Every tilt and every compass bearing, simulated separately and shown at once. Not "what will my
roof produce" — that is the output calculator — but
how far your roof sits from the best one available at this latitude.
What do kWp and kWh mean?
kWh — kilowatt-hour
A unit of energy, and the thing your electricity bill charges you for. A
1,000-watt heater running for one hour uses one kWh. A typical home uses somewhere between
2,000 and 10,000 kWh a year depending on where it is and how it heats.
kWp — kilowatt-peak
A unit of capacity — how big the solar array is, not how much it makes.
It is the output the panels would produce under standard test conditions: bright, cold and
perfectly aimed. Real roofs rarely see those conditions, which is why a 4 kWp array does not
generate 4 kW for most of the day. One modern panel is roughly 0.4 kWp, so 4 kWp is about ten
panels.
Putting them together
kWp is the size of the system; kWh is what it produces over time. The ratio between them
— kWh generated per kWp installed, per year — is the honest way to compare
locations, because it strips out how big the system happens to be. It runs from roughly 700 in
cloudy high latitudes to over 1,800 in sunny deserts.
30°best tilt here
180°best bearing — south
4063kWh a year at the best
<1%cost of your roof
If your roof is pitched between 10° and 50° and faces anywhere within 60° of
south, there is a 52% chance it is
already within 5% of the best orientation available here.
Across the whole chart that share is only 11%, because the chart includes
north-facing walls that nobody would choose. That gap is the point. Orientation is not a dial to
be tuned — it is a cliff to be avoided. The worst orientation shown loses 55% against
the best, but almost all of that loss is concentrated in orientations you would never propose.
Once a roof is roughly right, the exact angle stops being what limits the system.
The whole surface
Rows are tilt from flat, columns are compass bearing: 0° is north, 180° is south. The
amber ring marks 35° facing south. Every one of these 120 cells is a
separate simulation of that exact orientation — none is interpolated from its neighbours,
because the surface is not flat enough for that to be honest.
Show the surface as a table
Percentage of the best orientation
Tilt
0°
30°
60°
90°
120°
150°
180°
210°
240°
270°
300°
330°
0°
91%
91%
91%
91%
91%
91%
91%
91%
91%
91%
91%
91%
10°
85%
86%
88%
91%
93%
95%
96%
95%
93%
91%
88%
86%
20°
79%
80%
84%
89%
94%
98%
99%
98%
94%
89%
84%
80%
30°
72%
74%
79%
86%
93%
98%
100%
98%
93%
86%
79%
74%
40°
66%
68%
74%
82%
90%
97%
99%
97%
90%
82%
74%
68%
50°
60%
63%
69%
78%
87%
94%
96%
94%
87%
78%
69%
63%
60°
55%
58%
64%
73%
82%
89%
92%
89%
82%
73%
64%
58%
70°
52%
54%
60%
67%
76%
83%
86%
83%
76%
67%
60%
54%
80°
49%
50%
55%
62%
69%
76%
78%
76%
69%
62%
55%
50%
90°
45%
46%
50%
55%
62%
68%
70%
68%
62%
55%
50%
46%
How to read this
The dark band across the middle of the chart is the plateau. Anywhere inside it, orientation is
not what limits the system — panel count, shading and budget are. The pale region is the
cliff: the worst orientation here collects 55% less than the best, and no amount of extra
panel efficiency recovers that. Read the chart to find out which side of that edge you are on,
not to shave a degree off the top.
Two things this surface does not know about your roof. It assumes nothing shades it,
and a single obstruction can outweigh every difference shown here. And it ranks orientations by
annual total, which is the right measure when exports pay well and the wrong one
when they do not — if you are paid little for what you export, a west-facing array that
generates into the evening while you are home can be worth more than a south-facing one that
produces more in total.