This document explains how HomeShark calculates energy savings estimates, efficiency scores, similar-home comparisons, and solar projections. All estimates are models based on publicly available data — they are not guarantees of actual savings. See our Terms of Service for full disclaimers.
| Data Type | Source | Notes |
|---|---|---|
| Property characteristics (sqft, year built, stories, HVAC, roof) | ATTOM Data Solutions | Public property records; may lag recent renovations |
| Solar potential, roof area, peak sun hours | Google Solar API | Based on satellite imagery and irradiance modeling |
| Street view photography | Google Street View | Falls back to satellite imagery if street view unavailable |
| Geocoding and address validation | Google Geocoding API | – |
| Utility bill data | User-uploaded (optional) | Extracted via Anthropic Claude AI; bill deleted after processing |
| Regional electricity rates and usage | EIA Electric Sales, Revenue, and Average Price (Table 5a, 2023) | State averages; used when no bill is uploaded and for the similar-home comparison |
| Federal tax credits | IRS guidance on Public Law 119-21 | Homeowner credits (25C, 25D, 30C) have ended and are not included in estimates |
| State and utility rebate programs | Program administrators and utility websites | Reviewed November 2026; verify current amounts with the program |
The HomeShark Efficiency Score is calculated in code from your home's characteristics and, when you upload a bill, your actual usage. The same home and bill always produce the same score.
The score is an estimate. A professional energy audit by a BPI- or RESNET-certified auditor will produce a more accurate assessment.
When no utility bill is provided, monthly usage starts from the typical similar home described above and is adjusted by the property score: a home that scores below a typical home is estimated to use more, and one that scores above it less. The state's average electricity rate from EIA is used to estimate the bill.
When an actual bill is uploaded, the extracted kWh and rate replace these estimates.
Google Solar API provides panel layouts for your roof with the expected yearly production of each. HomeShark shows two systems: Recommended, the smallest layout expected to cover about 100% of your annual electricity use, and Roof Maximum, the largest layout your roof supports. Panels are modeled at 400 W.
Google's DC production estimate is converted to usable AC output with an 85% factor for inverter and wiring losses:
annual_kWh_produced = yearly_DC_kWh × 0.85
annual_savings = self_used_kWh × rate + exported_kWh × rate × 0.25
Power you use yourself is valued at your electricity rate. Power beyond your annual use is credited at 25% of that rate, reflecting net billing programs such as California's. Utilities with full net metering credit exports at a higher rate, so savings there may be higher.
Installation cost is estimated at $2,800 per kW of system size. Actual prices vary by market, installer, and system design.
No federal credit is applied. The residential clean energy credit (25D) ended for systems installed after December 31, 2025. Solar leases and power purchase agreements may carry a commercial credit through the installer, which would show up as a lower price in their quote.
payback_years = install_cost ÷ annual_savings
This is a simple payback calculation. It does not account for loan financing costs, utility rate escalation, system degradation, or state and utility incentives (which would shorten payback). A full financial model from a licensed installer will be more accurate.
The "vs. Similar Homes" percentage compares your actual or estimated monthly kWh with a typical similar home in your state: the EIA average for residential customers in your state, adjusted for your home's square footage and heating type. It is a statistical comparison, not a measurement of your neighbors' usage.
| Recommendation | Savings Basis | Source |
|---|---|---|
| Solar panels | Annual production × local rate | Google Solar API + EIA rates |
| Heat pump / HVAC upgrade | ~18–25% reduction in HVAC energy cost based on home size and existing system type | ENERGY STAR, DOE HVAC studies |
| Attic/wall insulation | ~15–20% reduction in heating/cooling costs | DOE Building Technologies Office |
| Smart thermostat | ~8% heating, ~10% cooling savings | ENERGY STAR program data |
| EV charger | Avoided Level 1 charging costs + public charging premium | DOE Alternative Fuels Data Center |
| Windows | ~7–15% reduction in heating/cooling based on climate zone | ENERGY STAR window savings estimates |
| Air sealing | ~11% reduction in heating/cooling costs | DOE Building Technologies Office |
For a professional-grade energy audit, we recommend:
HomeShark's quote request feature can connect you with licensed local installers in all these categories.