Passive house vs low-energy house / photovoltaics

Hello dear people,

I have just spent a long time browsing this forum because I am also going to build a house this year and have been looking here for tips to find answers to my questions. Some things have already become clear to me, but others have not, so I decided to write a post after all. Our plan is for a single-family house (detached house) for five people (parents + 3 children) with approximately 150-170 m2. I have already renovated some houses, but have never built one.

[*]We definitely want to build a low-energy house and the reason is clear – we want to save heating and energy costs. At the beginning of our planning, a passive house seemed like the ideal solution, but after further research, we concluded that might be overdoing it – maybe a "normal" low-energy house that is well insulated would be enough? Do you perhaps have experience with that? What I keep wondering – don’t these passive houses with their glass south-facing walls turn into greenhouses in summer?
[*]We would also like to install photovoltaic systems on the roof, but we found two different solutions: for the hot water boiler or for electricity generation. The latter would of course be ideal, but I also ask for practical experiences here – is it worth it and can photovoltaic systems produce enough electricity (also for winter)?
[*]Following on from that – are heat pumps recommended and do they work everywhere, or do certain geothermal prerequisites have to be met?
[*]Can ventilation systems with heat recovery also be installed in normal low-energy houses and is it worth it?
[*]I have read in several places that it is cheaper (both for building and later for living) to do without a basement and additional floors, and instead plan a single-story ground floor building if the plot allows. Would you confirm that?

Basically, we would like to avoid gas and coal (on the one hand for cost reasons, on the other hand to protect the environment), but we do not know whether that is practically possible. We live in the north, where it often gets colder (although not this winter).

I would be happy to receive answers and tips.
Best regards

1. You have to weigh up; every cm of insulation more and other measures cost money that might never be saved. In other words, you have to find the golden mean for yourself.

2. Solar thermal is only worthwhile if you can get it cheaply on the roof. So basically, rather rare. Photovoltaics are more likely. But of course, you have little to no yield in winter. There are experts in the forum who can definitely help you.

3. Depending on the energy source you use for your heat pump, which can be, for example, air, water, earth, etc., it must be clarified with the municipality whether it is allowed or not. Air works everywhere but usually has the lowest yield.

4. Controlled residential ventilation systems can be installed in any type of house and always provide fresh air. You should actually do this. Worthwhile in terms of energy savings and monetary value? No, it’s not really worth it. However, a controlled residential ventilation system is an enormous comfort gain and saves you time that you can use elsewhere.

5. Basements are always more expensive than an upper floor, going wider as well. So basically, a simple 1.5-story house on a slab foundation is the cheapest you can have if you want something a bit bigger.

Solar energy for hot water = Solar thermal — Not worth it.

Solar energy for electricity = Photovoltaics — Still worth it.

But in winter you will have a hard time covering even the basic electricity demand. Storage is not worth it — they are too small in summer and too large in winter.

You still lack a lot of basic knowledge, you can tell. Read up more. I think a KFW40 or KFW40 Plus would probably be quite suitable for you.

Forget about solar thermal. It doesn't make much sense. Plan a photovoltaic system for electricity generation. And if possible, try to orient your house accordingly. So roof pitch towards east and west. No chimney (you don't need one in a low-energy house with a heat pump anyway). If possible, no skylights. Use the entire roof area. That way you can put together a system that can reach about 20 kWp. And THEN in winter you’ll get a good amount of electricity. I produced 678 kWh in January with my 24.5 kWp system. If you plan and set the heat pump properly, you can thus generate a significant part of the electricity for the heat pump yourself. And that actually in one of the worst months of the year.

Especially in new construction you can plan properly from the start and align everything optimally etc.
And then it’s worth it, even though the opposite is often claimed.
Of course, I won’t be able to cover the entire electricity demand of the heat pump. But in the "transition months" that could work, and in the really cold months (Dec, Jan, Feb) you can still cover a significant part.

Oh, and about the storage. Actually, it’s not worth it... BUT if I get a subsidy of 6,000,- through the KFW funding, then it’s worth it!

maybe a "normal" low-energy house that is well insulated is enough?

That is every new building today. Whether I have 20€ or 30€ monthly heating costs basically does not matter.

is it worthwhile and can photovoltaic systems produce enough electricity (also for winter)?

They can, but not in winter. In my opinion, always do photovoltaic, solar thermal only if there is no other option (it produces a lot of hot water in summer - when it is not needed - and in winter not due to lack of sun).

Are heat pumps recommended and do they work everywhere or do certain geothermal prerequisites have to be met?

Yes. Geothermal prerequisites only apply for drilling. However, there are also air-to-air heat pumps and air-to-water heat pumps.

Can ventilation systems with heat recovery also be installed in normal low-energy houses and is it worth it?

Not can, but should.

Don’t these passive houses with their glass south-facing walls turn into greenhouses in summer?

This "problem" occurs with every new building. Not only insulation but also shading is part of house planning.

to do without basements and upper floors, but instead (if the plot allows) to plan an extensive single-story building. Would you confirm that?

Basement = expensive. Useful, for example, on slopes or small plots. Bungalow = expensive, due to high land consumption as well as higher building costs per sqm (unfavorable building shape).

Basically, we would like to do without gas and coal (partly for cost reasons, partly to protect the environment), but don’t know if that is practically possible. We live in the north, where it often also gets colder (although not this winter).

You will always use coal if you don’t have gas. It is at least part of the electricity mix. And yes, a heat pump works basically all over Germany. Read up more and feel free to ask questions. You still need more basic knowledge.

Thank you very much for your expert answers! I am aware that I still lack a lot of knowledge, otherwise it would not have been necessary for me to write a post here.

However, we are now quite sure that we want to build a low-energy house (not a passive house) with an energy consumption of a maximum of 50 kWh/m². The passive house seems a bit too risky and expensive to us.

Regarding the photovoltaic system, I am still uncertain because I have seen many pros and cons online. I am building the house first, so I can orient it as I like; I thought it would be best to orient the house to the south, but here you are writing about an east-west orientation?

The more you dig into the subject, however, the more questions arise – and that already starts with the foundation (slab?), the exterior walls (single-, double- or triple-layer?) and their materials (aerated concrete vs hollow brick) or the type of thermal insulation (styrofoam or wool). There are many questions, so I am grateful for experience-based knowledge!