Sizing tool · usage in, kW + panel count out
How many solar panels do I need?
Plug in your annual utility usage, pick a climate region and roof orientation, and the calculator returns the DC system size and panel count to offset your target fraction of annual consumption. Production factors are anchored to NREL PVWatts typical US residential output1.
Updated May 16, 2026.
Your roof + usage
Sizing result
Targeting 100% offset on 12,000 kWh/yr usage. After integer-panel rounding, this system offsets 101% of your annual usage. Numbers above 100% mean the system over-produces — useful if you expect rising consumption (EV, heat pump, larger family). Whether the over-production has financial value depends on your utility's net metering vs net billing policy.
What this sizing can't see
Your actual roof area (the number of panels you can physically fit may be less than what your usage calls for). Site-specific shading from trees that grow or neighbors that build. Local microclimate variation. Roof age — replacing shingles before installing is much cheaper than removing panels to re-roof in 5 years. This is a first-pass sizing tool; verify with an installer + PVWatts for your exact ZIP and roof geometry before sizing for purchase.
How the sizing thinks.
Required system size = (annual usage × target offset) ÷ effective production per kW. Effective production per kW = region baseline × azimuth factor × tilt factor × (1 − shading%). Region baselines are tuned to NREL PVWatts' typical US output range of 1,000-1,600 kWh/kW at default 14% system losses1. Azimuth penalties follow PVWatts' sensitivity to off-south orientations; tilt penalties stay modest because the optimal tilt is broad (5% loss range across most of the 10-40° band).
Comparison point. LBNL Tracking the Sun 20242 reports the 2023 national median residential system size at 7.4 kW. Your specific number depends entirely on your usage — homes with electric heat, EV charging, or larger footprints often size to 10-12 kW; smaller or efficient homes often size to 5-6 kW.
Run the audit: once you have a kW number and an installer quote, the quote calculator tests whether the price and production numbers on the proposal match what your sized system should cost and produce.
- 1. NREL PVWatts (v8) — annual production estimator using NSRDB irradiance data with default 14% total system losses (soiling, shading, snow, mismatch, wiring, connections, light-induced degradation, nameplate rating, age, availability). Typical US residential output: 1,000–1,600 kWh/kW annually. Verified 2026-05-16. pvwatts.nrel.gov · API docs ↩
- 2. Berkeley Lab, "Tracking the Sun, 2024 Edition" (Executive Summary, August 2024; data through year-end 2023; sample ~3.7M U.S. distributed PV systems). State-level median residential installed price in 2023: $3.20–5.20/W. Loan dealer-fee gap, verbatim: "a large portion of residential systems are loan-financed, and installed prices reported for these systems likely include dealer fees, adding anywhere from 5-50% to the total up-front price paid by the customer." Verified 2026-05-16. emp.lbl.gov · Tracking the Sun 2024 (PDF) ↩
Next: How to read a solar quote — the five numbers worth checking once you have a quote in hand.
Ask a TrueSolarCost question
Quick answers about TrueSolarCost's calculators, the public-data benchmarks, and how to read a residential solar proposal. Free, no signup. Not personalized advice — for tax-position questions talk to a CPA, for roof/structural questions talk to a roofer or engineer, for utility-rate questions talk to your utility.
Hi, I'm the TrueSolarCost assistant. I answer questions about how to read a residential solar proposal, what the calculators on this site compute, and what the public-data benchmarks (NREL PVWatts, EIA, IRS, LBNL, DOE, DSIRE) mean for the numbers in your quote. I'm not a tax professional, CPA, structural engineer, or licensed installer — for tax-position decisions talk to a CPA, for roof-condition or structural questions talk to a roofer or engineer, for utility-rate or interconnection specifics talk to your utility.