How many kW does a home need: a guide to solar PV sizing

How many kW are really needed for an 80, 100, or 150 sqm house?
If you're thinking of installing a home solar system, this is the first question to ask yourself. Proper sizing allows you to avoid waste, save on your electricity bill, and recoup your investment faster.

Conversely, a system that's too small risks not covering your actual consumption, while one that's too large incurs excessive initial costs and longer payback periods.

In this guide, we'll cover:

• the average consumption of an Italian family,
• how to estimate your home's energy needs,
• practical examples of kW needed based on square footage,
• how to choose the ideal power for your solar system,
• what to do if you don't have a suitable roof.

Average Consumption of an Italian Family

A good starting point is to look at the official data fromARERA, the Italian Regulatory Authority for Energy, Networks and Environment.

According to 2023 data:

• A typical family of 2-3 people consumes on average 2,700-2,900 kWh per year,
• with a contracted power of 3 kW.

These values are calculated based on utility bills and provide a reliable snapshot of average Italian consumption. Of course, this is a reference figure: your actual consumption depends on many factors, such as the size of your home, the number of occupants, and the type of appliances used.

How to estimate your home's energy needs

To understand more precisely how many kW your home needs, it's helpful to consider three key variables.

1. Number of people in the household

More occupants mean higher consumption:

• more washing machines and dishwashers,
• more hot showers and hair dryers,
• more electronic devices in use simultaneously.

2. Appliances and usage habits

• Appliances of older generation consume much more than modern models in class A or higher.
• If you frequently use induction hobs, heat pumps, or electric water heaters, your consumption will quickly increase.
• The time of day also matters: consuming during the day allows for better utilization of solar energy.

3. Home thermal insulation

A well-insulated home reduces the need for air conditioners and heat pumps, lowering overall electricity demand.

Practical examples: how many kW are needed for 80, 100, and 150 sqm homes

The size of the home affects energy requirements, especially for lighting, air conditioning, and heating. Here are three reference scenarios for a family of 3 people:

• 80 sqm home
  Average consumption: approximately 3 kW of committed power, sufficient for common household appliances.
• 100 sqm home
  Average consumption: approximately 4.5 kW, also considering high-consumption appliances like electric ovens and air conditioners.
• 150 sqm home
  Average consumption: approximately 6 kW, suitable for managing more energy-intensive appliances and a higher demand for air conditioning and heating.

👉 Please note: these are indicative values. For an accurate estimate, I recommend checking your bills and calculating your annual consumption in kWh, which is an essential basis for sizing your photovoltaic system.

How to choose the power of your photovoltaic system

Once your home's energy consumption has been estimated, you can assess the ideal system size.

• If you choose an undersized, you risk not covering your energy needs and reducing potential savings.
• If you opt for an oversized, you'll spend more on purchase and installation, leading to longer payback periods.

Practical tip

The correct sizing should cover at least 70-80% of your annual consumption.
For example:

• for a family consuming 4,500 kWh/year, a system of approximately 4.5-5 kWp is adequate.

A good installer will perform a precise simulation, taking into account not only the square footage and consumption, but also:

• roof exposure and inclination,
• geographical location,
• possibility of installing storage batteries.

And what if you can't install a photovoltaic system?

It may happen that, due to technical or architectural constraints, it's not possible to install panels on your roof.

In this case, you're not excluded from the benefits of solar energy: you can participate in shared solar farm projects or renewable energy communities.

A practical example: agrivoltaics

Some innovative projects, such as those developed by GridShare in Italy, combine solar power generation with agricultural land use (agrivoltaics).
This model allows for the following:

• generating green energy without taking up space for crops,
• making solar power accessible even to those without a roof,
• contributing to the democratization of renewable energy.

Conclusion

Understanding how many kW a home needs is the first step in properly sizing a solar PV system.

• The average Italian figure is about 2,700-2,900 kWh per year for families of 2-3 people.
• The required power varies depending on square footage, number of occupants, appliances, and home insulation.
• Practical examples show that approximately 3 kW are needed for 80 square meters, 4.5 kW for 100 square meters and 6 kW for 150 square meters.

With this information, you can better navigate quotes and simulations, avoiding costly errors. Whether you install panels on your roof or participate in a shared energy project, solar PV remains one of the most tangible solutions for reducing energy costs and contributing to the transition to a future Green.