Introduction
The most expensive solar mistakes are made before installation day — in skipped measurements, unverified assumptions, and contract terms nobody read. This checklist covers everything to verify, measure, and confirm before you sign a contract or schedule an install, in the order to do it.
Start with your baseline numbers: the Solar Panel Calculator estimates system size, panel count, roof area, and rough cost from your monthly kWh and sun hours. Then work through this list to make sure the plan behind those numbers is sound.
Usage and Sizing Checks
- 12-month kWh average computed — from utility portal history, not a single bill. (How: estimating guide.)
- Coming load changes accounted for — EV, heat pump, addition, or household changes added deliberately.
- Target offset chosen — 100%, 80%, or daytime-load, based on your utility’s current export compensation rules.
- Peak sun hours verified — location-specific figure (e.g., NREL PVWatts), not a guess; orientation derate applied if not south-facing.
- Shading assessed — trees, chimneys, dormers, neighboring buildings mapped for 9 am–3 pm; professional shade analysis scheduled if any doubt.
- Calculator result sanity-checked — system kW, panel count, and roof area cross-checked against the formula guide’s worked example.
Roof and Site Checks
- Usable roof area measured — gross plane minus obstructions, minus fire setbacks and clearances (usable is typically 15–25% less than gross).
- Roof age and condition confirmed — 10–15+ years of remaining life; if not, re-roof first or bundle the projects.
- Roofing material identified — attachment hardware and cost differ for shingle, tile, metal, and flat roofs.
- Orientation and pitch recorded — for each candidate plane.
- Structural adequacy — installer or engineer confirms the roof carries array + wind/snow loads; know whether your AHJ wants an engineering letter.
- Attic/roof access — wiring routes from array to inverter to panel identified.
Electrical Checks
- Main panel capacity confirmed — busbar rating and the 120% rule checked for the planned backfeed breaker; upgrade/derate cost in the quote if needed.
- Inverter architecture chosen — string, microinverters, or optimizers, matched to roof complexity and shading (see the material guide).
- Rapid shutdown compliance — design meets NEC 690.12 per your AHJ’s adopted code edition.
- Monitoring included — panel- or system-level production monitoring you can access.
Quotes and Contract Checks
- 3+ quotes obtained and normalized to $/W, gross price, and net price after incentives (cost guide).
- Exact equipment listed — panel make/model/wattage, inverter make/model, racking type. No generic “premium panels.”
- Workmanship warranty in writing — duration and what it covers (roof penetrations, labor defects).
- Manufacturer warranties documented — panel product + performance terms, inverter term.
- Who handles permits, interconnection, and inspections — named in the contract, with timeline expectations.
- Payment schedule sane — never full payment upfront; final payment tied to PTO (permission to operate).
- Production estimate in writing — first-year kWh the installer stands behind, so underperformance is actionable.
- Change-order policy — how extras (panel upgrade, trenching, main panel work) are priced and approved.
Permits, Utility, and Legal Checks
- AHJ requirements confirmed — permit types, adopted code editions, setback dimensions, inspection sequence (code compliance guide).
- Utility interconnection process understood — application filed, PTO timeline known; system NOT energized before PTO.
- Net metering / export terms confirmed current — in writing from the utility, not the salesperson.
- Incentives verified — current federal/state/local programs, your eligibility, and (for tax credits) your tax liability — confirmed with a tax professional.
- HOA / historic district approval — submitted and approved where applicable.
- Homeowner’s insurance notified — array scheduled on the policy.
- DIY only: owner-builder permitting allowed by AHJ; licensed electrician lined up for interconnection; incentive eligibility confirmed for self-installed systems (see the DIY vs pro comparison).
Timing: When to Do Each Check
The checklist above is in dependency order, but it helps to see it on a calendar. A realistic planning timeline:
- 8–12 weeks out: usage and sizing checks — 12-month kWh average, target offset, sun hours, shading assessment. This is the research phase; nothing here costs money except your time.
- 6–8 weeks out: roof and site checks — measure usable area, confirm roof life, identify the electrical panel situation. If the roof needs replacing, the timeline resets around the roofing project.
- 4–6 weeks out: collect 3+ quotes, normalize to $/W, and verify equipment lists and warranties. Simultaneously confirm AHJ permit requirements and HOA rules.
- 2–4 weeks out: sign the contract (with permit responsibility, payment schedule, and production estimate in writing), and confirm the installer has filed the utility interconnection application — PTO queues are often the longest wait.
- Install week: be available for the inspection; do not make final payment until PTO is granted and the system is producing.
Rushing the first two phases is where most planning errors originate — a week spent measuring and verifying inputs saves months of regret. The common mistakes guide catalogs what goes wrong when steps are skipped.
Final Go/No-Go
Do not sign until every box above is checked or consciously deferred with a plan. The five most common deal-breakers discovered too late: roof needs replacing, panel needs upgrading, utility PTO takes months, export credits weaker than assumed, and the “cheap” quote excluded half the scope. Catch them here and the installation itself is the easy part.
Related Guides
- Complete Guide — the full solar sizing overview with worked example.
- Estimating Guide — reading your bill and measuring your roof.
- Code Compliance — permits, NEC Article 690, and inspections.
- Cost Guide — per-watt pricing, savings, and payback math.
- DIY vs Pro — honest trade-offs of self-installation.
- FAQ — quick answers to common solar sizing questions.
Get Your Number
A checklist only works if the numbers behind it are right. Run your usage and sun hours through the Solar Panel Calculator, work every item above, and you’ll walk into installer meetings as the best-informed customer they’ve quoted all month.
Disclaimer: Calculator results are planning estimates based on the inputs you enter. This checklist is general planning guidance, not professional advice. Verify sizing with a licensed solar installer or electrician — and permits, codes, incentives, and utility requirements with your local code authority, utility, and tax professional — before signing contracts or starting work.
