Solar on a detached garage

Garage roofs are simple. A typical two-car garage has two clean rectangular planes with no dormers, few vents and no chimney, so the panels lay out in tidy rows and there’s less waste. House roofs on the Front Range are often chopped up by hips, valleys and skylights, and a 6 kW system that needs three roof faces on the house may fit on one face of the garage.

Age matters too. Plenty of Denver-area garages were re-roofed after the 2017 or 2023 hail seasons while the house roof wasn’t, or the garage was built decades after the house. Putting a 25-year array on the newer roof means you’re less likely to face a re-roof under the panels. We don’t remove and reinstall panels for a later re-roof, so this choice is worth making carefully up front.

Orientation and shade are the deciding factors. If the house’s only south face is shaded by a neighbor’s cottonwood and the garage roof is wide open, the garage wins on production even if it’s smaller. We model both roofs and show you the numbers rather than assuming.

Most detached garages already have a feeder from the house: a buried cable or conduit supplying a small subpanel or a single circuit. If the garage has a subpanel with enough capacity, the inverter output can land there and flow back through the existing feeder to the main panel. The electrical code limits how much backfeed a given panel and feeder can carry, so we check the subpanel rating, the feeder size and the main panel’s bus rating before assuming the existing wire will do.

When the existing run is too small, or the garage only has a lighting circuit, we trench a new conduit from the garage to the house. That’s usually a 24-inch-deep trench with PVC conduit, and the cost depends mostly on distance and what’s in the way (concrete, mature landscaping, a patio). A 40-foot run across lawn is a modest line item; 150 feet under a driveway is not.

Long runs also mean voltage drop, so we size the conductors for the distance, not just the amperage. Undersized wire on a long garage run quietly costs production every day for 25 years.

The garage is where the car lives, so it’s the natural place for a Level 2 charger. A Tesla Wall Connector or Enphase IQ EV Charger draws 7–11 kW, which is more than most garage subpanels were sized for. If we’re trenching new conduit anyway, upsizing the feeder to carry both solar backfeed and a charger circuit is far cheaper than doing it twice.

On Xcel’s time-of-use rates, the on-peak window of 5–9 pm on weekdays costs roughly 2.7 times the off-peak rate as of September 2026. Scheduling the car to charge overnight or during solar hours is where most of the EV savings come from; the panels on the garage roof don’t have to feed the charger directly to do that.

A garage array needs the same electrical permit, usually a building permit, and the same utility interconnection application as a house array. The permit set includes a structural check on the garage framing. Older detached garages with undersized rafters or sagging ridges sometimes need sistered rafters before they can carry panels plus a Front Range snow load, and a few can’t reasonably be made to work.

Colorado’s HOA statute (C.R.S. 38-30-168) covers a garage on your lot the same way it covers the house: the association can set reasonable aesthetic rules but can’t prohibit the array or impose changes that raise cost or cut output significantly. The garage roof is often the layout an HOA prefers anyway, since it’s less visible from the street.