DC Availability Loss - difference between entered value and simulated loss

In both SAM2020 and SAM2025 desktop, I have been simulating a detailed residential PV system.

I have been trying to enter constant loss under System Availability > DC Losses.

I enter a constant loss of, say, 34.68% (using an unrealistically high value just to illustrate the point).

When I run my simulation and inspect the simulated losses shown on the losses tab, it reports 
"DC availability and curtailment" loss = -33.14%

The loss seems to have reduced?

On a hunch, I noticed that the losses for module mismatch, diodes and connections, and DC wiring were -2%, -0.5%, and -2%.

If I just add those, I get 4.5%. But if I use for the formula 100% * [1 - the product of ( 1 - loss/100%)], then I get 4.44% as the total across these, which is what is reported on the DC losses input page.

If I multiply 34.68% by (1-0.0444) I get 33.14%, the result that is shown in the losses page of the simulation results.

So my question: in the simulation results losses diagram, why are the simulation result values for the module mismatch, diodes, DC wiring loss the same as what I entered as input, namely 2%, 0.5%, and 2%, while the DC availability loss I entered (34.68%) has been weighted down by the other losses that were calculated first, and is being shown as -33.14% in the simulation results? 

 

Hi Stephen,

I think this is a bug in the way SAM calculates values to display in the loss diagram. I agree that the DC availability loss should appear as you entered it, not adjusted by other losses.

SAM calculates values for the loss diagram in a separate step after simulations are finished, to this issue does not affect how the loss is used to calculate the system's output.

We are investigating and will fix the loss diagram for the next version of SAM.

Beest regards,
Paul.