Photovoltaics: how many kWp do I need?
Decided to install a solar power plant (SPP) — great! But what capacity should you choose? What are kW, kWp, and kWh? How to account for an electric vehicle and a heat pump? We answer all these questions in one article.
As soon as you decide to install solar panels, a whole range of new questions immediately arises: what is an inverter, do you need an energy storage system, do you plan to buy an electric car in the future — and what does all this mean for the size of the system? How many kWp does your specific house need?
First, let's sort out abbreviations like "kW" and "kWp" and find out how they relate to power consumption in your home. And then — a few practical tips on calculating your own needs and the number of solar panels on the roof.
Basics: kW, kWp, and kWh — what's the difference?
"The abbreviation 'kW' is a common unit of power. It stands for 'kilowatt' and is familiar to anyone who uses the power grid."
How many kWh per year does your home consume?
The number of kilowatt-hours a household consumes per year depends on many factors. The most obvious one: more people — more electricity.
"Individual electricity consumption in kWh can vary significantly depending on who lives in the house: only working people, or if there is also electric vehicle charging or the use of a heat pump — the situation significantly affects the result."
If you want to know your exact consumption, check the latest annual bill from your electricity supplier. A rough estimate can be made based solely on the number of residents. A one-person household consumes about 1,500 kWh per year, while a family of 4 consumes over 3,500 kWh.
| Number of residents | Average annual consumption |
|---|---|
| 1 person | ~1,500–2,000 kWh |
| 2 people | ~2,000–2,800 kWh |
| 3 people | ~2,800–3,500 kWh |
| 4 people | ~3,500–4,500 kWh |
| 5 people | ~4,500–5,500 kWh |
With this basic data, you can determine the size of the SPP based on a general rule: 1 kWp of the system generates about 1,000 kWh per year.
Electric vehicle, heat pump, and air conditioner: how to account for additional loads
The figures above do not include heat pumps, air conditioning systems, or electric vehicles. However, they are some of the most energy-intensive consumers in the house.
Electric vehicle
An average electric vehicle with a mileage of 13,000 km/year consumes about 2,000 kWh.
+ 2 kWp to the systemHeat pump
For a 120 m² house, the annual electricity consumption is about 2,400–4,300 kWh.
+ 3.5 kWp on averageAir conditioner
With 300 hours of operation, the system consumes about 1,500 kWh per year.
+ 1.5 kWp on average
How many solar panels do you need?
Now that you roughly know your annual consumption — how many panels will you need? This primarily depends on the power of the selected modules.
Table: kWp → number of modules
Below is the estimated number of modules depending on the desired system capacity (based on ~400 W per module).
The exact number depends on the manufacturer and model of the panels.
| System capacity | Number of modules (≈) |
|---|---|
| 3 kWp | 8 |
| 5 kWp | 13 |
| 10 kWp | 25 |
| 15 kWp | 38 |
How much roof area is needed?
One solar panel takes up about 1.7 m², meaning that for each kWp of power, you need approximately 5 m² of roof space.
In short
"kWp" is the maximum power of a photovoltaic system. Plan to add 1 kWp for every 1,000 kWh of annual consumption. Before buying, ask yourself: are you planning for an electric vehicle or a heat pump? For such loads, add 2–3.5 kWp to the system size.
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