Bidirectional meters for rooftop solar
Short answer. A bidirectional meter keeps separate import and export registers, and the bill settles the difference. An ordinary meter cannot be used for this — its ratchet prevents reverse counting and on some models feeding it exported energy raises a tamper flag instead of a credit.
Who this is for: Anyone with rooftop solar under net metering, or preparing an application, who needs to understand what the meter is actually recording.
Two registers, and how to read them
Import is what you drew from the network; export is what you pushed back. Both are displayed as the meter cycles, typically coded 1.8.0 for import and 2.8.0 for export.
Photograph both on your reading date every month. Settlement disputes on net-metered accounts turn entirely on these two figures, and having your own record of them is the whole defence.
Checking that export is actually registering
Pick a clear day around noon with household load minimal. Note the export register, wait an hour, and note it again.
It should have advanced by roughly the array's output for that hour less whatever the house consumed. If the inverter reports generation and the export register has not moved, something is wrong between the inverter and the meter — a polarity error at commissioning is the usual cause.
Catching this in the first month rather than the sixth is worth several months of unrecorded export.
Why so much of your generation is exported and reimported
Solar generates in the middle of the day; households consume most in the evening. Unless you have storage, a large share of what you generate leaves the house and comes back later.
Net metering is what makes that economically neutral, and it is why the arrangement matters far more to the economics of a rooftop system than the panel efficiency does.
Settlement and banking
Surplus export in a month is credited and carried forward against future import, building up through the long-day months and drawing down in winter.
Judge a system on its annual position, not on a single month. A December bill on a net-metered house tells you very little about whether the installation was a good decision.
Frequently asked questions
Can I install solar before the bidirectional meter arrives?
The panels can be installed, but the system must not export to the network before the meter is in place and the connection is approved. Doing so is unmetered export and creates exactly the kind of dispute that is difficult to resolve afterwards.
Does the bidirectional meter cost more in meter rent?
Yes, it carries a higher rent than a standard single-phase meter, and the meter itself is part of the consumer's application cost.
Related meter guides
Go further
All 10 guides are listed in the meter guides index. To check the reading against your actual bill, open the official duplicate.