Salt River Project management has proposed dramatic changes to its residential electricity rates that carry significant impacts for its more than 12,000 rooftop solar customers.
How Not to Install PV - Shadow Considerations
This PV array was installed under a tree and as a result the branches of the tree were casting shadows on the PV modules.
These shadows have a severe impact on system performance because the current produced by a PV module is determined by the least illuminated cell in the PV module. In this case all three PV modules have shadows cast by the over-hanging tree.
In full sun we measured an output of about 5 amps with the shadows shown above. There was also an area of sap over one of the solar cells (photo does not show this). After the branches were trimmed back, the current increased to about 9.5 amps. Cleaning the sap covered area increased the current to 10.5 amps, the expected value for the three PV modules.