PV AC Output Shows Added 2700 kWh many days

On a SAM run for a 25,000 kW DC field, looking at the hourly Gross AC output, there is an extra 2700 kWh thrown in most days of the year. In these hours there is NO Sun, NO DC output at all, just the added 2700 kWh of AC. It is always the hour before dawn or after sunset. Sometimes it is there for two consecutive hours. I checked several different manufacturer's modules, same result. I changed the array size from 25,000 kW to 27,000 kW, same result. What is happening here?

This happens at any size field -- I ran it at 1 kW, and the 2700 kWh still shows up -- pretty funny to get 2700 kW output from a 1 kW field! Then I saw a coincidence -- I was using a single point efficiency inverter, the 2700 kW Emerson unit. I ran it with a Solar Edge 5kW inverter, and now it shows a loss for those hours instead of a gain. That actually makes sense. So somehow the single point efficiency inverter model does not show offline losses, I guess. So should I just delete those 500 or so bogus 2700 values?

Hello,

Would you mind attaching a .zsam file that demonstrates the problem to a reply to help me troubleshoot?

Best regards,
Paul.

This looks like it might be related to an issue we found (and have fixed for the Fall 2012 release) that causes the single-point efficiency inverter model to report an AC output value equal to the rated capacity of a single inverter when it should be zero for some hours under certain conditions (typically in the hour of the day before the hour that the array starts generating electricity).

If you are using the hourly results for your analysis and it is practical for you to replace those values with zeros, then you can do that.

For systems with multiple inverters, the error may not have a significant impact on the total annual output of the system, which is the value that gets passed to the financial model to calculate LCOE, payback, NPV and other financial metrics.

Best regards,
Paul.