Net-metering relies on a simple import meter that operates normally when you take electricity off the network and effectively “runs the dial backwards” at times when you export your excess DG capacity back to the network. 

Net-billing provides the same outcome as net-metering but the meter used is an import/export meter and the “netting” is done by the retailer subtracting the exported energy quantity from the imported energy quantity and then billing on the net (subtracted) amount.

The NZ distributed generation regulations effectively prohibit the use of net-metering by requiring an import/export metering installation in all cases.  There’s nothing in law that either requires or prevents net-billing in this country but in NZ’s competitive retail electricity market there are currently no known retailers that offer this as an option for DG owners.

Absent being forced to by regulation, there’s no purely commercial incentive for a retailer to offer a net-metering DG option or indeed any other option that values the exported electricity at a higher level than their normal wholesale energy purchase price. However, there might be other reasons why retailers may offer more generous buy-back rates - as these can change over time, it's certainly worth shopping around. Net-metering effectively requires the retailer to pay you at their full retail sale price for your exported electricity.  Retailers buy goods at wholesale prices and sell them to customers at (higher) retail prices.  They incur fixed and variable costs in the process of carrying out their business and seek to make a profit for their shareholders.  Exported DG electricity that exceeds your own needs is commercially a wholesale purchase opportunity for a retailer that they will weigh up against their alternative energy purchase options.

In countries where they are used, feed-in tariffs (i.e. regulated fixed minimum prices that retailers must pay DG owners for their exported electricity) and net-metering arrangements are invariably put in place by governments pursuing specific energy policy goals.