The five things that matter
Five factors decide how well solar will work on a specific house: roof orientation, tilt, shade, usable area, and roof condition. None of these are deal-breakers on their own — but compound problems add up, and a good installer will check all five. This chapter walks through them so you know what to flag when you request quotes, and the panel placement tool above lets you sketch your actual roof to see what fits.
Orientation and tilt
The ideal direction for solar panels is toward the equator — south-facing in the northern hemisphere, north-facing in the southern. East and west are typically close behind, at roughly 85–90% of ideal yield. Panels facing the opposite direction usually land around 60–70% of ideal (depending on your latitude and roof pitch) — meaningfully less, but often still worth installing, especially with modern high-efficiency panels.
Worth noting: “ideal” isn’t only about total generation. If you use most of your electricity in the morning or evening, don’t have a battery, and your feed-in tariff is low, east- or west-facing panels can beat equator-facing ones for your bill — because they generate when you’re actually using the power.
Tilt matters less than most people think. Anything between near-flat and 45° works, with a sweet spot close to your latitude for maximum annual generation. A steeper tilt (more upright) catches more of the low winter sun at the cost of some summer peak — worth considering if your usage is winter-heavy. Flat roofs use tilt frames (a normal setup). Very steep roofs add installation complexity but aren’t a blocker.
Shade
Shade is the most commonly misunderstood factor. Two things worth knowing. First, on systems with older string inverters, shade on a single panel can drag down the whole string. Modern micro-inverters and optimisers largely solve this at extra cost. Second, not all shade is equal. Morning and late-afternoon shade cost you less than mid-day shade, because mid-day is when generation peaks. A tree that shades your roof for an hour at 7 am is barely worth worrying about; an hour at noon is. Use the panel placement tool to sketch your roof and see what fits around chimneys, vents, and neighbouring buildings.
Usable roof area
Panels need unbroken rectangles where possible, and fire-code setbacks from the roof edge reduce usable area further (the specifics vary by country). Most panels are roughly 1.7 × 1.1 m, so a quick rule of thumb is about 2 m² per panel of usable space. Complex roofs with dormers, skylights, or multiple planes can still host a good system — they just need planning.
Roof condition and structure
Solar is a 25-year asset; your roof should match. If your roof is near the end of its life, replace it before installing — removing and reinstalling panels to redo the roof underneath is expensive. Heavy tile, metal, and timber structures each have different structural considerations, and engineer sign-off is a normal part of installation in most markets. Flag any known roof issues to your installer early.
What you can do with a less-than-ideal roof
Five options if your roof isn’t textbook. Split the array across two orientations. Use micro-inverters or optimisers to limit shade losses. Prioritise the sunniest area, even if smaller. Trim or remove problem trees, if realistic. Consider ground-mount if you have the space. A sub-optimal roof usually slows payback rather than ruling solar out — see our chapter on whether solar is worth it for how to re-run the numbers in those cases.
