alt Hacker NewsIn Uk, If an old (rare) mechanical meter the meter will go backwards, the ideal. If a dumb digital meter the meter will simply pause counting up. If a smartmeter again the import reading will pause but a separate export reading will count up, for which you get no credit or debit but its nice to know. Ideally as battery prices drop you end up buying a battery that soaks up any surplus for later and so you don't lose any back to the grid. If you pay up for a commercially installed solar you can get paid for what you export but with plug in solar you just give it away.
In the UK as a consumer you can (always AFAIK) get a smart meter for free, and your retail supplier is required to offer you a non-zero rate (the "Smart Export Guarantee") for what you export back to the grid. That can be as high as about half the rate to import.