Put it together & simulate

You’ve made every design choice — groups, strings, MPPTs, inverter, battery. Now run it and read the scorecard. Good designers don’t nail it on the first try; they simulate, read the losses, and iterate.

The headline number: Performance Ratio

PR measures how much of the sunlight that hits your panels becomes usable electricity, after all real-world losses. A perfect-but-impossible system is 100%; good real systems land roughly 75–85%. A low PR is a flag that something in your design is bleeding energy.

Read the loss breakdown

Each loss line maps back to a design lever you’ve learned:

• Near shading — your orientation/grouping choices (Module 3).
• Heat & module losses — temperature; partly mounting and climate.
• Clipping — your DC/AC ratio (Module 6). High here? Trim panels or size up the inverter.
• Angle (IAM), soiling, wiring, inverter — orientation, environment, and equipment quality.

The point isn’t to eliminate losses — it’s to spot the fixable ones.

P50 vs. P90 — planning for a normal year

Weather varies year to year. P50 is the expected (median) production; P90 is conservative — you’d beat it 9 years in 10. Use P50 to estimate typical savings and P90 if you want a cautious, finance-grade number.

Iterate

Change one thing at a time and re-run: split a mixed orientation, adjust the inverter to cut clipping, add a battery to use more of your own solar. Watch PR and the loss lines respond. Two or three passes usually gets you a clean design.

Last module: turning your finished design into a permitted, switched-on system — and where the pros take over.

Prefer to just try it? Open the simulator.