Hi Michael,
On the PV system design page, the PV system has an AC capacity of 3,181 kWac.
On the Battery Cell and System page, the battery has a maximum discharge power of 558 kWac and storage capacity of 3 hours.
On the Electric Load page, the peak annual load is 1,212 kWac, and the total annual load is about 6.4 million kWhac.
To avoid using grid power at night, the battery discharge capacity needs to be high enough to cover the peak nighttime usage, which is higher than the 558 kWac for your battery. The battery storage capacity also needs to cover the period from sundown to sunup, which is longer than the 3 hours for your battery. In order to both cover the daytime load and charge the battery sufficiently to meet the nighttime load, the PV system will need to be larger.
When you use REopt to size the battery, it generates a time series (hourly or subhourly) battery dispatch profile that minimizes the project NPV. It does not generate a dispatch profile to avoid or minimize grid usage. (Depending on the rates on the Electricity Rates page, minimizing NPV may effectively reduce grid usage.)
Best regards,
Paul.
