ᐅ Photovoltaic System for a KfW 55 Semi-Detached House with Heat Pump: Tips on Storage and Orientation Choices
Created on: 4 Dec 2025 22:10
J
JAMO_HH
Hello everyone,
We have a semi-detached house (new build, KfW 55 standard) with a gable roof facing south-southeast/north-northwest and an electricity consumption of around 2,500 kWh household electricity (currently about 1,500, but our three children are still small...) plus 3,000 kWh for the heat pump. We don’t have an electric car at the moment, but possibly in the future. If it turns out to be cost-effective, we would like to install a photovoltaic system on the south-southeast side – only 11 modules fit there (possibly +1 on the dormer) because we have a dormer, window, and tree on that side, so roughly 5 kWp. I am a complete layperson on the subject, so we obtained four different quotes.
The first said: It does not pay off.
The second said: Definitely worth it, but he would also cover the north-northwest side with an additional approx. 6 kWp and install a battery plus cascade control for the heat pump – that would pay off. (Quote is about $17,000 for approx. 11 kWp; 25x Trina Vertex S+ + 8.76 kWh Sigen battery + 10 kW Sigen Energy Controller inverter) + additional recommendations: Stiebel Eltron ISG Connect for heat pump control using photovoltaic surplus + Sigen EnergyConnect HomePro.
The third said: It’s worthwhile, he would only cover the south-southeast side + battery (quote about $10,000, including 11x Trina Vertex S+ or AIKO Neostar 2S+ + 5 kWh Ecoflow PowerOcean battery + 8 kW PowerOcean hybrid inverter).
The fourth said: It’s worthwhile, he would only cover the south-southeast side but also the dormer and no battery, because that would not pay off – and definitely use German manufacturers, everything else is nonsense because no one is reachable in case of warranty issues (main consumption is in winter when the photovoltaic yield is very low). (Quote about $13,000, including 12x Solyco R-BG 108nBC.6 specially for partial shading + 10 kW Neeom Staak Eco inverter).
(The reason they all suggest somewhat larger inverters is that we might eventually cover a carport still to be built with modules if it makes sense.)
So, I have four completely different opinions on one thing where, given the same assumptions, one would expect similar conclusions and results... I am totally confused. My research as a layperson and my own payback calculations show that a battery is probably not profitable, so I would leave it out initially and possibly add it after 2 or 3 years when we know the exact yield and self-consumption. I also think that a photovoltaic system – if at all – would only somewhat pay off with the cheapest quote for 11 or 12 modules on the south-southeast side.
Am I completely off track or what do you think? I would especially be interested in which basic configuration you would recommend (with or without battery? covering the north-northwest side or not? using Stiebel Eltron ISG Connect or not? definitely German manufacturers or not?) or if it’s better to avoid it altogether?
Best regards and many thanks in advance for any advice, Jan
We have a semi-detached house (new build, KfW 55 standard) with a gable roof facing south-southeast/north-northwest and an electricity consumption of around 2,500 kWh household electricity (currently about 1,500, but our three children are still small...) plus 3,000 kWh for the heat pump. We don’t have an electric car at the moment, but possibly in the future. If it turns out to be cost-effective, we would like to install a photovoltaic system on the south-southeast side – only 11 modules fit there (possibly +1 on the dormer) because we have a dormer, window, and tree on that side, so roughly 5 kWp. I am a complete layperson on the subject, so we obtained four different quotes.
The first said: It does not pay off.
The second said: Definitely worth it, but he would also cover the north-northwest side with an additional approx. 6 kWp and install a battery plus cascade control for the heat pump – that would pay off. (Quote is about $17,000 for approx. 11 kWp; 25x Trina Vertex S+ + 8.76 kWh Sigen battery + 10 kW Sigen Energy Controller inverter) + additional recommendations: Stiebel Eltron ISG Connect for heat pump control using photovoltaic surplus + Sigen EnergyConnect HomePro.
The third said: It’s worthwhile, he would only cover the south-southeast side + battery (quote about $10,000, including 11x Trina Vertex S+ or AIKO Neostar 2S+ + 5 kWh Ecoflow PowerOcean battery + 8 kW PowerOcean hybrid inverter).
The fourth said: It’s worthwhile, he would only cover the south-southeast side but also the dormer and no battery, because that would not pay off – and definitely use German manufacturers, everything else is nonsense because no one is reachable in case of warranty issues (main consumption is in winter when the photovoltaic yield is very low). (Quote about $13,000, including 12x Solyco R-BG 108nBC.6 specially for partial shading + 10 kW Neeom Staak Eco inverter).
(The reason they all suggest somewhat larger inverters is that we might eventually cover a carport still to be built with modules if it makes sense.)
So, I have four completely different opinions on one thing where, given the same assumptions, one would expect similar conclusions and results... I am totally confused. My research as a layperson and my own payback calculations show that a battery is probably not profitable, so I would leave it out initially and possibly add it after 2 or 3 years when we know the exact yield and self-consumption. I also think that a photovoltaic system – if at all – would only somewhat pay off with the cheapest quote for 11 or 12 modules on the south-southeast side.
Am I completely off track or what do you think? I would especially be interested in which basic configuration you would recommend (with or without battery? covering the north-northwest side or not? using Stiebel Eltron ISG Connect or not? definitely German manufacturers or not?) or if it’s better to avoid it altogether?
Best regards and many thanks in advance for any advice, Jan
In November, we still produced nearly 600 kWh, and with a 12 kWh battery, we used 86% of that ourselves, including charging losses.
However, we have a hipped roof with solar panels installed on the north side as well, totaling 14 kWp. I'm surprised how much electricity the roof generates even though it’s just daytime.
We also have a high electricity consumption due to a heat pump, about 8,000 kWh per year. The house includes a granny flat and six people live there. Because of this, the system will probably pay off after about seven years.
I would always install panels on the north side. However, I paid less than 1,000 euros per kWp, including assembly and installation. I bought everything myself and found the electrician and installation company. When I see what some companies charge for the components.
However, we have a hipped roof with solar panels installed on the north side as well, totaling 14 kWp. I'm surprised how much electricity the roof generates even though it’s just daytime.
We also have a high electricity consumption due to a heat pump, about 8,000 kWh per year. The house includes a granny flat and six people live there. Because of this, the system will probably pay off after about seven years.
I would always install panels on the north side. However, I paid less than 1,000 euros per kWp, including assembly and installation. I bought everything myself and found the electrician and installation company. When I see what some companies charge for the components.
tomtom79 schrieb:
In November, we still managed to produce nearly 600 kWh, and with a 12 kWh battery, we used 86% of that ourselves, including charging losses.
We have a hipped roof, and the north side is also equipped, totaling 14 kWp. I’m surprised by how much electricity comes from the roof even though it’s only autumn.
You must have had extremely good weather and be located far south?
I have a similarly sized system with panels on all four sides and only generated 360 kWh, which is actually slightly above the expected values for November.
You can easily calculate this yourself. You can find out how many kWh per kWp you can generate in the north using PVGIS. Then you compare that with the costs. If you install it yourself and only pay a few hundred € per kWp, it makes sense to do it; but if the installer charges 1000 € per kWh, then it doesn’t.
Musketier schrieb:
You had extremely good weather and are quite far south, right?
With a similarly large system and 4-sided shading, I only got 360 kWh of output and am slightly above the projected values for November. Well, we are at about 500 meters (1,640 feet) altitude, and November usually has a lot of fog, but the days without fog were great for photovoltaic production.
November will still reach about 440 kWh.
Yesterday I overheard a conversation: "Yes, we now have a heat pump, and soon there will be a photovoltaic system producing the electricity for it," well, if only.
Even with the 12 kW battery, I can’t make it through the night.
Filling the hot water storage once uses 3–4 kWh, but that happens twice a day. I tried optimizing the lockout times and circulation, but since we shower irregularly, it ran cold even with a smaller hysteresis.
Only the lockout time for the heating works, but then it switches on at 8 a.m. when it’s foggy outside—so I left everything as is and just enjoy the comfort.
What helps a lot is scheduling laundry and dishwasher runs during the day.
@gerald dc Installation costs per kWp currently range between 150 and 200 euros.
Electricians for the AC connection are now available for under 2,000 euros, including registration and installation.
All with invoices.
A few days ago at Solarhandel24, a 15 kWp system with Huawei and Trina storage was priced at 6,000 euros plus mounting rails, so roughly 7,500 euros total. That means around 11,000–12,000 euros for everything. If you do some of the work yourself, you can get under 10,000 euros.
tomtom79 schrieb:
@gerald dc installation cost per kWp is currently between 150 and 200 eurosI believe this depends a lot on the location. Here, the low material prices have not really become common knowledge yet, and prices continue to be very high. I'm glad that my electrician handles the connections for the new build at his regular hourly rate, so I can rely on that.
Similar topics