What Is an Interconnection Agreement? How Solar and Home Batteries Get Utility Approval
An interconnection agreement is the signed contract between a home system owner and the local utility. It lets solar panels or a battery connect to the grid. The document sets the technical, safety, metering, and billing terms. In California, Electric Rule 21 governs this process. That includes rules for non-export batteries. No system may run before receiving Permission to Operate (PTO).
Imagine your solar panels are fully installed on the roof. They are still switched off. You must wait for an official letter from your utility before powering on. That waiting period is part of the interconnection process. The agreement is the binding contract at its center.
State utility commissions and local utility tariffs establish the rules. Because of this, requirements vary across the country. This article explains the key documents and the steps from application to PTO. It covers real PG&E fees and review timelines. It also details what changes when you add a home battery or set up a non-export system.
What an Interconnection Agreement Covers and Who Signs It
An interconnection agreement is a contract between the utility and the customer who owns or hosts the solar or battery system. Your installer usually prepares and submits the paperwork, but you may need to sign the agreement as the utility customer.
The agreement establishes how your equipment can connect to and operate alongside the utility's electrical grid.
What does the agreement include?
The specific terms depend on the utility and system configuration. Generally, the agreement addresses:
Technical and safety requirements: Approved inverters, disconnecting equipment, protective settings, and other requirements for safe operation.
Metering and billing: How the utility measures electricity and which rate or billing tariff applies. For new qualifying California interconnections, the Net Billing Tariff applies to applications submitted since April 15, 2023. PG&E calls its program the Solar Billing Plan.
Operating rules: When the system can operate, how it must behave, and whether changes require another review.
Grid upgrades and costs: Whether utility equipment needs upgrades and how the associated costs are allocated.
In California, the California Public Utilities Commission (CPUC) oversees Electric Rule 21 for applicable utility interconnections. The rule establishes procedures, technical requirements, fees, and other terms.
Four documents homeowners should know
Document | What It Is | Who Submits or Signs | When It Happens | Source / Authority |
Interconnection Application | The formal request to connect, detailing equipment models, system size, and a single-line electrical diagram. | Submitted by your installer on your behalf. | Before or during the physical installation. | Utility Interconnection Portal / PG&E NEM Guidelines |
Interconnection Agreement | The binding contract establishing technical, safety, metering, and rate terms. | Signed by the customer and countersigned by the utility. | Signed during review; takes legal effect when PTO is granted. | CPUC Electric Rule 21 / Utility Tariffs |
Final Building Permit | Official sign-off proving local city or county inspectors approved the electrical and structural work. | Submitted by the installer to the utility. | Completed after installation, prior to final utility review. | Local City/County Building Department |
Permission to Operate (PTO) Letter | The utility's written authorization allowing you to energize your system and export power. | Issued directly by the electric utility. | The very last step; the system must remain powered off until received. | Electric Utility (e.g., PG&E, SCE, SDG&E) |
The application starts the utility's review. The agreement establishes the terms of the connection. Inspection documents confirm that the installation meets applicable local requirements. Finally, the PTO letter authorizes operation.
Keep copies of all four documents. Ask your installer which ones have been submitted and which approvals are still outstanding.
Once your system is officially connected and running in parallel with the grid, your utility tracks both the electricity you pull and the excess power you send back. That flow directly determines your energy credits and monthly bill under net metering for grid-tied solar.
With the documents clear, the next step is the order in which they happen.
The Solar Interconnection Process Step by Step (PG&E Example)
The solar interconnection process follows a similar pattern across many US utilities. However, application requirements, fees, review periods, and approval rules vary by utility and tariff.
PG&E provides a useful California example because it publishes its application requirements and typical PTO timelines.
The standard interconnection steps
Design and quote: Your installer evaluates your roof, assesses your electrical panel, and sizes your system. They select certified inverters and panels listed on your state’s approved equipment database.
Application submission: The installer submits the interconnection application along with the signed agreement form via the utility’s online portal.
Utility engineering review: The utility evaluates your local transformer capacity and verifies that your inverter settings meet grid safety requirements.
Installation and local inspection: Contractors install the panels and wiring. Next, a local city or county building inspector visits to confirm compliance with national and local electrical codes.
Final document submission: Once the city signs off on your permit, your installer uploads the final building permit and inspection certificate to the utility portal.
Permission to Operate (PTO): The utility performs a final review of the completed package. Once satisfied, they issue your official PTO letter. Only then can you safely flip the breaker.
Real utility rules and timelines: PG&E breakdown
Item (PG&E) | Figure or rule | Source |
Application fee, NEM2 programs up to 1 MW | $145 | PG&E net energy metering page |
Application fee, Solar Billing Plan (Net Billing Tariff) | Not listed on PG&E’s net energy metering page. Confirm the current application fee with PG&E or your installer before you apply. | PG&E net energy metering page does not list it |
Time to PTO after complete documents, standard systems | Typically 5 to 10 business days, maximum 30 business days | PG&E net energy metering page |
Old NEM2 applications (filed before April 15, 2023) | Applications submitted before April 15, 2023, must be fully completed before April 15, 2026. Otherwise moved to the Solar Billing Plan | PG&E net energy metering and interconnections pages |
Operating before PTO | Not allowed: "against Electric Rule 21 guidelines" | PG&E contractor resources |
Note: If you live outside California, check your local utility's distributed generation portal. Companies like Oncor in Texas, FPL in Florida, or National Grid in the Northeast maintain their own fee tables and review tracks.
Before submitting paperwork, make sure you know how to size a solar system accurately. Your total kilowatt rating determines which review path your utility assigns to your project.
Adding a battery backup setup introduces additional technical reviews, which we cover next.
Interconnection When You Add a Home Battery
A home battery connected to your home's breaker panel still interacts with the electrical grid. Because of that, adding storage requires formal utility interconnection review, even if your battery never exports electricity.
Under California Electric Rule 21, the utility explicitly regulates "Non-Export" facilities. The utility must confirm that your storage inverter cannot accidentally backfeed lines during a neighborhood blackout, which could endanger line workers.
Interconnection storage classifications
Paired solar and storage: When you install panels and a battery simultaneously, your contractor files them under a unified application. The utility evaluates the combined inverter capacity, whether you use an AC-coupled or DC-coupled configuration.
Non-export storage: In a zero-export setup, certified software controls or physical hardware prevent stored battery power from flowing past your utility meter. PG&E provides standardized single-line diagrams for non-export systems with inverter ratings of 10 kVA/kW or less under Protection Options 3 and 6.
Adding storage later: If you already have solar panels operating under PTO and decide to add a battery down the road, you cannot just wire it in quietly. You must file an interconnection modification or a new standalone storage application.
Operating a non-export battery does not exempt you from building permits, electrical inspections, or an interconnection agreement. Furthermore, residential home batteries do not sell power back to the grid by default; they require specific program enrollment and export configurations.
Choosing the right home battery setup
Selecting the right storage capacity makes the permitting and interconnection review process much smoother. If your daily energy consumption is modest or you want reliable backup for key household circuits, a balanced power station provides reliable coverage.
Two EcoFlow TITAN models fit homeowners who plan a battery alongside the interconnection work, split by how much solar they connect directly.
The EcoFlow TITAN 5000 delivers dependable split-phase power for standard households, keeping primary appliances, lighting, and cooling systems running without requiring complicated electrical retrofits.
For homes with larger energy demands, multiple air conditioners, or high-capacity rooftop solar arrays, extra direct solar intake and surge capacity are essential. The EcoFlow TITAN 5000 Plus provides dual direct solar inputs and higher power output, making it ideal for larger properties managing extensive rooftop production alongside grid power.
The EcoFlow TITAN 5000 features a 7.2kW rated output and supports up to 4kW of direct solar input, scaling from 5kWh up to 30kWh of capacity. The TITAN 5000 Plus increases direct solar input capacity up to 8kW across two separate solar inputs, supporting up to 10kW output when paired with solar.
When tying into existing rooftop solar, AC coupling requires the Smart Home Panel 10 (SHP10 240V) along with dedicated current transformer (CT) sensors. A licensed electrician must complete the installation.
Your contractor must verify that your equipment matches your existing inverter specs and local utility interconnection rules. Neither model acts as a substitute for standard utility review or building permits.
If severe weather resilience matters more to you than generating your own power on the roof, you can still protect critical circuits by using a home backup battery without solar.
Even when all equipment is selected and submitted properly, administrative delays can still pop up.
Common Delays and How to Avoid Them
Missing fields, inconsistent documentation, and equipment changes made after submission can delay an interconnection application. Check your utility’s submission requirements and keep the application consistent with the installed equipment.
Top reasons applications get stalled
Missing final building inspection sign-off: Utilities will not issue PTO based on a pending permit. The installer must provide an official, stamped final inspection card from your local city or county building department.
Unlisted equipment and missing inverter specs: Utilities maintain strict databases of approved smart inverters. If your installer specifies an unlisted model, they must supply an NRTL/UL 1741 certification sheet or manufacturer specification package to prove grid compatibility.
Post-approval equipment alterations: Swapping out panel brands or upgrading inverter capacity midway through the project invalidates your engineering review. Even minor hardware changes can push your application back to step one.
Early system operation: Do not operate your generating system in parallel with the utility grid before receiving written permission to operate. PG&E’s NBT agreement warns that unauthorized parallel operation can cause personal injury or damage to equipment or property. PG&E may disconnect a facility if its operation endangers people or the safe and reliable operation of its electric system.
What to do if your application stalls
If your application experiences unusual delays, contact your installer and ask for your utility project tracking ID. You can verify whether the utility is waiting on missing paperwork from your contractor or reviewing transformer capacity.
In California, Electric Rule 21 Section K sets out interconnection dispute procedures. For missed timelines, contact your utility’s Rule 21 ombudsman. The CPUC’s expedited dispute process is temporarily suspended; until further notice, Energy Division handles disputes through its informal staff process. See the CPUC’s current Rule 21 dispute-resolution guidance.
If you live in California, the tariff under which you interconnect determines your compensation rates for surplus power and shapes what NEM 3.0 means in California for your ongoing monthly electricity costs.
The key points fit in a short checklist.
Conclusion
An interconnection agreement establishes the terms for connecting your solar panels or home battery to the utility grid. The application starts the review, inspection documents confirm the installation requirements, and the Permission to Operate letter authorizes the system to run.
Before your project is complete, ask your installer for copies of the application, signed agreement, final inspection documents, and PTO letter. Keep the system off until the utility authorizes operation.
If you're adding home storage, compare the EcoFlow TITAN 5000 and TITAN 5000 Plus based on your backup loads and solar input needs. Include the battery in the installation plan early so your installer can confirm compatibility and coordinate the required interconnection review.
FAQs
What is an interconnection agreement for solar?
It's the contract between the system owner and the utility that establishes technical, safety, metering, and billing terms for connecting solar to the grid. The system may operate only after the utility issues Permission to Operate.
Who signs the interconnection agreement?
The electric account holder (the homeowner or property owner) signs the agreement, and an authorized utility representative countersigns it. While your solar installer typically prepares the paperwork and engineering line drawings, you remain the official legal party to the contract.
Do I need an interconnection agreement for a battery that does not export?
In California, applicable non-export storage facilities are covered by Rule 21. A system's zero-export setting doesn't automatically eliminate interconnection requirements. Check your utility's rules if you live elsewhere.
How long does interconnection take?
Timelines vary by regional utility, system size, and local grid capacity. For standard residential systems with completed paperwork and building permit sign-offs, PG&E typically issues PTO within 5 to 10 business days, with a tariff maximum of 30 business days.
Can I turn on my solar panels before Permission to Operate?
No. You must never turn on your solar system before receiving your official PTO letter. Operating ahead of schedule violates Electric Rule 21 guidelines, can feed unmetered electricity into the grid that you will not be credited for, and presents safety risks for utility line crews.
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