Searching best solar panel cost returns headline $/W. Groundwork models what matters: 25-year net with degradation, inverter, and net-metering — so a cheap quote that degrades faster doesn't win.
| Input | Groundwork model | Typical quote site |
|---|---|---|
| Degradation | 0.5%/yr (editable) + 25-yr net | Year-1 only |
| Net-metering | By utility, editable | Flat assumption |
| Where math runs | Client-side, auditable | Server-side |
Try it: Solar Payback & Battery ROI Calculator →
It models net-metering rules by utility, annual degradation (~0.5%), inverter replacement, and 25-year net — all client-side. Quote sites typically show year-1 savings only. Groundwork's inputs (kWh, rate, system cost) stay on-device and are auditable in lib/domain adapters.
Tesla often advertises low $/W before adders, but final cost depends on roof complexity, inverter choice, and installer. Use the calculator to input your actual $/W, not the headline price, and compare 25-year net — not just upfront cost.
Normalize to $/W, then run the same kWh and rate through Groundwork's model. Check degradation and net-metering assumptions — a 0.3% vs 0.7% degradation changes 25-year net by ~8%.
Factual only — Tesla is a trademark of Tesla, Inc. No affiliation. Data as of 2026-08-28.