With the digital meter, part of your network charge is based on your highest quarter-hour peak. Switching everything on at once costs you money, even if your total consumption stays low.
What it means for solar panels
Power you generate during the day and use right away is worth the most. What you export earns much less. Self-consumption has therefore become more important than the total output on your roof.
What to do about it in practice
Run the washing machine, the dishwasher and the car during the day rather than all together in the evening. And have the output of your installation matched to your actual consumption.