This document explains how HomeShark calculates energy savings estimates, efficiency scores, neighbor 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 | EIA (Energy Information Administration) | State-level averages updated annually |
| Federal tax credit amounts | IRS guidance, IRA legislation | Reflects law as of effective date; subject to change |
| State rebate programs | DSIRE (Database of State Incentives for Renewables) | Updated periodically; verify current amounts with providers |
The HomeShark Efficiency Score is a composite index from 0 to 100, where 100 represents a home using energy at maximum efficiency. It is calculated as:
Score = 100 × (1 − relative_usage_penalty) × age_factor × solar_opportunity_factor
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 energy usage is estimated using:
Estimated kWh = (square_footage × regional_intensity_factor) + heating_adjustment + cooling_adjustment
When an actual bill is uploaded, the extracted kWh figure replaces this estimate entirely, making all downstream calculations significantly more accurate.
Maximum system size is determined by Google Solar API's maxArrayPanelsCount and roof area measurements. We model a system using standard 400W panels.
system_kW = panel_count × 0.4 kW per panel
Google Solar API provides yearlyEnergyDcKwh for the maximum panel configuration. We apply a standard 80% performance ratio to account for inverter losses, wiring losses, and temperature derating:
annual_kWh_produced = yearlyEnergyDcKwh × 0.80
annual_savings = annual_kWh_produced × local_rate_per_kWh
This assumes full net metering (1:1 credit for exported power). Many utilities offer full net metering, but policies vary and are subject to change. Homes with battery storage may see different outcomes.
The 30% Investment Tax Credit (ITC) under IRA Section 25D is applied to the estimated gross installation cost:
federal_credit = install_cost × 0.30
Installation cost is estimated at $2,800 per kW of system size, based on NREL benchmark data for residential solar (2024). Actual prices vary by market, installer, and system design.
Important: The ITC is a non-refundable tax credit. You must have sufficient federal tax liability to use it. Excess credit may be carried forward one year. Consult a tax professional.
payback_years = (install_cost − federal_credit) ÷ annual_savings
This is a simple payback calculation. It does not account for loan financing costs, utility rate escalation, system degradation, or state incentives (which would shorten payback). A full financial model from a licensed installer will be more accurate.
The "vs. Neighbors" percentage compares your estimated (or actual) monthly kWh usage to the estimated average for similar homes in your ZIP code. "Similar" is defined as homes within 20% of your square footage and built within 15 years of your home's year built.
This comparison uses EIA RECS data segmented by state, home size, and construction era. It is a statistical comparison, not a direct measurement of your specific 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.