I don't think you work 48 weeks per year in Germany (or in general, most of the EU). You have to subtract national holidays and vacation. The latter should be 4 weeks minimum (i.e. for a young person). At least based on what we have here, in Hungary. I think it goes up to 6 weeks. I'm pretty sure Germany is not worse off. In general you have about 220-225 working days a year (which translates to 44-45 weeks).
So that's about 125k invoiced income as an entrepreneur. It's not your salary yet. Again, depends on the country (you may have to pay lower taxes as a solo-preneur than what would be paid by someone employing you), but the employer usually pays more than what the employee makes in gross salary. Calculating with the Hungarian wedge, one of the highest in the EU, the net is about 50% of what the employer pays in total.
My guess is that it's probably equal to around 85-100k of gross salary. Definitely not bad (based on what I can see from here), seems to be on the higher and, but doesn't seem exceptional either.
Oh, well and you also have to account for downtimes as you'll probably won't quit before finishing your project (and if you won't, you'll almost certainly will have unpaid down times between projects).