Roof, if your roof is under ten years old, faces south, has nothing shading it, and you have no plans to add load.
Ground, if any one of those is missing — an east-west roof, shade from a tree you like, a roof with ten years left in it, or a shop and an EV coming.
The difference is mostly the angle, and it is bigger than the brochures suggest.
We do not install on roofs, so if the answer is roof, we are telling you to go somewhere else.
Illustrative — not a production estimate.
That is the sun's arc over a house at this latitude, and the shape of what an array sees across a day. The numbers under it come from a model, not from your roof — what your house does depends on which way it faces and what is standing between it and the south.
A roof points where the builder pointed it. A ground mount points south, at the tilt we choose.
Here is what that is worth, from our own PVWatts runs at the thirty degree tilt we build.
| Roof faces | Weatherford | McKinney |
|---|---|---|
| East | +23% | +23% |
| West | +21% | +21% |
| South-east | +7% | +7% |
| South-west | +5% | +5% |
| South | — | — |
A roof that faces south-east or south-west is a much smaller loss — about 5 to 7% against true south.
That is the honest shape of the “10 to 25%” you see quoted: it is not one number, it is a range that depends entirely on which way your roof happens to face.
If your roof faces south, the angle argument mostly evaporates. If it faces east and west, it is worth about a fifth of your production every year for twenty-five years.
Air moves under a ground mount. A roof-mounted panel sits in a shallow gap above hot shingles, and a hot panel makes less power.
Ground mounts typically run 10 to 15°F cooler than the same panels on shingles, because air moves under them. On Mission Solar's −0.29%/°C coefficient that is worth about 1.6 to 2.4% more output while the gap holds — real, and about a tenth of what the angle is worth.
If somebody tells you the heat difference is fifteen percent, they have confused degrees with percent.
Thirty degrees is close to optimal at this latitude, and it is what we build. A roof is whatever pitch the roof is.
That difference is usually small compared with the direction, which is why the direction gets the paragraph above and this one is three sentences.
A ground mount costs more up front. That is not in dispute and we are not going to argue it away — it buys a steel structure, a foundation and a trench, none of which a roof install needs.
What is in dispute is the number people quote. The commonly repeated “about 41% more” is a whole-system comparison inflated by ground-mount systems being bigger on average.
Per watt, the same source's own figures work out closer to 14%. Ours is priced differently again, which is why the cost page publishes what we charge and what moves it rather than a percentage. What ground mount solar costs in Texas
Then price it over twenty-five years. An asphalt roof and the panels are on similar clocks, and the roof usually runs out first.
When it needs replacing, the panels come off first and go back on after, at a cost the cost page puts a figure on. Then every mounting point gets drilled and flashed into your brand new roof. What rooftop solar costs over twenty-five years
Maintenance is the same story. Anything on a roof needs fall protection and two people.
A ground mount is walked, inspected and serviced standing on the ground, and nothing about it is holding rain out of your house.
A roof array is finished the day it goes up. The roof is the size it is, it faces where it faces, and the only way to add is to start covering a plane that faces the wrong way.
A ground array is built as tables — four panels high on IronRidge racking at thirty degrees. Extending an existing table along its own rails is the cheap direction: the footing line is already surveyed, the rails run longer, and the wiring picks up where it left off.
A second table is the dear direction, because it needs its own foundations and has to stand far enough back not to shade the first.
Two things decide what it actually costs. The first is the inverter. There is room under the array and the posts carry the electrical wall, so more inverter capacity can go in later if the array outgrows what is already there.
Whether it has to depends on the capacity of the one you started with.
The second is the trench, and it is priced by system size: one conduit up to 10 kW, the same conduit five percent dearer to 20 kW, two conduits above that. Crossing either line re-prices the run, not just the panels.
So panels that join an existing string, with no new inverter, come out somewhat lower per panel than the first ones did.
We do not publish a figure for that, because it depends on your string, your inverter and where the new panels land. Put the bigger array through the design tool and compare it against the one you were going to build. What ground mount solar costs in Texas
It takes yard. Four hundred to six hundred square feet for a normal house, and more if you want to cover everything.
It costs more up front, and the trench is the part people forget — the array has to reach your meter and that run is priced by the foot.
An HOA can confine it to a fenced yard and cap it at the fence line, and some cities have their own height and setback rules on top. What a Texas HOA can and cannot refuse
It is at ground level, which means it is reachable — by livestock, by mowers, by anyone who wanders in.
And you can see it. Though where you see it from is your choice, which a roof does not offer.
You get no say in the angle. The panels go where the roof faces, for twenty-five years.
There are holes in your roof. Done properly they do not leak; done badly, what fails is the seal between the array and the only thing keeping rain out of your house.
The roof underneath ages on its own schedule, and when it needs replacing the panels have to come off and go back on.
Everything about maintenance is harder and more expensive because it is up a ladder.
And it is hot up there, which costs you a little production every summer afternoon.
Land: under about an acre, the setbacks, the shade and the run to the meter usually leave nowhere sensible. Roof.
Roof age: under ten years and sound, roof. Fifteen or more, put them on the ground and stop paying to move them.
Direction: a south-facing roof is a good roof. An east-west roof gives up about a fifth of the production a ground mount would make.
Shade: a tree you will not cut is an argument for the ground, because the array can move and the tree cannot.
Future load: a shop, a well pump, a second EV. A ground mount grows in a way a roof cannot.
It takes yard, it costs more up front, and it needs a trench from the array to your meter that is priced by the foot.
An HOA can confine it to a fenced yard and cap it at the fence line.
It sits at ground level where livestock, mowers and passers-by can reach it.
And you can see it — though unlike a roof, you choose from where.
Usually, and how much more depends almost entirely on which way your roof faces.
Our own PVWatts runs at our thirty degree tilt put a south-facing array about 23% above an east-facing one and about 21% above a west-facing one.
Against a roof that already faces south-east or south-west, the gap is about 5 to 7%.
Against a true south roof with no shade, close to nothing.
Up front, yes.
It buys a steel structure, a foundation and a trench, and none of those exist on a roof job.
The figure most often quoted — about 41% more — is a whole-system comparison inflated by ground-mount systems being larger; per watt the same source lands nearer 14%.
Over twenty-five years the arithmetic changes again, because a roof gets replaced and the panels have to come off and go back on.
On an acre with a clear south-facing spot and a short run to the meter, usually.
On a small lot with a sound south-facing roof, no — put them on the roof and keep the money.
That is not a sales position, it is what the arithmetic says, and it is why this page has told you twice.
Yes, and it is worth less than you would think.
Ground mounts typically run 10 to 15°F cooler than the same panels on shingles, because air moves under them, and on Mission Solar's −0.29%/°C coefficient that is worth about 1.6 to 2.4% more output while the gap holds.
It is real.
It is not the reason to choose one.
And if the answer is your roof: we do not do roofs, so we are not the company for you. Find a roof installer and ask them the same six questions we would want asked of us. How to pick a ground mount installer
No salesman. No home visit to get a number.
