What are the optimum conditions for solar charging?

Angle towards the sun
	To get the best results the solar panel has to be positioned in a 90° Angle towards the sun.
Time of Day
	The earth’s atmosphere diffuses the sun’s power. When the sun is high in the sky the light has to travel a shorter way through the atmosphere than when it is low. From 9:00AM to 15:00PM the sun’s light has to  travel shortest, and solar conditions are optimum. Periods after and before are less efficient.
Cloudiness
	Foliage & Cloudy weather significantly impede the working of solar. A sunny and bright day with blue skies will bring the best solar efficiency possible.
Position on the earth
	Your position on the earth determines the angle towards the sun and therefore the efficiency. The closer you are to the equator the better the result will be.
Direct sunlight
	The charger needs to be in direct sunlight, without any surfaces (such as glass/plastic windows) in-between. Windows can block UV-light and solar energy.
Power & Duration Calculation[1]
Sunlight hours per Day[2]	To get the readings spot on, divide the time you need to charge a device by the number of hours of sun per day (not to be confused with daylight hours).

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[1] Under optimum conditions

[2] Depends on country and time of year