Parametrics

Good morning,

I am writing because I have designed a PV+battery system for residencial use. Now I am using the parametrics tool to find the system configuration which maximizes the NPV. For this I am varying the inputs: array size (kWdc) and bank capacity (kWh), and the output is the NPV. The thing is that every time I run these parametrics I get different optimums without changing anything in the model, and that does not make sense. Here you can find attached the model and the weather file I am using.

Hope you can help me to fix this problem or to understand what is going on.
Kind regards,
Alejandra

Hi Alejandra,

There are a couple of reasons your parametric simulations are not working as expected:

1. You have chosen "Desired array size (kWdc)" as a parametric input variable, but Estimate Subarray 1 configuration is not enabled on the System Design page.

2. On the Inverter page, the inverter's rated power is 3 kWac, which will result in an oversized inverter for the desired array sizes of 1 kWdc, 2 kWdc, and perhaps 3 kWdc.

3. On the Battery Cell and System page, Desired bank power is 3 kWdc, which may result in an oversized battery for the smaller array sizes.

4. I recommend adding the "Battery average roundtrip efficiency" and "Performance ratio" or "Energy yield" to the parametric output variables so you can verify that the different size systems are performing reasonably well.

Best regards,
Paul.

Good morning,

Thank you for your reply. I understand, now I have decreased the inverter power to 0.5kW and enabled the estimate subarray 1 configuration, so that an appropiate number of inverters can be selected to keep a DC to AC ratio close to 1.2. I have also dereased the battery power to 2kW. I have also added the other variable outputs you suggested.

However, now when I try to run the parametric simulation I get this message several times.
Then I get this message,
 

Hi Alejandra,

SAM's automatic sizing algorithm is described in the Help topic for the System Design page, under "Estimate Subarray 1 Configuration": samrepo.nrelcloud.org/help/pv_system_design.html

For some of the desired sized in the parametrics table, the sizing algorithm fails. For example, Run 31 fails:

 

You can see what the inputs are for Run 31 in the Parametrics table:

 

You can test that desired array size on the System Design page:

 

A better approach might be to disable the Estimate Subarray 1 configuration option, and instead change the number of strings in parallel to change the system size. You'll also have to change the inverter size. Or you could try using a small module (maybe around 120 Wdc) and small inverter (around 100 Wac to work with the 1.2 DC/AC ratio).

Best regards,
Paul.