For customers with micro-generation facilities, the production we report is reduced by the household's consumption. This is the so-called surplus electricity that is delivered to the grid via the electricity meter.
Since both consumption and production are measured instantaneously, it can sometimes happen that the customer both buys and sells electricity during the same hour. For example, consumption may be higher than production during the first 15 minutes of an hour. During the last 45 minutes of the same hour, production may be high enough to cover both own consumption and still deliver to the grid.