Realistic construction time for a bungalow?

I want to have a bungalow built in Niedersachsen next year as a prefab house, completely from planning to moving in. It should have approximately 150 m² of living space and, of course, consume little energy, so with photovoltaics, an E-storage system, and also geothermal heating. A plot of land is available. How long is a realistic construction time including planning, approval, and the complete construction until moving in? Are there differences between the providers?

So apart from an idea, nothing has been done yet?

Then 2 years...

Look up the development plan, is a bungalow even permitted? Is geothermal energy allowed?

Find a general contractor, get to know them, request offers, evaluate and compare them. The order books for next year are probably already quite full, if you're not just throwing money around, this step alone could take up to half a year.

Then planning, approval,... depending on the planner, your special requests and the municipality, also up to half a year.

And then you can calmly have your construction project completed for occupancy in 8 months in 2024 (without outdoor facilities).

With luck and money, you would have a shell structure by Christmas 2023, but that is wishful thinking at the current stage.

Thank you very much for the quick response. When you look at the various providers, you read different numbers. But I am realistic, yes, I have also heard something like that before. I will probably plan for two years.

We built a bungalow last year. It didn’t take even a year from the initial planning ideas to moving in. But we were lucky that our building authority only needed 6 weeks of processing time. Others here waited 9 months. So I would first call the building authority and ask about their processing times. Then it depends on whether you are building with a general contractor or a prefab house provider. The general contractor was much faster for us to realize; with all the prefab house providers, we wouldn’t have built last year anymore, as they all had lead times of at least 9 months from approval. So, you can’t say that in general. You have to deal with it and then ask around.

So apart from one idea, nothing has been accomplished yet?
Then 2 years...

That will not be enough: I do not see the original poster starting at zero, but far before that: first of all, the misleading part of the word "Fertig" in "Fertighaus" must be "unlearned." Nothing goes faster there!

I want to have a bungalow built as a prefab in Lower Saxony next year, completely from planning to move-in. It should have about 150 m² of living space and of course consume little energy,

"Consume little energy" and "bungalow" is not impossible, but tends initially to be a contradiction. What the non-compact building body has in more envelope area and consumes more when heating, a larger collector area will not compensate for.

A plot of land is available.

Well, then bring it on!
(where there is a concrete plot, one can also explore its development plan or similar).

How long is a realistic construction time including planning, approval and the complete build until moving in? Are there differences between providers?

Yes, there are gigantic differences in the audacity with which some providers advertise how quickly you can reach your goal with them: while in Villabajo you are still stuck in the waiting loop of order book entry, in Villariba you are supposedly already celebrating the topping-out ceremony – "guaranteed," of course. Whoever believes that will be saved. And that is only an initial exercise regarding the value of fixed-price promises!
By the way, with both kinds of nonsense, the "solid" house providers are absolutely on par with the "prefab" house providers. Therefore, see above ;-)

Provider search, planning: at least 3 months Building application and approval: 2 months (if with notification procedure etc.) - 6 months (slow building authority) --From here on, someone will even schedule you.-- At least 10 months until move-in A prefabricated house is quick to erect, but the waiting time until the installation date is long. Sometimes very long. The neighbor two houses down had the building permit in November 2021, target installation date is the end of Feb 23. Not all providers have such a big backlog of orders, and last year they probably sold significantly fewer new houses. With solid construction companies, it takes a bit longer until the shell is finished, but they may start earlier. Still, I consider anything under 1.5 years extremely ambitious. Depending on the development of the material situation, it can also be significantly longer.