- Inputs reviewed
- Production, retail electricity value, installed cost, federal credit, export policy, and incentive context.
- Outputs published
- Worth-It Score, conservative payback range, savings context, and source-dated comparison notes.
- Review cadence
- Major public-data and policy inputs are labeled with review dates and refreshed when source assumptions change.
- Property limits
- Roof shade, financing, installer quote terms, tax appetite, and battery configuration require a property-specific review.
Solar payback core equation
Annual production is multiplied by the local value of electricity and adjusted for policy. Net installed cost is reduced by modeled incentives. Payback is the net cost divided by expected annual savings.
The equation is deliberately presented as a screening model rather than a promise. A homeowner still needs a property-specific quote, a roof and shade review, utility rate confirmation, tax-credit eligibility review, and a check of whether exported energy is credited at retail, avoided cost, or another tariff-defined value. The model keeps those limits visible so a short payback estimate does not hide the assumptions that can change the result.
| Production | Modeled annual kWh from a representative residential system. Roof-specific shade and azimuth are not included in state preview pages. |
|---|---|
| Electricity rate | Residential retail electricity value, reviewed as a dated public-data input and shown as cents per kWh. |
| Installed cost | State or national installed-cost context expressed in dollars per watt before credits. |
| Federal credit | Modeled as a tax-credit reduction when the scenario assumes eligibility. Homeowner tax appetite is not guaranteed. |
| Export credit | Policy factor for exported energy, with weaker values under net billing or reduced-export regimes. |
| Range | Published as conservative-to-typical years rather than a single decimal. |
Worth-It Score
The 0-100 score is a relative indicator that blends payback range, electricity rate, production potential, installed cost, and export-credit policy. It is a comparison tool, not a guarantee for any roof.
A higher score means the public inputs look more favorable under the same conservative framework. It does not mean every quote in that place is a good deal. Installer pricing, system size, panel orientation, roof condition, financing cost, utility interconnection rules, and household tax position can move the final answer. Use the score to decide what to verify next, then compare the actual proposal against the sources below.
Source policy
NREL PVWatts v8
Solar generation modeling
U.S. Energy Information Administration
Residential electricity rates (2024)
LBNL Tracking the Sun
Installed cost by state (2024)
DSIRE
State incentive and net metering policy
How to test the model
A useful review starts by separating facts from assumptions. First write down the system size, installed price, expected annual production, retail rate, export-credit treatment, financing cost, and any incentive assumption in the quote. Then compare each item with the matching input category above. If a quote uses a different unit, date, or policy definition, normalize it before comparing the result. A cheaper price per watt can still produce a weaker outcome if production or export value is modeled more aggressively.
Next run a sensitivity check. Lower production, increase installed cost, reduce the export-credit factor, and remove an incentive assumption when eligibility is uncertain. The point is not to select the most pessimistic number; it is to see which input controls the decision. If a small change in one input moves the payback by several years, that input deserves a property-specific document or a current utility confirmation before a contract is considered.
The state preview is intentionally less specific than a quote. It uses representative production and public rate, cost, and policy context so locations can be compared on one frame. It does not know a roof's azimuth, shading, structural work, household load shape, battery dispatch, or financing terms. Use the calculator to replace the public assumptions with a transparent scenario, then keep the quote and bill beside the output so the comparison can be audited later.
A model result is strongest when its date and source trail are visible. The data registry records review dates for the state rows, and the source cards above identify the public organization used for each input family. A review date is not a freshness guarantee for every local tariff. It tells the reader when the site last checked the underlying reference and where to begin a new check. Policy pages, utility tariffs, tax rules, and installer pricing can change independently.
Minimum questions before relying on a quote
- Which utility tariff and export-credit rule are used, and what document supports them?
- What production loss, shade, degradation, and battery assumptions are included?
- Is the installed price before or after incentives, financing, and required electrical work?
- Which incentive assumptions require tax eligibility or an application deadline?
- What part of the proposal changes if the household uses more power during solar hours?
What the model excludes
- Roof orientation, shading, panel choice, financing, and household usage can change the result.
- Policy and incentive rules change, so dated source labels are part of the product.
- County and state pages should be treated as screening tools before installer-specific quotes.
- Installer workmanship, warranty strength, battery attachment rates, and property-specific tax treatment are not scored.
Where to go next
Solar Payback Map estimates are general information for comparing locations, not financial advice or a guarantee for any individual property.