Solar Scope of Work: What GCs Need to Include When Buying Out a Solar Sub

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.

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.
• 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 (NEC 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.
• 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. 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. 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 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.

• 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.

• 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.