The $260 string: what every app missed for 22 days

A 29-kilowatt residential system. Three strings, installed and commissioned without incident. One string disconnects. Nothing catches fire. Nothing trips. No error code appears. The inverter now has two strings where it used to have three, and it carries on reporting the two it can still see.

The manufacturer's app showed green. It was not broken or misconfigured. It was doing the job it was built for, which is to report the status of equipment it can talk to. Two strings were producing normally. The system was online. Every indicator a homeowner or an installer would think to check said the system was fine.

What the app had no way to say was that the system should have been producing more. Answering that needs a second number: what this system, at this location, under today's irradiance and temperature, ought to be generating. Then you subtract. Against that baseline the gap was 54 kWh a day, every day, for twenty-two days before anyone looked.

At residential rates, roughly $260 a month walking out of the house. Nobody was going to find it. The homeowner had no reason to suspect anything; their app was green. The installer had no alert, because no alert existed to fire. The loss would have run until someone compared one year's bill against another and went looking for an explanation.

The uncomfortable part is not this one system. It is that the same failure is invisible everywhere it happens. A dead string. A failing optimiser. A tree that has grown into the afternoon sun. All of them produce output that looks plausible on its own and wrong only against expectation. Multiply by every roof a company has ever touched, and the question stops being whether losses like this exist in an install base. It becomes how many.

This is the service business hiding inside an install base that is already paid for. Not new customers. The same customers, on the same roofs, with a problem worth finding.