Solar panels offer the best financial return if you install just enough panels to cover your building's annual electricity consumption. The most important factor in determining the number of panels you need is therefore your company's annual electricity consumption. You'll find the exact number of kWh consumed in the previous year on your supplier's electricity bill.
Evidently, you shouldn’t install more solar panels than needed on your roof. A standard solar panel measures around 1.65 m², although more compact versions of about 1.30 m² or larger ones of roughly 2.00 m² are also available. If there’s not enough space on the roof of your building to accommodate the power you want your system to generate, then it might be worth opting for fewer, but more powerful panels with a higher peak output per unit. Monocrystalline solar panels — often referred to as ‘black panels’ — are a popular choice for this reason. While they are more expensive than traditional polycrystalline (blue) panels, they offer higher efficiency and are therefore a better option when roof space is limited.
You should also take into account other factors that could lead to lower performance of the panels, such as the slope of your roof, an unfavourable orientation, or possible shading.
The impact of installing solar panels on your building's PEB is another important factor to consider. After all, as of 2028, the certificate will be mandatory for all buildings in Wallonia. In Flanders, it will already be required from 1 January 2026 for all non-residential buildings. For large non-residential units in Flanders with a usable floor area greater than 1,000 m², the obligation has even been in place since 1 January 2025. The more energy your panels produce, the more sustainable your building will be and the better your PEB score will be. How much you can improve your PEB score by installing solar panels depends, among other things, on the type of panels, the current value of your PEB, and the surface area of the building.
Based on all these factors, you can calculate the total capacity of your solar panel installation and the number of panels required.
"}},{"componentType":"sectionTitle","title":"How do you calculate the number of solar panels you need?"},{"componentType":"paragraph","richBody":{"value":"To work out how many panels you need, you first need to figure out two things:
Once you know this, you can calculate the efficiency of your installation, expressed in watt-peak (Wp). Since your energy consumption is measured in kilowatt-hours (kWh), you’ll first need to convert that number using what’s known as the yield factor of 0.85. Because Belgium often has cloudy weather, it’s assumed that solar panels reach only 85% of their peak capacity, meaning that 1 Wp corresponds to 0.85 kWh.
"}},{"componentType":"highlight","title":"For example:","richBody":{"value":"To produce 4,000 kWh of solar energy a year, you need to install solar panels that, together, produce around 4,705 Wp (4,000 divided by 0.85). Do you consume 5,000 kWh a year? Then you need to install solar panels with a peak power of around 5,880 Wp.
The last thing you then need to know is the amount of electricity produced by one solar panel to calculate the number of solar panels you need for your property. The maximum wattage of a single panel depends on the type and brand, but typically ranges between 300 and 450 Wp today. On average, this amounts to around 250 to 350 Wp per square metre.
In addition, there are also bifacial or large-format industrial solar panels available that can produce up to 600 to 700 Wp. These can be a smart option if you have a large industrial or commercial roof surface.
If you opt for 4000 Wp solar panels, you will need around 12 panels to meet your consumption of 4,705 Wp, and around 14 panels for 5,880 Wp.
"}},{"componentType":"highlight","title":"Want to invest in solar panels?","richBody":{"value":"Save on energy costs with theING Eco Renovation Loan.
"}},{"componentType":"sectionTitle","title":"The cost of solar panels"},{"componentType":"paragraph","richBody":{"value":"Even though solar panels are a smart investment that will pay for itself over time, partly thanks to certain premiums, you obviously still want to have an idea of their total cost. In 2025, the average price of solar panels will average between €0.95 to €1.23 per watt-peak (Wp). In concrete terms, an installation of 12 panels with a total capacity of 5 kWp costs between €5,000 and €8,500 (excluding VAT), but the final cost will depend on several factors:
There are big differences between the many solar panel suppliers, so we advise you to compare several quotes before making your choice.
"}},{"componentType":"sectionTitle","title":"You want to improve the energy performance of your buildings?"},{"componentType":"paragraph","richBody":{"value":"The ING Sustainable Buildings Guide is a free digital tool that helps you identify which investments to make to improve the energy performance of your properties.
"}}]},"complementaryZone":{"flexComponents":[{"componentType":"sectionTitle","title":"Also consider"},{"componentType":"cards","cards":[{"componentType":"productCard","cardType":"product","cardSize":"small","title":"Sustainable Buildings Guide","intro":"Improve the energy performance of your buildings","image":{"transformBaseUrl":"https://assets.ing.com/transform/8a34edd0-5b47-4598-b3cd-43fa67c4534b/houseenergylabel1","type":"image","width":0,"original":"https://assets.ing.com/m/5e21728928954868/original/houseenergylabel1.svg","extension":"svg"},"link":{"url":"/en/business/sustainable-business/sustainable-buildings-guide-en"}},{"componentType":"articleCard","cardType":"article","cardSize":"medium","title":"Non-residential PEB: what is it?","body":"Article | With the introduction of the Non-Residential (NR) EPC, the certificate will soon be mandatory for every commercial building. Find out what this means for property owners.","image":{"transformBaseUrl":"https://assets.ing.com/transform/6b11d56b-bcbf-42c7-9d53-884d0800cb0c/Full-length-of-woman-standing-on-skateboard","type":"image","width":6720,"original":"https://assets.ing.com/m/bf4c48d89fe13/original/Full-length-of-woman-standing-on-skateboard.jpg","extension":"jpg"},"date":"2023-10-24","link":{"url":"/en/business/sustainable-business/peb-non-residential"}}]}]}}}