Solar system for rent - is the offer okay?

If you really consume only 757 kWh per year as proven, you should rather work on a guide for saving electricity.

I'm completely stuck: Why should I even get such a system right now?

For the environment.

Well, many have already said that these rental models are too expensive.
But surely there were some great economic calculations included in the offer?

It is important to set the self-consumption as high as possible. I also don't believe that you have an annual self-consumption of 757 kWh. The higher the better, and your system will pay off much faster if you buy or finance it. I do not recommend renting.

Let's not get into the discussion about photovoltaics yes/no. This is about a financing model. The original poster wants to rent instead of buying. Whether this is worthwhile requires comparing both financing methods. At first glance, the present offer seems catastrophically bad. However, there may be reasons to do it this way (no cash available, no creditworthiness for external capital, …)

1,700 kWh is the annual average own consumption here. The 7xx kWh are only fed in by the system according to the invoice.