Two meters are involved once an array is on the roof and people routinely confuse them. The generation meter counts everything the panels make. The smart meter at the supply counts what crosses the boundary with the grid, in both directions. Neither one on its own tells you what the array is worth, and the export payment depends on the second rather than the first, which is why a household with solar and no smart meter is usually leaving money on the table.
The generation meter counts what the panels make
The generation meter sits with the inverter and counts every unit the array produces, whether that unit is used in the house or sent to the grid. It is the number to look at when asking whether the system is performing, because it is unaffected by how much you happened to use that day. It is also the number a maintenance visit reads against expectation, and a fall in it year on year that is larger than the panels' rated degradation is the signal that something is wrong rather than the weather being poor.
The smart meter counts what crosses the boundary
A smart meter records import and export separately, and it is the export figure that an energy supplier pays on. Without one, there is nothing measuring what you send back, which is why the Smart Export Guarantee requires a meter capable of half hourly readings. This is the practical reason to have one installed alongside solar rather than a preference: the panels work perfectly well without a smart meter and the export payment does not exist without it.
What the two numbers together tell you
Generation minus export is what the house consumed directly from the array, and that self consumed figure is worth far more than the export rate, because it displaces electricity you would have bought at the full price. Reading both meters for a month is the cheapest way to find out whether a battery would pay, since a household exporting a great deal in the middle of the day is exactly the one storage helps and a household using most of what it makes already is not.
Reading them without guessing
The generation meter is a simple cumulative total: note it on the same day each month and the difference is that month's output. On the smart meter, import and export are separate registers rather than one net figure, and the in home display usually shows consumption rather than export, which is where most of the confusion starts. If the supplier's app shows no export at all on a system that is clearly generating, the usual causes are that the meter was never configured for export or that the export tariff was never actually applied to the account, and both are the supplier's to fix.
Questions people ask about smart meters and solar panels
Do I need a smart meter for solar panels?
Not for the panels to work, but yes to be paid for what you export. The Smart Export Guarantee requires a meter capable of half hourly readings, so without one there is nothing measuring what you send back and nothing for a supplier to pay on.
How do I read a solar generation meter?
It is a cumulative total of everything the array has produced. Note the reading on the same day each month and the difference between two readings is that month's generation. That figure is the one to compare against what the system was quoted to produce, because it does not depend on how much you used.
Does a smart meter show how much my solar panels generate?
No. The smart meter measures import and export at the boundary with the grid, so it sees only the surplus you send back, not the electricity the panels made and the house used. Generation is the other meter, and you need both numbers to know what the array is actually worth.
Why is my export reading zero when the panels are working?
Usually either the meter was never set up to record export or the export tariff was never applied to the account, and both are for the supplier to put right. It can also be genuine on a household that consumes everything it generates, which a month of readings from both meters will tell you.