i am not against this product, but i think the solar panel is just a gimmic.
let me put it this way
"Solar Panel: 5.5V/127Ma(0.8W). 17% transfer efficiency.
Outputvoltage/Current: 5.0V/500MA " cited from the seller
a battery of 2600maH need some current to charge. assume 100% charging efficiency, Using solar panel, 2600/127 = 20.5 hours Using external power supply, let say a common (for LI cell) 5V 500ma input, 2600/500 = 5.2 hours.
Now, calculate using 80% energy conversion rate for both system Solar Panel need 20.5 X 1.2 = 24.6 hrs External power 5.2 X 1.2 = 6.24 hrs
Since seller state can just leave it beside window,so energy being reflected + not in correct angle. Solar panel efficiency only left 25%. External power remain the same. Solar panel need 24.6 X 4 = 98.4 hrs External power maintain 6.24 hours.
put in the factor of only 8 hours a day for sun light, solar panel need 12.3 days to complete charging.
Other than use the 2600mah lithium battery for external power, Solar Panel is just one extra gimmic and it is too insufficient for doing charging. (IMO)
i will only buy it for the battery, not the solar panel.
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