Battery Storage on AC vs. DC bus

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tmartin
Battery Storage on AC vs. DC bus

Hi everyone,

This may be obvious to some, but why is the battery storage model on the AC bus only? In practice is this how systems are designed? It would seem to me that placing the battery on the DC bus would negate the additional DC-AC, AC-DC, and then back DC-AC efficiency losses created by placing the battery on the AC bus as opposed to the DC bus.

If in practice the battery is on the DC bus would that be a feature that could be added back to SAM? I read elsewhere that SAM used to have it.

Tane

Paul Gilman

Hi Tane,

We plan to add a DC-connected battery option in the next version of SAM tentatively scheduled for release in January 2017. For now, you can effectively model a DC-connected battery by using the AC to DC conversion efficiency to represent charge controller losses (with no rectification losses), and using the DC to AC conversion efficiency to represent losses associated with converting battery DC power to AC.

For this first iteration of the battery model, we chose to model batteries on the AC bus so that it could work with the output of SAM's PV model. To accurately model batteries on the DC bus, we need to make some modifications to how the PV models the DC bus voltage.

Best regards,
Paul.

tmartin

Thanks Paul,

Thanks for the tips on how to model.

So does this mean that the reasoning is module-related? Just curious if it was related to practical residential storage application (with which I don't currently have much experience) limitations or standards.

Thanks,

Tane

Paul Gilman

Hi Tane,

Our decision to model the battery as AC-connected had more to do with modeling limitations than with current common practice in the storage market.

Best regards,
Paul.

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