Reference is now made to FIG. 5A, which illustrates a method 50 for wake-up and shutdown of module 405, according to embodiments of the present invention. Method 50 is applicable to both systems 20 and 40. In step 501, active control circuits, e.g. microcontroller 306, are turned on. Active control circuits are typically turned on (step 501) in the early morning when there is sufficient light to power the active control circuits typically with voltage of DC voltage source 101 reaching three volts. In decision block 503, when voltage output—or power output—from DC voltage source 101 is sufficiently high and stable (e.g. voltage input to module 405 is ten volts for a period of 30 seconds), then module 205,405 begins operation (step 53) in a safety mode. In safety mode, output current and/or voltage from module 405 is limited, for instance output voltage is limited to 2 volts and output current is limited to 10 mA so that a person can touch the wires of serial string 203,423 without any danger of electrocution. Note also, that in this case even if 25 modules are connected in series, the maximum output voltage of the string doesn't exceed 50V—which means the string voltage is still safe. Referring back to FIG. 3, safety mode may be achieved by controller 306 in module 405 by turning on FET 330 and turning off FETS 328, 348, and 350. Output wire 412 is held close to zero volts. Alternatively, the controller 306 may alternate the switches (e.g. switches 324 & 326 of buck converter) at a low duty-cycle in order to maintain a low output voltage.