Solar cost calculator

What this calculator can and cannot know

It works from a small number of inputs and a set of stated assumptions, which makes it useful for orientation and useless as a quote. The three things it cannot see are the three that decide your actual outcome: your roof's shading across the year, the shape of your electricity use across the day, and which utility serves your specific meter.

That last one matters more than people expect. South Carolina is served by investor-owned utilities, the state-owned Santee Cooper and member-owned cooperatives, each setting export terms through a different mechanism, so there is no single statewide export rate. Myrtle Beach carries the lowest retail rate we work with at about 11.4 cents per kilowatt-hour and is the one territory with a genuine upfront rebate. Dominion territory sits near 14.4 cents with no rebate. Those pull payback in opposite directions.

The assumptions behind the number

Installed cost is benchmarked against roughly $2.59 per watt before incentives in South Carolina as of July 2026. The 30% federal residential credit is not applied, because it expired for systems placed in service on or after 1 January 2026. If you have used another calculator that produced a much lower net cost, that is almost certainly why.

South Carolina's 25% state credit on Form TC-38 is capped at $3,500 in any one tax year and at 50% of your annual state liability, with a ten-year carry-forward, so a system generating a larger credit delivers it across two or three returns rather than at purchase. Georgia and Virginia have no state income tax credit for residential solar at all.

Payback is best read as a range rather than a date, because it moves with how much of your production you consume on site instead of exporting. Where export credits sit well below retail, that single behavioural variable can shift the answer by years.

How to use the result

Treat it as a filter, not a decision. If the figure is nowhere near workable for you, that is genuinely useful information and you have saved yourself a survey. If it is plausible, the next step is twelve months of your actual bills, because every meaningful refinement comes from real usage rather than from more inputs.

And if you are holding a contractor's proposal, compare its price per watt against the benchmark above rather than comparing totals. Two quotes for different system sizes cannot be compared on totals, and two quotes for the same system usually differ on their export and rate-escalation assumptions rather than on hardware.

What actually moves the installed price

Roof complexity is the largest single factor after system size. A simple south-facing plane takes less labour per watt than an array split across four planes with dormers and vents to work around, and the difference shows up in the per-watt figure rather than as a line item.

Electrical work is the second. Where the main service panel lacks capacity or space, an upgrade becomes a substantial cost, and it is the most common reason two quotes for similar systems diverge sharply. It is also why a quote produced without anyone looking at your panel is an estimate rather than a price.

Roof covering matters: asphalt shingle, metal and tile each need different mounting and flashing approaches, and tile in particular is slower and less forgiving. On the coast, wind loading governs attachment spacing and fastener specification, and salt-air exposure drives material selection for racking and fixings. The correct hardware for a coastal roof costs more than the catalogue default, and substituting it is a saving that surfaces years later.

Working in the other direction: larger systems generally cost less per watt, because a fixed share of the job (the survey, the permit, the interconnection paperwork, getting a crew to site) does not scale with size. That is a real effect and also the mechanism behind a common oversizing push, so it is worth separating the genuine economy of scale from a reason to sell you more panels than your usage justifies.

Sizing, and why bigger is not automatically better

This tool sizes from your bill and a target offset, which is the standard approach and a deliberately blunt one. The refinement that matters is how much of your production you can consume as you generate it, because where exported power is credited below the retail rate, a kilowatt-hour used on site is worth the full retail rate you avoid paying while an exported one is worth only the export credit.

The wider that gap, the less sense it makes to size for 100% of annual usage. A household that is out from eight to six exports most of its midday production and buys back in the evening at retail, which is a poor trade under current terms. A household at home during the day, or with electric water heating, a pool pump or an EV charging in the afternoon, converts far more at the higher value.

That is also why battery storage is a genuine question here rather than an upsell, and why the answer differs by state. Georgia has the widest gap in our territory (exports around 7.2 cents against retail near 13 cents), so storage does the most economic work there. Virginia's one-for-one retail net metering means the grid already credits exports at full retail, so storage there is largely a resilience decision instead.

Turning an estimate into a quote

The gap between this page and a real price is closed by four things: twelve months of your actual usage, confirmation of which utility serves your meter read from a bill, your roof's age and covering, and shading modelled across the year rather than judged on the day of a visit.

Shading is the one people most often underestimate. Mature tree cover that is bare in February can shade a roof substantially in July, so an assessment made in winter will be wrong in the direction that flatters the sale. Roof age is the one that most often changes the recommendation outright, because mounting an array over a roof with a few years left means paying to remove and reinstall it later, normally more than re-roofing first would have cost.

If the number this tool produces is nowhere near workable for you, that is genuinely useful and you have saved yourself a survey. We would rather you found that out here than after a two-hour appointment.

Reading your own bill before you do anything else

Almost every refinement to the number above comes from your bill rather than from more inputs on this page, and there are four things worth locating on it before you speak to anyone.

Your annual kilowatt-hours, not your annual dollars. Rates change; consumption is the stable quantity and it is what a system is sized against. Most bills show a twelve-month history somewhere, often as a small bar chart, and that chart is more useful than any single month's total.

The seasonal spread in that chart. A household whose summer is three times its winter has a different design problem from one that is flat across the year, because a system covering annual usage will still export heavily in July and buy back in January. Where exports are credited below retail, that mismatch is a real cost rather than a rounding error.

The name of the provider, exactly as printed. In the Charleston metro this genuinely matters: Dominion and Berkeley Electric territory interleave, Daniel Island has both, and two houses on the same street can be on different providers with different export terms. An address does not reliably tell you which.

And the rate schedule, if it is shown. 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.

What this page deliberately does not do

It does not produce a savings figure or a payback date, and that is a choice rather than an omission. Both require assumptions about export credits and about how fast electricity prices will rise over twenty-five years, and small differences in the second compound into very large differences in a headline total. A calculator that produces a confident twenty-five year saving is showing you the assumptions of whoever built it.

It also does not apply a 30% federal credit, because that credit expired for systems placed in service on or after 1 January 2026. If another calculator has given you a markedly lower net cost, check that first: the error is common, it always runs in the same direction, and everything built on it is wrong by the same margin.

And it does not ask for your contact details to show you a result. A tool that withholds its own output until you hand over a phone number is a lead form wearing a calculator's clothing, and you are entitled to the number without the follow-up call.

Finally, it does not know your roof. Two houses with identical bills on the same street can need materially different systems because one has a clear south-facing plane and the other has four small planes broken up by dormers, vents and a chimney. Area alone does not tell you usable area, and usable area is what a system is actually built on.