I am designing an off grid system for developing countries for charging cellular phone, tablets pad and notebook computers. Design aim is to use low cost, simple, mature (slightly older) and mass-manufactured technologies. Your idea and contribution are mostly welcome.

  1. I plan to use ready made modules from ebay, etc.

  2. Is mono crystal solar panel better for this task? What point to take care on choosing PV panel and controller? 100W panel seem mainstream size.

  3. For notebook charging, I plan to use off the shell, 12V boost to 19 V, simple boost converter, 6 to 8A. Many excellent information in this post. Why do many laptops run on 19 volts?

  4. To what extend is 19V 'standardized'? Some posts mentioned some brands use special '3 wires' charger that communicate between notebook PC and charger, so that non brand charger will not work.

    To what extend is the power connector size standardized? Do I need to get those multiple size adapter kit? https://en.wikipedia.org/wiki/DC_connector

  5. For charging of 'slightly older' phone (USB 2, 5V, 0.5A), I plan to use an off the shelf 12 to 5V USB simple buck converter module.

  6. How about those latest phone and notebook that use USB 3.1, USB C, Quick Charge, Power Delivery mode, that are higher current, voltage or both? Are they backward compatible? What will they do when connected to a simple (no intelligent communication) buck converter supplying 5V?

    For use in developing countries, there is no need to chase the cutting edge. However, if it is low cost and easy to do, what are the prospect of something better than the basic "USB 2 at 5V 0.5A"?

  • 1
    \$\begingroup\$ Please don't ask so many, quite different, questions in one question. It's hard to impossible to provide an answer which will answer all of your questions in a good manner. \$\endgroup\$
    – Arsenal
    Dec 7, 2017 at 14:42
  • \$\begingroup\$ Sorry, will note in future. It is a single project \$\endgroup\$
    – EEd
    Dec 7, 2017 at 14:45
  • \$\begingroup\$ There are several companies producing this type of power system either for lights or vaccine fridges - a bit of research should help... \$\endgroup\$
    – Solar Mike
    Dec 7, 2017 at 16:21

2 Answers 2


There are quite a few questions here. Lets try to get them in order.

  1. MonoCrystalline PV panels are just a type of panel. They have their own intrinsic properties and for a long time (and still to a certain extent) had/have a better photon efficiency (more current per unit light). PolyCrystalline are just fine as well; they tend to be cheaper to make and buy. As to your project, I don't see a particular reason why you'd NEED one over the other, so either would be fine.

  2. Boost converters are likely not the way to go for laptops. Most require a decent AC line for their power bricks and even if you wanted to charge them with DC (which you can) there are a range of voltage tolerances and not every laptop charges at "19V." There are plenty of manufactures and chargers vary between 19V, 19.5V, and 20V. Charging a laptop at the wrong voltage will damage it and may cause a fire. For your convenience and for the convenience of anyone using your solar station, find an Inverter that can put out a few hundred watts and have two standard wall outlets for whichever nation you're taking this to be used in. This also helps in that you don't have to have 15 different DC barrel jacks laying about to keep track of.

  3. USB 3.1 chargers are 5V @ 900mA. USB charging on older phones could range up to 5V @ 2.1A. USB-C is complicated. Power Delivery standard uses the CC pins to negotiate the Voltage AND the Current.These range from 5V @ 500mA all the way to 20V @ 5A. Quick charge (Qualcomm)is proprietary and so is Dash Charge (OnePlus). You'd likely run into some issues implementing those. Since you asked for a suggestion, 5V @ 2.1A with a USB-A port is the best bet and supports the most phones. Anything other than that is rarer in use and another good reason to have an Inverter for AC lines. If you have those you can have people bring and use their own chargers for their own phones and not run into any issues with charging speed, intellectual property, or other mishaps

  1. As Dave notes, the voltage is not totally standardised. It could be 18V or 20V or something else. The connectors are not standardised at all. Some laptops, including DELL, use a third wire. This allows the laptop to communicate with the charger, to make sure they are compatible.

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