Capacity Factor for DC/AC Ratio sensitivity analysis with sub-hourly data

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Capacity Factor for DC/AC Ratio sensitivity analysis with sub-hourly data

Dear Paul,

I am trying to gain a better understanding of DC/AC ratio sensitivity analysis using sub -hourly data. I have modeled a basic system with only system costs, financial parameters, Incentives and electric rates and loads as default values which SAM has for a nearby location. After simulating, though other values seems reasonable, the capacity factor is only 0.2 and payback period is showing as NaN. What might be the reason for this?
Do you have any suggestions or recommendations? Any help will be highly appreciated. Please find the attached project file.

Best regards

Paul Gilman

Dear Rana,

There are a few things going on here:

First, I think there is a bug in how SAM calculates the Energy Yield (kWh/kW) with subhourly simulations. For one-minute data, if you multiply the number SAM reports by 60 minutes, you should get the correct value. You can see the value with more significant digits on the Data Tables tab of the Results page by displaying the "First year kWh/kW)" variable under Single Values. We are investigating that and will fix it the next time we update SAM.

Is your weather file for a location near Knoxville, TN? If so, the longitude should be negative 84.3 rather than positive 84.3.

In order for SAM's bill calculations to be accurate, when you use subhourly weather data, you should also use subhourly load data. In your case, you are using one-minute weather data with 60-minute load data.

I think the net present value and payback period values are reasonable given the project costs you have defined. You may want to experiment using hourly data first (perhaps the TMY2 file for Knoxville that comes with SAM for the weather file) to find a combination of financial assumptions that produce the results for payback period and net present value that you expect, and then switch to the subhourly data once you have results that make sense.


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