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  1. Larry Schlussler
  2. Cold chain equipment
  3. Tuesday, 18 June 2019

EHC is a valuable method of obtaining excess energy from an SDD refrigerator, however an autonomous solar direct system powering USB ports is a simpler, more reliable and less expensive method of providing auxiliary power.

USB ports can be powered directly from a solar panel, no batteries are required. The conversion device is simple and reliable; these ports can be used for charging cell phones, ipads, lights and AA or AAA batteries.There are a large variety of lights available: lanterns, directional lights, headlamps and lights with motion sensors. Jump starting car batteries can also be charged by a USB port. If desired a 12 volt port could also be incorporated to power a fan and if needed a 12 Volt battery. USB charged devices typically require an average of 3 watts of charging power. Twelve watts of solar per USB port will supply reliable charging at the beginning and end of the solar day and during overcast conditions. For 4 ports a 48 watt module would provide highly reliable power. This would charge at least 8 devices each day.

Having an autonomous system for auxiliary loads has a number of advantages:

- With EHC’s the controller is designed for a specific brand and model of refrigerator. An autonomous solar system will work with all types of refrigerators.
- As a consequence of working with only a specific brand and model of refrigerators the aggregate cost of testing will be very high.
- Testing must also be carried out for each specific type of load, resistive, battery charging, etc.
- Trouble shooting system in the field will be much simpler with an autonomous power system there will not be the possibility of interaction between the two systems.
- The autonomous system with USB ports would be inexpensive and easy to install.
- When solar conditions are poor the autonomous system will provide more reliable power for a greater portion of the day.

I would be glad to discuss the pros and cons of this system further. EHC’s are a good concept because a 60 watt load is typically powered by a 300 watt array. However, I think a separate autonomous system is a more appropriate solution.



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