Battery State of Charge (SOC)

Hi,

I downloaded and then deleted your attached .sam file.

You can email me attachments directly at sam dot support at nrel dot gov.

Best regards,
Paul.

Hi,

Attached is a version of your file with a "System A rev" case where I modified some of the battery parameters to be more realistic. You can use File, Inputs browser to see a table showing the variables that I changed.

Here is a graph showing the battery state of charge (%) in blue, and electricity to battery from system (kWac) in red, and electricity to load from battery (kWac) in orange. You can see that immediately after the battery discharges, it charges back to full charge with power from the PV system.

 

This next graph shows the same time period with electricity to load from battery (red), electricity to load from grid (blue), and electricity to load from system (orange). Here you can see that the battery discharges during the peak load in an attempt to reduce power from the grid. The battery is very small compared to the load, so it does not contribute very much to reducing grid power.

 

In the time steps after the battery discharges, the peak shaving algorithm uses PV power to charge the battery instead of meeting the load in anticipation of reducing the demand charge. This is because the dollar value of reducing the demand charge is greater than the cost of using grid power during that brief charging period.

Best regards,
Paul.

 

Hello,

Here are the steps I used to create the graph:

1. Run a simulation and go to the Results page.
2. On the Time Series tab, clear the check box for "System power generated".
3. Use the left-hand check boxes to display the three electricity to load variables in the top graph: From grid, from system, and from battery. (You can type "load" in the search box to filter the list of variables.)
4. Use the right-hand check box to display the battery state of charge variable in the bottom graph.
5. Use your mouse to select a three or four days (Feb 5-7 in this case).
6. Click the button with a wrench icon at the bottom right corner of the graph and check Stacked area on left Y axis.

 

 

The peak shaving algorithm attempts to discharge the battery to reduce the monthly peak demand. Because it uses a 24-hour look ahead period, it does not know when the peak monthly demand occurs, so it dispatches each day. This graph shows the load for February, and how the algorithm successfully dispatches the battery to help reduce the peak load on February 20. At the beginning of the month, it discharges the battery for each successive daily peak until it reaches February 20. It does not discharge the battery after February 20 because the peak loads on those days are less than the February 20 peak.

 

Best regards,
Paul.