Battery is not running in simulation

Hi,

I'm new to SAM so bare with me. I'm trying to model a PV+battery system using my own load in the simpler version PVWatts to begin with, but somehow it doesn't seem like the battery are used in the simulation. The battery do not charge from neither the PV nor from the grid and moreover it doesn't cycle at all in the simulation.

I suspect that some of my parameters are wrong since I also get a negative NPV.

If someone could help me with this I would be thankful!

I'm attaching the file for the simulation that I'm running.

Hello,

We're here to help, especially if you are new to SAM. Starting with the PVWatts version is a great way to familiarize yourself with SAM before diving in to the more complicated Detailed Photovoltaic model.

There are a few causes of the results you describe:

• The battery power is high compared to the battery capacity. A good rule of thumb is for the battery capacity in kWh to be twice the value of the battery power in kW. For your design, changing the battery size to either 5 kW / 10 kWh or 3 kW / 6 kWh results in a system that cycles the battery. To see battery cycles, on the Results page, go to the Heat Map tab and display the "Battery state of charge (%)" variable.
• The big peaks in your load data tend to be at night, and the peak shaving algorithm charges the battery as soon as the peak period is finished rather than waiting for the daytime, so it ends up charging the battery from the grid more often than from PV.
• On the Cash Flow tab of the Results page, you can see that even with the tax incentives, the annual electricity bill savings (ranging from $180/yr to $249/yr in constant dollars) are not sufficient to cover the initial $10,800 installation cost. That's causing the negative NPV, even with adjustments to the battery size.

Thanks,
Paul.