Solar panels for flat roofs: Higher costs, better savings

Solar panels shouldn’t be laid flat. To maximize their time in the sun, solar panels should ideally face south and tilt between 15 and 40 degrees. Most sloped roofs are in this angle range, which makes for an easy installation. But that doesn’t mean that flat roofs aren’t fit for solar, too.

With a flat roof, you'll just need additional racking equipment to position your panels at the best angle and direction. While flat roof installations tend to cost more than sloped roof installations, they offer more flexibility in system design: You can install your panels at an optimal angle for peak solar production, making them more efficient.

A flat roof solar panel installation is entirely feasible and worth it. You'll just need more racking equipment to ensure your panels face south and are at an optimal angle. 

In some ways, flat roof solar panel systems are actually more advantageous than traditional slanted roof systems. Flat roofs aren't constrained by natural roof features and allow you to install them at any angle, making it easier to get the most out of your solar panels.

The biggest challenge with flat roofs is installer availability. Especially in some areas of the country where flat roofs are uncommon, it may be difficult to find an installer willing to add solar panels to a flat roof. Some national solar leasing companies won't install solar on flat roofs because they work with a limited equipment selection and standardize system designs to minimize costs.

You can install solar panels on flat roofs as long as you don't lay them flat. If you do, you'll run into some pretty big issues.

• Low energy production: In the U.S. (and the entire northern hemisphere), the sun moves from east to west during the day across the southern part of the sky—so south-facing solar panels get the most sunlight. You'll miss out on a lot of electricity production if you lay your panels flat against a flat roof.

• Dirt build-up: When solar panels are at an angle, dirt can slide off them, or at least wash off when it rains. With a flat roof, dirt will build up much more easily. The dirt blocks the sun, lowering your solar panel system's production.

• No warranty coverage: Many manufacturers include clauses that void the warranty if the panels are installed flat against a flat roof. Water can pool on top of horizontal solar panels, increasing the risk of water damage.

These problems are all easily avoidable with a flat roof—you just need to install your solar panels at an angle.

Your flat roof installation should be relatively straightforward once you find a solar company to perform the work. It’ll probably cost more than sloped roof installations, but it will also be safer for your installer and could help you save more money over time.

Why do flat roof installations cost more?

As we've mentioned, solar panels on flat roofs generally require specialized racking equipment to get them at the right orientation and angle. Instead of simply laying solar panels flat on a sloped roof, your solar installer will use angled mounts. These mounts tilt your solar panels, exposing them to the sun for as much of the day as possible. The extra equipment typically increases the price tag for flat-roof solar panel systems.

Flat roof installations are usually easier and safer

Installing solar panels on a flat roof is much easier and safer for your solar company than installing them on sloped roofs. Workers can move freely on the roof without special equipment, and most of the roof materials used on flat roofs can easily handle the wear and tear.

Your solar installer also won't need to make roof penetrations to install flat roof solar panels. Sloped roof solar installations typically use "penetration mounts." In these mounting systems, installers affix racking equipment to your roof by drilling multiple holes. Instead, flat roof systems often use a weighted mounting system called a "ballast system," which uses gravity to keep your equipment in place.

How to get more solar power and money out of a flat roof

Solar panel systems on flat roofs often perform better than those on sloped roofs, resulting in better long-term savings.

Ideally, solar panels should face south at an angle equal to their latitude, about 15 to 40 degrees. Flat roofs offer more flexibility than sloped roofs in terms of your solar panel system design. You can orient your panels to face south and mount them at the optimal angle to maximize your solar energy generation. In contrast, sloped roof systems are limited to the existing angle and direction of the roof.