I am a high school robotics teacher (no formal engineering training) and I am taking a group of students to Kenya this summer to work with high school students there. The organization we are travelling with has asked us to help out with a side project at a small rural village that has no electrical power grid. They have said that most of the households have no lights in their homes but they all have cell phones. The problem is that along the equator days and nights are essentially 12 hours each all year long. This makes it difficult for students to study at night and for parents to work much after sunset. In addition, only a few individuals have the ability to charge phones which means others must wait in line for charging.

The proposed solution is a solar system for individual homes. I am trying to design something to test with the idea that the more we can purchase with the funds we have will mean we can help more families. Here is what I have so far.

  1. We are assuming that the system will have an LED light which needs 10.5 W and a USB port which needs 18W. I have drawn up a simple schematic for everything but the USB. I am not sure where the USB would go. I am thinking between the LED and the battery. I am also wondering if this product would work.

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  1. I am also trying to calculate battery requirements. I have used the following formula to estimate storage capacity:

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What am I missing with these estimates? Once I have this figured out, how do I calculate the minimum power requirements for the solar panels?

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    \$\begingroup\$ So, is it the case that you want to supply sufficient power during the day to provide both complete recharging the cell phones and also charging of some battery system that will provide night-time lighting for homework and studying? If so, you have to total up the energy required for cell phone charging plus the total energy required for reasonable nighttime use of lighting for study. Also, you have to take into account the relative angle of the sun during the day to the solar panel (cosine function.) They will need energy storage (batteries.) \$\endgroup\$ – jonk Mar 31 at 6:34
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    \$\begingroup\$ Have you searched for this? It has been done many times and people posted blogs, schematics, videos etc Even one full write-up in the HomePower magazine... \$\endgroup\$ – Solar Mike Mar 31 at 7:04
  • \$\begingroup\$ Which edition of HomePower has the write up? Their site does not appear to be very serachable. \$\endgroup\$ – SteveC Mar 31 at 16:23
  • \$\begingroup\$ I was trying to calculate for charging a cell phone for 3 hours during the day and then powering one LED bulb for 4 hours at night. I am trying to keep the battery discharge above 50% and account for the possibility of only being able to charge every other day. From that, I came to the conclusion that it will need a battery with 43 Amp Hours storage. Do those calculations look reasonable for the battery size? \$\endgroup\$ – SteveC Mar 31 at 16:30
  • \$\begingroup\$ My next step was to find the solar panel appropriate for the design. It looks like I am going to determine the average azimuth of the sun at that latitude and also consider the roof design of the houses. Anything else I might be missing? \$\endgroup\$ – SteveC Mar 31 at 16:30

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