Wall-Mounted Solar Calculator
Enter wall dimensions, orientation, and tilt angle — get panel count, annual kWh as a percentage of optimal roof production, and payback comparison.
How to Use This Calculator
Measure your wall and choose orientation
Measure the usable wall height and width where panels would be mounted. Standard 400W panels are 6.5 ft tall and 3.5 ft wide in portrait orientation — you need at least 6.5 ft of clear wall height and 3.5 ft width per panel column. A south-facing wall 20 ft wide and 8 ft tall fits 5 panels across and 1 panel tall (5 panels total). Select the compass direction your wall faces — south is optimal; east and west still viable; north is generally not recommended.
Set the panel tilt angle
0° means panels are flush to the wall (fully vertical). Tilting panels away from the wall using angled brackets increases production by allowing the sun to hit them more directly in summer. Each degree of tilt adds production but also means the mounting brackets extend further from the wall — a 30° tilt requires brackets extending ~3-4 ft out from the wall. For aesthetics and minimal intrusion, 10-15° is a common compromise.
Account for shading
Roof overhangs and eaves cast shadows on panels mounted directly below them, especially during summer when the sun is high. Enter the estimated percentage of production lost to shading. Most residential eaves shade wall panels 5-20% annually. Commercial facades with no overhang may have 0% shading.
The Formula
Wall-mounted systems typically produce 50-78% of optimal roof mount production depending on tilt and orientation. The lower production is the key tradeoff against the benefit of utilizing otherwise-unused wall space when the roof is unavailable, occupied, or facing the wrong direction.
Example
Tom — South wall, 8 ft tall x 20 ft wide, flush mount
Tom has a south-facing garage wall 8 ft tall and 20 ft wide. His roof is north-facing and unsuitable for solar. He wants to know how much a flush wall mount would produce vs if he could put it on an optimal roof. He pays $0.13/kWh, latitude 38°N.
Result
Tom's wall mount produces about half of what the same panels would produce on an optimal south-facing roof, with a longer payback (13 vs 8 years). But if his roof is unsuitable, a south wall at 0° still provides meaningful generation — and tilting panels 15° would improve production by about 22%, improving the economics significantly.
The Winter Advantage of Vertical Panels
One often-overlooked benefit of wall-mounted (vertical) solar panels is their seasonal production profile. In summer, the sun is high in the sky — it strikes flat roof panels nearly perpendicularly, but hits vertical wall panels at a very shallow angle, reducing output. In winter, the sun is low in the sky — it strikes vertical panels much more directly, while sloped roof panels receive more oblique light.
When this matters
For heating-dominated climates (northern US, Canada, northern Europe), peak electricity demand is in winter — for electric heating, heat pumps, or EV charging in cold weather. A wall-mounted solar system on a south-facing wall will produce relatively more in December-February and less in June-August compared to a tilted roof system. If your electricity usage peaks in winter, this seasonal shift may actually improve the economics of wall-mount solar compared to what the annual average suggests.
Quantifying the effect
At latitude 40°N with a flush south wall: December production is roughly 90-110% of July production. For a 30° tilted roof at the same latitude, December production is typically 60-70% of July production. The wall system's winter/summer ratio is more balanced — sometimes better than tilted roof in northern climates for self-consumption purposes.
Wall-Mount vs Roof Mount: When Does Wall Win?
When wall-mount solar makes sense
Wall-mount solar is worth considering when: (1) the roof faces north or is heavily shaded; (2) roof structural integrity doesn't support panel weight; (3) the roof is rented or has HOA restrictions; (4) the building is a commercial facade with large south-facing wall area; (5) you want a solar installation that's architecturally integrated into building design (BIPV).
When to choose roof mount instead
If your roof has south/southwest/southeast-facing sections that are unshaded, rooftop solar almost always has better economics. Roof panels produce 22-50% more than wall panels (depending on tilt), cost less per watt to install, and have shorter paybacks. Wall mount is an alternative when roof mounting isn't viable, not a replacement for good roof conditions.
Commercial building-integrated photovoltaics (BIPV)
At commercial scale, south-facing glass facades can be replaced with solar glass or thin-film panels that serve as both building cladding and energy generation. BIPV typically produces 40-65% of an equivalent ground-mounted system but replaces the cost of curtain wall glazing. The dual function (building envelope + energy generation) makes the economics work differently than pure energy calculations suggest.
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