Construction costs are currently skyrocketing

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In short: Don't get your hopes up too high regarding the expansion of existing networks: The biggest challenge is the transition to renewable energies in this area.

All serious studies I know do not assume that (green) hydrogen can be produced in such quantities that it makes sense to burn it extensively in heating systems.
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Above all, it is always said that green or blue hydrogen can be mixed with natural gas and that the existing pipeline system in Germany can transport it without damage. Unfortunately, this is a misconception; it simply cannot be done. In an ideal world, I would wish for renewable surplus energy with which we can then produce, transport, and store hydrogen and subsequently use it meaningfully and CO2-neutrally in high-energy environments (steelworks, etc.). But life is not a bed of roses :oops:

How much longer do people want to keep sugarcoating the pre-war technology "heating with an open flame" with the hydrogen lie? Not even the heating system manufacturers really believe anymore that they will be able to exceed 30% hydrogen in the near future – and even that will only be possible once the very last consumer has switched to an H2-ready heater. So eventually, the old lady with the non-H2-ready gas heater, always cited by the self-proclaimed heating preservers, will have to throw it out – exactly what they always accuse the evil Greens of. So even if one day all heaters really were H2-ready and hydrogen could be fed in – where is it supposed to come from? The roadside is littered with the skeletons of companies that promised exactly that.

Even if there were enough hydrogen, it would first be used precisely where nothing else is possible, namely where high temperatures are needed. So everywhere except in private heating.

No one would drive a 36-ton truck into the city center to go to the bakery if they had a bicycle or a small car available – but with private heating, that's exactly what we do when we heat with an open flame. In the end, it always boils down to a radically egoistic "because I want to and can afford to." Nonsense for the environment, nonsense for the neighbors, nonsense for tomorrow.

On the other hand, district heating networks in metropolitan areas struggle with the problem of renewable heat supply. Example Hamburg: There are certainly approaches there, but I am curious how the three coal power plants Moorburg, Tiefstack, and Wedel, which predominantly supply heat to the Hamburg district heating network, are supposed to be converted to renewable energies. Hanging heat pumps in the Elbe? Wind to heat? Deep geothermal energy? I am curious.

Hamburg is of course a prime example of how narrow-minded politics ("coal is evil") can ruin an otherwise good solution. Moorburg was not built so close to the city by chance, but for connection to a district heating network. Of course, if you only consider coal power generation, you end up with a problem. In the medium term, it is clear that district heating networks will be operated to a large extent with fossil fuels. But that is not a problem if you do not operate it as a pure district heating network, but rather through sector coupling. In winter, we will have a significantly higher electricity demand than before. An increase in electricity production from reliable sources fits perfectly here. And an increase from 90% efficiency to 150% and above may not satisfy the absolutist demands of some Greens, but in practice it is not to be underestimated. In the long term, geothermal energy is probably a good idea. In every neighborhood, there are larger areas suitable for probe fields. Parks, playgrounds, and sports fields. In addition, one can of course tap larger bodies of water. Be it the Elbe or various projects here at Lake Constance. Where those possibilities do not exist, large air-water heat pumps can be built. Suitable options will be found depending on the respective conditions, and the rest will initially be fossil-fueled via combined heat and power plants. It is not a perfect solution, but for now good enough. Along with the renovation of the old energy guzzlers with >200 kWh/sqm, emissions will be significantly reduced. It is not zero and may not suffice for net-zero either, but doable and good enough for the next 10-15 years. The supposedly perfect solution is the natural enemy of "good enough."

Hamburg is of course a prime example of how narrow-minded politics ("coal is bad") can ruin an actually good solution. Moorburg was not built close to the city by chance, but for connection to a heat network.

I know. At the time, as a student in Hamburg, I followed the development process and also experienced planning and construction (one of my professors was consulting for Vattenfall back then). I even saw the large combustion chamber and the heat exchanger inside during construction. Probably the most modern coal-fired power plant in Germany ... but still coal.

Long term, geothermal energy should be a good idea. In every neighborhood, there are larger areas suitable for probe fields.

About 10 years ago, there was a project to develop deep geothermal energy under Hamburg Wilhelmsburg. The targeted heat output at the time was just under 10 MW. And that was a 3000-4000m borehole. Now it is being implemented as well. For the Hamburg heat network, significantly more is needed. 2-3000 MW? I told you, it will be exciting.

In Berlin Lichtenberg, to the best of my knowledge, the waste-to-energy plant was converted to gas not too long ago. Maybe at least that works?

There was a project about 10 years ago to develop deep geothermal energy under Hamburg Wilhelmsburg. The targeted heat output at that time was just under 10 MW. And that was a 3000-4000m drilling. Now it is being implemented as well. For the Hamburg heating network, much more is needed. 2-3000 MW? I say, it will be exciting.

We should move away from the idea of immediately finding the big solution for the entire city. It’s better to start small. Next to our old housing complex is a large playground, plus a youth center with a skate park. A probe field here could supply the surrounding apartment blocks. There is a railway line that has a 20-30m wide strip for a bike path. A probe field could also be installed here without disturbing anyone and supply the surrounding buildings via a short route. For Konstanz, I can think of dozens of undeveloped areas near larger offices or apartment blocks. Here, geothermal networks with a few hundred meters of piping could be implemented everywhere, quickly supplying around a thousand people.