Flat collector vs tube collector

In advance: Sorry if I don’t address the collector question. I consider this technical question premature and would look at the project as a whole again if I were you.

In terms of environmental considerations as well as cost-saving measures, I see many upgraded roofs, which leads me to think that I should also behave a bit future-oriented.

What others do is not always consistent, and with solar thermal this is usually not the case. If you want to upgrade the roof and do something meaningful, I would cover east and west with photovoltaics. Morning sun, evening sun, midday sun. Photovoltaics pay off financially through feed-in. You can use the electricity for all kinds of things, including hot water production with storage. The latter only as a thought aid, it is not sensible.

Solar thermal can be economical as in your case with own labor and as a replacement for electric hot water production, but I would still weigh it against other measures (photovoltaics, energy consulting, heating optimization).

Since I am a confirmed DIYer with some experience in all trades, I want to put up a collector, couple it with a storage tank, and test on various sunny days to what extent and in what amount my shower water can be produced more cost-effectively. If this leads to a positive result, I can install a larger system completely on my roof.

That’s nonsense. Either all or nothing, research yields beforehand (see very top). What do you do with the storage tank if your experiment fails? Very bad environmental karma.

In summer my heating (oil) is off and I shower electrically.

Does the heating have such high losses that it makes sense to use expensive electricity for hot water in summer? If you ever replace your heating, solar thermal may limit you or cause additional costs with the new heating system. And at the latest with the next heating system I would provide it for hot water production in summer or reckon against ST, which would drastically reduce the savings (compared to hot water by electricity).

Unfortunately I don't have a south-facing roof available for installation, which is why I am skeptical whether the effort is really worth it.

Calculate what you could save at best with an optimal south orientation before proceeding.

Calculation example (rough layman estimate, please use your own numbers):
1. 3300€ investment = 800€ hot water storage + 1500€ collectors + 500€ accessories + possibly 500€ solar-compatible instantaneous water heater
2. 200€ = annual electricity costs in summer for hot water production

3300€ / 220€ p.a. = 17 years. That means starting in the 17th year it begins to pay off, assuming no defects/maintenance costs. As said, just an example, you could also end up with 5 or 100 years.

Manufacturers and installation companies of course always have the position that it would be worthwhile, even if only a cup of warm coffee comes out in the end.

West orientation can already provide sufficient yields, google this in other forums.

You seriously want to hang solar cells around his neck in an old building with oil heating?!

No, he wants to install solar thermal on the roof. That is far less sensible than photovoltaics for electricity generation.

Or do you mean me? Yes, I would do that in his place.

As already mentioned. ST is actually only done to be allowed to build a gas heating system cheaply. On the other hand, for photovoltaics not to be worthwhile, you must have a very sh***** roof or be surrounded by tall trees.

Thank you for the partially detailed answers and suggestions. Regarding the suggestions about photovoltaics, I can only say that photovoltaics is not an option for me. I have researched extensively in the photovoltaic sector and found that it (personal opinion) is not worthwhile. When considering all factors, a lot is added on top of the prices offered by companies. (Decrease in the performance of collectors year by year, decrease due to dirt, additional problems with electricity buyback due to different conditions of electricity producers (I Berlin-Vattenfall), change of provider because of electricity prices, meter installations with additional lightning protection measures, different efficiencies of inverters, self-consumption times (if the sun shines nicely during the day, I need the least electricity) in case of self-storage through battery systems - their maintenance and lifespan....etc.... With precise calculation, which does not sugarcoat but includes all actual costs, I came to about ~15 years payback time, which led me to abandon the project! Therefore, the switch to solar-assisted hot water generation. As already explained, the oil heating is off in summer. My 80-liter hot water boiler is heated once with 3KW and then lasts the entire day. The solar support should therefore only provide an additional effect, which I want to try first. The measurement and control technology is no problem for me, and I have a small storage tank as well as installation materials on hand for the trial. So in summary: Photovoltaics no! Water collector possibly yes, if the west-facing orientation provides sufficient performance. I determine the performance experimentally over various days (clear, cloudy, dull, cold) and see what hot water temperatures I achieve. Then I can extrapolate that to a large system on the roof area in order to decide whether I want to take it on. This results in the core question of the thread opening flat or tube. Does the tube collector deliver "significantly" more even with diffuse western solar radiation? I will invest in one collector for the test (if it does not meet my expectations, you will find my collector special offer again on E-Bay) I have already heard the statement "gas or nothing" from the providers, who have already congratulated me that after 10 years at Easter I would have golden eggs in the nest. Greetings from the warm showerer :-) who unfortunately over the years has become a skeptic

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I have thoroughly researched the photovoltaic sector and found that, (personal opinion), it is not profitable. When you consider all factors (...) self-consumption times (when the sun is shining nicely during the day, I need the least electricity), in case of self-storage through battery systems - their maintenance and lifespan....etc......

ST has the same problem:
If you don’t need it, you don’t know what to do with the amount of heat, and if you urgently need it, nothing is available.

To put it in numbers, which come from a photovoltaic system (but can be transferred almost 1:1 to ST):
June, sunshine, measured power at noon 9.8 kW (daily amount ~80-100 kWh)
December, sunshine, measured power at the same time: 0.6 kW (daily amount 2-3 kWh)

ST has the disadvantage that you can only use it yourself. Photovoltaics, on the other hand, are sold when there is surplus and are therefore more economical.

If you consider all factors, there is quite a bit added on top of the prices offered by the companies. (Degradation of the collectors' performance year by year, degradation due to dirt, additional problems with electricity buyback due to different conditions of electricity producers (e.g. Berlin-Vattenfall), changing providers because of electricity prices, meter installations with additional lightning protection measures, various efficiencies of converters, self-consumption times (when the sun shines nicely during the day I need the least electricity)

Then you are not fully informed. Personal experience (W/S/W orientation): amortization in just under 8 years. 10 years warranty on 85% performance and inverters. Problem with electricity buyback: It does not exist because there are legal regulations. Lightning protection not necessary, why should it be? By the way, you can influence self-consumption yourself: for example, do not run washing machine, dryer and dishwasher at night.

Water collector possibly yes, if the west orientation provides sufficient output.

The effectiveness is even lower there because you have an abundance of warm water in summer (you can't shower and bathe that often) and in winter it doesn't really work.

I believe you are not to be convinced anyway, although basically every answer here says: Take photovoltaic and no ST.

8 years is really quite good. I rather assume 10 years for myself, but 15 is already quite unrealistic... Nowadays, 25 years performance guarantee is also completely normal, and if the inverter breaks down, it doesn’t cost a fortune either. To operate a photovoltaic system uneconomically, you really have to let yourself be seriously overcharged in the offer.