Words for what you see

The compass direction a panel faces. Due south is 180 degrees; east and west roofs make less at midday and more at the ends of the day.

Your array’s normal output on clear days, taken from recent data. We pull 30 days before a visit to compare against afterwards. See where it matters

Yellow or brown discoloration in the layer over the cells, usually from age and UV. It cuts light reaching the cells and is a warranty question, not a cleaning one. See where it matters

A day with no clouds over the array, so the daily curve is smooth. Only clear days give fair before and after comparisons. See where it matters

When panels produce more than the inverter can convert, so the daily curve flattens at the top. Normal on bright days and not a fault.

Mesh fitted around the array edge to keep birds from nesting underneath. Fitted by installers or wildlife specialists; we document the need. See where it matters

Water with dissolved minerals filtered out to near zero, so it dries without spots. We filter it on the truck and wash with nothing else. See where it matters

Layers of a module separating, seen as bubbles or cloudy patches. It lets moisture in and goes to the installer under warranty. See where it matters

Our visual inspection of each module during a wash: cracks, browning, loose clips, debris and nests, photographed. Visual only, no electrical tests. See where it matters

A cell running hotter than its neighbors, often because a dropping, leaf or crack blocks it. Over time it can damage the cell. See where it matters

The box that turns the panels’ direct current into household alternating current. Most apps read their numbers from it.

The sealed box on a panel’s back where its wiring connects. We never open one; faults there go to the installer or an electrician.

Kilowatt, a rate of power. A system’s size, like 7 kW, is the most it is rated to produce at one moment. See where it matters

Kilowatts of direct current: the panels’ combined rating before the inverter. Commercial care is priced per kW a year. See where it matters

Kilowatt-hour, an amount of energy: one kilowatt for one hour. Your bill and your app count production in kWh. See where it matters

A small inverter under each panel, so each one reports on its own. It makes one weak panel easy to spot in the app. See where it matters

One solar panel: cells, glass, frame and junction box together. We use module and panel to mean the same thing.

Billing in which power you send to the grid is credited against power you draw. It is why your bill alone is a rough guide to production.

A small device on each panel that tunes its output and reports it, paired with one central inverter. Like microinverters, it allows panel-level data. See where it matters

A meter that counts only what the array makes, separate from the utility meter that nets use against export.

The rails, clamps and mounts that hold panels to the roof or ground. Loose clips and rusted bolts go to the installer.

Thin dark lines across a panel, often tracing tiny cracks in the cells. Worth a photo and a call to the installer. See where it matters

A wide, soft-bristle brush on a water-fed pole, the tool panel makers allow. Stiff bristles and scrapers can scratch. See where it matters

Anything on the glass that blocks light: dust, pollen, droppings, ash, sap. An NREL-led study found soiling losses of up to 7% at U.S. sites. See where it matters

A set of panels wired in series to one inverter input. One shaded or faulty panel can pull the whole string down.

Stress on glass from a sudden temperature change, like cold water on hot panels. It is why we wash early and use water at air temperature. See where it matters

The angle of panels from flat. Steeper panels shed rain and snow better; low-tilt arrays hold dust longer. See where it matters

Output below what the weather allows. One research method flags below 60% of expected for three clear days as major, below 80% for seven as minor. See where it matters

A light carbon pole that carries pure water to a brush at its tip, so the crew can reach panels without stepping on them. See where it matters