Energy cost-free house by Octopus Energy and Roth Massivhaus?

And in winter at -10 degrees and snowfall?

Well - it's a question of which period I consider and as also writes - in the end I sell significantly more than I have to buy and in total it ends up roughly neutral at the end of the year.

Marketing. You just throw out a few buzzwords, garnish them with some English, and a lot of people fall for it. Example: highly efficient heat pump: that's a normal run-of-the-mill heat pump from Vaillant. Every photovoltaic system has a smart meter. Overall, it’s a kfw 40+ house. But that doesn’t sound so great. Final energy demand 14kWh according to the energy certificate. But woe betide if the resident(s) don’t behave according to the standard. and so on and so forth. When I then read that it’s the first house in Germany with no energy costs, that’s already liable to warning.

when I then read that the first house in Germany has no energy costs,

This reads differently to me. It is only "energy cost-free" for the residents. "Zero-energy-cost house," here the zero does not refer to consumption but to the costs, limited to 5 or 10 years. One has a quota and lets it be centrally controlled by Octopus. "The zero-bills concept is simple: we manage the complexity, our customers don’t have to worry about anything. Green technology like solar systems, batteries, and heat pumps in the houses makes it possible! Under these assets we place our technology platform Kraken, which intelligently controls and optimizes the consumption. We want it to be easy for our customers. Hardly anyone wants to constantly manage the energy consumption of their house. The zero-energy-cost house takes the risk completely off their shoulders.”

That reads differently to me. It is only "energy cost-free" for the residents.

Okay, then I'll just rephrase the sentence so that you feel reassured. In the end, it's the same result. And if I add x euros to my selling price beforehand, I can even guarantee 0 energy costs for y years. That's just fooling people.

Zero-energy houses are the logical next step from passive houses and by now quite old hat. For those dealing with the best possible balance, the goal now is to implement plus-energy houses (i.e., to generate more energy in the balance than one needs oneself).

Fraunhofer has had, I believe, for about 10 years an Effizienzhaus+ calculator, which then allows you to play with the parameters to see what is needed to achieve such a standard.

Alright, then I'll just rephrase the sentence so that you feel reassured.

I'm not getting upset.
It's just that this is not about the house at all, but about the concept of the octopus. It reads like a 5-year contract with a quota of energy that the octopus controls for you from the outside. They release energy for you when it is cheaper. The fact that the house already consumes very little due to photovoltaics and storage is just passive house. But it is about the additional energy that the passive house requires.
“However, the concept of Zero Bills Homes does not allow you to consume unlimited amounts of energy in the residential buildings. In the Zero Bills homes, there is a so-called ‘fair amount’ that is individually based on the consumption of your household. This is the free allowance of electricity that Octopus Energy grants you as a Zero Bills customer. If the annual free electricity allowance is used up, you can automatically purchase the additional electricity you need via the provider’s cheapest basic tariff.”