Everything runs in your browser using the numbers you enter. Assumptions last reviewed October 2026.
Year-by-year model (25 years)
- Your usage: (monthly bill − fixed fee) × 12 ÷ electricity rate = kWh per year. If you copy numbers from your bill instead, we use your yearly kWh (best) — or, as a rough estimate, that bill's kWh × 12, which can be far off because seasons differ — and your own rate = (electric charges − customer charge) ÷ kWh on that bill.
- Solar output: system kW × output per kW — or the year-1 production printed on your quote — reduced each year by panel loss.
- Used at home: output × "used at home %", capped at your usage. Each of those kWh saves the full retail rate.
- Exported: the rest of the output. Exports up to your remaining yearly use are credited at retail × export credit %; any yearly surplus beyond your total use is credited at retail × yearly surplus %.
- Net benefit: savings + export credits + any projected SRECs you enter (only for the years they're paid) − upkeep − the inverter replacement in year 13 (skipped for microinverters or a 25-year inverter warranty). We also show payback and value today without the SRECs, because SREC prices aren't guaranteed.
- Payback: when cumulative benefits recover the net upfront cost (quote − incentives). If a later cost pushes the total back below zero, payback is the final time it crosses zero.
- Electricity prices grow by the rate-growth % you set (default 0%, which is conservative).
Quick vs. advanced estimate
Quick estimate: your state's illustrative values plus standard assumptions. Advanced estimate: you've changed anything under Advanced settings (output, export and surplus credit, usage pattern, costs, discount rate). Both are annual models: they can't price hourly or time-of-use electricity rates, demand charges or battery dispatch. For time-of-use tariffs (most of California, parts of Arizona and elsewhere), ask each installer for an hourly bill-savings estimate using your actual tariff, or use NREL SAM with your utility rate.
Scenario range (favorable and cautious cases)
Under the payback number we rerun the model twice: favorable (5% more output, rate growth 2.5 points higher) and cautious (8% less output, rate growth 1 point lower). This is a "what if" check on two uncertain assumptions — not a statistical or guaranteed range. A different price, export rule or usage pattern can move results outside it.
Fair-price check
Price per watt = cash price ÷ (system kW × 1,000), rounded to the cent, compared with your state's average cost per watt before incentives from EnergySage (2026 data; state table updated Oct 2, 2026). These are averages of competitive marketplace quotes for typical system sizes; smaller systems usually cost more per watt. Up to 10% above or 15% below is fair; more than 10% above is high; more than 15% below is low (good, but check equipment and warranty terms).
Size suggestion & coverage
Suggested size = your yearly usage ÷ output per kW (rounded to 0.5 kW). "Solar covers" = first-year output ÷ your yearly usage.
Value today (NPV) and solar cost per kWh
Value today = −upfront cost + each year's net benefit ÷ (1 + discount rate)year. A positive 25-year cash total can still be a weak investment if value today is below $0. Solar cost per kWh = (upfront cost + upkeep + inverter) ÷ total 25-year output.
"What would make it worth it"
We find the highest cash price that pays back within 12 years, stays paid back through year 25 and keeps value today at $0 or more, and show it as a price per watt.
Federal tax credit
The IRS says the Section 25D residential clean energy credit is not available for property placed in service after December 31, 2025, so homeowner-owned systems installed in 2026 get $0 federal credit (IRS page last reviewed July 2026). IRS guidance ↗
Illustrative state starting values
These are typical, simplified values to get you started — not your utility's actual tariff. Utilities within a state can differ a lot. Replace them with numbers from your bill, your utility's net-metering rules and your installer's production estimate.
| State | Rate | Output kWh/kW | Export | Yearly surplus | Avg $/W (EnergySage, Oct 2026) | Export rule (summary) |
|---|
| U.S. average | $0.18 | 1,300 | 60% | 50% | $2.60 | Other states: rules vary, 60% is a cautious middle |
| Arizona | $0.15 | 1,650 | 40% | 40% | $2.27 | Export rates well below retail (APS, TEP) |
| California | $0.35 | 1,550 | 20% | 20% | $2.52 | NEM 3.0 net billing; exports ~5–8¢/kWh |
| Colorado | $0.17 | 1,500 | 100% | 50% | $2.64 | Net metering at retail |
| Connecticut | $0.24 | 1,200 | 90% | 50% | $2.68 | Retail-based netting tariff |
| Florida | $0.15 | 1,400 | 100% | 50% | $2.12 | Net metering at retail |
| Illinois | $0.20 | 1,250 | 60% | 50% | $2.95 | Since 2025 most new customers get supply-only credit |
| Maryland | $0.22 | 1,250 | 100% | 50% | $2.57 | Net metering at retail |
| Massachusetts | $0.30 | 1,200 | 90% | 50% | $2.90 | Net metering; credit varies by utility |
| New Jersey | $0.25 | 1,250 | 100% | 50% | $2.59 | Net metering at retail |
| New York | $0.29 | 1,200 | 90% | 50% | $2.76 | Net metering plus a monthly fixed charge |
| North Carolina | $0.15 | 1,350 | 80% | 50% | $2.45 | Duke time-of-use netting |
| Pennsylvania | $0.22 | 1,200 | 100% | 50% | $2.60 | Full-retail kWh credits roll over monthly; leftover credits are paid yearly at the price to compare (PECO ≈11.6¢, about half of retail) |
| Texas | $0.16 | 1,450 | 40% | 40% | $2.25 | No state net metering; depends on your retail plan |
- Rates: EIA Electric Power Monthly, Table 5.6.A, average residential price, June 2026 (includes some fixed charges, so your variable rate may be a bit lower).
- Output: typical south-facing, unshaded rooftop values based on NREL PVWatts patterns. Your installer's estimate is better.
- Price per watt: EnergySage solar cost data, 2026, before incentives. Marketplace quotes tend to run lower than door-to-door offers.
- Export credit: simplified summaries of 2026 state and utility rules. Rules vary by utility and change often, so check yours.
Export-credit limits of this model
- Exports are credited at one flat % of the retail rate for the whole year. Real utilities may net usage monthly or by time of day, carry credits forward, apply minimum bills, or reset credits once a year.
- Yearly surplus: if your system makes more than you use in a year, many net-metering utilities pay the leftover at a lower supply, "price to compare" or avoided-cost rate rather than retail. The model credits it at the separate yearly surplus % (illustrative default: 50%, or your export % if lower). Check your utility's annual settlement rule.
- Time-of-use rates (common in California and Arizona) can make exported midday power worth much less than evening power. Use a lower export % if you're on such a plan.
Not included
Financing, batteries, taxes, roof work, time-of-use rates and monthly billing detail. Payback and the 25-year total are simple cash sums (not discounted); Value today is the only figure that applies your discount rate.
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