Your solar kit’s production of electricity is almost never the exact same as the consumption of your household. If you consume more than you produce, then 100% of your production is used on the spot, maximizing the economic profitability of your kit as you take full advantage of the savings.
If you produce more than you consume, you have several options:
Feed the surplus energy into the power grid. In Spain you can certify your kit with us, and get compensated for your surplus by your power company.
Add storage with a smart meter, and store all excess energy during sunshine hours, to use it when the sun doesn't shine.
Install a “zero discharge” device or “smart meter” on your distribution panel, that lowers your kit’s production and avoids any spillover of excess electricity to the power grid. This is the least attractive option, since you incur the cost of the smart meter and installation, and get no benefit from it.
If you feed a lot of energy to the power network, for example because you’re not at home during the day or use your home only sporadically, a storage system is probably the smartest solution. Most storage systems are modular, so you can start small and upgrade as you see the need for it.