Solar panels for grid-connection can supplement power demand in a house or for other use. Usually it is not possible to use all the power in the house, as most electricity comes during summer days. Therefore it is often needed to have an agreement with a power company to sell power. In any case, it is necessary to have a registration or permission with the local power company to connect a PV system to the grid, even in your own house. A system consists of solar panels and an inverter that produces the 230 V or 400 Volt used in the grid. Some systems also include a battery to store electricity from day to evening, where homes need more electricity.
Each kW of solar PV panel costs in bulk 250 €, single panels around 1000 €, a 1 kW inverter is around 300 € while a 5 kW is around 500 €.
Prices varies. A 1 kW system costs around 1300 € for PV panels + inverter while a 5 kW system is around 5000 €, but prices varies a lot and with bulp purchase, it can be much cheaper, but beware of quality
Local solar yield, see https://globalsolaratlas.info/