Adding Solar in Vermont Can Reset Your Net-Metering Adjustors: The 5% / 15 kW Rule

Adding panels can seem like a straightforward answer to a Vermont homeowner's remaining electric bill. But an expansion proposal should explain what happens to the billing treatment of the system already on the property. Vermont's net-metering rules contain a specific capacity threshold that can replace the siting and renewable energy credit adjustors applied to the entire amended system. The financial review needs to include the existing installation as well as the proposed addition.

The expansion threshold is the larger of two numbers

Sections 5.108(C) and 5.109(D) of Vermont PUC Rule 5.100, effective March 1, 2024, address pending and approved systems. They say that an amendment or series of amendments increasing capacity by more than 5% or 15 kW, whichever is greater, triggers the most recently adopted siting and REC adjustors for the entire amended system's output. The PUC's registration guidance, adopted the same date, states the same test.

The phrase whichever is greater matters. This is not a rule that every increase above 5% automatically resets the adjustors. Calculate 5% of the relevant system capacity, compare that result with 15 kW, and use the larger threshold. The increase must exceed that threshold. The rule also includes a series of amendments, so the review cannot safely look only at the latest addition while ignoring earlier changes.

For a simplified example involving an original 10 kW AC system with no intervening amendments, 5% is 0.5 kW. The larger threshold is therefore 15 kW. An increase of 2 kW does not cross this particular reset threshold, even though it exceeds 5%. An increase of 16 kW does. An increase of exactly 15 kW does not exceed 15 kW. These examples explain the arithmetic, not whether a proposed project qualifies for approval or how a specific account will be billed.

Use AC inverter capacity, not panel count

Under Section 5.103, a solar plant's capacity is the aggregate AC nameplate capacity of its inverters. The rule also says derating an inverter does not change its capacity for this purpose. A proposal describing only the number of panels or their combined DC rating does not supply the same measurement.

Ask the installer to identify the original approved AC capacity, any previous amendments, the proposed aggregate AC capacity, and the resulting increase. Request the equipment schedule and the capacity figures used in the regulatory filing. This is a document comparison for a homeowner to request, not an instruction to select, alter, or configure electrical equipment.

If different pages of the proposal use different units, ask for a written reconciliation before accepting the savings estimate. A panel-production forecast can still be useful, but it should not silently substitute for the capacity measurement used by the PUC. Keep the answer with the original Certificate of Public Good and the proposed amendment.

Why the whole system matters

Siting adjustors relate to the system's location and applicable category. REC adjustors relate to the treatment of renewable energy credits. They are adjustments applied to production, not a universal cash rebate or a single guaranteed retail export price. Crossing the expansion threshold can therefore change the adjustment on generation from the original installation, not merely generation attributed to the new equipment.

Ask for two complete comparisons: keeping the existing system unchanged, and operating the amended system under the applicable new adjustors. Each comparison should identify its source date, production assumptions, utility tariff, financing or lease payment, and charges that credits cannot offset. An estimate that values only the added panels can omit the effect on the rest of the system.

Do not assume that the value shown in an old sales proposal is still the value available for a new amendment. Rule 5.128 provides for biennial updates. Green Mountain Power's currently posted tariff, effective for bills rendered on or after August 1, 2026, includes newer adjustor periods. Its tariff is relevant to GMP customers; it is not a substitute for another utility's billing schedule. This article does not promise a fixed future credit or assign one rate to every Vermont household.

A billing threshold is not permission to build

Being below the adjustor-reset threshold does not make an expansion automatically exempt from paperwork. Section 5.109 separately requires Commission approval for substantial changes to approved plans. The registration route and the application route have different procedures. The rule also requires utility approval before proposing an amendment that is a material modification under Rule 5.500.

The PUC registration FAQ separately distinguishes systems larger than 15 kW, for which utility interconnection approval is needed before registration, from systems of 15 kW or less, for which registration also acts as the interconnection application. That is a total-system interconnection distinction. It should not be confused with the increase-based adjustor test. Ask the installer which process applies to the amended project and which approvals must be obtained.

Check an older system’s history

Older installations need an additional check. Section 5.125 defines eligibility for pre-existing net-metering systems using application timing and other conditions, including the expansion threshold. A complete application before January 1, 2017 is part of that definition, but the date alone does not establish continuing eligibility. Commissioning history, prior amendments, and the applicable tariff also matter.

If you bought a home with solar, obtain the existing Certificate of Public Good and amendment history rather than relying on the seller's recollection of the original deal. A lease or financing obligation and the utility's billing treatment answer different questions. An expansion offer should not obscure a payment obligation that continues under the original agreement.

Review the expansion promise before signing

Before signing, request a written account of the existing and proposed billing treatment, the capacity calculation, the approvals required, and who is responsible for those filings. Ask whether the forecast applies updated adjustors to all production when required. If the salesperson says the old incentives will remain unchanged, ask where that assurance is supported in the proposal and the applicable rules.

Keep dated copies of the original proposal, expansion proposal, signed agreements, bills, monitoring records, and regulatory approvals. If the numbers do not reconcile, describe the discrepancy precisely: an unexplained capacity figure, omitted prior amendment, changed billing assumption, or payment that the savings presentation did not include. Those records make a review more useful than an unsupported claim that the expansion is automatically unlawful or cancelable.

Use the Vermont document-review guidance to organize the records. Review related utility-billing questions, payment issues, and selling a home with solar where relevant. You can request a Solar Exit agreement review if the expansion promise and your documents do not line up. A review does not guarantee cancellation, a refund, or any particular outcome.

General consumer information, not legal, tax, financial, or electrical advice. Exit Your Solar is not a law firm. Applicable rules, utility tariffs, system history, agreement terms, and individual facts matter. Consult the appropriate qualified professional for advice about your situation.