Technical Article
Understanding Utility Upgrade Costs Before They Derail Your Project
Commercial solar and storage projects rarely move in a straight line from design to construction. Even a well-planned project can run into unforeseen utility-related costs, often surfacing once a feasibility or transmission study gets underway. These costs tend to fall outside the visible scope of the project itself, tied instead to what the utility requires on its side of the interconnection. Switchgear compatibility, transformer sizing, transmission line capacity, and substation capacity can all add cost and time. None of which are easy to predict without a closer look at the specific site and utility involved.
Key Points to consider when adding solar and storage systems
- Utility studies determine capacity requirements and have variable time and cost impacts
- Switchgear age affects compatibility
- Transformers often require resizing
- Substation capacity shortfalls may add cost
Utility Studies and Interconnection Timelines
Nearly every utility upgrade cost can be traced back to capacity, and capacity is typically evaluated through a feasibility study or a transmission and interconnection study conducted by the utility. Timelines vary a great deal depending on project scope. Massachusetts commercial solar projects typically see interconnection approval timelines of three to six months for standard projects, stretching beyond twelve months when substation upgrades are required. More broadly, solar interconnection processes tend to run three to twelve months, depending on project complexity, queue position, and the specific utility, ISO, or RTO involved.
On the cost side, feasibility assessments for commercial or utility-scale installations range from roughly $3,000 to over $100,000, with study timelines from a few weeks to upwards of six months, depending on project complexity. In California, commercial projects in the 5 MW to 20 MW range see a median of eighteen months in study alone, according to LBNL's Queued Up 2025 report. Smaller Rule 21 projects tend to clear initial review in a matter of weeks unless they get bumped into a supplemental or detailed study.
Main Switchgear Compatibility
Main switchgear usually sits at or near the point of common coupling, and comes with its own set of risks as a project moves toward interconnection. Older switchgear may not be able to accept new equipment, and in some cases the original manufacturer is no longer in business, which complicates compatibility. Hookup size compatibility can also become an issue.
When a project requires upsizing the main switchgear, that conversation often extends to the utility itself, since the utility may need to upgrade service to reach the necessary ampacity. This is a hidden cost that rarely shows up until the switchgear question is raised directly. Major infrastructure changes involving utility coordination and switchgear replacement can run $100,000 to $150,000 or more.
Utility Transformer Sizing
A project's utility transformer needs to be evaluated early, since it may not be sized correctly for what the project requires. When a larger service is needed, the transformer may need to be upsized to reach the correct kVA rating, though this generally only applies to service upgrades. There may also be cases where the existing main service is large enough to support the project, but the utility transformer is undersized.
Utility transformers are sometimes smaller than what a project actually needs, and utilities can request payment to make the necessary changes. Uninstalling and replacing a transformer adds cost, and scheduling that work can take months.
Transmission Line Capacity
Transmission line capacity becomes more relevant for larger scale projects, generally those at 1 MWac and above. This factor comes into play during the interconnection phase, when a utility engineer reviews the lines to determine whether they can handle the added energy. That review typically takes a couple of weeks and often costs a few thousand dollars, which is one reason many developers choose to reduce system size to under 1 MWac (e.g., 999 kWac) to lower both cost and project timeline.
If a utility determines the transmission line isn't sufficient to support the project, it can request that the project share in the cost of upgrading that portion of the system. The 1 MW threshold is the most common baseline used for utility scale classification in EIA reporting and most state RPS definitions, and projects above 5 MW typically require a more involved FERC interconnection study process.
Substation Capacity
Substations often support more than one site, and if a substation lacks the capacity a new project requires, the utility will request a share of the associated upgrade costs. Utilities will also require upgrades to protective relays as part of this process. Depending on scope, substation upgrades can add anywhere from thousands to millions of dollars to a project's total cost.
One documented example comes from an SPP Interconnection Facilities Study, where a new generating facility required updated relay settings and electrical modeling work at the substation. That work was estimated at $15,000, and the utility required four months' notice prior to energization in order to complete the relay setting update.
Summary
Utility upgrade costs are rarely visible at the outset of a project, yet they consistently rank among the factors most likely to affect project budget and timeline. Main switchgear compatibility, site-specific conditions, transformer sizing, transmission line capacity, and substation capacity all play a role, and each one carries its own potential for added cost and delay. Building these considerations into early planning, rather than discovering them mid-project, gives developers a much clearer picture of what a project will actually require.
Mayfield Renewables' engineering consulting services help project teams identify these utility-related impacts early, before they threaten a project's budget, timeline, and ultimately viability overall. Reach out to discuss how we can support your project!
