0
\$\begingroup\$

If I have a photovoltaic system that outputs 100 kWh from 1PM - 2PM on a given day and I am trying to figure out what the average 15 minute kW would be during that time period, would that be equal to 100 kW?

The reason I'm trying to figure this out is so I can model the MN Xcel Energy PV Demand Rider Tariff outlined below. I have production data hourly for an entire year for the system we are trying to model this against but no one seems to be able to tell me if the data I have will work or if I need to convert it somehow. The specific part I am trying to model is the verbiage under the CREDIT KWH LIMIT paragraph.

PHOTOVOLTAIC DEMAND CREDIT RIDER RATE CODE A86. Customer Charge per Month $25.75. Credit per kWh of Peak Period Solar Photovoltaic Generation (A86 - Standard) $0.069648

CREDIT KWH LIMIT

The maximum kWh applied to the Rider credit per kWh each billing period is the Peak Period maximum 15-minute Solar Photovoltaic kW output for the billing period times 100 hours for billing periods ending in the months of June, July, August or September and 75 hours for billing periods ending in other months.

CREDIT LIMIT The maximum credit for each billing period is the applicable standard or on-peak billed demand charge from the base tariff associated with this Rider. For Peak-Controlled Service and Peak-Controlled Time of Day Service customers, the maximum credit for each billing period is the billed demand charge for Firm Demand.

DEFINITION OF PEAK PERIOD

Peak period hours are the six hours between 1:00 p.m. and 7 p.m. for all days.


Update:

The size of the system is 180 kW DC, 450 x 400 watt panels. The data I have shows me hourly kWh produced for every 1 hour period over a year. This is a theoretical system modeled for a customer using Aurora's modeling tool, what I am doing is trying to model the saving credit for a year based on the top performing 1 hour period of each month and using the multiplier stated in the Tariff.

I realize that I might be under estimating by a little bit but I am fine doing that, don't want to over estimate, the assumption I am making is that to produce 100 kWh over a 1 hour period, then my peak has to be at least 100 kW during that period. I realize in reality that peak will probably be higher during a portion of that hour and lower during other portions of that hour, but the peak minimum has to be at least 100 kW to produce that.

Also so everyone is aware, the Aurora modeling I am doing has 16% loss built into it for things like snow load, soiling on the panels, potential for loss in the wiring etc... this system is also taking into account an potential shading and the different angles and azimuths the panels will be placed at.

After reading everyone's comments, I think I will be good to model the savings with the numbers I have, note this Tariff also has a max credit limit that can not exceed the amount of the billed demand charge. If my 100 kW minimum Max peak assumption is good, then I can use that formula from the yearly data I have for each month and then model that savings for each year pretty easily in a spreadsheet, also reflecting the panel degradation that is expected for each year.

\$\endgroup\$
1
  • 3
    \$\begingroup\$ You are essentially upsampling the data. You could assume (from your example) that the average is 100 kW per 15 minute period. Or you could look at the data before and after, and attempt a curve fit. Perhaps the average was 95 kW in the first and last 15 minutes, and 105 in the middle? NSRDB also has historical 30-min data you might be able to use to get a bit closer. \$\endgroup\$
    – LShaver
    Mar 26 at 1:00

1 Answer 1

6
\$\begingroup\$

Wow, people are so confused. In the absence of any further information, if the only thing you know is that between 1pm and 2pm you collected 100 kWh of ENERGY, then the best guess for the average RATE of energy collection during any time in that interval is 100 kW.

So that is a long winded way of saying, yes, 100 kW is the best guess average, unless you have additional data points you have not shared with us.

Note that kWh are a measure of energy, and kW are a measure of the RATE of energy collection. I absolutely cannot make heads or tails of all the rest of your legal verbiage. Good luck with that.

As a final comment, it seems that unless you have an industrial sized installation, 100 kW is a lot of power to get from a solar array. So if that is really what you think you are getting, and you have a modest array, you probably have a mistake in there somewhere. But if you have way more panels than the typical single family home, then fine, maybe it is 100 kW.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.