Distributed Generation Interconnection Rules

Connecting a solar power system isn’t as simple as plugging in a new appliance.

Because rooftop solar arrays generate energy that can flow into UES’s local energy grid, they can affect the reliability of electric service for nearby homes and businesses. For that reason, the Arizona Corporation Commission (ACC) established Distributed Generation Interconnection Rules (DGIRs) that UES and other regulated utilities must follow when connecting new distributed generation (DG) solar power systems.

These rules establish technical standards, safety requirements, processes, and rights and responsibilities for utilities and customers. The rules have been incorporated in the Arizona Administrative Code (A.A.C.) and can be downloaded from the ACC website for review.

It’s important for solar installers and their customers to understand how these rules could affect their planned projects. In some cases, compliance with the rules might delay UES’s review of your project and/or require design changes that add significant cost and/or restrict energy exports to UES’s grid.

The DGIR rules require that PV projects with a capacity of 20 kilowatts (kW) or less (A.A.C. R14-2-2617) comply with three “screens” (A.A.C. R14-2-2615(A), (E) and (F)):

  • Screen A – This screen gauges the amount of DG capacity that can be safely added to a utility circuit, a subsection of the local energy grid that can serve up to several thousand customers. This amount varies and must be determined by UES based on the minimum amount of power that all customers on each circuit might be using at any time during daytime hours. The rules direct UES to limit total DG capacity on any circuit to either 15 percent of peak usage levels or its “hosting capacity,” whichever is greater. UES sets circuit hosting capacity based on minimum daytime load, a level that usually exceeds 15 percent of peak usage. DG systems that aren’t designed to export excess energy to the grid – including non-exporting systems of any capacity and inadvertent export systems with a maximum capacity of 20 kW, as defined in the rules – are exempt from this screen.
  • Screen E – The proposed DG system size and the sum of all other existing DG systems served by the same UES distribution transformer shall not exceed 75 percent of that transformer’s nameplate capacity rating.
  • Screen F – If the proposed DG system is single-phase and will interconnect at 120 volts (V), the DG system size in kilovolt-ampere (kVA) shall not cause an imbalance of more than 20 percent on the 240/120V center-tapped winding of the UES distribution transformer.

Improvements are being made to our system to accommodate as many new interconnection requests as possible, particularly in areas where many PV solar systems are already connected to UES’s local grid. Even so, there may occasionally be some areas in which satisfying Screen A, in particular, may be challenging.

Failing any of these required screens will add time and cost to your project. Applicants can request a supplemental review in accordance with A.A.C. R14-2-2620, but this review costs $500, can take up to 21 days to complete and is very unlikely to change the outcome, as a key element of the review – minimum daytime load – is incorporated in UES’s Screen A evaluation.

UES strongly encourages installers and customers to familiarize themselves with the rules, requirements and applicable timeframes to understand how these may affect projects. The rules are posted on the ACC's website.

UES is available answer your questions and assist you every step of the way. Please feel free to contact us at renewables@uesaz.com. We share your interest in promoting the use of clean, renewable energy to reduce our carbon footprint and greenhouse gases.