We're going to need a lot of solar panels

> But even the former source mentions 1977 as its index year which already alleviates the external effects of WW2, people did not just live without houses for 30 years, the lost housing of WW2 was mostly rebuilt in the 50s.

It does not sufficiently alleviate the effects of WW2 and other developments.

For instance, the population got reduced to 82% due to WW2 [1]. Also, living space per person has increased a lot over time. I can't find a source for 1945, but here is one from 1971 to 2014. The number of squaremeters per person has almost doubled during that time. [2]

So no, people didn't live without houses for 30 years. But they needed/used way fewer houses overall.

[1] https://de.wikipedia.org/wiki/Liste_der_Volksz%C3%A4hlungen_... [2] https://option.news/wohnraum-im-wandel/

> Also, I do think that your claim is not valid. I do understand that the source I gave for economic lifetime, and also the norm I quoted is acting with fictions required for taxes and accounting reasons. The thing is: These fictions are intended to reflect reality. So I don't get why you are so hung up on where these calculation models originate, as they are specifically designed to reflect reality.

You are misinterpreting them. They don't literally say "houses are worseless on average after a 100 years". They say "houses are worseless on average after a 100 years without doing anything to increase their value". And this is certaily more or less accurate. However, most people don't just let their buildings rot. Some do, but most don't that's why buildings are on average not being rebuilt after a 100 years.

> Why would you spend more money today to build a house with better materials, when you don't even live to see the rewards in the form of lower maintenance and renovation costs in a 100 years.

I find it a bit offtopic, but a very common example is that parents want their children to inherit it so that they don't have to worry about rent or can rent it out for some extra income. Other examples include people who don't necessarily want to stay in the house forever but want to increase the value to sell it later to a higher price. Some people also just enjoy building something that lasts (I am one of those). I think you can agree with that, no?

> My grandparents are absolutely stubborn in that they want to replace it with a completely new oil-based heater. The literally only reason is: They are old and don't want to try out something new, even if it is functionally exactly the same (like a wood pellet heater). (...) and they are unable to offer any other rational explanation.

First, let me say that I understand how you feel about that. I know the situation and sometimes it pains me to see what people do. I would have adviced the same as you. However, without knowing the situation, I think that sometimes in these situations the problem is safety concerns.

The fact that they are unable to "offer any other rational explanation" really makes me think that there is quite the chance that they do have a reason and they are just tired of providing it. If I had to make a bet, I would say they had some bad experience with modern technology in one way or the other. And they maybe also know a time where the winters were cold and heating didn't work. They do not understand heat pumps (not even I fully do) and they are afraid that when something stops working, they are helpless. For them, it feels like a total lack of control over something that is crucial to their life. But would you accept that answer? Probably not. Maybe they already hinted at it - try to remember if they did that and if you properly acknowledged their fears. With oil, not only do they use a technology that has worked for a long time and is much more well understood by them - it actually also makes them more independent of restrictions to power/heating compared to other solutions - at least as long as they have a full tank.

Unfortunately they could very well not be irrational but very rational when considering their situation. Is the decision good? No, I don't think so. But it is not irrational.

Of course, maybe I'm totally wrong. But it wouldn't be the first time that I see a conflict like you describe.

In the end, let me give you some advice to your situation. If you think that it could really be feeling of control and safety that makes them stay with oil, then how about offering them to install an aircon? Aircons are heat pumps as well, and very efficient ones as well (usually more efficient than air/water heatpumps). They can keep their oil, but the aircon might make it able to reduce the oil consumption by a huge chunk, depending on the circumstances. It doesn't cost too much and you even get BAFA Förderung. And on top of that, you can use it to cool/dehumidify of course - heatstroke is also a common reason for elders to end up in hospital. That solution is what I would try in your situation.

> And some people just want to live in their house and don't give any thought to it until there is an emergency. Then people will have expensive repairs and still won't think twice about changing their behavior.

This is not irrational, only lazy. Irrational means to do something even though you know it's wrong. E.g. out of a mood.

> It does not sufficiently alleviate the effects of WW2 and other developments.

Remember, we are still talking about the claim that renovation of the building stock takes approximately 100 years.

It does not matter whether we are building more because people need more space, or because houses are actually replaced. All that matters is that the percentage of the building stock built under modern energetic regulations rises sufficiently fast.

This is why this discussion is so frustrating for me. It's all about semantics that don't matter, when my point was actually just disproving a point I thought to be ridiculous (which with the new research I did for my rebuttals was actually sort of disproved, as Germany seems to be really good at renovating the building stock compared to e.g. Eastern Europe), which is also why this will probably be my last post in this thread.

> You are misinterpreting them. They don't literally say "houses are worseless on average after a 100 years". They say "houses are worseless on average after a 100 years without doing anything to increase their value". And this is certaily more or less accurate.

You seem really hung up on the topic of depreciation accounting (AfA) and don't seem to get my point. Depreciation is regulated and does not exist in a vacuum.

Depreciation is a legal fiction to model the reduction in value of assets in such a way that it is easy to calculate, but also close to the actual value that would be fetched on the market due to the depreciation.

You are essentially claiming several things with your argument: 1. depreciation is not correlated with actual value loss, and therefore 2. the economic lifetime model used to calculate depreciation does not correlate with actual use lifetime.

The first is correct: Renovation expenses can be used to raise the book value of the asset making them balance-neutral. The second is not and especially does not follow from the first for the reason that I told you, the lifetime model used in depreciation calculation is based on the observed lifetimes in reality. There is also feedback in the other direction as engineering decisions are taken based on the best practices in economic lifetimes, which is why I cited the relevant DIN norm for cost calculation for builders in my first post.

> That solution is what I would try in your situation.

Thanks for your advice. But I already tried that. And it's pretty funny that you literally try to explain the mentality of my grandma to me. But what do I know it's only my grandma.

Let's just let the topic rest, I do not really care about this discussion anymore.

You can - trackers are absolutely a thing, and historically tended to be used a lot. Back when solar was $10/W. Adding even $5/W for tracker structure and equipment was far cheaper than additional solar panels.

Now, with panels sub-$0.50/W, you can accomplish the same thing (more power) for far less money by just putting more panels on. You get less production per nameplate panel watt, but the total system costs are usually lower. And you can push your DC:AC ratios pretty high if you want - cap your inverter out on sunny days, but still get more power on cloudy days. It just depends on what you're trying to optimize for.

I still see trackers on occasion - they're cool. But the only place they're useful is if you have some stiff limit on nameplate capacity. Out here, you're limited to a 25kW system for residential, and you can't exceed your local transformer capacity in panel area - not inverter output (why, I have no idea, I've gotten a range of BS reasons that mostly center around somehow changing the system, blowing up the transformer, and then the power company being on the hook for a new transformer). So if you want to run a large "residential" site (think a ranch or something like that with a bunch of outbuildings), you can hit the 25kW limit quickly, and then need to go to a tracker to increase kWh generated on your 25kW system.

But outside edge cases like that, just put more panels on. The systems I'm helping people with are mostly A-frames, with east-west facing panels for long solar days, and a fairly high DC/AC ratio. I've got 7kW of panel on 6kW of inverter, though I rarely see the inverter past 4500W, which is by design - I don't like pegging out power electronics for long periods of time, and prefer to run things at 80% of design load or lower for longevity reasons.

I would say on the contrary, French people start stuff pretty much at the same rate as everyone else, as long as things are done under the radar. But the moment a topic becomes twitter-fodder, we develop pockets of resistance, and, all clichés aside, "being in a pocket of resistance" is at the earth of French persona. (We still teach kids and conservatives that Asterix and De Gaulle won their wars.)

We had three presidential candidates running on a platform of "windmills are ugly, let's not do that", and at least three on the platform of "nuclear plants are dangerous, let's not do that". I'm kinda worried that "solar panels are ugly, let's not do that" is gaining traction; and I wonder who's going to be the first to oppose dams, but there's a niche.

Efficiency isn't the goal here. Energy density & re-using existing infrastructure are the points.