Solar on Duke Energy in SC

Two Duke utilities, and the difference matters

Duke operates in South Carolina through two separate utilities, Duke Energy Carolinas and Duke Energy Progress, and they are distinct regulated entities with their own rate schedules rather than two names for one thing. Our Upstate work sits on one and our Pee Dee work on the other.

For a homeowner this matters because "I am with Duke" is not enough information to model against. We establish which of the two serves your meter before anything else, and we read it off a bill rather than assuming from the region, because the boundary does not follow county lines neatly.

Both are investor-owned electrical utilities, which places them inside South Carolina’s net energy metering chapter and under Public Service Commission ratemaking. Their terms come out of a Commission process with a public record, which is a different and more legible arrangement than a cooperative board’s policy or Santee Cooper’s board.

Why the statewide figure does not apply here either

The export figure quoted on most South Carolina solar pages is Dominion’s. Duke Energy Carolinas and Duke Energy Progress each have their own approved terms, and a model built on Dominion’s numbers will be wrong on a Duke meter in a direction nobody can predict without checking.

This is a recurring theme across all four of these guides and it is not an accident of how South Carolina is organised. The state has investor-owned utilities, a state-owned generator and a set of member-owned cooperatives, each setting terms through a different mechanism. There is no such thing as the South Carolina export rate.

We confirm the applicable rate schedule and export arrangement for your specific meter and the programme version that applies at your interconnection date. If that sounds like a lot of checking for a quote, it is, and it is the checking that separates a model from a sales projection.

Upstate and Pee Dee conditions

Duke territory takes us away from the coast, and the build changes accordingly. Coastal wind loading and salt-air material selection, which govern our Lowcountry and Grand Strand work, are not the drivers here. Roof pitch, shading from mature tree cover and winter production are.

Tree shading is the most common reason an Upstate roof does not work as well as its area suggests. Shade modelling across the year rather than on the day of the survey is what catches it: a roof that is clear in February under bare branches can be substantially shaded in July.

Roof age is the other one that changes the plan. Installing on a roof with a few years left means paying to remove and reinstall the array later, and it is usually cheaper to re-roof first. We say so when we see it, which occasionally means recommending you spend money with a roofer before spending any with us.

Seasonal shape matters more inland than people expect. Production swings further between a Piedmont December and a Piedmont July than it does on the coast, and a system that covers your annual usage will still leave you buying power in winter and exporting in summer. Where export credits sit below retail, that seasonal mismatch is a real cost rather than a rounding error, and it is why we model twelve months rather than annualising from a good one. It is also why we would rather show you a monthly production profile than a single annual percentage: the percentage hides the months that actually cost you money.

How interconnection actually runs

Two separate approvals sit between a signed contract and a working system, and they are not the same thing. The building permit is local, issued by your city or county. The interconnection agreement is the utility’s, and it is what allows your system to be connected to their network and to export at all. We file both, but they run on different clocks and only one of them is predictable.

The interconnection application goes in with the system design, the equipment specifications and the single-line diagram. What follows is a review against the utility’s technical requirements, and the timeline depends on their queue rather than on anything the installer controls. An installer who promises you a specific interconnection date is promising something that is not theirs to promise.

After installation there is an inspection, and then the utility issues permission to operate. Until that arrives, the system is physically complete and producing nothing, because it stays switched off. This is the stage that generates the most frustration, and it is the reason we say the timeline plainly at the quote rather than at the handover.

If a quote you are comparing does not distinguish between installation time and time to permission to operate, it is describing the easy half. Ask which number you are being given.

What we confirm before we model anything

We read your provider off an actual bill rather than inferring it from a postcode. In the Charleston metro particularly, territory boundaries run between streets and sometimes down them, and a postcode-level assumption is how a quote ends up modelling the wrong export credit entirely.

We confirm the current export arrangement that applies to your meter, and the rate schedule you are on. A provider can have more than one, and the relationship between what you pay and what you are credited is the number that drives everything downstream: system size, whether storage earns its place, and what payback honestly looks like.

We use twelve months of your own usage, not an average. A system sized from a single summer bill is oversized for the year; one sized from a mild month underperforms every August. The shape of your usage across the day matters as much as the total, because where export credits sit below retail, the power you consume as you generate it is worth more than the power you send out.

And we confirm what has changed. Export terms, rebate availability and programme caps are all revisable, and several have been revised in our territory. We would rather re-check before quoting than carry a figure forward because it was true last year.

Reading a competitor quote on this utility

Check the export assumption first. It is usually not stated outright; it is buried in the savings projection. If two quotes show different twenty-five year totals for a similar system, the difference is far more likely to be the export and escalation assumptions than the panels.

Check whether the 30% federal credit has been subtracted. It expired for systems placed in service on or after 1 January 2026, and proposals built on older templates still carry it. A quote that nets it out is overstating your position by a large margin, and it is the single most common error we see on competitor paperwork right now.

Check the production figure in kilowatt-hours. A dollars-saved headline embeds assumptions about both the export rate and future rate rises; a kilowatt-hour figure can be checked against your own bill and against the roof. Ask for the production estimate and the assumptions separately.

Check who performs the work and who holds the warranty. A large share of residential solar in the Southeast is sold by one company and installed by a subcontractor. That matters the day a penetration needs revisiting. Our crews are our own and the roof-penetration warranty is ours.