part time residency

How to determine the amount of PV power and amount of battery storage required for a residential owner to minimize average annual cost for a system to offset grid electricity purchases for this situation:

1. Home occupied for 6 months per year, very low monthly load when unoccupied, nearly constant monthly load when occupied,
2. Electric utility charges $0.45/kWh to purchase electricity, pays only $0.05/kWh to buy excess electricity generated.

Hi Douglas,

You could model this scenario in SAM using either the Detailed PV - Battery / Residential or the PVWatts - Battery / Residential configuration.

For the load (defined on the Electric Load page), you would need to import a time series load profile over one year to represent the constant load with a period of low load.

For the electric utility charges, on the Electricity Rates page, under "Metering and billing," if excess generation is calculated based on monthly total usage and generation, choose Net energy metering with $ credits. If excess generation is calculated on a time series basis (hourly or 15-minute, for example), choose Net billing. Then under "Energy Charges", enter 1 Number of entries, and type 0.45 in the Buy ($/kWh) column and 0.05 in the Sell ($/kWh) column. Then set the weekday and weekend schedule matrices to 1 for all months and hours by selecting the entire matrix and typing the number 1.

Once this is set up, you'll need to experiment with different PV system sizes, battery sizes, and battery dispatch options to find the system design that meets your requirements.

Please refer to the Help system for more details. The Help topics for the Electric Load page and Electricity Rates pages provide more information about the steps I describe above, and you can refer to other topics for help with the PV and battery inputs.

The videos on the Battery Storage Videos and other pages on this website may also be helpful:  sam.nlr.gov/battery-storage/battery-videos.html .

Best regards,
Paul.