Using the battery for nighttime inverter load instead of pulling from the grid

Hi all,

I'm modeling a PV-battery single owner system, and using retail electricity rates for any electricity purchases. Battery dispatch is: 'automated dispatch' where the battery can charge from the system and clipped system power but not the grid, and uses a perfect one day look behind (although I've tried a perfect-look-ahead with 28 hours and shows the behavior below).

I see costs in the cash flow line item "Energy from grid (kWh)" that I'm assuming are the nighttime inverter losses. This makes sense to me that we need some power at night for the inverter, but thinking about it, I'm wondering why the battery system does not keep enough charge to supply this power so that they system can pull from the battery at night instead of the grid. Exporting power earns less even in the peak periods than importing energy from the grid (I've tested with PPA prices significantly below the retail electricity rate to check), so it would make sense for the battery to hold onto some power to cover that nighttime load.

I've made sure that the utility power rates are above the 'cycle degradation penalty' value. I've also checked out this slightly related issue, but I don't think that it applies:  github.com/NREL/SAM/issues/370
- Colin

Hi Colin,

For the PV Battery configurations, SAM's automatic dispatch options do not dispatch the battery to meet nighttime inverter consumption.

There is one exception that is a special case: For behind-the-meter systems with grid outages, the battery does meet the inverter nighttime load during a grid outage.

Best regards,
Paul.