Solar 101

Your system makes less in winter than in summer, and that is expected. Winter days are shorter, the sun sits lower in the sky so its light reaches your panels at a slant through more atmosphere, and cloudy days are more common.

Solar panels are made of silicon cells, and silicon converts sunlight to electricity more efficiently when it is cool. Panels are rated at 77°F (25°C) cell temperature. For every 1.8°F (1°C) hotter than that, most panels lose about 0.3% to 0.5% of their output. On a sunny day, panels often run 35°F to 70°F hotter than the air around them.

Your system makes nothing between dusk and dawn, and your inverter goes to sleep. Some monitoring apps show "offline," "sleeping," or "no communication" overnight. This is normal. Production should start again shortly after sunrise.

On a clear day, production rises in the morning, peaks around midday, and falls in the afternoon, making a smooth hill on your monitoring chart. On very bright days, the top of that hill may look flat. That happens when your panels can produce more than your inverter is rated to convert, so the inverter caps the output at its limit. This is called clipping, and designers often size systems this way on purpose because it makes more energy over the whole year.

If you have solar without a battery, your system shuts off when the utility power goes out, even on a sunny day. This is required by safety code. It keeps your system from sending power onto lines that utility crews are repairing. Your system restarts on its own a few minutes after grid power returns.

Your system's size and your estimated savings were based on the electric bills you gave the solar company, usually your past year of use. If you start using more, your savings will drop. Running your air conditioner twice as long, adding an electric vehicle, or switching a gas appliance to electric (like replacing a gas oven with an electric one) all add load your system wasn't sized for.

Your system's expected production was based on the trees and plants around your home at the time it was installed. Trees keep growing. As they begin to shade your panels, production drops, and fixing that is up to you. Tree shade is rarely, if ever, covered by a warranty.

Inverters have built-in thermal protection. If one gets too hot, it reduces its output or shuts itself off to protect itself, then turns back on once it cools down. An inverter mounted outside on a south or west facing wall in full sun can heat up, shut down, cool off, restart, and repeat the cycle through a hot afternoon. Hot weather alone can disrupt your system's output this way.

Squirrels, rats, birds, and other animals can crawl under your panels on a roof or ground mount and nest there. Some chew on the wires. The wire under your panels has a tough, outdoor-rated coating, but animals can still chew into and through it, which can stop your system from producing and create a safety hazard.

In the U.S., south facing panels produce the most. East and west facing panels also work well. East facing panels produce more in the morning, west facing panels produce more in the late afternoon and evening, and both produce well around midday. North is the worst direction for panels on a roof or a ground mount.

The wires under your panels should be tied up off the roof surface using approved methods. Wires that hang loose can drag on the roof. Over time, wind and movement rub them against the shingles, which scrapes away the insulation and can eventually cause a fault that shuts your system down.

Your roof vents need to stay open and clear. Some installers cut down roof vents and cover them with panels. That can keep bathroom exhaust and plumbing vents from venting properly, which can cause moisture problems and bad smells coming back into your house.

When your system is installed, ask your installer for photos showing everything underneath all of your arrays. Use them to check the quality of the work:

A film of pollen, dust, or dirt from nearby construction can cut your production, and in Georgia spring pollen is the most common culprit. A good rain often washes most of it away. If it doesn't, you can usually rinse your panels yourself without ever leaving the ground.

Panels shade your roof. They absorb sunlight that would otherwise bake your shingles, and air moving through the gap between the panels and the roof carries much of that heat away. A UC San Diego study measured about 38% less heat reaching the roof under panels and ceilings about 5°F cooler during the day. A cooler attic can mean your air conditioner works less on hot afternoons. Results vary with climate, roof type, and how the panels are mounted.

Source: UC San Diego, 2011

The roofing under your panels is sheltered from direct sun, hail, and wind-driven rain, which can help those materials last longer. Keep in mind the mounting points themselves need to stay well sealed. If you ever see a leak near a mount, have it checked.

Studies have found that buyers pay more for homes with owned solar. How much depends on your local market and your system. Leased systems can add steps when you sell.

Solar panels have no moving parts and make no noise. Most inverters are quiet too, with at most a faint hum or a small cooling fan.

Most panels come with a product warranty and a performance warranty, often 25 years or longer, that guarantee they will still produce a set share of their original rating decades from now. Inverters and batteries have their own, usually shorter, warranties. Keep your paperwork. SolarTriage can store it with your system.