How a home solar electric system works
Your panels produce direct current whenever there is daylight on them. An inverter converts that into the alternating current your house uses and feeds it into your electrical panel. Your home takes what it needs first. Anything left over goes out to the utility.
How that surplus is credited depends on your utility and on the interconnection agreement in place for your property. That agreement is one of the most useful documents you own and one of the most commonly lost, which is why it is worth keeping a copy somewhere you can find it.
How to identify your panels and inverter
Almost every homeowner can find this out in about five minutes without going near the roof.
- The inverter is the box near your electrical panel, in the garage, or on an outside wall. Its label carries the manufacturer, the model and the serial number. Photograph the label.
- If there is one large box, you have a string inverter. If there is a box on the wall plus a small unit under each panel, you have optimizers. If there is no large box at all, only a small unit under each panel, you have microinverters.
- Panel make and model are printed on a label on the back of each panel. You will usually find the same information on your original proposal, permit paperwork or the sticker on the electrical disconnect.
- The permit placard near your meter often lists panel count, panel model and inverter model in one place.
Understanding your production figures
A solar electric system does not produce a flat amount every day, and a lower number is usually weather rather than a fault.
Compare like with like. This March against last March tells you something. This March against last June tells you only that the days got longer. Cloud, rain, shading from a tree that has grown, and dust or pollen on the glass all move the number without anything being broken.
What is worth investigating is a step change: one string that stops, a day that reads zero when the sun was out, or production that drops and never recovers.
Common inverter warnings
Most inverters signal with an indicator light, a screen code, or an alert in the manufacturer app. The words vary by brand but the families are consistent.
- Grid voltage or frequency out of range. The inverter is refusing to export because it does not like what it sees from the utility. Often clears on its own.
- Arc fault or ground fault. A safety trip. Photograph the code and stop resetting it. Repeated resets on a real fault are exactly what the protection exists to prevent.
- Isolation or insulation fault. Usually moisture somewhere in the direct current wiring. Common after heavy rain, and it may clear as things dry out.
- Communication or gateway offline. This is a reporting problem, not a production problem. The system is very often still making power.
Why monitoring stops reporting
A blank monitoring app is the single most common thing homeowners contact us about, and it is usually a communications problem rather than a solar problem.
- The home network changed. A new router, a new provider, or a changed network name or password leaves the gateway with nothing to connect to.
- The gateway or communications device was unplugged, often during other work.
- The manufacturer account was created in the installer's name and email. When that company disappears, so does the login.
- A cellular monitoring device reached the end of its paid data arrangement.