Assessment of photovoltaic system, sizing

, you have put an impressive amount of thought into your house. It should not go unmentioned that for many the motivation is, however, economic efficiency or, if you will, CO2 reduction. From that perspective, many of your recommendations are, in my opinion, counterproductive.

String lengths, shading: clearly that is important, but there are solutions for it without having to give up surface area.

The reference to another forum has already been made; I also received many helpful tips for our system there, which I then discussed with my solar installer and also implemented.

The standard modules are connected in series. A dormer casts a shadow. Shadows on series connections reduce total output. Ask the photovoltaic installer about the distribution and why they give this recommendation and calculation. Anyone who simply fills everything with series-connected panels and promises full output despite shading has on paper a better kWp/€ ratio but delivers, in case of doubt, the worse-performing system. Greed sometimes eats the brain, and that's how these guys get their orders. Also, you pay an energy levy for production over 10 kWp. It will rise significantly in 2020. Tip: Design generously according to your own consumption, use a hybrid inverter, and store excess energy in an appropriate range in batteries and hot water storage. If you don’t want to disfigure the house visually, take solar tiles. Although much more expensive, they also increase the value of the house (so a good investment) – and with a low-voltage system on the roof and parallel connection, you also don’t have shadow problems, no electrician on the roof, no fire load entry, and no high voltage over the living rooms. These are all disadvantages of standard photovoltaic panels that no one talks about and everyone accepts because nowadays no one questions them anymore.

I do not want to leave a few points uncommented: The Renewable Energy Act levy is rising for consumers. The current levy on self-consumption will soon be abolished by an EU regulation window. So that should not be a reason. A proper solar technician will provide a shading analysis. From this, you can see losses due to shading and consider which areas are worth covering. Normal modules today have bypass diodes, and good inverters have shading management. This avoids losses from individually shaded modules, e.g., due to the dormer. Visually appealing systems can also be built with normal modules. These are also available entirely in black. On black roofs, you can hardly see them. Solar roof tiles are rare, get hotter, are less efficient, and age faster as a result. Unless you absolutely have to do it for monument protection, you should leave it. The systems usually have a maximum of 1000 V. This is not high voltage but still the same category medium voltage as mains voltage at the socket. The fire department knows this today and can handle it. Magnetic fields can be avoided by good cable routing. You should do this anyway for lightning protection. One kWh from your system costs about 6 to 7 cents. One kWh from a storage costs 40 to 50 cents. So it’s not worthwhile at all! Conclusion: find a good offer with the help of the Photovoltaic Forum and fill the roof. It’s worth it.

A proper solar installer will provide a shading analysis. From this, you can see losses caused by shading and consider which areas are worth installing panels on.

Exactly what I meant – the OP was puzzled by the relatively small area offered compared to the area he calculated as possible.

The systems usually have a maximum of 1000V. That is not high voltage but still the same category medium voltage as the mains voltage at the socket.

That’s correct. That’s why an electrician has to go on the roof. Below 120V this is no longer the case, and such solutions do exist. The reference to a technical and optical alternative does not make the mature and technically flawless standard systems any worse. They are the first choice purely from a profitability perspective. Some people invest in the design of their house, the outdoor areas, the lighting, the colors – in this case, a reference to design possibilities of the roof can certainly be valuable and not “counterproductive.”

a reference to design options for the roof can certainly be valuable and not "counterproductive."

Your comments are of course valuable, I did not write it that way either. I just did not want the references to storage and possibly smaller areas or orientation towards self-consumption to stand as a blanket recommendation, as these clearly conflict with other goals and this is not always obvious to beginners.

Read a bit here in the forum. Then you'll quickly move away from solar tiles (various reasons...), especially if economic viability and CO2 balance are important to you,... the efficiency just suffers far too much. I am also a fan of good aesthetics, but my green conscience ultimately prevailed.

Regarding sizing: simple rule: as much as possible... Even if you have to pay the energy surcharge because of it (various calculations can be found here in the forum). Regarding shading, many inverters now have really good shade management (together with good string planning, already a good step forward).

Depending on the roof color, you can take all black modules, which look clearly better than the standard modules (with only a minor efficiency loss). On black or anthracite roofs, the look is okay, sometimes hardly noticeable.

Everything about batteries has already been said, nowadays in the single-family home sector rather a plaything if you feel like it, but you usually burn money with it. It also has no ecological advantage, because the electricity not stored without a battery is not lost, but goes into the grid.

Hello everyone,

sorry for the late response. We asked our architect to follow up again. Apparently, it was not made clear enough that we want to fill the roof as much as possible under certain circumstances.
The solar installer then responded that an increase to 9.96 kwp would only result in a cost increase of about 350 €, basically nothing.
Unfortunately, he did not answer our actual question of how much can be installed on the roof at most.
Instead, he explained what additionally needs to be installed for over 10 kwp and how this affects the costs and generally how the return on feed-in decreases as a result.

So at least we know that obviously more can go on the roof than previously offered. But the actual question of how much fits on it and whether it is so much that the additional feed-in compensates or outweighs the Renewable Energy Act surcharge + additional costs is still unanswered.

Nevertheless (because I feel very well taken care of and advised), I would also ask you, how can I calculate from which kwp the Renewable Energy Act surcharge becomes profitable. As silly as it sounds, I’m really bad at math and therefore unsure how and with which variables I should set up the calculation....