Freshwater station and buffer tank: technically better choice?

How much of the photovoltaic can the heat pump take? And when will the energy be needed again? Losses until then? And what if the sun doesn’t shine? Who heats the buffer then? The calculation is not quite that simple.

The buffer is not heated up but "overheated". As an example, my underfloor heating is currently running at 33°. If the sun shines now, the system overheats our buffer storage as much as possible, so that in the end I might have 45° in the buffer. The heat pump then switches off in the evening until the limit of 33° is reached again. This means I can heat all night on good days without taking expensive electricity from the grid. Of course, I also have losses here, but I have those with any energy storage. Only a buffer storage costs me a fraction of a normal electricity storage.

You just have to consider on a case-by-case basis whether it makes sense or not.

Yes, how do the 45 degrees get into the buffer? The heat is generated by the heat pump. Sure, with photovoltaic electricity, but that costs you at least the feed-in tariff that you don’t get. Besides, your heat pump has to heat to less efficient higher temperatures; otherwise, you don’t buffer anything. Ergo, you have a worse COP when heating the buffer than if you didn’t do it. And yes, the stored excess temperature is lost again through losses. Additionally, you have higher acquisition costs because your buffer tank is larger and therefore more expensive than if you only have one for hot water or hot water preparation. And again, who heats your buffer to the necessary temperature when the sun isn’t shining? Then you also have to heat the 1000 liters instead of just 500, for example. No one said anything about comparing this with a battery.

What I mean is more factors belong in the calculation. In my opinion, a heating buffer (in connection with heat pumps, pellets, etc. it's different) is rarely an efficient solution. Better to buffer 1–2 degrees above temperature into the tons of screed and regulate that together with the photovoltaic system so that it happens at the time when the sun is most likely shining… simpler and in most cases more efficient.

But there is plenty of information about this on the internet, especially in the already mentioned forum.

You also have to heat the 1000l instead of just 500, for example.

In this case, of course, you have to use a stratified buffer. The buffer cost me almost nothing, so it is worthwhile for us. I also said that you have to calculate on a case-by-case basis.

What I think is nonsense is to overcontrol the underfloor heating. During the day, the rooms already heat up additionally through the sun, so overheating the underfloor heating is counterproductive for the living comfort.

And also once again, who heats your buffer to the necessary temperature when the sun isn’t shining?

So basically throughout the entire winter with expensive electricity from the socket. And in summer, when the photovoltaic system produces well, you don't need the buffer storage at all. face26 explained it well.

In this case, of course, you have to use a layering buffer. The buffer cost me almost nothing, so it pays off for us. I also said, you have to calculate on a case-by-case basis.

But in 99% of all cases, this is not the case, so this argument only helps those who also get such a storage "for free."
However, this does not change the other arguments, which carry much more weight.
It is simply the case that combined with a properly sized heat pump (especially modulating), this makes little sense in 95% of all cases, not even with photovoltaics.

What I think is nonsense is to over-control the underfloor heating. During the day, the rooms warm up anyway due to the sun, so overheating the underfloor heating is counterproductive to the living comfort.

You forget the time delay until the energy arrives in the room, the sun may no longer be shining, but whatever, that is not the main factor either.

And a buffer tank can also cause hydraulic problems. Since the average consumer has to pay for the storage, the simplest solution is to buffer the photovoltaic power in the screed and sell further surpluses.