Cost of Solar Panels Calculator

How to use this calculator

The calculator turns your real electricity usage into a kW system size, then prices that system at U.S. market rates and applies the federal ITC. Five inputs:

1. Monthly electricity use (kWh) — pull the most recent 12 months of bills and average them. The 2026 U.S. residential average per EIA is 875 kWh/month, but ranges from 575 kWh in Vermont to 1,200 kWh in Tennessee. If you have an EV, add 250 to 350 kWh/month. If you have central A/C in the South, add 200 to 400 kWh/month for summer.
2. Target offset (%) — 100% means a system sized to match your full annual consumption. Most NEM-1 and NEM-2 customers should aim for 100%; NEM-3 customers in California should typically size to 70 to 90% with battery to maximize self-consumption. Going over 100% is rarely cost-effective in 2026 — most utilities now compensate exports at avoided-cost (about $0.04/kWh) instead of retail.
3. Peak sun hours/day — your local annual average. Use NREL PVWatts (free at pvwatts.nrel.gov) for an exact number. Phoenix gets 6.5; Denver 5.5; Atlanta 4.8; Boston 4.2; Seattle 3.4; Anchorage 2.9.
4. Installed cost per watt — the all-in turnkey price including equipment, labor, permitting, and interconnection. The 2026 EnergySage median is $2.85/W. Use the actual quoted figure once you have one. Below $2.50/W usually indicates lower-tier equipment or under-scoped electrical work.
5. Tax credit / rebate (%) — 30 for the federal ITC alone. Add state and utility rebates: NY-Sun adds 5 to 10% in some sectors, Massachusetts SMART adds 8 to 12% NPV equivalent, Illinois Solar for All adds full coverage for low-income households, Maryland adds a $1,000 grant.

How the math works

The calculator sizes your system from annual kWh and peak sun hours, then prices it:

annual_target_kWh = monthly_kWh × 12 × (offset% / 100)
system_kW         = annual_target_kWh / (peak_sun_hours × 365 × 0.78)
gross_cost        = system_kW × 1000 × $/W
net_cost          = gross_cost × (1 - incentive% / 100)
range_low/high    = gross_cost × 0.85 / 1.15

The 0.78 derate factor accounts for inverter efficiency (96-98%), wiring losses (2-3%), soiling and shading (4-6%), and ambient temperature derating (3-5%) — this is the NREL PVWatts default, validated against thousands of metered residential systems.

Worked example for a Phoenix home using 1,000 kWh/month:

• Annual target: 1,000 × 12 × 1.0 = 12,000 kWh
• System size: 12,000 / (6.5 × 365 × 0.78) = 6.49 kW
• Gross cost at $2.85/W: 6,490 × $2.85 = $18,497
• Net cost after 30% ITC: $18,497 × 0.70 = $12,948
• Typical range: $15,722 to $21,272 gross

U.S. cost-per-watt by state (2026)

EnergySage H2 2025 marketplace data, median residential quote, gross of incentives:

Sources: EnergySage H2 2025 Marketplace Report, NREL Tracking the Sun 2025, Wood Mackenzie U.S. Solar Market Insight Q4 2025.

What is and is not included in $/W

A typical $2.85/W turnkey quote includes:

• Tier-1 monocrystalline panels (Q CELLS, REC, Silfab, Hanwha, Trina)
• String inverter or microinverters (Enphase IQ8, SolarEdge HD-Wave)
• Racking and flashing (IronRidge, Unirac, EcoFasten for tile)
• DC and AC wiring, conduit, junction boxes
• AC disconnect, rapid shutdown
• Permits, plan review, electrical inspection
• Utility interconnection application and final inspection
• 25-year panel warranty pass-through, 10-year workmanship warranty

What it does not include (price these as adders):

• Main panel upgrade to 200A — $1,500 to $3,000 (very common in homes built before 1980)
• Sub-panel or critical-loads panel for battery backup — $1,200 to $2,500
• Tree removal for shading — $500 to $5,000
• Roof replacement if the roof has under 10 years of life — $7,000 to $20,000
• Battery storage — $9,200 to $15,000 for 13.5 kWh Tesla Powerwall 3 or equivalent
• EV charger circuit if installed concurrently — $800 to $2,500

Why getting multiple quotes matters

Wood Mackenzie’s 2024 customer-acquisition study found a 28% spread between the cheapest and most expensive quote on the same project, and a 14% spread between the median two quotes. The U.S. residential CAC (customer-acquisition cost) is one of the highest in the OECD at $0.41/W — nearly double the German $0.22/W — so installers with high lead-cost models pass that on. Quote shopping is the single biggest lever you have on price.

EnergySage, SolarReviews, and Solar.com all aggregate quotes from local installers. Verify each installer is NABCEP-certified, check their state contractor license, and read SolarReviews and BBB reviews specifically about post-installation service (warranty claims and monitoring) since that is where most buyers regret their installer choice.

Pair this with the payback calculator, ROI calculator, and savings calculator

Cost gives you the up-front capital outlay; payback tells you when you break even; ROI gives you the lifetime return; savings shows you the year-over-year cash flow. Run all four with the same inputs to see the full financial picture before signing a contract.

Sources

• EnergySage Solar Marketplace Report H2 2025 — installed cost-per-watt benchmarks by state
• NREL Tracking the Sun 2025 — residential PV system pricing trends
• SEIA / Wood Mackenzie U.S. Solar Market Insight — market and policy data
• DSIRE database (NC State) — state and local incentive details
• HomeAdvisor solar cost guide 2025 — labor and adder pricing
• DOE SETO solar cost benchmark — itemized cost breakdown