US Home Solar Calculator — Built for 2026, Not 2024

What this estimate does

Most solar calculators still subtract a 30% federal tax credit from your quote. That credit no longer exists for a homeowner-owned system installed in 2026. IRC section 25D was terminated for expenditures made after December 31, 2025 by Public Law 119-21, and the IRS treats the expenditure as made when the original installation is completed — not when you sign or pay a deposit. HelioCalc starts from the law as it stands today: your federal credit is $0, and every number below is computed without it. Change the state, your monthly bill, your installer's price per watt, the export rate your utility actually pays, and the roof conditions. The calculator sizes the array, prices it, applies only incentives we could verify, and runs a 25-year cash flow with escalating rates and panel degradation.

How this is calculated

The model first turns your bill into an annual usage figure (monthly bill × 12 ÷ retail rate), then reverses the production equation to find the array size that delivers your target offset: kW = annual kWh × offset ÷ (peak sun hours × 365 × system derate × roof factor). Production is that array size multiplied back through the same yield. Cost is kW × 1,000 × $/W plus optional storage. The only subtractions are a verified state credit or grant, a confirmed utility rebate, and a federal credit of zero. Annual savings split production between energy you use on site — worth the full retail rate — and energy exported, worth the export credit your tariff pays. Each year then applies your escalation assumption to the rate, 0.5% degradation to output, and 2% growth to maintenance, producing payback by interpolation, NPV and IRR.

A worked example

Take a California home with a $150 monthly bill at the EIA August 2026 state rate of 29.75 ¢/kWh. That is about 6,050 kWh a year. At the Southwest insolation band (6.3 peak sun hours), a 0.84 derate and a south-facing 20° roof, a 90% offset calls for roughly 2.82 kW. At the EnergySage September 2026 California benchmark of $2.52/W the array prices near $7,100. California has no statewide residential tax credit, and the federal credit is $0, so the net cost is the gross cost. Under NEM 3.0's ~4.2 ¢/kWh export credit, year-one savings land near $920 and the modeled payback near 8.3 years. Change the export setting to full retail and watch the same system behave differently — that single input is now the largest lever in most states.

What this tool does not do

This is a planning model, not a quote, a tax opinion, or a utility tariff. It does not know your interval data, time-of-use schedule, fixed monthly grid charges, non-bypassable charges, roof condition, electrical panel upgrade, or the interconnection rules of your specific utility. It cannot tell you whether a lease contract's escalator or buyout is fair. Get three written quotes and a bill-impact analysis built on your actual 12-month interval data before signing anything.

Practical checks before you compare quotes

• Ask each installer to state the $/W before incentives in writing — it makes quotes comparable and exposes financing fees hidden in a monthly payment.
• Request your utility's export credit in cents per kWh, not a percentage. Under net billing a '75% of retail' claim can be misleading.
• Compare the cash, loan and lease/PPA rows on a 25-year basis. A low monthly payment can hide a 2.9% annual escalator.
• If your proposal shows a 30% federal credit on a 2026 installation, treat that as a serious accuracy problem with the whole proposal.

Common mistakes

• Using last year's tax-credit assumption and discovering the shortfall at signing.
• Sizing to 100% of annual usage under net billing, where exported kWh are worth a fraction of retail.
• Comparing a cash price to a financed price without adding dealer fees and interest.
• Ignoring fixed grid charges, which solar does not reduce.

Why 2026 needs its own calculator

The One Big Beautiful Bill Act (Public Law 119-21) terminated the section 25D Residential Clean Energy Credit for expenditures made after December 31, 2025. The IRS has stated that the expenditure is treated as made when the original installation is completed — so a 2026 installation does not qualify, even if a deposit was paid earlier. A model built for 2024 overstates savings and understates payback by years. HelioCalc makes the federal line explicit at $0 so you can verify it was not quietly applied.

What is left matters more than what disappeared: your retail rate, your utility's export credit, your installed price per watt, and the state programs that still exist. We publish all 50 states and DC with EIA August 2026 residential rates, label which installed-cost figures are measured and which are modeling benchmarks, and default to a conservative export credit where no statewide rule could be verified.

What you can check here

• Array size in kW, a 450 W panel count and the roof area required, capped by the usable area you enter.
• An itemized cost stack: array, optional battery, state credit or grant, utility rebate, and a $0 federal credit.
• Full-retail net metering versus avoided-cost net billing, with the export rate you enter in cents.
• Cash, loan and lease/PPA on one 25-year basis, including a PPA escalator.
• Payback by cash-flow interpolation, NPV, IRR, a four-point escalation sensitivity table and a CSV of every year.