To be precise (Germany): 800W inverter, 2kWp solar panels (maximum 4 panels). This allows you to get the 800W during long periods of daylight (e.g. east/west configuration). You only need to add the installation to a public database and plug in the inverter. Before it was more complex (special plug needed, only 600W, need allowance from grid operator) and still we have ~1.5 GW installed plug-in solar plants. It's almost always a no-brainer, RoI is typically 3-4 years while the lifespan is 20 years.

Edit: My state had a subsidy of 300€ when I bought mine, so the RoI was instant ;-)