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System Advisor Model (SAM)

Electric Load - on-peak and demand charges?

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Achilles11
Topic Author

16 Oct 2017 19:02 #5779 by Achilles11

Electric Load - on-peak and demand charges? was created by Achilles11

Under PVWatts Commercial, I've entered the applicable TOU utility rate and total monthly electric load. Because I can't enter monthly off-peak/on-peak or monthly demand charges, SAM is underestimating the total electric utility charges and, therefore, the benefit of PV. If all I have are monthly utility bills, how can I accurately reflect the actual electric load/utility costs in SAM?

Revised>>>>
Also, the electric load in question is winter-daytime peaking (ski area). SAM's load normalization seems to automatically normalize the data on a daily basis, so I'm not sure if it's missing peak demand and associated charges. I did modify the energy usage data to show that the peak loads are between 9AM-4PM during the winter months. Should I normalize or not? Maybe the seasonal variation doesn't matter too much, in the end.

Based on your guidance, the only change I made was to enter the fixed demand charge ($/kW) for each month (which were initially zero). The demand rates by TOU were already there, so I didn't change those values. Do I need to change the Peak (kW) value (1e+038)?

The total electric costs for this electric meter are closer to $200k/yr, but SAM's estimate of the costs is closer to $165k/yr. I'm wondering if I'm missing something obvious.

Thanks!!

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pgilman

16 Oct 2017 20:31 #5780 by pgilman

Replied by pgilman on topic Electric Load - on-peak and demand charges?

Hello,

SAM supports fixed, time-of-use and tiered demand charges, so you should be able to enter monthly demand charges, and peak and off-peak charges.

It looks like your question about the load got cut off. Remember that when you use the "Normalize supplied load profile to monthly utility bill data," SAM scales the underlying time series data. That underlying data determines the shape of the daily load profile, and the monthly values you enter for normalization determine the seasonal variation of the load.

If you'd like me to look at your .sam file, you can attach it to your original post above by editing it, or you could email it to me using the Contact form (see link above),.

Best regards,
Paul.

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Achilles11
Topic Author

17 Oct 2017 20:53 #5781 by Achilles11

Replied by Achilles11 on topic Electric Load - on-peak and demand charges?

Revised>>>>
Also, the electric load in question is winter-daytime peaking (ski area). SAM's load normalization seems to automatically normalize the data on a daily basis, so I'm not sure if it's missing peak demand and associated charges. I did modify the energy usage data to show that the peak loads are between 9AM-4PM during the winter months. Should I normalize or not? Maybe the seasonal variation doesn't matter too much, in the end.

Based on your guidance, the only change I made was to enter the fixed demand charge ($/kW) for each month (which were initially zero). The demand rates by TOU were already there, so I didn't change those values. Do I need to change the Peak (kW) value (1e+038)?

The total electric costs for this electric meter are closer to $200k/yr, but SAM's estimate of the costs is closer to $165k/yr. I'm wondering if I'm missing something obvious.

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pgilman

17 Oct 2017 22:34 #5782 by pgilman

Replied by pgilman on topic Electric Load - on-peak and demand charges?

Hello,

The "normalization" is a very simple calculation (see the description in Help): SAM calculates the monthly sum of the time series load data you imported (hourly in your case) A, and uses the monthly value you provide in the normalization table B to calculate a scaling factor F = B / A. It then multiplies each time series load value in that month by the scaling factor F. That approach preserves the daily load shape while scaling the monthly total to match the value you provide.

You can see the original and scaled data by clicking View data on the Electric Load input page -- you should see the daily shape of both datasets are the same. You can use those graphs to confirm that the load data is what you intend it to be.

On the Electricity Rates page, you have specified demand charges as follows:

1. A monthly demand rate of $7.65/kW for all months. You can see the resulting demand charge on the Results page Data Tables tab under Monthly Data, "Demand charge (flat) with system ($)." In my test, that demand charge is higher in winter months than summer.

2. You also defined three time-of-use periods for demand charges: Period 1 is Jun-Jul weekdays 8 am to 7 pm at $7.65/kW, Period 2 is Sep-May weekdays 8 am to 7 pm at $5.63/kW, and Period 3 is 8 pm to 7 am weekdays and all hours weekends at $0/kW. The resulting demand charge is "Demand charge (TOU) with system."

SAM adds the two demand charges together to calculate the total demand charge in each month.

I hope that helps. Let me know if you need more clarification on these calculations.

Thanks,
Paul.

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