Roof-mounted PV looks straightforward, but it's a system that mixes fall hazards, structural loads, and high-voltage DC. Many jurisdictions require licensed trades for electrical tie-in and inspection. Use this guide as a professional-grade checklist; if any step is beyond your comfort or licensing, hire a qualified installer.
Step 1 - Feasibility & Roof Assessment
Sun & Shade Study: Confirm at least 5–6 peak-sun hours/day with minimal shading between 9:00–15:00. Use a solar pathfinder or app; note trees, chimneys, neighboring buildings.
Orientation & Tilt: South (N. Hemisphere) or north (S. Hemisphere) facing with tilt near your latitude is efficient, but roof pitch typically suffices.
Roof Condition: Solar will stay ~25 years. If shingles are near end of life (≤5 years), re-roof before PV.
Structure Check: Determine rafter/truss size, spacing, and spans. Typical loads add racking + modules (~12–18 kg/m²) + wind/snow uplift. Have a structural pro verify capacity and anchorage, especially in high wind/snow regions.
Electrical Capacity: Identify main service rating, busbar limits, and breaker spaces. Decide on grid-tie vs hybrid (battery) and where equipment will land.
Step 2 - Permits, Utility Approval & Design Package
AHJ Permits: Most areas require a building/structural permit and an electrical permit. Prepare a one-line diagram, site plan, racking cut sheets, attachment details, wire schedule, labels, and data sheets.
Utility Interconnection: Apply for net metering (or export tariff). You'll submit system size, inverter model, anti-islanding details, and metering plan.
Fire Setbacks & Access: Roof arrays often require clear pathways and ridge/hip setbacks for firefighter access. Lay out modules to comply with your local rules.
Rapid Shutdown & Equipment Listings: Select certified inverters/microinverters/optimizers that meet current rapid-shutdown and safety requirements in your region.
Step 3 - Choose Your System Architecture
Module Level: 400–600 W mono-PERC or TOPCon modules are common; verify dimensions and clamp zones.
Power Electronics:
Microinverters (AC at each module): shade-tolerant, easy expansion, simpler DC runs.
DC Optimizers + String Inverter: module-level MPPT and monitoring; central AC point.
String Inverter (unoptimized): simplest hardware; best on uniform, shade-free roofs.
Roof Attachment Type:
Asphalt/Composite Shingle: lag-bolted flashed L-feet into rafters; butyl or form-fit flashing under shingles.
Standing-Seam Metal: clamp to seams-often no penetrations.
Corrugated Metal: specialized brackets with gasketed fasteners into structure.
Tile (concrete/clay): tile hooks or replace-tile flashings; never rely on tile for load.
Racking: Rails (aluminum) or rail-less systems rated for local wind/snow. Confirm span tables, clamp locations, bonding paths.
Step 4 - Materials & Tools (Core List)
PV modules, racking/rails, mid/end clamps, L-feet/flashings or seam clamps
Inverter(s) / optimizers / microinverters, AC/DC disconnects, combiner if needed
Copper conductors (PV-rated), EMT or UV-rated conduit, fittings, roof-penetration boots
Grounding/bonding lugs and jumpers; equipment ground conductor
Labels (per electrical code), warning placards, rapid-shutdown switch (if external)
Torque wrench, impact driver, stud/rafter finder, chalk line, level, shears
Fall-arrest: full-body harness, lifeline, roof anchors; ladder with standoff
Sealants compatible with roofing material (butyl tape, high-quality flashing sealants)
Step 5 - Layout, Marking & Attachment
Find Structure: Mark rafter centers with a stud finder from attic or roof. Snap control lines to align attachments in straight rows.
Flash & Fasten:
Shingle roofs: lift the course, insert flashing so the upper edge is under the shingle above, seal per manufacturer, and lag into rafter (predrill).
Metal standing seam: position seam clamps to manufacturer torque-no penetrations.
Tile: remove tile, mount hook or base to the deck/rafter, install a flashing pan, then trim/replace tile for clearance.
Rails On: Level and square rails; check rail splice torque and integrated bonding teeth if present. Maintain array perimeter setbacks.
Step 6 - Wire Management (Do It Like A Pro)
Keep DC/AC home runs under array where shaded from UV and mechanical damage.
Use UV-rated clips and stainless hardware; avoid zip ties that embrittle.
Create drip loops before entry points; use listed roof boots for conduit penetrations.
Separate communication conductors from power where required; avoid sharp bends and abrasion points.
Step 7 - Module Mounting & Bonding
Place First Row: Set modules, check squareness to eaves/ridge.
Clamping: Use only the approved clamp zones on module frames; torque to spec.
Equipment Grounding: Most modern rails/modules provide bonding teeth; add grounding jumpers where rails break. Terminate to the system grounding point.
Electronics: Install microinverters/optimizers per module or connect strings per the voltage window and string sizing (open-circuit voltage at lowest expected temp, current limits, and MPPT ranges).
Step 8 - Roof Penetrations & Weatherproofing
For any conduit or junction box, use flashed, listed penetrations with proper counter-flashing.
Seal around fasteners only where the manufacturer allows; flashing, not caulk, is your primary waterproofing.
Keep penetrations high on the shingle where possible; avoid valleys.
Step 9 - AC/DC Protection, Metering & Interconnection
DC Side: Fused combiner (if needed), DC disconnect at the inverter/string input, proper labeling of polarity and hazard.
AC Side: Inverter AC disconnect (lockable where required), backfeed breaker sized per busbar rules or supply-side tap if permitted.
Rapid Shutdown: Install/label the initiator at the readily accessible location near service equipment if required.
Monitoring: Commission gateway/CTs for production (and consumption if desired).
Surge Protection: Add SPD on AC and DC where recommended-especially in lightning-prone areas.
Step 10 - Commissioning & Inspection
Mechanical QA: Verify torque on all attachments, clamps, and splices; shake test rails; confirm no wire is pinched or rubbing.
Electrical QA: Check polarity, insulation resistance (megger if specified), open-circuit voltage and short-circuit current per string; confirm inverter firmware and settings.
Labels & Diagrams: Apply permanent labels at service equipment, disconnects, and rooftop equipment; keep a laminated one-line near the main panel.
Witness Test: With utility approval, energize per procedure. Confirm rapid-shutdown function, inverter operation, and monitoring data.
Aftercare: O&M For A 25-Year Life
Annual Visual Check: Look for loose hardware, animal intrusion, chafing, cracked boots, or broken clips.
Cleaning: If soiling reduces output, rinse with soft water and a soft brush at cool times; avoid pressure washers.
Firmware & Alerts: Keep monitoring current; set alerts for string underperformance to catch shade or connection issues.
Roof Warranty: Keep documentation; PV attachments installed to manufacturer specs typically preserve roofing warranties where approved products are used.
Common Mistakes (And How To Avoid Them)
Missing rafters / weak anchorage: Always pilot-drill and verify embedment; never trust sheathing alone.
Over-reliance on sealant: Flash first, sealant second.
Wire sag & UV damage: Use proper clips every 30–45 cm; keep conductors off abrasive edges.
Ignoring thermal expansion: Provide rail expansion gaps and flexible conductor slack.
String overvoltage in cold: Calculate Voc @ lowest temp; choose inverter MPPT accordingly.
Blocking attic vents or gutters: Maintain airflow and drainage paths.
No fall protection: Tie off. Every time.
FAQ
Can I install over an old roof?
Not recommended. Replace aging shingles first; it's cheaper than removing a PV array later.
Do I need batteries?
No for standard grid-tie. Batteries add backup and time-of-use shifting but increase cost and complexity.
How long does it take?
A professional crew often completes a typical residential system in 1–2 days on site after permits-complex roofs take longer.
Will panels leak my roof?
Properly flashed attachments do not cause leaks. Most issues trace back to skipped flashing or misaligned fasteners.
