Hi,
my photovoltaic system planning is likely going to end up at around 38 kWp (kilowatt-peak). The pitched roof will be fully covered on the south and north sides.
My main concern is that I was told (in the relevant forum) that the inverters get quite warm and that I shouldn’t install them in the utility room. We don’t have a basement, and our utility room is about 8.3 m² (90 sq ft). It will be a KfW 40 energy-efficient house. The garage is on the opposite side of the property and is planned to be built later, not directly connected to the house. A carport is planned directly adjacent to the utility room. Currently, I would probably try to install the inverters there. We will have two inverters because of the system size and string configuration. However, our house manufacturer uses a very light plaster, and the inverters are too heavy to mount directly on it. So I would need to mention this during the final selections and have wooden beams installed under the plaster, which would be expensive. Alternatively, I could somehow mount them on the carport itself, but I don’t want to significantly reduce the driveway width since it’s already quite narrow. I could also take the risk and install the inverters in the utility room after all. However, I have heard of cases where temperatures of 40°C (104°F) were reached there. Some people use fans to get rid of the heat. In our KfW 40 house, that probably wouldn’t even be allowed.
I can hardly find any information about this online. Some people report no problems even with 2 m² (22 sq ft) utility rooms; others have temperatures around 30°C (86°F). There is never information about the type of houses, and some posts are up to 10 years old. We are building a 103 m² (1,109 sq ft) bungalow for two people, with an Alpha Innotec Hybrox 5 (70 m² to 150 m²) air-to-water heat pump and a decentralized ventilation system.
Has anyone here had experience with inverter heat? How would you approach this issue? The battery storage obviously has to go in the utility room; it can’t be installed elsewhere.
my photovoltaic system planning is likely going to end up at around 38 kWp (kilowatt-peak). The pitched roof will be fully covered on the south and north sides.
My main concern is that I was told (in the relevant forum) that the inverters get quite warm and that I shouldn’t install them in the utility room. We don’t have a basement, and our utility room is about 8.3 m² (90 sq ft). It will be a KfW 40 energy-efficient house. The garage is on the opposite side of the property and is planned to be built later, not directly connected to the house. A carport is planned directly adjacent to the utility room. Currently, I would probably try to install the inverters there. We will have two inverters because of the system size and string configuration. However, our house manufacturer uses a very light plaster, and the inverters are too heavy to mount directly on it. So I would need to mention this during the final selections and have wooden beams installed under the plaster, which would be expensive. Alternatively, I could somehow mount them on the carport itself, but I don’t want to significantly reduce the driveway width since it’s already quite narrow. I could also take the risk and install the inverters in the utility room after all. However, I have heard of cases where temperatures of 40°C (104°F) were reached there. Some people use fans to get rid of the heat. In our KfW 40 house, that probably wouldn’t even be allowed.
I can hardly find any information about this online. Some people report no problems even with 2 m² (22 sq ft) utility rooms; others have temperatures around 30°C (86°F). There is never information about the type of houses, and some posts are up to 10 years old. We are building a 103 m² (1,109 sq ft) bungalow for two people, with an Alpha Innotec Hybrox 5 (70 m² to 150 m²) air-to-water heat pump and a decentralized ventilation system.
Has anyone here had experience with inverter heat? How would you approach this issue? The battery storage obviously has to go in the utility room; it can’t be installed elsewhere.
At some schools around here, the inverters are installed outdoors, often without full weather protection. That doesn't seem to be a problem.
However, my inverter is very loud. It’s not an issue in the technical room in the basement, but if it were mounted outside, it would be more of a nuisance than the heat pump.
The noise is also complementary (when it’s light and warm) to the heat pumps (when it’s cold and dark outside)...
I would pay close attention to this, especially if it’s a larger unit.
However, my inverter is very loud. It’s not an issue in the technical room in the basement, but if it were mounted outside, it would be more of a nuisance than the heat pump.
The noise is also complementary (when it’s light and warm) to the heat pumps (when it’s cold and dark outside)...
I would pay close attention to this, especially if it’s a larger unit.
N
nordanney3 Jun 2025 18:30Bierwächter schrieb:
At first, I was thinking maybe just 5-7 kWh (5-7 kWh).Why? Why not go directly for 25 kWh (25 kWh)? It’s not much more expensive, especially if you’re doing everything yourself.W
wiltshire3 Jun 2025 18:38Bierwächter schrieb:
Has anyone here had experience with heat from the inverter? How would you approach this issue? The battery storage obviously has to be in the utility room; it cannot be placed outside.At full capacity, inverters always generate some heat, but the amount can vary significantly depending on the device type and sizing. With two inverters and a total of 38 kWP, you can expect a noticeable amount of heat output that will warm the utility room. A reasonable estimate based on slightly over 2% electrical efficiency loss at full load suggests a heat output of about 1 kW. To put this into context: this is enough to keep a 40 sqm (430 sq ft) room in a KfW40-standard house at 20°C (68°F) when the outside temperature is 0°C (32°F).
Many inverters are rated IP67 and can easily be installed outdoors. However, I would still recommend providing a small roof or cover to protect them from direct sunlight and rain. Whether you mount them on the house wall or on a separate frame to avoid altering the building is not particularly important.
If combined with an AC-coupled storage system, I would prefer outdoor installation.
M
MachsSelbst3 Jun 2025 18:59No, there is no significant fluctuation. Modern inverters have efficiency rates between 96 and 98%. Period.
That means with a 38kWp system and a deliberately high-quality inverter, you’re looking at 0.7–1.1 kW. And that heat will definitely be produced, because it’s unavoidable.
By the way, the losses in an inverter don’t scale directly with power output, since switching losses play the main role.
So it’s best not to overthink it and just install it outside. Where should the problem be? Wall chargers, outdoor sockets, submersible pumps… electrical devices can be made waterproof. IP67 or, if necessary, even IP69.
That means with a 38kWp system and a deliberately high-quality inverter, you’re looking at 0.7–1.1 kW. And that heat will definitely be produced, because it’s unavoidable.
By the way, the losses in an inverter don’t scale directly with power output, since switching losses play the main role.
So it’s best not to overthink it and just install it outside. Where should the problem be? Wall chargers, outdoor sockets, submersible pumps… electrical devices can be made waterproof. IP67 or, if necessary, even IP69.
W
wiltshire3 Jun 2025 19:38MachsSelbst schrieb:
No, there’s no significant fluctuation. Modern inverters have efficiencies between 96% and 98%. Period.The inverter with 96% efficiency delivers 100% more heating output than the inverter with 98% efficiency. And you’re talking about no fluctuation?Bierwächter schrieb:
Can you maybe share a bit more about that? Room size? Ventilation system? KfW40? Domestic hot water heat pump installed? Those remove heat from the room.Sure: 13 square meters in the basement
Insulation meets KfW40 standard
Controlled mechanical ventilation installed
No domestic hot water heat pump
I checked today when about 20 kW system output was running. Slightly warmer than hand temperature. The inverter is a SolarEdge SE25K-RW00IBNM4, operated with SolarEdge power optimizers (if that’s relevant…).
According to the manufacturer, the efficiency is a “unique” 98.3%.
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