African Solar

This design is © Copyright. In spite of its simplicity, it has involved much thought and learning through experience.  It describes a small “African Solar” system, which I have decided to put up here for the reason that it could be helpful to many. It is taken from my electronics book 6 or Less. I call this design “African” because it is unusually cost effective, its components should be readily available, and it is specially designed for installation without any adjustment or electronics tools—apart from a soldering iron and solder. The total cost of this small system is likely to be below R250 ($25), however potentially below R150 ($15), particularly if mass produced. OBSERVATION: The voltage which is produced by a typical 12V solar panel in full sun may exceed 20 Volts. The purpose of this circuit is to control both the voltage and current which recharge B1, a 12V 1.2 Amp-hour (Ah) battery.  Ideally, B1 will be charged at 10% of its Ah rating, which is 120mA, and at about 13.4 Volts.  Since this circuit puts out less than 100mA in full sunlight, it is recommended that R1, ZD1, and D1 and D2 be twinned with an identical circuit for increased charge current.  In this case, only points A, B, C, and D are wired together (A to A, B to B, and so on)—with, of course, the chosen solar panel and battery (these are not twinned). While this circuit does not pamper a battery, it does not punish it.  It does the job. Resistor R1 limits current from the solar panel, and should be rated 5 Watts minimum. Zener diode ZD1 limits the voltage to an "adequate" 13V, and should also be rated 5 Watts minimum.  In practice, rectifier diode D1 increases the 13V to about 13.5V, and serves to protect the circuit against mistakes while installing.  D2 again decreases the 13.5V to about 13V, and also protects the circuit, particularly from unwanted discharge of the battery.  D1 and D2 are rated 1A.  Some might consider this to be too tame a charge. If two 6.8V 5W Zener diodes are available, these may be wired in series for 13.6V, raising the charge voltage to an "upper" 13.6V. Alternatively, an additional 1N5401 in series with D1 will raise the voltage to about the same. The solar panel may be about 5 Watts upwards.  While a larger panel (say 25W) will not provide more power here, it will charge the circuit for longer, and in poorer weather.  The cost will of course be higher. The battery size may be increased, with appropriate modifications to the circuit to charge a battery at about 10% of its Ah rating.  As an example, if a 4Ah battery is used, five of these circuits may be wired in parallel—again wiring only points A, B, C, and D together.  A 10W solar panel may then be used, although 5W would theoretically be adequate.  This 1.2Ah system will power two 12V 1.5W 80 candelas LED light-bulbs for an evening, every evening, as well as powering and recharging small electronic devices (a 12V car socket might be useful for plugging in chargers).  In Africa, many homes have no lights or electricity at all—and with this in mind, even this modest system would represent an appreciable step up. For a home which is used to a few candles, 80 candelas is “wow”, and could for instance light up a kitchen and lounge simultaneously. It makes quite some difference how the solar panel is mounted.  Ideally it will face the sky, perhaps being slanted towards the sun. Points A and B may be crimp terminals for easy installation, and a terminal block may be used for easy attachment of peripheral components (such as lights) to battery B1. This circuit will run fairly hot in full sun.  As long as the components are suitably rated, they are designed to withstand such heat.  One should be able just to touch them still in full sun—but if they reach a burning heat, one may have wired up the circuit incorrectly—disconnect immediately and check. Low power lights would be required for this circuit.  The Osram 12V 1.5W 80 candelas LED Parathom would be an excellent choice, offering both low power and good light output.  These lights are the expensive part (R140 / $14 each), but are a once-off investment.  One could even find them at a car / auto scrap-yard.  While cheap, old-fashioned torch / flashlight bulbs could be used, they are comparatively ineffective and wasteful.  You may click on the image to enlarge. A number of small homes are successfully powered off this design.