Every so often a clean application comes back with an answer nobody quoted for: the local grid can't take the system as designed. The culprit is usually the neighborhood's shared service transformer — sized decades ago for consumption, now asked to absorb export from a street's worth of rooftops. It's still the exception on Texas residential jobs, but it clusters (new-build neighborhoods where one builder's solar partner saturated a transformer; older streets with small cans), and it's arriving more often as penetration climbs. Knowing the play keeps a constrained job alive instead of dead.
Why it happens
A pad-mount or pole-top transformer serves a handful of homes. Utility screens compare proposed generation against that equipment's capacity — and aggregate DG on the transformer counts, so your customer's application can be the one that tips a can their three solar neighbors already loaded. The regulatory frame contemplates exactly this: the PUCT's interconnection framework pairs streamlined review for small certified systems with system impact review where appropriate, and provides for utility equipment upgrade costs on projects that need them (Oncor's larger-system track states it plainly: costs for utility equipment upgrades or modifications necessary to accommodate the requested generation will be provided, with payment before construction). Residential-scale outcomes are the small end of the same logic. The PUCT's DER rulemaking may restructure these screens; see our rulemaking tracker.
What it looks like when it hits
The utility's response typically takes one of four shapes: a cap ("approved up to X kW"), a study (with fees and weeks on larger or borderline projects), an upgrade offer (a bigger transformer at the customer's cost — quoted, and frequently deal-shaping money on a residential job), or conditions (export limitation as an approval term). None is a rejection of solar; each is a negotiation over size, export, or money.
The plays that keep the job alive
- Design to the constraint. Right-size to the cap where the customer's self-consumption math still works (in much of Texas, exports earn less than avoided retail anyway).
- Export limitation. Inverter export-limiting and PCS-based control can hold grid impact at an approved level while the array serves the house at full size — where the utility accepts the configuration and the enforced code recognizes the equipment.
- Storage as a pressure valve. A battery that absorbs midday production changes the export profile that worried the screen — increasingly the constructive answer in saturated neighborhoods.
- Price the upgrade honestly. When the transformer swap is the only path to the desired size, present the utility's quoted cost as a customer decision, not a surprise. Some take it; most resize.
- Escalate on facts. Aggregate-DG screens depend on the utility's records; a polite, data-backed conversation with the DG engineering team occasionally moves a borderline answer.
The operational layer
Two disciplines make constraints manageable at portfolio scale. First, flag risk at design: shared-transformer new builds, visible small cans serving several homes, and streets where you've already installed are worth a caution note before the size is promised. Second, map what the utility teaches you: every cap, study, and condition is a data point about a specific piece of grid — capture it against the location so the next sale on that street starts informed. TexPTO tracks the interconnection stage on every job and ages it against the utility's own standard, so a capacity hold or study is a visible state with a clock on it rather than a silent wait. Building the constraint map itself is still your work — and it is worth the discipline, because no vendor can hand you the history of your own streets.
FAQ
Can a Texas utility limit my customer's system size? Approvals conditioned on grid capacity — caps, studies, upgrade costs, or export limits — are a recognized part of the interconnection framework, though uncommon on typical residential jobs.
Who pays for a transformer upgrade? The framework puts necessary utility equipment upgrade costs on the requesting project — quoted before construction. Most residential deals resize instead.
Does a battery help? Often — storage reshapes the export profile that triggers concern, and export-limited configurations can preserve array size where accepted.
Is this getting more common? Directionally yes as penetration rises, which is exactly what the PUCT's DER rulemaking is grappling with — worth watching.
Sources
- PUCT §25.211 framework (streamlined review; grounds and structure for utility review): https://www.puc.texas.gov/agency/rulesnlaws/subrules/electric/25.211/25.211.pdf
- Oncor Application for Certified Systems 500 kW or Greater (system impact review; utility upgrade costs; payment before construction): https://www.oncor.com/content/dam/oncorwww/documents/smart-energy/energy-system-developers/Oncor%20Interconnection%20Application%20for%20Certified%20Systems%20500%20kW%20or%20Greate....pdf.coredownload.pdf
- PUCT Project 54233 (DER rulemaking context): https://interchange.puc.texas.gov/Documents/54233_89_1498635.PDF
General information. Screen thresholds, study triggers, and upgrade-cost practices vary by utility and are being restructured in rulemaking — verify per territory.