How do you work out the number of solar panels needed for your home?
If you’re planning to have solar panels installed to save on your energy bills, it’s useful to know how many solar panels you need to benefit from their installation. Read on to find out how to work this out for your home.
Why solar panels are (still) a smart choice
Before we delve more deeply into calculating the number of solar panels you need, we will briefly touch on why solar panels are (still) a smart investment today.
Although solar panels have both benefits and drawbacks, many people are opting for solar energy to save on their energy bills. According to official figures from the Flemish energy regulator, you immediately consume an average of 36% of the electricity produced by your panels. This can save you hundreds of euros on your annual energy bill.
You do have to weigh that 36% against the amount of energy your solar panels will generate.
A second common reason why many people make the move to solar panels is that they improve the energy performance of your home. An energy-efficient house gives you a better EPC rating, which in turn increases the value of your home.
How do you work out the number of solar panels you need?
To work out how many solar panels you need, you first need to know how much energy you consume. You can then calculate how much energy your panels will yield. We explain how to do this below.
Step 1: Work out your energy consumption
You will find your annual energy consumption on your energy bill. If you can’t immediately find this figure, you can base your calculation on an average energy consumption figure:
- 1 200 kWh per year for one person
- 2 350 kWh per year for a two-person household
- 3 500 kWh per year for a household of three to four people, with a dual meter
Tip: Take future plans into account when calculating your energy consumption. For example, you may have plans to buy an electric car, which usually means doubling your energy consumption. Or perhaps you are planning to have a heat pump installed in the near future. In that case, you should reckon on a good 4 000 kWh extra per year. So it’s better to install slightly too many panels than too few.
Step 2: Calculate the yield of your solar panels
To calculate the yield of your solar panels, you need to know the exact power output. Power is expressed in ‘watt peak’ (Wp). That is the maximum power output, based on the optimum amount of sunlight in the most ideal conditions. The higher the watt peak, the greater the productivity of your solar panels.
To calculate the potential yield of your solar panels, you need to convert watt peak to kilowatt hours (kWh). That is the unit in which your electricity consumption is expressed.
To convert watt peak to kilowatt hours, we use a conversion factor of 0.9 (or 0.897 to be precise). This is the conversion factor used by the Flemish energy regulator. So a 400 Wp solar panel produces 360 kWh per year, provided the panel is facing south.
Step 3: Work out the number of solar panels
To calculate how many solar panels you need, you then divide your annual energy consumption by the yield of one panel. You now know how many panels you need to generate the amount of electricity you consume annually.
Calculation example:
You have a household of four people and you consume 4 000 kWh of electricity per year. On average, a solar panel achieves 90% efficiency. This means you need a total output of around 4 444 Wp (4 000 / 0.9). If your solar panels have a peak output of 400 Wp, you will therefore need 11 panels (4444 / 400 = 11).
Average number of solar panels
The table below gives an overview of the average number of solar panels, based on the above calculation example and average energy consumption figures.
Bear in mind that the actual price for your solar panels may vary depending on the type of panels, the time required for installation and the current market price of solar panels at the time of purchase.
| Number of people | Average annual consumption | Number of panels required (400 Wp) | Average price (excl. VAT, incl. inverter and installation) |
| 1 | 1 200 kWh | 4 | 3 000 euros |
| 2 | 2 350 kWh | 7 | 3 500 euros |
| 4 | 3 500 kWh | 10 | 4 600 euros |
| 6 | 5 000 kWh | 15 | 5 700 euros |
Other things to bear in mind
You should be aware that there are a number of factors that affect the yield of your solar panels, and therefore the optimum number of panels to install. This is because the yield is not the same for every installation. You should take the following factors into account:
- Location: Solar panels produce most when they receive a lot of sunlight. Try to avoid shade from trees or other obstacles.
- Orientation and pitch: The panels theoretically work best when facing south with a pitch of 35 degrees. However, a combination of east- and west-facing panels often delivers more energy, as they capture a large part of your daily energy peaks (your east-facing panels provide electricity in the morning and the west-facing panels take over in the evening).
- Surface area: The size of your roof and the space available to install solar panels. You need around 2 sq.m. for each panel.
To summarise: when working out how many solar panels you need, it’s particularly important to know your (future) energy consumption and the output of your panels in kilowatt hours. This will give you a good idea of the number of panels you need.
The additional ‘Solar panels and battery’ service in KBC Brussels Mobile lets you easily work out the estimated output and cost of your solar panels. If you are interested, you can also obtain a no-obligation quote from a reliable contractor from the network of our partner ‘Impact us today’. They will contact you within five business days to set up an appointment.
FAQs
You can install solar panels yourself, but it is quite a challenge which requires specialised skills. For example, you need knowledge of electrical systems and roofing systems. Working at height and with electricity also involve risks. If you install your panels yourself, this could also affect the warranty.
Solar panels generally last 25 to 30 years. Several factors can affect their lifespan, including:
- The quality of the panels
- Correct and professional installation
- Regular maintenance
- Environmental factors, such as areas with a lot of snow or very warm temperatures
Maintenance of your solar panels is necessary to maximise their yield and lifespan. Here’s what you need to do:
- Inspect your panels regularly to see whether they are dirty or damaged
- Most solar panels today are installed with a smart inverter, enabling you to keep an eye on their performance and receive an alert if a problem arises
- If your panels are dirty, clean them with soft water and a sponge (you can also use a little mild detergent), or you can hire a cleaning company to clean them
If you have limited space on your roof, for example because you have skylights fitted or because there are shadows on your roof, that needn’t necessarily be a problem. You can opt to install high-efficiency panels. These are slightly more expensive to buy, but generate more power per square metre, so you will recoup the extra cost in the long run.
If the available area is really very small and you can only fit a few panels on it, the savings might not outweigh the investment.
In the past, you could receive a grant for installing solar panels. However, the Flemish government has ended this scheme for panels installed on or after 1 January 2024.
The price of solar panels may have come down, but they are still a major expense. At KBC Brussels, you can apply for an energy loan and pay a lower rate than you would for our other loans. Find out more. Remember, borrowing money also costs money.
The KBC Brussels Energy Loan is an instalment loan. Lender: KBC Bank NV, Havenlaan 2, 1080 Brussels, VAT BE 0462.920.226, RLP Brussels, FSMA 026256 A. Subject to your loan application being approved by KBC Bank NV.