Solar Powered Portable Charger
Due to limited testing resources (phones), a voltage regulator was connected to ensure a constant voltage for the USB connection. Doing so allowed us to simplify the initial testing.
Complications lie in the USB connection.
Voltage across the regulator behaves as expected with increasing output corresponding to increasing input. However, the phone had issues charging with the test circuit.
With
Voltage
Regulator
Without
Voltage
Regulator
Adding the voltage regulator seemed to load the system too much to power the USB. Removing the regulator allowed it to charge, when the voltage was maintained within 5V and 7V. This can be worked with.
A project group in EE 413 Advanced Electronic Design had the opportunity to test a prototype of this system in-depth. They similarly got this circuit to work, even with a solar DC source. However, one student of the group noted that in the system, "there are current spikes and voltage stability problems. When starting the system... the diodes change their characteristics." It was possible to charge the phone for a moment, but maintaining it was difficult, due to the inconsistency of solar power.
Cooking smoke is estimated to cause 3-4 million premature deaths annually. (see Wilson)
As of April 2016, Kuyere has reached at least 1000 households and helped them install solar. At that time, they estimated that they'd have helped with 13,000 households by 2019.
A typical 10 kJ mobile phone battery provided 5V and 1 A, well within reason if the power supply is a solar panel:
5V * 1A = 5 W = 5 J/s.
10 kJ / (5 J/s) = 2000 s ~= 30 minutes.
3200 mAh = 3.3 Ah.