Quick answer
Roof Solar Potential is an estimate of how much solar electricity a roof could produce in a year, based on its usable area, direction, tilt, shade and local sunlight, before money, wiring or utility rules are taken into account.
It answers “how much could this roof make?”, not “should I go solar?”. Free online tools give a first number in minutes. A site visit then checks what those tools cannot see.
Quick facts
The key facts about roof solar potential, with sources:
- Usually given as
- kW of panels that fit and kWh a year they could make
- US rooftop technical potential (NLR, 2016)
- 1,118 GW; 1,432 TWh a year; 39% of national electricity sales 1
- Small-building roof area suitable for PV
- 26% of total small-building roof area 1
- NLR minimum for a suitable roof
- One unshaded plane of at least 10 m² footprint 1
- Best roof per DOE
- South-facing, slope between 15 and 40 degrees 4
Key takeaways
- Roof solar potential is the physical upper limit for one roof: how many panels fit and how much they could make.
- It comes from four things: usable area, direction, tilt and shade, plus local sunlight.
- NLR (formerly NREL) found only about a quarter of small-building roof area is suitable, yet small buildings hold most of the national potential 1.
- Free tools like Project Sunroof and PVWatts give a quick first number. They cannot see rafters, roof age, your electrical panel or utility size caps.
- Your real system is usually smaller than your roof’s potential, because of budget, size caps and how much power you use.
What “potential” means here
Researchers use “technical potential” for the most a resource could produce with today’s equipment, if every suitable spot were used. NLR’s rooftop study says its results “do not exclude systems based on their economic performance” 1. Cost is left out on purpose.
Roof solar potential is the same idea for one house. It is the answer to: if we covered every good part of this roof, what would it make? It is a ceiling, not a recommendation.
This is different from a solar site assessment, where a person checks the roof, structure and wiring before a design. The potential is the screening step that tells you whether an assessment is worth booking.
Sources: [1]
From roof to estimate
- Aerial or lidar data → roof planes, each with a tilt and direction
- Shade model → removes planes that trees and buildings shade too much
- Area and direction filters → keeps planes big enough and facing the right way
- Local sunlight data → kWh a year for the panels that fit
How the estimate is made
NLR’s study shows the method in detail. It used lidar, a laser scan from aircraft, to map every roof plane in 128 cities 1. Then it dropped any area that failed four tests.
Shade. A plane had to get enough sun to make at least 80% of what the same plane would make with no shade 1. Direction. Planes facing northwest through northeast were dropped 1. Tilt.
Planes steeper than 60 degrees were dropped, on installer advice 1. Size. A roof needed at least one good plane with a 10 m² footprint, enough for about a 1.5 kW system 1.
Google’s Project Sunroof works in a similar way for single addresses. Google says it builds a model of roof direction and tilt from imagery, finds shading objects like trees, and averages a year of weather 2. The sunlight input itself is covered on our solar irradiance page.
Kinds of roof potential estimate
| Kind | Scale | What it gives | Example |
|---|---|---|---|
| Address screen | One roof | Usable area, rough kWh, sometimes savings | Google Project Sunroof 2 |
| Production model | One system you describe | kWh by month for set size, tilt and direction | NLR PVWatts 3 |
| Utility screening tool | One customer | A size and cost estimate for that utility | Georgia Power Solar Advisor Tool 5 |
| Regional study | City, state, nation | Total GW and TWh rooftops could host | NLR rooftop technical potential study 1 |
| Installer design | One roof, measured | Panel layout and production for a real quote | Site visit plus design software |
Rooftop potential in South Carolina, Georgia and Virginia
| State | Installed capacity potential | Yearly generation potential | Share of state electricity sales | Suitable roof area |
|---|---|---|---|---|
| Georgia | 34.6 GW | 44.1 TWh | 33.8% | 251 million m² |
| Virginia | 28.5 GW | 35.8 TWh | 32.4% | 205 million m² |
| South Carolina | 15.2 GW | 20.0 TWh | 25.5% | 108 million m² |
| United States | 1,118 GW | 1,432 TWh | 39% (38.6%) | 8.13 billion m² |
Example: reading the numbers
Take Georgia. NLR estimated that rooftops there could, in theory, meet about a third of the state’s electricity sales 1. Atlanta alone could host about 1.7 GW, enough to meet an estimated 41% of the city’s use 1.
Now one house. If an address tool says your roof could hold 10 kW, that is the roof’s potential. It does not mean you should build 10 kW. Your yearly use, your utility’s size cap and your budget usually set a smaller number. Our solar system sizing page shows how that real size is chosen.
Sources: [1]
Where you will meet a roof potential estimate
- An online address search, such as Project Sunroof, often before any installer contact 2.
- A utility website. Georgia Power links customers to its Solar Advisor Tool 5.
- The first page of an installer proposal, as “roof capacity” or “max system size”.
- City and state planning reports that quote rooftop potential in GW.
- Our own panel count tool and system size calculator, which start from your usage instead.
What free potential tools do well, and badly
Good at
- A fast, free first look before you talk to anyone selling solar.
- Showing which roof faces are worth using and which are shaded.
- Giving a neutral number to compare against a sales proposal.
- PVWatts lets you change tilt, direction and losses to test “what if” 3.
Bad at
- Old imagery can miss a new tree, an extension or a replaced roof.
- No look at rafters, roof age or your electrical panel.
- No knowledge of your utility’s size cap or export rules.
- Savings figures depend on assumed prices and usage, not yours.
What free tools miss
Each item below can cut the real system well below the screen’s number.
- Roof age and condition. DOE tells homeowners to consider roof age and how soon it will need replacing 4. See re-roofing before solar.
- Structure. Whether rafters can carry the panels is an engineering check, not an imagery one. See panel weight and roof loading.
- Fire-code access paths. Local codes keep parts of the roof clear for firefighters, which shrinks usable area.
- Your electrical panel. A small panel may need an upgrade first. Our panel upgrade check helps.
- Utility limits. Size caps can be lower than what fits, such as 10 kW for Georgia Power’s RNR export program 5.
- Local shade changes. Trees grow, and neighbours build.
Roof potential and cost
Roof potential has no price tag of its own; the free tools cost nothing. For system prices, see our cost by system size guide.
The potential does shape cost in one way. A roof with lots of good south-facing area lets an installer use fewer, simpler rows, which tends to keep labour down.
A roof with many small or shaded faces needs more design work, and may need microinverters or optimizers. Ask each installer to explain how your roof’s layout affects their price.
How to check your roof’s potential
- Look up your address in Project Sunroof for a first estimate of usable area and sun.
- Run PVWatts with your roof’s real tilt and direction to get kWh by month 3.
- Pull a year of usage from your bills. Compare it with the yearly kWh the tools suggest.
- Check your utility’s size cap and export terms before you set a target size.
- Book a site visit with a licensed installer to check structure, roof age and the electrical panel.
- Compare the installer’s design with your free estimates. Ask about any big gap.
Our roof-before-solar tool helps you decide whether the roof needs work first.
Keeping your roof’s potential
- Trim trees that start to shade the best roof faces, and plan new planting away from them.
- Ask before adding vents, skylights or a satellite dish to a good south or west face.
- Re-check potential after a re-roof or an addition; the usable area may change.
- If you plan to add panels later, keep the best open area free and note it in your design file.
Warning signs and when to get a second opinion
- A proposal shows more panels than any free tool says will fit.
- A salesperson uses only a satellite view and never asks about roof age or your panel.
- Panels are placed on north-facing planes with no reason given.
- The design ignores a large tree you know shades the roof in winter.
- You see sagging, soft spots or leaks. A roofer or engineer should look before any solar goes up.
Safety rule
Do not climb onto your roof to measure it. Online tools and a licensed installer with fall protection can do this safely.
Is there a standard for roof potential?
No. No code or standard defines how to calculate a roof’s solar potential, and each tool uses its own filters. NLR set its own thresholds for its study: the 80% shade test, no planes facing northwest to northeast, no tilts over 60 degrees, and a 10 m² minimum 1.
The rules that turn potential into a real system are separate: the building and electrical codes your state adopted, local fire-code roof access, and your utility’s interconnection and size limits.
In South Carolina, a “Solar Panel Installer” registration exists under the Residential Builders Commission 7. Our licence check guide covers how to verify an installer.
Roof solar potential vs related terms
| Term | Question it answers | How it differs |
|---|---|---|
| Roof solar potential | How much could this roof make? | — |
| Site assessment | Can and should we build here, and how? | An in-person check of structure, wiring and shade |
| Solar production | How much does the system actually make? | Measured after install, not estimated |
| Peak sun hours | How much sun does this place get? | A climate input, not a roof property |
| Solar access | Can sunlight legally and physically reach the roof? | Rights and shade, not output |
Common misconceptions
- Myth If the tool says my roof can hold 12 kW, I should install 12 kW.
- Reality Potential is a ceiling. Use, budget and utility caps set the real size.
- Myth Only south-facing roofs have potential.
- Reality NLR kept east, west and south planes; it only dropped those facing northwest through northeast 1.
- Myth Most roofs are suitable.
- Reality NLR found only 26% of small-building roof area suitable 1.
- Myth A free screen replaces a site visit.
- Reality It cannot see structure, roof age or wiring.
Roof potential in South Carolina, Georgia and Virginia
NLR estimated rooftops could meet 25.5% of South Carolina’s electricity sales, 33.8% of Georgia’s and 32.4% of Virginia’s 1.
In practice, utility caps often bind first: Georgia Power’s RNR export program takes home systems of 10 kW or less 5, and Berkeley Electric Cooperative in South Carolina sizes home systems from use (annual kWh ÷ 1,800) 6.
When roof potential matters to you
- You are not sure solar suits your home. A free screen tells you whether to spend time on quotes.
- Your roof is small or shaded. Check whether the potential covers a useful share of your use; if not, look at community solar or a ground mount.
- You have a quote. Compare its size and kWh with your own free estimate.
- You plan an EV or heat pump. Make sure the roof has room to grow the system later.
- Next step: get a measured design from vetted installers through Get Solar Options.
Questions about roof solar potential
How do I find my roof’s solar potential?
Start with a free address tool such as Google Project Sunroof, then run NLR’s PVWatts with your roof’s tilt and direction. Both give a quick estimate of usable area and yearly kWh. A licensed installer’s site visit then checks structure, roof age and wiring, which no free tool can see.
Is Google Project Sunroof accurate?
It is a good first screen. Google says it models roof tilt and direction from imagery, detects shade from trees and averages a year of weather. But imagery can be old, and it cannot check rafters, your electrical panel or your utility’s rules. Treat its number as a starting point.
What makes a roof good for solar?
Enough unshaded area facing south, east or west, at a moderate slope. DOE says panels do best on south-facing roofs with a slope of 15 to 40 degrees. The roof should also be sound and not due for replacement soon. Shade from trees is the most common deal-breaker.
How much of a typical roof can hold panels?
Often less than people expect. NLR’s national study found only 26% of small-building roof area suitable for solar, after removing shaded parts, north-facing planes, very steep planes and small pieces. Fire-code access paths, vents and chimneys shrink usable area further on a real roof.
Can a north-facing roof have solar potential?
Usually very little. NLR’s rooftop study counted planes facing northwest through northeast as unsuitable. A low-slope north face may still produce some power, but east, west and south faces almost always come first. A ground mount may beat a north roof.
What is rooftop technical potential?
It is the most power rooftops could produce with current equipment if every suitable area were used, ignoring cost. NLR put US rooftop technical potential at 1,118 GW and 1,432 TWh a year in 2016, about 39% of national electricity sales.
Why is my installer’s system smaller than my roof’s potential?
Because potential is a ceiling. Installers size to your yearly use, your utility’s size and export rules, your budget and your electrical panel. A bigger system can also push more power out at a low export rate, which adds cost without much value.
Does roof potential include the cost of going solar?
No. Technical potential leaves out money on purpose. Some address tools add a savings estimate, but it rests on assumed prices and usage. For real numbers, get several written quotes and compare them with an independent cost guide.
Sources
- Gagnon, Margolis, Melius, Phillips and Elmore, Rooftop Solar Photovoltaic Technical Potential in the United States: A Detailed Assessment, NREL/TP-6A20-65298 (Jan 2016), National Laboratory of the Rockies, retrieved .
- Google, Project Sunroof, retrieved .
- NLR (formerly NREL), PVWatts V8 API documentation, retrieved .
- US DOE Solar Energy Technologies Office, Homeowner’s Guide to Going Solar, retrieved .
- Georgia Power, Behind-the-Meter Interconnection Summary for Residential Customers (rev. 15 Aug 2025), retrieved .
- Berkeley Electric Cooperative, renewable energy (Renewable Surplus Rider), retrieved .
- SC LLR, Residential Specialty Contractor registration (Solar Panel Installer), retrieved .
Expert review
Written by the HyreSolar Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Study method and figures were read in the NLR report (NREL/TP-6A20-65298) on 8 Oct 2026, including the state table for all building sizes and Atlanta’s city row.
Project Sunroof’s method is from Google’s own description; PVWatts inputs from the NLR API documentation; roof guidance from DOE’s homeowner guide. Utility limits are from Georgia Power’s residential summary and the verified sc-local facts file.
Suggest a correction. We fix errors and say what changed.