What Is a Solar System Commissioning Inspection
A solar system installation involves multiple approval steps before it can legally operate. Most homeowners are aware that building permits are involved, but fewer know that there's typically a second, utility-side inspection that happens separately — and that without this step, the system isn't authorized to run in grid-tied mode.
Understanding both approval steps helps homeowners follow the timeline and know what's happening between installation and the day the system starts generating credits on their electricity bill.
The Two Approval Steps
Building department permit and inspection. This is the local government side. Your installer applies for an electrical permit, the system is installed, and a building inspector comes out to verify the installation meets current requirements. This process is handled similarly to any other permitted electrical work — the inspector reviews the panel connections, the wiring, the mounting, and relevant safety components.
Utility inspection and Permission to Operate (PTO). This is the utility side. Before a grid-tied solar system can legally export power to the grid, the utility must review and approve the installation. They may send their own inspector to physically verify the system, or they may conduct their review based on the submitted documentation and interconnection application. Once satisfied, they issue Permission to Operate — the formal authorization to turn the system on in grid-tied mode.
Both must be completed before the system can operate legally in grid-tied mode. Most installers manage both processes, but homeowners should understand that the timeline involves both.
What the Building Inspection Covers
A building inspector reviewing a solar installation typically looks at:
- The AC disconnect and any new panel connections
- Conduit runs from the array to the inverter and from the inverter to the panel
- The inverter mounting and connections
- Required labels on the equipment (solar systems have specific labeling requirements so emergency responders can understand the system)
- Roof penetrations — whether they're properly flashed and sealed
- The inverter's disconnection means
The specific scope varies by jurisdiction, but this is the general territory. The building inspection is about confirming the installation was done to applicable standards.
What the Utility Inspection Covers
The utility's review focuses on grid interconnection concerns:
- Is the inverter on the utility's approved equipment list?
- Is the system configured with required anti-islanding protection — the safety feature that shuts the system off when the grid goes down?
- Is the metering configuration appropriate for net metering billing?
- Does the physical installation match the approved interconnection application?
Some utilities do a physical site visit; others conduct a desk review of submitted documentation. The result is the same: PTO issued when everything checks out.
The Timeline Between Installation and PTO
This is one of the most common sources of frustration for new solar owners: the system is physically installed, it's sitting there on the roof, and they can't turn it on yet because approvals are pending.
Building inspections typically happen within a few days to two weeks of installation, depending on the building department's schedule. Utility PTO timelines vary considerably — some utilities are very efficient and issue PTO within days of receiving a complete application; others have longer review queues, particularly during periods when many new systems are being connected.
Your installer should be able to give you a realistic estimate of the PTO timeline based on experience with your specific utility. If they don't mention it, ask.
What You Can and Can't Do While Waiting for PTO
While PTO is pending, the system should remain off in grid-tied mode. Most inverters can be put in a standby or isolation mode that allows basic testing without grid-tied operation.
During this window, your installer should be configuring the monitoring system, completing any outstanding commissioning work, and coordinating with the utility on the PTO application.
After PTO
Once PTO is received, the system can be turned on in full grid-tied mode. This is when net metering billing starts, when the monitoring data becomes meaningful as a production record, and when you start to see the impact on your electricity bills.
Your installer should notify you when PTO is received and confirm the system is operating correctly. If you have a monitoring platform, this is the moment to establish your baseline production data.
Questions to Ask Your Installer
- Who manages the building permit application and utility interconnection application?
- What's the realistic PTO timeline for my utility?
- What do I need to be available for during the inspection period?
- When PTO is received, what are the next steps to bring the system online?
Ready to Move Forward With Solar?
If you want to understand what the installation, inspection, and PTO process would look like for your specific home and utility, request a solar service quote and we'll walk through the full timeline.