Issues with Battery Discharge to Grid in Winter

Hi,

I am looking for some assistance with an issue I am having with a SAM model I am currently developing.

I am trying to model a system with summary and winter arbitrage of the battery in peak/off-peak times allowing the battery to feed the load and back into the grid in peak periods and allowing the charge of the battery via the grid in off-peak times.

Everything seems to be working well in summer, however, in winter the battery doesn't discharge to grid in peak periods and I can't find a reason why this happening. I have attached the model and also please see pictures below, indicating the problem.

Please could assist if possible?

Summer:
 

Hi Craig,

Based on the inputs on the Battery Dispatch page, the battery is allowed to discharge to the grid in Period 3 (Jan-May, 7am-9am and 6pm-7pm; Sep-Dec, 6pm-7pm) and Period 6 (Jun-Aug, 6am-8am, 5pm-6pm).

This is a Southern latitude.

On January 1 and 2, Electricity to grid from battery is from 7am-9am and 6pm-7pm. During these periods, the system meets some of the load, and battery power is available for the grid:

 

On September 14 and 15, Electricity to grid from battery is from 6pm to 7pm:

 

On August 10 and 11, Electricity to grid from battery is zero. Power from the PV system is not available to meet the load, so the battery is delivering power to the load instead of to the grid.

 

Best regards,
Paul.




 

Hi Paul, 

Thanks for the prompt response. So, am I right in saying that the battery can either discharge to the load or the grid but not discharge to both simultaneously? 

If that is the case, is this a limitation of SAM or is it a limitation of the particular inverter that I am using (I did check inverter and battery settings but couldn't see anything)?

Thanks,

Craig

Hi Craig,

The battery may discharge to the grid and load simultaneously. For example, in your file, on April 17 - 20, the battery discharges to the grid (blue) and load (orange):

 

I'm using a different weather file than yours, so my results won't exactly match yours.

Best regards,
Paul.

Hi Paul,

Thanks again from your response and I did notice then when I was looking through my model. What I don't understand is the discharge for the battery seems to drop from 840 kW to 700 kW from the 29th May to the 28th August (which is roughly the winter period). This is despite the SOC of the battery being 100% at the start of the discharge (peak tariff) period for all times of the year. Is there a reason for this? I can't see anything in my battery settings that would have caused this.

 

There is a bug that we will fix for the first update to SAM 2023.12.17: github.com/NREL/ssc/issues/1112

Best regards,
Paul.