Variation of Round Trip Efficiency with Battery SOC range

Hi,

While modelling a battery-only case using Detailed PV and 100% losses, I just noticed that the round trip efficiency of the battery is heavily varying with the SOC range of operation, which is not expected. Please find below the output of parametric table for 3 different SOC ranges.

	batt_maximum_SOC (%)	batt_minimum_SOC (%)	average_battery_conversion_efficiency(%)
1	100	0	36.811
2	90	10	69.633
3	80	20	81.219

Could you please explain why these variables are linked? How can this problem be resolved? I am attaching a .SAM file for your reference.

Thanks
Arun Joshy

batt_minimum_SOC (%)

Hi Arun,

On the Battery Storage page, under "Voltage Properties" you should see a voltage discharge vs depth of discharge graph. For Lithium-ion batteries, the voltage drops steeply as depth of discharge increases for depth of discharge values above about 80%. That causes the lower roundtrip efficiencies you are seeing as you allow the battery state of charge to increase above that point.



Best regards,
Paul.