Methodology
The calculator is designed for early planning. It uses transparent formulas and visible assumptions instead of claiming installer-grade precision.
Methodology updated 2026-09-04.
Source stack
Production evidence: California has a saved full PVWatts response; eight states have successful API yields recorded to two decimals. Colorado, Illinois and Pennsylvania retain explicit author assumptions. The download distinguishes these evidence levels.
$0.3474/kWh
34.74 ¢/kWh
EIA Table 5.6.A, June 2026 residential column; published August 26, 2026. Divide the published cents/kWh by 100. This preliminary statewide average is a fallback, not your utility tariff. Use your bill's energy-only rate; fixed charges remain payable.
1,595.2 kWh/kW/year
kWh/kW/year
PVWatts V8 typical-weather model at an author-selected reference point in the state: 4 kW DC, roof mount, 20° tilt, 180° azimuth, 14% system losses. Annual AC kWh ÷ 4 gives kWh/kW/year. Losses are already included and are not deducted again. Neither a statewide average nor a ZIP or roof survey. Shade and ±10% production bounds are separate author scenarios.
$1.98–$2.98/W
$2.48/W × 0.8…1.2
EnergySage's state marketplace average, table updated August 28, 2026. We calculate an author-selected range of average × 0.8 to average × 1.2, rounded to cents/W. This ±20% scenario is not an observed price distribution or confidence interval. Cash solar only, before incentives; compare like-for-like local quotes.
Production evidence: California has a saved full PVWatts response; eight states have successful API yields recorded to two decimals. Colorado, Illinois and Pennsylvania retain explicit author assumptions. The download distinguishes these evidence levels.
Original calculator output for 12 states × 3 direct-use shares (30%, 55%, 70%) × 3 export values (10%, 35%, 100% of retail). Every row uses 900 kWh/month, 400 W panels, low shade and a 100% annual energy target. This is a synthetic model comparison, not measured customer performance or a forecast of your tariff.
At 55% direct use and 35% export value, 100% energy coverage offsets this share of modeled energy charges: 70.75%
55% + 45% × 35% = 70.75%. Fixed charges are additional. This identity follows from the model's assumptions, not from observations.
| State reference | System size | Annual energy savings | Remaining energy charge |
|---|---|---|---|
| California | 6.8 kW | $2,654 | $1,097 |
| Texas | 6.6 kW | $1,218 | $504 |
| Florida | 7.0 kW | $1,154 | $477 |
| Arizona | 6.3 kW | $1,160 | $480 |
| Nevada | 6.2 kW | $1,002 | $414 |
| New York | 9.2 kW | $2,253 | $932 |
| New Jersey | 7.9 kW | $1,906 | $788 |
| Massachusetts | 8.3 kW | $2,263 | $935 |
| North Carolina | 8.1 kW | $1,126 | $466 |
| Colorado | 8.1 kW | $1,309 | $541 |
| Illinois | 10.0 kW | $1,520 | $628 |
| Pennsylvania | 10.0 kW | $1,660 | $686 |
Reproduce a row by entering its complete input object into the calculator. JSON includes inputs, formulas, source snapshots and limits; CSV contains all 108 results. The table below selects 55% direct use and 35% export. Data version: September 4, 2026.
Quick answer
It is a first-pass planning range built from your usage, a production assumption, visible system losses, direct solar use, export value, and gross cost benchmarks. It is not an engineering design, utility approval, tax determination, production guarantee, or installer quote.
| Label | Meaning | Use before a decision |
|---|---|---|
| Calculated estimate | A formula result based on entered and default assumptions. | Change assumptions and compare a range. |
| Manufacturer specification | A value published for a named equipment model. | Confirm the exact model and datasheet. |
| Government incentive | A program claim tied to an official source and eligibility rules. | Verify current status and personal eligibility. |
| Utility information | Tariff, export, interconnection, or billing terms from the serving utility. | Confirm the exact account and rate plan. |
| Installer quote | Project-specific price, equipment, scope, and production proposal. | Compare written assumptions and contract terms. |
Incentives are not applied by default unless they have a source URL, updated date, eligibility note, active status, and explicit inclusion in the data model. This is especially important for 2026 homeowner estimates after federal credit-status changes.
View sourcesOnce the assumptions make sense, run the calculator and keep the source notes handy when comparing installer proposals.