ᐅ Photovoltaic System: How Many kWp Are Sufficient for a House?

Hello everyone!

We are building a semi-detached house and want to install a photovoltaic system on the roof. The orientation would be south/west and north/east. We intend to use most of the electricity ourselves. A battery is not planned, as the cost is quite high for such a system and it probably doesn’t make financial sense.

We have received an offer that includes:

- 14x IBC MonoSol 360 (there is still space on the north/east side... does that make sense?)
- SMA SB 3.6-1AV-40 inverter
- DEHNcube YPV SCI 2MPP surge protection device
- Meter cabinet (+ accessories)
- Installation

The price is about 7,500€ gross.

The system will have a capacity of 5.04 kWp.

Currently, there are three people living in the house (2 adults, 1 child). Four are planned.

Our roof is quite simple but well oriented.
We are wondering if 5.04 kWp is sufficient?

Our electricity consumption in the apartment was always below 3,500 kWh per year, but we expect it to increase with the house. We estimate about 4,500 kWh.

Regarding the 24/7 electrical loads:
There will be an air-to-water heat pump from Novelan and a ventilation system with heat recovery.

I would really appreciate some advice.

lin0r87 schrieb:

We are wondering if 5.04 kWp is sufficient?

Sufficient for what exactly?
To generate the same amount of electricity as your household consumes? - No.

Search for PVGIS online, and you can estimate the expected output of your system. Roughly speaking, if it is oriented south and unshaded, you can expect about 900–1000 kWh per kWp of installed capacity per year. Approximately.
If your expected household electricity consumption is 4500 kWh, add roughly 3000 kWh for the heat pump.

Your quote is somewhat acceptable but tends toward being expensive.
The question is, in a new build, what exactly the solar installer plans to do at the meter cabinet or what is meant by that position.

Whether placing panels facing north/east makes sense can be clarified by the professionals on site. The rules for string configurations aren’t my specialty, but with 5 panels of 360 W on the north side, you won’t get much output, and the string might even fail. But the experts there will know much better.

lin0r87 schrieb:

We are wondering if 5.04 kWp is sufficient?

With that, you will still generate much more electricity than you need in the summer. In winter, far too little. A battery won’t help with that either. But this is the case with almost every system, no matter the size. Tip: photovoltaic, as guckuck2 suggested.

The system should be as large as possible (and, of course, sensible regarding northeast orientation).
It’s not just about your electricity; it’s about the global energy transition. Financially, it should be worthwhile for you (based on the current situation).
This can’t be conveyed quickly here.

The costs are way too high for such a small setup.
Fill the roof completely (as far as it makes sense).
The environment and your wallet will thank you.

Whether this is sufficient cannot be answered without more detailed information, which you have not provided.

- House size?
- Basement yes or no?
- Electric vehicle planned in the next few years?
- Main energy consumers?
- When are you at home?
- Your specific requirements for the system?

You can most likely forget about the 4,500 kWh per year if you have over 140 sqm (1,500 sq ft) of living space without a basement, especially if you already use 3,500 kWh in an apartment. However, this is just my personal opinion without detailed information. Currently, since July 21, I have a meter installed and a photovoltaic system of 8.7 kWp plus an electric vehicle, with a grid consumption of 5,171 kWh for 140 sqm (1,500 sq ft) plus a 70 sqm (750 sq ft) basement (heated for one month).
My estimate for 12 months is around 7,500 kWh.

My consumption:
150 m² (1600 sq ft) without basement, no electric car, air-to-water heat pump installed indoors, 4 people. Window ventilation. Building envelope KfW 40, no controlled residential ventilation.
Move-in date 08.08.19.
Meter reading yesterday 2619 kWh for everything.
It shows that electricity consumption is very individual to assess.