Savings Methodology
Last reviewed: January 2026
Formula
The 0.78 displacement factor represents the share of annual grid consumption a correctly sized residential system is expected to offset after accounting for night-time draw, seasonal generation variance, and inverter losses, based on NREL PVWatts averages across the metros we currently index.
Assumptions
- System is correctly sized to ~78% of annual kWh consumption.
- Net metering or equivalent export compensation is in effect.
- South or south-west roof orientation, minimal shading.
- Utility rate held flat — no inflation escalator applied.
- Federal ITC and state incentives are not added to the displayed annual savings figure; they apply to upfront system cost, not recurring savings.
Limitations
Outputs are educational estimates, not binding quotes. Final pricing, system sizing, and warranty terms are set by the matched installer based on a site survey. Homes with significant shading, complex roofs, or specialty tariffs (time-of-use, demand charges) may see materially different economics.
What we exclude
Battery storage economics, EV-charging load growth, and resale-value uplift are excluded from the headline savings figure. These can move the total payback meaningfully and are quoted by the installer directly.