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Technical Summary

When operating in a mobile outdoor environment, there are many factors that impact ability to gather solar energy. Some of the larger factors are:

  • Solar Resource – On a bright sunny day, there can be approximately 1000W/m2 coming from the sun. In high altitude environments, this can go as high as 1200W/m2 while an overcast day can bring down the power significantly.
  • Orientation to the sun – To maximize energy harvest, the solar module must be pointed within 20 degrees of the sun. At angles further away from +/-20, the power rolls off as a function of the cosine law (power = max power * cosine (angle))
  • Behind glass – When behind either a standard window or windshield, the amount of solar power is reduced.


Based on these factors, Alta has selected 4 common use conditions that are used in the energy calculator.

  • Direct sun – the device is placed in direct, bright, outdoor light and angled toward the sun. We assume 1000W/m2 in this instance.
  • Indirect sun – the device is outdoors but is not actively pointed toward the sun. The device may be on a backpack, a belt, a table or otherwise moving. We assume an average of 500W/m2 for this condition.
  • Window sill – the device is placed flat on a window sill in direct sun. No consideration is made to point the device to the sun. This results in an average of 200W/m2.
  • Near window – the device is within a few feet of a window and will experience some direct sun during the day. Once again, no consideration is made to point the device at the sun. The average energy is estimated at 100W/m2.


These common use conditions are then used to calculate an estimate of how much solar power is incident on the solar material across a single day. For instance, if the user states they are an outdoor worker, then the total irradiance seen during the day is 1 hour at 1000W/m2 and 5 hours at 500W/m2 or 3.5kWh/m2. This number is used with the efficiency of the Alta material and the active area to determine the quantity of watt hours generated.




Alta Devices
545 Oakmead Parkway
Sunnyvale, CA 94085
1-408-988-8600

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