Good sizing looks at the future, not just the current bill
An installation may seem too large today while remaining perfectly logical if a heat pump, a charging station or a battery are coming soon. Conversely, a project that is too tight can become limiting very quickly.
The 4-step method
Project consumption for the next few years
Add the likely uses of the home: terminal, heat pump, piloted balloon, more frequent teleworking. An installation is not made just for the photo of the moment.
Measure the marginal cost of additional panels
On a construction site already underway, additional panels often cost less than the core of the project. It is this marginal cost that must be compared to the future value of production.
Compare self-consumption and future injection
A larger installation will inject more if nothing changes in the home. But if you can electrify or control more uses, this margin becomes much more useful.
Decide according to the building strategy
If you are building a base for the next ten years, planning a little bigger may be rational. If you only want to cover the existing as closely as possible, you have to stay tighter.