unit, thus destroying the leds and its electronics.
We have to digg trenches to lay conduits and cables all over the orphanage compound for the installation of 24 lamps at different locations. Since we are covering long distances in the cable laying, sometimes more than 400 meters, we have to use a higher operating voltage other than 12Vdc. We operated at 24Vdc to overcome the losses from the voltage drop along the cables. Also, we used thick copper cables, 6mm diameter, to minimise voltage loss. Hence we have to connect 2 LED lamps in series so that it can operate at 24Vdc.
The controls for the solar charging is design around a charge controller from morning star. Simple to use and reliable. It has a build-in meter for charging and load current readings and also the battery voltage. This makes it convenient for testing and troubleshooting. The whole security lighting at the orphanage is divided into 4 zones and the switches are placed at the control box. In the morning, it is easy to switch off all the lamps because it is located at a central location. We used 4 lead acid batteries, each having a capacity of 120 AH. This provides enough stored solar charge for up to 3 days operation even on cloudy days where solar charging is minimum.
The mounting of the solar panels was a challenge. We finally were able to mount it on a pole using available resources such as dinning tables, stack up, from the orphanage.
The solar charging and discharging cycle is shown in the graph. When the sun rises, charging begins at around 7 am and peaks at 1 pm and begins to decline after 5 pm. At night at 7 pm, the lamps are switched on and the discharge cycle of the batteries begins. The terminal voltage of the battery never falls below 25 volts. Hence the system is balanced, i.e. day time charging is sufficient for the whole night operation.
Once completed, we switch on the system and it works as planned. The orphanage was litted by solar one!
