ᐅ How to Achieve KfW40 Standard? Energy Systems and Cost Efficiency

pagoni2020 schrieb:

Thanks for the information!
If I achieve KfW40Plus through structural measures, the construction is subsidized, not directly the purchase of the photovoltaic system or the battery storage. From what I understood so far, with KfW40Plus I was "required" to include a battery storage. Why would feed-in then be prohibited? We are in Saxony, and there’s not much financial support for batteries here.
Am I mistaken? Where does it say that feed-in is not allowed?

In 20 years, I will be over 80... so this question is less relevant for me. Besides, I don’t have to replace something just because the warranty expires. Mathematically, many technical systems will be outdated and obsolete after fewer years. The 30-year warranty is not a deciding factor for me, although it does suggest good product quality; I will probably choose the electrician who sells this product. So, I would also accept it if it were only 20 or 15 years.
Could you provide concrete sources for your statements before I spend a lot of time searching? That would be really helpful.

It can also work with 36.5 cm (14 inches) here, and yes, aerated concrete is rather difficult or hardly possible. Whether you then use a filled 36 cm (14 inch) brick, a 42 cm (16.5 inch) brick, or external insulation... in the end, it’s all calculations by the energy consultant. For us, it will be 36.5 cm (14 inches) brick plus various insulation measures.

Sorry, I can’t find this information anywhere; maybe you can help with some sources.

Why isn’t an aerated concrete wall with 24 cm (9.5 inches) thickness plus 12 cm (5 inches) WLG032 insulation board sufficient? I calculate a U-value of 0.167. Added proper perimeter insulation and roof insulation, good windows plus front door, controlled mechanical ventilation, geothermal heat pump, and possibly photovoltaic. That should put me on a good path.
Putting aside the aerated concrete debate, which I don’t want to start here. I know those endless discussions.

By the way, I’ve lived in an aerated concrete house for 9 years with 17.5 cm (7 inches) wall thickness plus 12 cm (5 inches) WLG035 insulation boards and a wall U-value of 0.20, and I’m very satisfied.

pagoni2020 schrieb:

In simple terms for beginners, what does "power limitation" mean? And what are the consequences?

Simply put: The maximum feed-in is limited to 70% of the rated capacity.

Sascha1977 schrieb:

• We would like to achieve the KfW40 standard. What measures do you recommend or consider essential?
• We have read very positive reports about the cost-effectiveness of photovoltaic systems with east-west orientation on flat roofs. How do you see this in relation to our maximum 30-degree pitched roof? And is 25 or 30 degrees better?
• Does a storage system make sense?
• Are there any module manufacturers you would particularly recommend?
• Can you recommend an energy consultant and/or an expert for photovoltaic installation in the Ruhr area/Sauerland?

Do you want to take advantage of the subsidy or build to the highest standard? Depending on your priorities, the recommendations differ.

East-west systems have the advantage of generating electricity for more hours per day but less during peak times. For some consumption profiles, this helps increase self-consumption rates and thus makes economic sense. The lower the sun’s elevation, the more beneficial a steeper tilt becomes. However, for a residential building, I wouldn’t push this to the extreme because the appearance of the house is also important to me.

Storage: Calculate yourself and understand the impact of the basic assumptions. Depending on those assumptions, a storage system may or may not be worthwhile.

Modules are now quite well developed, and there are many good manufacturers. If the appearance of your house matters, you can take that into account when choosing the system. We chose solar tiles from Autarq – of course, the design costs extra.

nordanney schrieb:

Clensolar. But they are from eastern Germany. Great company with good prices.

Or Actensys, but they are from southern Germany...

user386dx schrieb:

Whether a storage system makes sense—opinions differ, and facts clearly show it does not.

“The others have an opinion, and I have facts.” Funny reasoning that reminds me of a departing head of state. I agree with this point: opinions do differ. This is due to the assumptions made about cycling frequency, degradation, consumption patterns, lifespan, etc. There are no absolute “facts,” only assumptions that can be debated extensively. There are plenty of examples proving both economic viability and non-viability of storage systems, as not every system with storage operates under the same conditions. A general statement is therefore – as is fashionable nowadays – overly simplified.

Sascha1977 schrieb:

Putting aside the aerated concrete debate, which I don’t want to start here. I know the endless discussions.

I’m a pacifist, so I wouldn’t want to take part in an aerated concrete war.
I always!!! hold the opinion that feeling comfortable in a house does NOT depend on nominal values, etc.
I lived very well and comfortably for 30 years in a normally built Poroton house; colleagues of mine in timber and aerated concrete were also satisfied. I’m out of the war_O
During the days between Christmas and New Year, quite a bit was calculated by the energy consultant, and it mostly depended on the building envelope. I pointed out here that it does NOT necessarily have to be a 42cm (17 inches) block, because we stick to 36.5cm (14.5 inches) in brick. Ultimately, adjustments were mainly made to the roof insulation (external insulation), floor slab, etc. until it worked. I don’t yet have details.
In my opinion, aerated concrete of the same thickness has lower values, which is why I assume—and wrote—that it might be difficult or hardly possible, so in the subjunctive. Above all, achieving the overall targets depends on many factors, and the statement “it only works with 42cm (17 inches) or more” is incorrect.

Sascha1977 schrieb:

That means I must be on the right track

Yep, but the energy consultant basically holds the bible for you. As I said, I only implement measures that I would have done anyway without the funding program.

hampshire schrieb:

A general statement is therefore—as is currently fashionable—very simplified.

Exactly. It applies to the block, the insulation system, etc. Everything must fit the project and—most importantly—fit ME!
Even if a battery storage system doesn’t make financial sense for me, I might still use it; I would enjoy using some of my own energy in the evening. And there’s also the often overlooked individual lifestyle.
I wouldn’t dismiss the rather derogatory description of the battery storage as a “gadget” across the board. If I rejected every “gadget,” every house would look different here and cost much less. Our houses and our lives often ARE so-called gadgets. A battery storage system certainly makes more sense than many features that simply don’t add any value financially. Still, you can have it if you want.

user386dx schrieb:

Battery storage systems are unprofitable.

Not wrong.
However, many things are equally unprofitable: cars, fancy items, houses, beauty products, choice of clothing, more than 4 forks and knives, a new smartphone... just everything. If you applied that standard to your life, you’d be standing there in a loincloth 🤨. The battery may bring back less than it costs in many cases, but it does bring something back. Your car burns money from day one, so in my opinion that is a blanket dismissal.
Life, in my opinion, consists of more than just calculations, which you can adjust according to your needs!
You are right—and at the same time, wrong.

hampshire schrieb:

We chose solar roof tiles from Autarq – of course, the design costs extra.

Hello, this is an in-roof system and therefore more expensive, more complex (cooling and underlay), with significant efficiency losses and last but not least: warranty issues.

Everything is understandable. We are actually not that far apart in our views. I don’t have to reach a specific value at all costs.

By the way, I’m still considering whether to use the above-mentioned wall construction or a 42.5cm (17 inches) aerated concrete block without external thermal insulation composite system (ETICS). Building monolithically does appeal to me... but right now, I really have no idea about the percentage increase in structural shell costs.

Since the general contractor (GC) exclusively works with aerated concrete, it will definitely remain that way for the block. I’ve simply had good experiences with this person. And that counts too...