Net Metering and Rooftop Solar Interconnection
A rooftop array needs permission to touch the grid and a separate arrangement for what it sends back, and the two are decided by different rules on different timetables. Homeowners who learn this after signing an installation contract discover that the economics they were sold belong to the second one.
What this report covers
- Interconnection approval and export compensation are separate decisions with separate paperwork.
- Small residential systems normally clear a fast-track screening process without a full impact study.
- Export credit ranges from full retail net metering to an avoided-cost rate a fraction of it.
- Failed screens usually mean a distribution upgrade the applicant may be asked to fund.
- Legacy protection when a tariff changes is a defined period, not a permanent guarantee.
- Permission to operate, not mechanical completion, is the date the system may lawfully energize.
An installer sells production. A utility sells access. The homeowner who signs a rooftop solar contract has bought the first and has not yet obtained the second, and the gap between them is where most of the delay, and nearly all of the disappointment, occurs.
Two approvals, not one
Connecting an array to the distribution system produces two distinct instruments, and confusing them is the standard error. The interconnection agreement is an engineering and safety document: it establishes that the equipment may operate in parallel with the grid, sets the maximum output, requires certified inverters that disconnect during an outage, and defines who may isolate the system. The export tariff is an economic document: it decides what the utility pays, or credits, for energy the array sends back.
They move on different tracks. Interconnection is administered by the utility under rules a state commission has approved, and it ends with a formal permission to operate. Compensation is set by a filed tariff that the commission can change for the whole customer class without touching any individual agreement. A homeowner can hold a valid interconnection agreement and still see the value of exports fall by half.
An array that is physically complete and inspected still may not be energized until the utility issues permission to operate. Running it before that point is a tariff violation and, in most jurisdictions, grounds for disconnection.
What the utility reviews before it says yes
Nearly every state uses a tiered review borrowed from the model federal procedures. A small residential system is screened rather than studied, which is why approval is usually measured in weeks rather than months.
The screens ask a small number of engineering questions:
- Is the inverter certified to the recognized safety standard for utility interaction?
- Does aggregate generation on the circuit stay below a threshold share of peak load?
- Is the array small relative to the service transformer and the customer's own load?
- Would the addition raise fault current or voltage beyond tolerances at any point on the line?
- Is the service configuration one the utility already supports without modification?
Failing a screen is not a denial. It routes the application into supplemental review, and supplemental review either clears the system with conditions or identifies a distribution upgrade — a larger transformer, a reconductored segment, protective equipment at the substation. The applicant is frequently asked to fund that upgrade, and on a residential array the cost can exceed the value of the system. The common resolution is to shrink the array until it clears the screen.
How the credit is calculated
The phrase "net metering" is now used loosely for arrangements that differ enormously in value. What actually matters is the interval at which production is netted against consumption, and the rate applied to whatever is left over.
| Structure | How exports are valued | Practical effect |
|---|---|---|
| Full retail net metering | Exports offset consumption at the full retail rate | A kilowatt-hour sent out cancels one drawn in |
| Net billing | Consumption billed at retail, exports credited at a lower export rate | Self-consumption becomes far more valuable than export |
| Avoided-cost purchase | All output bought at the utility's avoided cost | Credit is a fraction of retail; bills change little |
| Time-differentiated export | Export rate varies by hour and season | Rewards storage and afternoon output, penalizes midday-only arrays |
| Aggregated or virtual metering | Credit applied across multiple accounts or subscribers | Enables shared and community arrangements |
Two mechanical details decide more than the headline rate. The first is the netting interval: monthly netting lets midday surplus offset evening draw, while hourly or instantaneous netting does not, and the same array can be worth substantially less under identical rates. The second is what happens to a credit balance at the end of the annual cycle — carried forward, cashed out at a wholesale rate, or simply forfeited.
When the tariff changes under an existing system
Commissions revise export compensation, and they do it while systems financed on the old terms are still on roofs. The standard response is a legacy period: systems interconnected before a stated transition continue on the prior tariff for a fixed number of years, after which they move to whatever then applies.
Legacy protection is narrower than owners assume. It usually attaches to the interconnection date rather than the contract date, which makes utility processing time consequential. It is commonly voided by enlarging the array. And it is a period, not a permanent right — the argument that a commission cannot alter a filed tariff for existing customers has generally failed, because the tariff was never a contract fixed for the life of the equipment.
Where the process stalls, and what to do
Three bottlenecks account for most delay. Incomplete applications sit unprocessed because a single line diagram or an inverter certification is missing. Local inspection lags, because the utility will generally not grant permission to operate without a signed electrical inspection, which puts the timetable in the hands of the building department rather than the utility. And private restrictions intrude: many arrays are also subject to an architectural review committee, though a majority of states now limit how far such rules may go in prohibiting solar equipment.
Most state interconnection rules impose deadlines on the utility for acknowledging an application, completing review and issuing permission to operate. Those deadlines are enforceable through the commission, and citing the specific rule in correspondence moves a stalled file more reliably than escalation.
Where a utility misses its deadlines, imposes an upgrade the applicant believes is unjustified, or applies a screen inconsistently, the route is a complaint to the commission, and the informal stage of that process resolves most such disputes without a hearing. Once the system is running, the recurring issue shifts to billing — whether credits appear correctly and whether the meter is recording export at all, which is a metering dispute rather than an interconnection one and is raised through a different channel.
Sources
- Cornell Legal Information Institute — 16 U.S.C. 2621, Federal Standards for Electric Utilities
The federal standards states must consider, including net metering and interconnection.
- Cornell Legal Information Institute — 16 U.S.C. 824a-3, Cogeneration and Small Power Production
The purchase obligation underlying avoided-cost compensation.
- eCFR — 18 CFR Part 292, Small Power Production and Cogeneration
Federal rules on qualifying facilities and the rates paid for their output.
- U.S. Department of Energy — Solar Energy Technologies Office
Federal technical material on distributed solar and grid integration.
- Cornell Legal Information Institute — Tariff
The filed instrument that fixes the terms of service and the export rate.
- Cornell Legal Information Institute — Public Utility
The regulated status that makes interconnection terms reviewable by a commission.
Questions readers ask
Can the utility refuse to connect a rooftop array at all?
Outright refusal is rare, but conditional approval is common. If your array fails a screen — usually because aggregate generation on the circuit is already high, or the transformer serving you is small — the utility can require a supplemental study and then a distribution upgrade before it will grant permission to operate. You are frequently asked to fund that upgrade. Reducing system size to clear the screen is often cheaper than paying for it.
What happens to my credits if I move?
Credits accrued on your account generally do not travel with you, and most tariffs settle any remaining balance rather than paying it out. The interconnection agreement, by contrast, usually runs with the equipment and must be assigned to the buyer, which means the sale paperwork should include it. If assignment is not completed, the new owner can find the system has no authorized standing on the utility's records.
Do I still need a building permit if the utility approves the system?
Yes. Utility interconnection and local construction permitting are independent, and the utility will normally not issue permission to operate until it sees a signed-off electrical inspection. Roof structural review, setback and fire-access pathway rules, and the electrical permit are administered by the building department, not the utility, and an array installed without them can be ordered removed or brought into compliance at the owner's cost.
