Bi-Directional Inverter for Battery systems

When modeling AC coupled FTM utility scale battery storage, either stand alone or in the hybrid options, I do not see the bi directional inverter accounted for in any of the costs. Is this cost included in the battery cost?

Hi Vikram,

There is not an explicit line item on the System Costs page for a bi-directional inverter that would be required for an AC-coupled battery, so you should be sure to include it as appropriate for your analysis. You can choose an appropriate category for the cost, perhaps as part of the inverter cost, or of the balance of system cost.

For information about battery costs, see sam.nrel.gov/battery-storage/battery-cost-data .

Note that the default costs in SAM are illustrative only, so you should review the costs for your analysis. The costs also do not change as you change the design of your system. So, for example, if you change the tracking option for a photovoltaic system from fixed to one-axis tracking, the installation and operating costs do not automatically change. Similarly, for the financial assumptions, if you change the location, the tax and incentive assumptions do not change automatically.

Best regards,
Paul.

Thank you Paul for this and your definition of hybrid in the other post.

Another question came up while using SAM for a stand-alone battery system (but I think this issue applies to all systems). When switching between the "No Electricity Rate" and "Enable Electricity Rate" options, no difference occurs in the simulation results. It seems to be using the "Enable Electricity Rate" parameters even when "No Electricity Rate" is chosen, rather than treating the nighttime inverter load as negative generation at the PPA price as stated. 

Can you help me to see if the issue is on my end, or if it is an issue within SAM?

Hi Vikram,

When you model a battery system with one of the power purchase agreement (PPA) financial models for a front-of-meter system, SAM uses the inputs on the Electricity Rates page to calculate the cost of electricity required to charge the batteries. It does not apply these rates to the inverter nighttime consumption -- that is considered negative power generation.

Also, if you are modeling a standalone battery system, meaning a battery with no photovoltaic system by setting the DC loss to 100%, SAM still considers nighttime inverter consumption. That is calculated as part of the model for the inverter that converts DC power from the array to AC power. To avoid that, you could use the Generic Battery model with the power plant nameplate capacity set to zero instead of PV battery with DC loss set to 100%.

Best regards,
Paul.

Paul,

Pardon me, I was a bit unclear in my question, I mean to refer to "power required to charge the battery", not "inverter nighttime load". On the Electricity Rates page, when  you select the "No Electricity Rate" option, a message appears stating that "any power required to charge the battery... is treated as negative power generation, which effectively reduces revenue from power sales at the PPA power price".

However, when I switch between this option and the "Enable Electricity Rate" option, which has an energy charge lower than the PPA price, my results don't change.

I am already using the Generic Battery model, but either way have the same problem specified, and this issue is also the same in my other PV plus storage models, where there is no change whether I select the "No Electricity Rate" or "Enable Electricity Rate" option.

Regards,
Vikram

Hi Vikram,

On the Battery Storage page, make sure you have configured the dispatch options to allow the battery to be charged from the grid.

You can then look at the "Electricity to battery from grid" output variable in the time series results to see whether the battery ever charges from the grid. If it does, and the retail electricity rate is different from the PPA price, you should see an impact in the financial metrics like net present value, etc.

Best regards,
Paul.