Parametric analysis of PV and battery configurations

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Achilles11
Parametric analysis of PV and battery configurations

Hi,

I'm attempting to determine the most financial beneficial configuration of net metered PV and battery capacity. This will be a municipally owned system, so various tax incentives won't apply. Also, the project is half-funded through a federal grant and the other half is a low-interest loan, so to account for the grant funding I've used a negative value (-65%)for the project contingency in System Costs to arrive a portion of the project cost that is covered by the loan.

I've uploaded the 15-min electric load information, applied the correct utility rate, and have specified a total PV system size of 200 KW and battery capacity of 200 KWh. I want to determine the optimum solar system size and battery capacity combination. In the parametric analysis I used varying battery capacity (0-200 KWh) and varying solar system size (0-1000 KW) as inputs and NPV as the output. When I run the parametric analysis, the NPV output doesn't seem to be affected by the battery size.

If I specify different PV system sizes and battery capacity, does the parametric analysis automatically adjust system cost and financial parameters? Also, because the goal of the battery capacity is to offset electric utility demand charges, does the parametric analysis incorporate the rate information?

Perhaps there's a better way to approach determining the optimum solar PV system size and battery capacity. Please advise.

Thanks,
Dale

Paul Gilman

Dear Dale,

The NPV and other metrics are not varying with battery capacity because you chose the wrong variable in your parametric study. Instead of "nominal bank capacity" you should choose "desired bank capacity." The "nominal capacity" is a calculated value on the Battery Storage page, and should not be available as a parametric variable because it is not a user-editable variable. I will fix that for the next version of SAM -- sorry for causing that confusion.

Be aware that the "desired" capacities for both the PV array and battery bank are target values. The actual value that SAM calculates for each may not be the same as the target value.

Also, to model the federal grant, you might consider using the "Investment Based Incentives" inputs on the Incentives page. There you can specify the incentive as a percentage of the total installed cost, and specify whether or not it is a taxable incentive for federal and state income tax purposes.

Best regards,
Paul.

Achilles11

Hi Paul,

I had initially tried to set the Investment Based Incentive to 50%, but then SAM financial projections considered the total project cost. The solution you provided me some time ago ended up working for me: "Based on your description, "half grant funded and half low-interest loan," it sounds like this project has no initial cost to the municipality (who installs, owns, and operates the system). In SAM, the IBI percentage applies to the total installed cost, but the debt percentage (on the Financial Parameters page) applies to the total capital cost, which is the total installed cost minus the IBI and debt-related costs. You can see how the capital cost is calculated on the Cash Flow tab of the Results page. I think the way to model the project's cost is to set the total installed cost on the System Costs page to 50% of the actual cost to account for the grant, and to set the debt percent to 100% to account for the 50% debt size."

I assume this is still the best way to set things up.

Thanks!
Dale

Achilles11

Hi Paul, it's looking like a 100 KWh battery system provides the best financial outcome. Is there a way way to identify what parameter(s) has the most influence on battery system size. I assume it has something to do with the utility rate.
Thanks,
Dale

Paul Gilman

Hi Dale,

It may be that no battery is actually the best outcome, if 100 kWh is the smallest size you considered. Did you try a simulation with no battery to verify that?

In general, in order for a battery to be economically feasible, the rate structure needs to have demand charges, and the battery has to be sized and dispatched in a way that reduces the demand charge. There are also other scenarios where a battery may make economic sense. In your case, it looks like the demand charge makes up about 40% the monthly bill when there is no renewable energy system. However, the load peaks roughly coincide with the PV array's output, so the battery may not add a lot of value for peak reduction. If the daily peak load happened later in the evening as the PV array output declines, I might expect batteries to be more attractive.

You can test the effect of the demand charge by running a simulation with the demand charge disabled to see what impact that has on the outcome.

Anyway, these are all great questions for SAM to help provide some insight as you develop answers.

Best regards,
Paul.

ndiorio

Hi Dale,

Also, please be sure and scale the battery voltage ("Desired bank voltage"). For batteries, the only two inputs you need to change are the desired capacity and voltage. The voltage is important because we do model it and consider the current throughput of the system. For instance, on some systems a 10 kWh capacity would be about 350V. If you don't specify the voltage, you may have large, unrealistic current if you scale the capacity upward.

Thanks,
Nick

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