Start by distinguishing the invoice lines
A Swiss electricity bill mixes several things: the energy purchased, the use of the network, the royalties and sometimes a fixed share. Solar energy mainly acts on the first block. This is important because this avoids vague promises such as “you will no longer have a bill”.
Self-consumption is the real variable
Two houses with the same installed capacity can have very different economic results. The one who consumes more during the day benefits much more from their own kWh. Hence the interest in piloting appliances, water heater, EV charging and, sometimes, storage.
What you can actually aim for
Without batteries, many well-designed residential projects revolve around 35 to 45% self-consumption. With advanced control and storage, you can go significantly higher. The right objective is not symbolic, it is to maximize the share of expenses that you replace with your own local production.