Commercial Solar Scope of Work: Modules, Inverters, NEC, and PTO
What to put in a commercial solar scope of work — PV module specs, racking, inverters, NEC compliance, structural attachment, utility interconnection, and the PTO milestone GCs miss.
Solar is one of the most underscoped trades in commercial construction. Most GCs are procuring solar subcontractors for the first time, and the gaps — from structural attachment engineering to utility interconnection to Permission to Operate — can run into six figures in change orders or commissioning delays. This guide covers what to include in a solar scope of work, organized by the trade-specific work, the package items subs routinely omit, and the coordination requirements between solar and your other trades.
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PV Modules, Racking, Inverters, and NEC-Compliant Electrical
The line items that govern a commercial solar buy-out — delegated engineering, module and inverter specs, racking and structural attachment, DC/AC wiring, and commissioning — that must be in writing before the design freeze.
System Design and Engineering
Delegated design: The solar sub must engage a licensed Professional Engineer to prepare, stamp, and seal structural attachment calculations, electrical single-line diagrams, and system sizing documentation. Confirm jurisdiction-specific licensing requirements before executing the subcontract.
Permit drawings: Sub is responsible for preparing and submitting all permit drawings required for the building permit and utility interconnection agreement (UIA). Confirm which permits are required in your jurisdiction — solar permits, electrical permits, and structural permits are often separate applications.
System sizing: Specify DC system capacity (kWp), number and type of modules, inverter type (string, micro-inverter, or power optimizer), and target annual energy production (kWh/year). If there's an owner performance requirement (net-zero, carbon reduction target), it must be in the scope — not implied.
Structural Attachment
Roof attachment system: Specify whether the system is ballasted, mechanically attached, or hybrid. For mechanically attached systems, require the sub to coordinate with the roofing sub on penetration and flashing details before any roof work begins. Improper penetrations void roofing warranties — this must be resolved in writing before installation.
Structural calculations: Sub must provide stamped structural calculations confirming attachment spacing based on actual roof dead load capacity and local wind and snow design loads. Do not accept default manufacturer attachment patterns without project-specific calculations. Where additional roof-level structural steel framing is required to carry array dead load or ballast, confirm scope split between the steel sub and the solar sub in writing.
Existing roof condition: On re-roofing or retrofit projects, sub must inspect and document existing roof condition prior to attachment. Any deficiencies that would void the roofing warranty upon solar attachment must be reported to the GC in writing before work begins.
PV Modules and Inverters
Module specification: Specify manufacturer and model (Tier 1 bankable manufacturers only for commercial projects), rated wattage (Wp), efficiency, temperature coefficient (Pmax), and warranty terms — minimum 25-year linear performance warranty, 12-year product warranty. Do not accept substitutions without written approval and re-engineering of string sizing.
Inverter specification: Specify brand, type, and monitoring integration requirements. Some utilities require specific inverter models for interconnection — confirm with the local utility before specifying. Rapid shutdown requirements per NEC Article 690.12 (2017 and later) must be specified for all roof-mounted systems.
Racking system: Specify material (extruded aluminum or galvanized steel), rail spacing, and snow and wind load certification. Ballasted systems require weight calculation per unit area — confirm the roof can carry it before ordering. For ballasted systems on buildings where the existing structural steel roof framing was not designed for added dead load, require a written sign-off from the structural engineer of record before procurement.
String sizing: Sub must provide string sizing calculations confirming Voc and Vmp are within the inverter's MPPT range under worst-case temperature conditions. Under-stringing and over-stringing are both common errors.
DC and AC Electrical
DC wiring: Listed PV wire (USE-2 or PV Wire) run in listed conduit on all roof surfaces, per NEC Article 690. All conduit must be UV-resistant. Confirm conduit color requirements with the local AHJ — many jurisdictions require red or orange conduit for DC circuits.
AC wiring: From inverter AC output to the point of interconnection (POI). Specify wire gauge, conduit type, and routing per NEC Article 705. Confirm whether the electrical sub or the solar sub carries this work.
Disconnects: AC and DC disconnects as required by local electrical code. The utility-side disconnect location must be confirmed with the AHJ before installation — many utilities have specific requirements.
Revenue metering: Many utility interconnection agreements require a revenue-grade production meter separate from the inverter's internal monitoring. Confirm whether this is required and whether it's in the solar sub's scope or the electrical sub's scope.
Arc fault protection: AFCI requirements per NEC 690.11 / applicable electrical code edition. Confirm code year in effect for the project's permit.
Commissioning and Utility Interconnection
System commissioning: Functional testing of all strings, inverter startup and configuration, monitoring platform setup, and verification of production against modeled output. This is a critical deliverable — do not release holdback without commissioning documentation.
Monitoring platform: Specify platform, data logging frequency (minimum 15-minute intervals for commercial), remote access requirements, alert notifications (production drop, communication fault), and whether data must integrate with the building BMS.
Permission to Operate (PTO): The solar sub is responsible for scheduling and attending the utility interconnection inspection and obtaining PTO from the utility. This process regularly takes 4–12 weeks after construction is complete — track this milestone independently. PTO is frequently the last item on the critical path for solar projects.
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Common Solar Scope Gaps at Buy-Out
Items routinely left out of solar bids — penetration flashing responsibility, AC home runs, structural reinforcement, snow guards, labeling, as-builts, and spare parts — that lead to interconnection delays or voided roof warranties.
Roof penetration flashing: On mechanically attached systems, confirm whether the solar sub or the roofing sub installs the penetration flashings. If the roofing sub does not install solar flashings, the roof warranty may be voided. Get confirmation in writing from the roofing manufacturer.
AC side electrical: Confirm whether all DC and AC conduit, junction boxes, and wiring are in the solar sub's scope, or whether the electrical sub carries the AC interconnection work. A common gap is the home run from the inverter combiner box to the main electrical room.
Structural reinforcement: If the roof structure requires reinforcement to carry solar dead load, confirm which trade carries the reinforcement — it is not automatically in the solar sub's scope.
Lightning protection and grounding: Equipment grounding for the PV array per NEC/CEC. Array bonding and ground continuity testing. If a separate lightning protection system exists, confirm coordination and bonding requirements.
Snow guards: Required on arrays where panel snow shedding creates a fall hazard for building occupants below. Often not bid. Check roof location relative to occupied areas, walkways, and entrances.
Labeling and signage: All NEC/CEC-required labels on DC conduit, junction boxes, inverters, combiner boxes, and disconnects. Many utilities also have specific interconnection labels — confirm requirements during design.
As-built drawings: Full as-built electrical single-line and roof layout drawings at project closeout. Many solar subs provide only a field-marked print — specify CAD and PDF deliverables.
Spare parts: Specify quantity of spare fuses, connectors, and replacement modules included in base scope. Minimum is typically one spare of each connector type and one spare module of each type used.
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Solar Coordination with Structural, Roofing, and the Utility
Interface items between the solar sub and the structural engineer, roofing sub, electrical sub, the utility, and the architect — the points where the array's success or failure is decided before any module is set.
Structural: Confirm roof dead load capacity with the structural engineer before array layout is finalized. Ballasted systems can add 15–30 psf to the roof — this must be verified before the system is designed, not after.
Roofing: Coordinate solar attachment and flashing details with the roofing sub before either sub starts work. On new construction, penetration locations must be established before the roofing membrane is installed. On existing roofs, the sequence of work must be agreed before any sub mobilizes.
Electrical: Confirm point of interconnection location, service panel or switchboard capacity, and whether a service upgrade is required before system sizing is finalized. If a new switchboard is part of the project, confirm who makes the solar inverter output connection to the distribution system.
Utility: Solar sub coordinates all utility interconnection requirements — application, technical review, metering, inspection, and PTO. The GC should track this milestone separately from construction completion — utility timelines regularly extend beyond the construction schedule.
General contractor/architect: Confirm roof access requirements for ongoing monitoring and maintenance: hatches, walkway pads, perimeter guardrails, and anchor points. These are frequently not included in the solar sub's scope and not addressed by the architect.
Solar Scope of Work — FAQ
What is included in a commercial solar scope of work?
A complete commercial solar SOW covers seven areas: (1) delegated design with stamped structural and electrical drawings; (2) module specification by manufacturer, wattage, and warranty; (3) inverter and racking system; (4) structural attachment — ballasted or mechanically attached — coordinated with the roofing sub; (5) DC and AC wiring per NEC Article 690 / 705 including rapid shutdown and AFCI; (6) commissioning and monitoring platform; and (7) utility interconnection through Permission to Operate (PTO). The PTO milestone — not mechanical completion — is the actual finish line.
Who installs the roof penetration flashings on a mechanically attached PV array?
This must be explicit in writing. The conservative approach — and the one most roofing manufacturers require for warranty preservation — is that the roofing sub installs all penetration flashings using the membrane manufacturer's approved details, and the solar sub mounts racking on top. Many membrane manufacturers will void the NDL warranty if the flashings are installed by a non-certified applicator. Get confirmation in writing from the roofing manufacturer before the subcontract is signed.
Does adding solar require a structural review of the existing roof?
Almost always, yes. Ballasted systems add 15–30 psf of dead load to the roof and are sensitive to wind uplift; mechanically attached systems concentrate load at fastener points. The structural engineer of record (or a retained engineer if no SEOR is available) must review the existing roof structure against the proposed array layout and ballast plan or attachment pattern. Do not skip this — array failure due to inadequate structural capacity is one of the most common solar litigation issues.
What is PTO and why is it on the critical path?
PTO (Permission to Operate) is the utility's authorization to energize the array and export power onto the grid. It is issued only after the utility has inspected the interconnection, set the revenue meter, and processed the interconnection agreement. PTO routinely takes 4–12 weeks after construction is mechanically complete, and the solar sub's scope must include managing every step. The system is not commissioned and the contract is not complete until PTO is granted.
What rapid shutdown requirements apply to commercial rooftop PV?
NEC Article 690.12 (2017 and later editions) requires module-level rapid shutdown for rooftop PV — initiated by a manual switch at a defined location accessible to first responders, the system must de-energize to under 80 V within 30 seconds. This is enforced by the AHJ at electrical inspection. The solar sub's scope must specify rapid shutdown components (typically module-level optimizers or microinverters with integrated RSD) and the location and labeling of the initiation switch.
Should the solar sub or the electrical sub run the AC home run to the main switchboard?
State the answer in the scope — this is one of the largest hidden costs on commercial PV. The default is that the solar sub carries everything from the modules through the inverter AC output, and the electrical sub carries from a defined disconnect or junction box to the main switchboard. On larger systems, the AC home run can be hundreds of feet of conduit and 4/0 cable — the cost difference between assuming the solar sub vs. the electrical sub carries it can be 5–6 figures.
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