Image Placeholder


Technical Note: TN0075 - Rev 01

Introduction:

The integration of a Pyranometer will allow you to measure the amount of total sunlight available at any point in time and help you to check the performance of your solar charging sources.

This in turn will enable the SP PRO to switch a controlled load on and off based on the amount of solar power available and help you maximize the use of your solar in an SP PRO based battery system.

Equipment needed:

  •  5W solar panel
  • 5W loading resistor
  • A connection of the above to one of the two analogue inputs of the SP PRO

Whilst the Solar Panel could be any size, something in the order of 5W would be most practical. It should be mounted alongside the main array and in the same orientation.
 
Theory of operation:
This takes advantage of the linear part of the solar panels I/V power curves, by loading the panel with a resistor that keeps the voltage it in the linear region, thus giving a current roughly linearly proportional to irradiance - as shown by the yellow line below, where “full sun (1000W/M2)” would give approximately 10V, that is V = I x R, so 0.31Amps x 33ohms = 10.23V.

Image Placeholder

 


This is of course an approximation though, as Isc does change slightly with the solar cell temperature. You can also purchase pre- assembled pyranometers.
 
Uses:
Can be used to enable a relay output, which if used in conjunction (connected in series) with an SOC enabled relay output, could be used to turn on via a contactor a load dump or discretionary load control of a Hot Water System or Electric Vehicle. For example, if the battery State of Charge is greater than say 95% and there is more than say 12V from the Pyranometer then we can assume there is spare Solar available to use.

As shown below, the points which are used to start and stop the above events is configurable.


 

Image Placeholder

Image Placeholder



Can be used to monitor instantaneous irradiance via the SP LINK.
Image Placeholder




Can be used by the performance data viewer to display historical insolation seen by the array.

Image Placeholder