Will the Solar Panel on my tactical bag charge my phone?
09 Sep 2019 / Linus Lin
My 21W solar panel arrived on 9 July 2019 which I ordered from Amazon.com!
It weigh only 0.6kg, foldable and waterproof. Fit nicely on my tactical bag too.
If 6-hour of sunlight can charge my phone to full bar that should settle all my energy need for the 12-day Everest Base Camp trek!
On 10 July 2019, I did a basic 1.5-hour solar power experiment on the pedal boat along Singapore river nearby the sports hub.
These are the results:
Experiment 1:
Weather - Mostly cloudy
Duration - 1 hour (2.30pm - 3.30pm)
Method - Continuous charging into my pink power bank which was previously discharged
Performance - Managed to use the power bank to charge my Samsung S7 from 55% to 77%. (Up 22%) while the phone was off.
Experiment 2:
Weather - Sunny 70%, cloudy 30%
Duration - first 15 min (3.30pm - 3.45pm)
Method - Continuous direct charge into my Samsung S7
Performance - Increased from 69% to 79% (up 10% in 15min!!!) while my phone was off.
Next 15 min, the phone was stuck at 79% which was strange. Later found out from a friend that the phone has a protective mechanism to stop charging if the electric source is unstable (due to moving clouds)
Conclusion that day:
Always charge into a power bank from solar panel and not into the phone directly.
This solar panel seems to be able to fully charge my Samsung S7 (through my power bank) in about 2.5 hours (!!!) if it is exposed to direct sunlight of about 70% of the time.
In cloudy day, it might be able to fully charge my Samsung S7 (through my power bank) in about 5 hours.
Since my trekking altitude is high from 2860m to 5643m and mostly sunny without shade for 6 - 7 hours a day, sunlight should stronger. I might therefore be able to fully charge my phone + my power bank everyday! (Woohoo!)
All in all, this is a good buy!
It's only US$37.08 from Amazon including shipment to SG which took 8 days.
Comparing to paying US$3-5 on the mountain to charge 1 device per time at the solar station. I will end up paying much more there.
Today, 30 July 2019 marks the last day of my mini home-based solar experiment after testing this solar panel for 20 days on my kitchen grill. I have learnt much more about it and how much 'free' energy I can get.
Main thing to take note, this 21W panel is seriously overpriced at $50.20 if your intention is to use it to save money from your electric bill (see calculation). 51 years to break even??
However, just saw on Decathlon website that a 10W solar panel is selling at $65.00 (!!). So I am happy 
I learnt that direct charging into the phone gets about 25% more energy than charging through a power bank but doing this runs a risk of spoiling phone battery faster.
Charging a smaller power bank using solar panel gets about 50% more energy than charging a larger power bank that is about 3 times more in capacity. (I am guessing bigger power bank has more resistance??)
Based on all these experience gathered, I now know how to use this solar panels to gain the most possible energy on my 14- day trek
PS: since the panel is only facing the sky in 1 direction only, my recorded reading is not a result of 100% utilizing the panel's capability. Maybe 50% of its full potential is harnessed in these experiment 
I certainly recommend you to buy one such solar panel for your own Everest Base Camp Trek.
