If you have looked closely at a modern solar design, you may have seen a phrase like “8,760-hour simulation” or a number labeled “solar access.” Both come from the same place: a model that traces how sunlight and shadow move across your specific roof for every single hour of the year. That count, 8,760, is simply 365 days multiplied by 24 hours. Instead of guessing your production from a rough rule of thumb, good software walks the sun across your roof hour by hour and records what each panel would actually see. This is how solar AI designs your system with real numbers rather than averages, and it is worth understanding before you compare quotes.
What 8,760 Hours Actually Means
A shading simulation is a time series. The software divides a full calendar year into 8,760 one-hour steps and asks the same question at each step: given where the sun is in the sky right now, which parts of this roof are lit and which are in shadow? Multiply one roof position by 8,760 sun positions, and you get a complete picture of light and shade across seasons, not a single snapshot.
The reason the granularity matters is that shade is not constant. A tree to the southwest might do nothing at noon in June but swallow half your array at 4 p.m. in December. An hourly model captures that difference because it evaluates the low winter sun and the high summer sun separately. This step sits inside the full solar design software pipeline, feeding the layout engine downstream. Coarser methods that use one annual shade figure cannot tell a morning loss from an afternoon loss, and that distinction is exactly where money is won or lost.
How the Simulation Is Built
Three ingredients combine to produce the hourly result. Each one has to be reasonably accurate for the output to be trustworthy.
A three-dimensional model of your roof and surroundings
The software first reconstructs your roof and everything near it as a 3D scene: roof planes and their tilt and orientation, plus trees, chimneys, and neighboring structures that can cast shade onto it. Most of this geometry is built from high-resolution aerial imagery of your roof combined with elevation data, so the model reflects your actual property rather than a generic template.
Sun-path geometry
For any location on Earth, the sun’s position at a given date and time is a solved problem. The simulation computes the sun’s azimuth and altitude for all 8,760 hours at your latitude and longitude, giving it the precise angle the light arrives from in each step. That angle is what decides whether a given obstacle throws a shadow onto a given panel.
Typical weather for your location
Raw geometry tells you where shadows fall, but not how much energy arrives. To translate shade into kilowatt-hours, the model layers in a typical meteorological year, a data set that represents normal cloud cover, temperature, and sunlight for your region. This is why two identical roofs, one in a foggy coastal town and one in a high desert, produce different estimates from the same panel count.
What the Simulation Produces
The headline output most homeowners see is a solar access percentage. If a panel has 95 percent solar access, it receives 95 percent of the sunlight it would get with no shade at all across the year. A panel under a heavy tree might show 60 percent. This single number is a yearly summary of thousands of hourly readings for that one location on the roof.
Designers also work with two related figures. Total Solar Resource Fraction, or TSRF, blends the shade result with how well the panel is oriented and tilted, so it reflects both shading and geometry. The output that matters most for your wallet is the annual energy estimate in kilowatt-hours, because the whole simulation exists to predict how much electricity your system will make in a normal year. When those numbers are built from an honest hourly model, the estimate on your proposal tends to hold up after installation.
Where the Shade Actually Comes From
A simulation is only as good as the obstacles it knows about. Several distinct sources feed into the shadow calculation, and a thorough model accounts for all of them.
Objects on the roof itself
Vents, chimneys, skylights, and HVAC units sit directly on the surface and cast short, sharp shadows that move through the day. The simulation can only shade around them if the design step that detects the vents, chimneys, and skylights has flagged them first, which is why obstruction detection and shade simulation are two stages of one workflow.
Trees and nearby buildings
The biggest shade losses usually come from tall objects near the home. A neighbor’s two-story house, a mature oak, or a chimney on an adjoining roofline can shade a large share of an array during the low-sun hours of winter. Because these objects are in the 3D scene, the simulation tracks their shadows moving across your panels hour by hour.
Self-shading between rows
On flat roofs and ground mounts, one row of panels can shade the row behind it when the sun is low. A proper simulation models this internal shading so the rows are spaced correctly, protecting production without wasting roof space.
Simulation Versus Shading Analysis
It helps to separate two ideas that sound similar. The 8,760-hour simulation is the computational method: the engine that produces the shade numbers. What happens next, when a designer uses those numbers to move panels, change string wiring, or drop a shaded location entirely, is the design response. If you want that second half in depth, our companion article on how shading analysis reshapes your layout covers the decisions the simulation informs.
Understanding the split protects you as a buyer. A quote can claim to account for shade while leaning on a crude annual figure, and it will read almost the same on paper as one built from a full hourly model. The difference only shows up later, in whether your real production matches the promise. Asking which method produced the estimate is a fair question to put to any installer.
How Axia Solar Uses the Full Hourly Model
Every Axia Solar design runs the complete 8,760-hour simulation on your specific roof, not a shortcut average, so the production estimate you see reflects your trees, your chimney, and your orientation. The result flows straight into an accurate, to-scale layout that places panels where the annual light is strongest and keeps them off the locations the model shows as chronically shaded.
Because no model is perfect, the numbers are also verified against a site visit when a roof is complex or when a tree line is hard to judge from imagery. A young tree will grow, a model can miss a thin branch, and a new structure can rise next door after the imagery was captured. Pairing the hourly simulation with human review closes those gaps and keeps the estimate grounded in the real property.
Reading the Numbers on Your Own Proposal
When you receive a design, look for a per-panel or per-area shade figure rather than one blanket percentage for the whole roof. A single number for the entire array can hide a badly shaded corner by averaging it against a bright center. Panels with lower solar access should either be justified by the layout or left off. If a proposal shows only a total production figure with no shade detail behind it, that is a reasonable prompt to ask how the estimate was generated and whether an hourly simulation stands behind it.
The Payoff of Simulating Every Hour
Running the sun across your roof 8,760 times is not busywork. It is the difference between a production estimate that is a genuine prediction and one that is an optimistic guess. The hourly method captures the seasonal swings, the afternoon tree, and the winter neighbor that averages quietly erase, and it turns them into a solar access number you can actually check against your first year of bills. When you are ready to see a full hourly shading model run on your own roof, you can request a custom solar design or get a free solar estimate and review the numbers before committing to anything.
Frequently Asked Questions
What does 8,760-hour shading simulation mean?
It means the software evaluates sunlight and shade on your roof for every hour of a full year, which is 365 days multiplied by 24 hours, or 8,760 total hours. Each hour uses the sun’s real position in the sky, so the model captures how shade changes across the day and across the seasons instead of relying on a single average.
What is solar access percentage on a solar proposal?
Solar access percentage is the share of available sunlight a given panel or roof area actually receives over the year after shade is accounted for. A reading of 95 percent means that location gets 95 percent of the light it would get with no shade at all. It is a yearly summary of thousands of hourly shade readings for that spot.
Why does hourly shading matter instead of a single yearly average?
Shade is not the same at every hour. A tree might have no effect at midday in summer yet block a large part of the array in a winter afternoon. Only an hourly model separates a morning loss from an afternoon loss, so it produces a far more honest production estimate than one blended annual figure.
Does the simulation include shade from trees and neighboring buildings?
Yes. The simulation builds a three-dimensional scene of your roof and its surroundings, so trees, neighboring homes, and adjacent rooflines are all included as shade sources. Their shadows are tracked moving across your panels hour by hour, which is usually where the largest seasonal losses come from.
How accurate is a shading simulation?
A well-built simulation is quite accurate because it uses your actual roof geometry, real sun-path data for your location, and typical weather for your region. Accuracy depends on the model catching every obstacle, so pairing the simulation with a site visit for complex roofs or fast-growing trees is the reliable way to keep the estimate true to the property.
