Solar Site Assessment: What Gets Checked and Why

What a site assessment means in plain terms

Before anyone designs a solar system, someone has to look at the place it will go. That look is the site assessment. Installers also call it a site survey or site visit.

The DOE notes that panels work in all climates, but some roofs are poor fits because of age or tree cover. It says panels usually do best on south-facing roofs with a slope between 15 and 40 degrees, though other roofs may work too ². A site assessment tests your roof against those points.

The result feeds straight into the system design: how many panels, on which faces, with which equipment. It also flags work that must happen first, such as a new roof or a bigger electrical panel.

How it works: the two stages

1. Remote check. Enter your address in Google Project Sunroof, which uses aerial imagery to model roof direction, tilt and shade from trees. Or use NLR PVWatts with your roof's angle and direction. Installers often run their own satellite tools before a first quote.
2. On-site survey. Someone visits to measure the roof, inspect it, check the attic framing and photograph the electrical panel and meter. The measurements replace the estimates in the design.

A quote issued before the on-site survey is provisional. Ask whether the price can change after it.

What an assessment records

Types of site assessment

Example: reading an online roof result against a model

Project Sunroof reports estimated sunlight hours, usable roof area and a savings estimate for an address. Google describes it as built on roof imagery, weather data and local electricity rates. It is a screening tool. It does not see your rafters, your panel box or a tree planted last year.

PVWatts answers a narrower question: yearly kWh for a system you describe. You can change tilt, direction and losses and see what each does.

Here is an example of why direction matters in an assessment. We ran PVWatts version 8 on 7 October 2026 for 7 kW DC on a Charleston, SC roof at a 20° tilt with 14% losses.

Facing south, it modelled 10,179 kWh a year. Facing east, 8,883 kWh. Facing north, 7,325 kWh. A good assessment tells you which of your roof faces sits where on that scale.

Sources: [4] [5] [6]

Where the assessment shows up in your paperwork

You may get a short site report with photos, a roof sketch and a shade figure for each face. Some installers fold it into the proposal instead. Either way, its numbers set the panel count and the yearly kWh on your quote.

The permit set relies on it too. The roof plan, the rafter sizes and the panel box details all come from the visit. Your building department reviews those drawings before work starts.

If the survey finds a problem, it may show up as a line item. Common ones are roof repair, tree trimming or a main panel upgrade.

What a good assessment gives you, and its limits

Limits of online roof tools

Online tools work from aerial images that may be months or years old. They guess roof pitch from the image. They cannot see inside the attic or the panel box. And they assume a typical weather year.

Use them to decide whether to get quotes, and to sanity-check a quote later. Do not sign a contract on an online screen alone. The solar hazard check and hosting capacity lookup add two more angles a roof tool misses.

What the assessment means for cost and lifespan

We do not quote dollar prices here. The survey is where hidden costs surface. See solar cost for current figures.

• The survey itself. Installers usually include it in quoting, but policies vary. Ask before you book.
• Roof work. An old roof may need replacing first, because re-roofing later means removing the array. DOE guidance says removal and reinstall would be needed if the roof is replaced ³.
• Structural work. Weak rafters may need extra framing before panels go on.
• Electrical work. A small or full main panel may need an upgrade. Try the panel upgrade check.
• Lifespan. DOE guidance says a system should produce for at least 30 years, with major parts typically under 25-year warranties ³. Your roof should be able to last that long too.

The process: what happens on the visit

A trained surveyor or installer does this. Do not go on the roof yourself to measure it.

1. Review 12 months of electricity bills with you.
2. Measure each roof face and its pitch, and note vents, skylights and chimneys.
3. Take shade readings or images from the roof to map the sun's path through the year.
4. Inspect the roof covering for age and damage.
5. Check the attic: rafter size, spacing and condition.
6. Photograph the main electrical panel, its rating and the meter.
7. Note where the inverter, disconnects and any battery could go.
8. Send the findings to the designer, who builds the layout and the final quote.

Keeping your site solar-friendly after install

The site keeps changing after the survey. Trees grow, and a neighbor may build. The DOE builder checklist suggests a landscape plan with low-growth plants near the array ¹. That advice suits any home with solar.

Watch your monitoring app each year. If output slowly drops in winter afternoons, new shade is a likely cause. A tree trim can be cheaper than lost output over many years.

Red flags: when to ask for a second look

Ask questions, or get a second installer's view, if you see any of these:

• A firm price with no on-site visit and no clause about changes after the survey.
• No shade figure for any roof face.
• No one checked the attic or the electrical panel.
• A design on a roof that is near the end of its life, with no mention of it.
• Sagging roof lines, soft spots or water stains found during the visit.

Safety

Rules that the assessment must satisfy

The survey gathers what the permit office will ask for. Your local building department enforces the building and electrical codes it has adopted. The DOE checklist asks for code-compliant documents on the roof's allowable dead and live loads, and recommends the roof can carry an extra 6 pounds per square foot for solar ¹.

Licensing matters too. In South Carolina, a registered Solar Panel Installer may install panels, but roof mounting, wiring and structural work each need the right license or classification ⁷.

The state has the 2021 building codes in force, and the 2024 International Residential Code is scheduled for local use from 1 January 2027 ⁸.

The DOE points homeowners to installers with NABCEP certification, the industry-standard credential ².

Site assessments in SC, GA and VA

Site assessment compared with related steps

Common misconceptions

Myth An online roof tool is as good as a survey.

Reality It cannot see your rafters, roof condition or electrical panel.

Myth Only south-facing roofs pass.

Reality East and west roofs still produce. In our Charleston model they made about 87% of a south roof.

Myth A roof in any condition can take panels.

Reality An old roof should usually be replaced first, because removing the array later adds work.

Myth The survey is a sales visit.

Reality A real survey measures, photographs and inspects. If no one goes in the attic or opens the panel cover, it was not a full survey.

What to ask for after the survey

• The shading report, with the annual percentage loss per roof face.
• Photos of the attic and the electrical panel, and whether a panel upgrade is needed.
• An opinion on roof age. If the roof will need replacing within the system's life, check whether to re-roof first.
• The modelled annual kWh, and the tool and loss assumptions behind it.
• Next step: read choosing an installer, then compare quotes with the proposal analyzer.

Related terms

Solar Design

Solar design is the engineering step that turns a site survey into a specific system: which panels go where, how they are wired and attached, and how they connect to the home's electrical service, documented in a plan set submitted for a permit.

Solar System Sizing

Solar system sizing is the process of choosing how many kilowatts (kW) of solar panels a property needs, by dividing the electricity it uses in a year by what one kW of panels produces there.

Solar Shading

Solar shading is any shadow that blocks sunlight from part or all of a solar array, from trees, chimneys, vents, nearby buildings or other panels, reducing the electricity the system produces.

Solar Panel Orientation

Solar panel orientation is the compass direction a panel faces, given as an azimuth angle in degrees clockwise from true north: 90° is east, 180° is south and 270° is west.

Solar Panel Tilt

Solar panel tilt is the angle between a panel and the horizontal ground, in degrees: 0° is lying flat and 90° is vertical.

Roof Penetration

A roof penetration is any hole made through the roof covering, and on a solar install it usually means each point where a mount is bolted through the shingles into a rafter to hold the racking.

Solar Production

Solar production is the amount of electricity a solar system generates over a period, measured in kilowatt-hours (kWh) and usually quoted per year.

Electrical Panel

An electrical panel, also called the main service panel, breaker box or load center, is the metal cabinet where utility power enters a home and is split into branch circuits, each protected by a circuit breaker.

Also referenced from: Solar System Sizing, Solar Panel Orientation, Solar Panel Tilt, Solar Azimuth, Solar Shading, Solar Access, Roof Solar Potential, Solar Design, Solar Mounting System, Ballasted Solar Mount, Roof Penetration