The Green Science Experiment

At a recent Stewardship Ministry meeting, Diane spoke about the lack of lighting in the far parking lot and expressed concern that this could lead to an avoidable problem.  It was decided that this presents a good opportunity for a science experiment involving solar lighting.

The problem with using solar power to light an area is that there is typically only an average of a few hours a day of sunlight bright enough to charge a battery, and that battery storage systems get very expensive as they get larger.  So, to be economically feasible, the power drain has to be kept to a minimum.  Doing this can be achieved by using high-efficiency, low-power bulbs and turning the lights on only when necessary.  The advent of inexpensive low-power, high-efficiency, LED lighting makes this possible.  For our system, three 12-Volt bulbs were used that consume only 9 watts each but produce over 350 lumens of light per bulb.  Just a few years ago, this efficiency would not have been feasible at a reasonable price.

To limit the turn-on time, a solar controller was chosen that not only keeps the batteries charged but also keeps the lighting system deactivated until after sunset, and then allows the period of activation to be adjusted to a given number of hours.  An inexpensive commercial wireless driveway alarm system was installed to sense cars or pedestrians entering the parking lot and to turn on the lights during the period that the solar controller is active.  A timer circuit was constructed to shut off the lights after 3 minutes.  This circuit was modified to retrigger the lights if additional cars or pedestrians enter the lot during the 3 minutes the lights are on.  In addition, a power-on reset circuit was added to keep the lights from triggering when the controller activates at sunset.

photo 5-6

Motion detector for solar lights

The system is now installed and running, and what remains to be seen is whether the solar panel is large enough to keep the batteries charged during the winter when sunshine is minimal and the system is activated for a longer period after sunset.

Solar powered lights for parking lot

Solar powered lights for parking lot

The prices for the major system components are as follows:

solar panel and cable                                       $110

2 deep-cycle solar batteries                            $170

solar panel charger, controller, regulator         $  25

LED bulbs and sockets                                   $  25

driveway alarm                                               $  15

Wire, parts for the fixtures and timer circuits, system housing, solar panel bracket etc. were donated out of stock by various people.

by Ira Hartman, Stewardship Ministry

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