15 minute simulation issue

Hello,

I have imported 15-minute load and weather data into SAM to run a detailed PV, commercial case study. The issue is that when I run the simulation and look at "electricity load" results all values are divided by 4. Are we supposed to import kWh load data instead of kW or is this a bug? (I have attached a graph of input load and output load which is divided by 4)

Thank you,
Babak

Dear Babak,

The load output data is in kWh, not kW as indicated by the units. When you provide 15-minute load data in kW as input, SAM determines the kWh required to meet the load over each time step as follows:

kWh = kW * minutes per time step / 60 minutes per hour

For example, for a 15-minute value of 100 kW, SAM would calculate 100 kW * 15 min per time step / 60 min per hour = 25 kWh.

The peak load in kW that SAM uses for peak load calculations is the maximum value of the kW load data over the period of interest. For example, for a 15-minute load data set, the monthly peak load for January would be the maximum of the 2976 kW values for January (31 days/month * 24 hours/day * 4 time steps/hour = 2976 time steps/month).

We will change the units that SAM reports for the output load to make that more clear.

Best regards,
Paul.

Dear Paul,

Thank you for the clarification. If I may ask a follow-up question:

I am trying to simulate an energy storage system with "Automated Grid Power Target Model" in SAM. For this purpose, I prepared the exact time series for grid target power and imported into SAM. But after the simulation, actual grid power is not always equal to imported target power. Can you please provide some more information about the dispatch logic behind"Automated Grid Power Target Model" and any reason that actual grid power could be different from target power? Thanks again!

Best,
Babak

Hi Babak,

The "Automated Grid Power Target" controller does seek to keep the grid power at or below the target power you specify, but may fail in some instances, particularly if other constraints are violated (minimum or maximum state-of-charge, exceed the maximum C-rate (current through-put), etc). Do to the non-linearity of the voltage curve, it is also possible that the amount of power dispatched will be less than or more than the amount requested, as the voltage changes.

Nevertheless, if the target is being violated and you still don't understand why, I'm happy to to take a look at your project. In which case, you can post here, or email me at nicholas.diorio@nrel.gov.

Best regards,
Nick DiOrio

Hi Nick,

Thanks for your message. I'll follow up this with an email.

Best,
Babak