Meters for your balcony solar system

Many inverters provide yield data via app – but not all, and not always reliably. A separate meter between the balcony solar system and the socket shows you independently how much energy actually flows into your home's circuit. That way you spot shading, dirty panels or a defect early and can estimate when the system will pay for itself.

As a rough guide in Germany: one kilowatt peak of panel output generates around 800 to 1,000 kWh a year with a good south-facing orientation. Mounted vertically on a balcony railing, facing east-west or partially shaded, the yield is usually considerably lower. Only a measurement shows where your system really stands.

Simple feed-in meters work like a plug-in energy meter but are designed for current flowing in the other direction. They show the current power and the kilowatt hours generated on the display. Smart plugs with metering also send the values to an app, so you can compare daily curves.

Since Germany's Solar Package I (Solarpaket I), plug-in solar devices may feed in up to 800 VA of inverter output, with up to 2,000 Wp of panel output. The system only needs to be registered in the Federal Network Agency's market master data register (Marktstammdatenregister); a separate registration with the grid operator is no longer required. An old Ferraris meter without a reverse-running lock may run backwards temporarily until the metering point operator replaces it with a bidirectional meter.

The meter at the socket does not replace this official meter; it is only for your own monitoring. Don't plug it in between several adapters or extension leads, and follow the inverter manufacturer's installation instructions.

Regularly compare the meter's readings with the inverter app or the bidirectional meter. Larger deviations indicate measuring errors, a defect or an incorrect setting. Note down the yield every month; after a year or two you'll be able to tell whether panels are getting dirty or new shading from growing trees has appeared.