What surface of solar panel for 3 kWp?

Are you looking for an economical and ecological solution to reduce your electricity bills while helping to protect our planet? You're not alone! More and more French households are opting to install photovoltaic panels on their roofs, and with good reason: this solution enables you to make considerable savings over the long term, while doing your bit for the environment.

If you are considering installing a small-scale 3 kWp plant, you may be wondering how much roof space you will need to dedicate to the project, and how much production you can expect in return. 

In this detailed guide, we give you all the information you need to determine the surface area of solar panels required for 3 kWp, as well as the ideal power for your project.

How much roof area should I mobilize to install 3 kWp of solar panels?

Is the roof of your home large enough to accommodate the surface area of solar panels needed to produce 3 kWp? This is the question you will have to ask yourself before moving forward with your photovoltaic project.

The amount of roof space required depends on two major factors: 

  • The unit area of the solar panels envisaged for your photovoltaic installation;
  • The unit peak power in Wp (peak Watts).

Recall that the Watt peak (Wp) is a unit of measurement used to describe the power rating of an individual solar photovoltaic panel or module. Like the kilowatt-peak (1 kWp = 1,000 Wp), the Watt-peak represents the maximum power that the solar panel can produce under ideal (and therefore theoretical) conditions.

Ideal sunlight conditions are generally defined as a solar irradiance of 1000 watts per square meter (W/m²) and a solar cell temperature of 25°C. Under these conditions, the solar panel produces its maximum power, expressed in peak watts. 

How many square meters is the average solar panel?

The type of cells used, the manufacturer, the power output... these variables all determine the size of the solar panels. The standard size is generally between 1.6 and 1.8 meters in length and 0.9 to 1.0 meters in width, with a thickness of between 30 and 50 mm. In terms of surface area, this is equivalent on average to 1.6 to 1.8 m².

What is the average power of a solar panel?

Again, many factors come into play, but the power of a standard solar panel is between 100 Wp and 400 Wp. To determine the number of solar panels required to reach a target power (3 kWp or 3,000 Wp in our case), simply divide this target power by the unit power.

Let's take an example If you are considering solar panels with a power of 250 Wp, you will need 12 panels to reach a total power of 3 kWp (250 x 12 = 3,000 Wp). If you choose panels with a power of 300 Wp, you will need to install 10 photovoltaic panels to obtain an installation of 3 kWp.

In short, the higher the individual power of each solar panel, the fewer modules you will need to reach the desired power. With the same dimensions, you can reduce the space required on your roof.

Here is a summary table showing different types of solar panels, their power and the number of panels to be installed to obtain 3 kWp:

Solar panel technologyBenefitsPanel power (Wp)Number of panels for 3 kWp
MonocrystallineHigh energy efficiency, better performance in limited spaces300 Wp10
PolycrystallineGood compromise between efficiency and cost, suitable for various conditions270 Wp12
AmorphousLower cost, flexible, works well in low light conditions150 Wp20

Power of 3 kWp: what surface of photovoltaic panel for my house?

After determining the number of solar panels required for your 3 kWp photovoltaic installation, it is time to calculate the total area needed to accommodate these panels. To do this, simply multiply the number of solar panels by the area of each panel in m² :

Total area (m²) = Number of solar panels × Unit area per panel (m²)

Let's take, for example, a unit area of 1.8 m² per panel (to be conservative). We would then obtain the following results:

  • 14,4 m² of total surface for 8 solar panels of 250 Wp each;
  • 16,2 m² for a total surface of 9 solar panels of 200 Wp each.

With this simple calculation method, you can easily determine the roof area needed to install 3 kWp of solar panels on your home. Attention Allow for safety margins for the installers (about 50 cm at the end of the roof).

How to convert 1 kWp into m² of solar panels?

To convert the power in kWp to m² of solar panels, simply divide the desired power by the maximum power per m² of the chosen technology. For example, if you want to install monocrystalline solar panels of 3 kWp, and the maximum power of these panels is 200 Wp/m², you will need :

3 000 Wp / 200 Wp/m² = 15 m² of monocrystalline solar panels

Photovoltaic installation: what is the maximum weight your roof can support?

The weight of solar panels can vary depending on the technology and the manufacturer. In general, the weight of a standard photovoltaic panel is about 15 to 20 kg/m² (not including the steel pan for waterproofing). If you include the tray, you can expect a weight of 20 to 25 kg/m².

For a 3 kWp installation, it is important to verify that your roof structure can support the additional weight of the solar panels. Only a professional will be able to estimate with a satisfactory accuracy the load-bearing capacity of your roof, taking into account the slope, the structure of the framework, the type of coating, etc. 

In case your roof cannot accommodate enough solar panels for the desired power (which can be the case with zinc, thatch, shingle or tar roofs), we will propose you an installation adapted to the ground. 

Why should I choose to mobilize up to 3 kWp for my solar installation?

A 3 kWp installation has several advantages, including:

  • An energy production capacity adapted to the needs of a small to medium household;
  • Relatively affordable installation cost;
  • The possibility of benefiting from various financial aids and incentives from the State and local authorities for installations of this size.

What can be powered with a 3,000 Wp solar panel surface?

With a 3 kWp solar system, it is possible to supply a large portion of the energy needs of a "standard" household, including lighting, appliances, heating and cooling. The exact capacity will depend on the actual output of the solar panels, which will vary depending on the amount of sunlight, the orientation and tilt of the panels, and the efficiency of the system.

If you drive an electric car, have a heat pump or a heated swimming pool, you will have to opt for a power higher than 3 kWp. Do not neglect the sizing stage: it conditions the profitability of your project!

What is the production capacity in kWh of 3 kWp of solar panels?

The production capacity in kWh of a 3 kWp solar installation depends on local conditions, such as sunshine and losses due to orientation, tilt and temperature. To estimate the annual production, the following formula can be used:

Annual_production (kWh) = Annual_sunshine (h) × (1 - Degressive_Rate) × Maximum_power (kWp)

The degradation rate is a percentage that represents the decrease in efficiency and energy production of a solar panel, according to the shading and temperature variations (it is generally estimated at 10 %). Considering an annual sunshine of 1500 hours and a degradation rate of 10 %, the annual production of a 3 kWp solar installation would be :

Annual production = 1500 h × (1 - 0.1) × 3 kWp = 4050 kWh

How much does it cost to install 3 kWp solar panels?

The price of a 3 kWp solar installation varies depending on the technology of the panels, the manufacturer, the quality of the components and the installation price. Count on average between 6,000 and 10,000 €, before taking into account the financial aid and incentives available.

What kind of state aid is available for 3 kWp of solar panel surface?

By opting for a 3 kWp plant, you can benefit from state aid to reduce your initial investment. Let's take a closer look.

#1 Bonus for self-consumption up to 3 kWp

The self-consumption premium is a financial aid granted to individuals who wish to install solar panels to produce their own electricity. This premium is increased for installations with a power less than or equal to 3 kWp. 

The amount of the self-consumption premium varies every quarter, depending on the number of connections made. Its amount has also changed since the beginning of 2022, taking into account an indexation coefficient "Kn". Thus, between February 1 and April 30, 2023, the amount of the self-consumption premium for a photovoltaic installation with a power less than or equal to 3 kWp is 500 € / kWp, or 1,500 € maximum.

#2 Sale of surplus: a higher feed-in tariff below 9 kWp

When you install solar panels to produce electricity, it is possible that your installation generates more energy than you consume. In this case, the excess energy produced can be sold back to the electricity grid by signing an OA Solaire contract, or feed-in tariff contract, with your approved operator (EDF OA or a local distribution company - LDC). With a 20-year term, this contract allows you to amortize the cost of your solar panels over the long term.

Photovoltaic installations of less than 9 kWp benefit from a feed-in tariff of 0.1 € / kWh. This rate increases to 0.06 € / kWh for installations of more than 9 kWp. Attention: the resale price varies quite regularly. 

By opting for a photovoltaic installation with a power of 3 kWp or less, you can save up to 70 % on your electricity bill. 

#3 The reduced VAT for surfaces of less than 3 kWp

Solar installations with a power less than or equal to 3 kWp benefit from a reduced VAT rate of 10 %, instead of the normal rate of 20 % that applies to installations above this peak power. 

This reduction applies to the purchase of equipment and installation work, which reduces the total cost of the project.

#4 Local Government Assistance

Some local authorities offer financial assistance to encourage the installation of solar panels. This assistance can take the form of grants, interest-free loans or tax breaks. Do not hesitate to contact your local authority to find out what is available.

#5 Photovoltaic taxation: a tax exemption up to 3 kWp

The income generated by the production of solar electricity is exempt from income tax when the power of the installation is less than or equal to 3 kWp. This exemption applies to both self-consumption and the sale of surplus electricity.

Which panel surface for a 3kWp installation: what you should know

In summary, a 3 kWp solar installation requires a variable roof area depending on the technology of the solar panels and their energy efficiency. On average, it takes between 15 and 20 m² of roof area to install 3 kWp of solar panels. This size of installation has several advantages, including a production capacity adapted to the needs of an average household, an affordable cost and the possibility of benefiting from various financial aid.

To estimate the production in kWh of a 3 kWp installation, it is necessary to take into account the sunshine and the losses related to orientation, inclination and temperature. Finally, it is important to verify that the roof structure can support the weight of the solar panels and to consult a professional for an accurate evaluation of the needs and costs associated with the installation.

Frequently asked questions (FAQ)

What is the production for a 3 kWp photovoltaic installation?

Generally, it is estimated that a 3 kWp photovoltaic installation produces around 4,000 kWh of electricity per year. 

How many solar panels for 9 kWp?

The number of solar panels needed to reach 9 kWp depends on the unit power of the panels. For example, you will need 24 solar panels of 375 kWp each to reach a total power of 9 kWp. 

What is the lifetime of a 3 kWp photovoltaic installation?

The lifetime of a photovoltaic system depends on the quality of the solar panels and their maintenance. In general, the average lifespan of a photovoltaic system is 25 to 30 years. However, the performance of solar panels will inevitably decrease over time, and it is possible that their efficiency will drop to 80 % of their initial capacity after 20 to 25 years.