How long does a green certificate last?

The validity of a green certificate was 5 years before January 2023 but following the modification of the Green Electricity Decree.

Since 2023, green certificates now have an unlimited lif espan!

We therefore advise our customers to hold on to green certificates as long as possible until the price of the green certificate rises. Speculation is rife, and the floor price guaranteed by ELIA (the high-voltage grid operator in Belgium and Germany) is €65 in 2023, but it was €95 in 2022. That's a difference of €30.



So if you had produced 10 green certificates with your solar panel installation, the difference could be 300€!!!! It depends on how much you need the money, of course!



Do solar panels make sense when renting out a property?

I plan to rent out my property. Are photovoltaic panels still interesting? In all cases, the answer is yes, despite some differences depending on your region.


  • À Brussels

As an owner, you benefit from the green certificate scheme for a period of 10 years. In other words, you can benefit directly from the sale of your green certificates. The electricity generated by the solar panels will be used by your tenant (on the principle of self-consumption, read our article here). Your tenant will therefore have a significant advantage in occupying your property, as he or she will see a portion of his or her electricity bill reduced.


What's more, it's important to note that adding solar panels to your property can also influence the home's energy performance certificate (EPB certificate). A higher EPB certificate reflects the property's energy efficiency and can be a selling point to attract tenants concerned about their environmental footprint and energy costs. As a result, you could potentially ask for a slightly higher rent, highlighting the economic and environmental benefits of solar panels.


  • In Wallonia and in Flanders

As the green certificate scheme no longer applies to new installations in these two regions, the main attraction of a photovoltaic installation lies in the fact that your tenant's electricity bill will be reduced according to the solar electricity produced. This means significant savings compared to renting a property without this advantage. In addition, there is a direct link between the photovoltaic system and the
EPB certificate
certificate of your home, and therefore its value.

Photovoltaic panels and EPB

Like other renewable energy sources, a photovoltaic installation has a direct positive impact on your home's EPB (Energy Performance of Buildings) score.

  1. Will my house increase in value? The answer is yes. With a lifespan of +/- 25 years, photovoltaic installations generate substantial savings that you or future buyers of your property can benefit from.
  2. Another point is that the EPB certificate is becoming an increasingly important factor in the decision to buy a home. The photovoltaic installation has a direct impact on the property's EPB rating and should therefore increase its value.

What is self-consumption?

Self-consumption is the amount of electricity generated by your panels that you consume directly.


  • If your self-consumption is 0%, that means you don't consume the electricity your panels produce at all. Everything is redistributed on the network.
  • If your self-consumption is 100%, that means you consume all the electricity your panels produce.

The greater your self-consumption, the lower your prosumer tax in Wallonia (if you have a smart meter). In Brussels and Flanders (from 01/01/21), you'll benefit from a higher increase in the price of your kWh. Indeed, the average purchase price of a kWh is 23 centimes, while the average resale price is closer to 5 centimes. Consuming electricity rather than feeding it back into the grid means you'll earn 4 times as much!

A recent article has been written on this subject for maximum understanding:




Battery compatibility

How compatible are batteries and storage systems?


Storage systems linked to electric batteries exist today. However, these are still very expensive, and their costs cannot be recouped over the entire life of the battery. It is therefore not yet worthwhile to undertake this type of investment at this time.


On the other hand, inverters sold today are compatible with the future installation of batteries. It may therefore be worth waiting a few years before considering the purchase of a battery for your existing photovoltaic system. Battery prices are falling sharply, so it's only a matter of time before they become profitable.

How can we contribute to the energy transition?

Years of carbon-free electricity generation.


According to the International Energy Agency(IEA), it takes between 2 and 3 years for a solar panel to generate the energy required to produce it. This figure is constantly falling, thanks to the ongoing development of panel performance. Given that the lifespan of an installation is between 25 and 30 years, that's as many years of carbon-free energy production. A real boost for the climate!


What's more, as Greenpeace details in this article, "... panels are 95-99% recyclable for most manufacturers. Whether they were built in China or Europe..."

What are the 3 parameters that influence the profitability of my photovoltaic system?

Three parameters influence the profitability of your installation:

1. Price per Watt-Peak

Himself influenced by:

  • The size of your plant: the rule is simple, the larger the plant, the greater the economies of scale. There are many fixed costs associated with installation (workers' travel, inverter, rental of a gondola, etc.). An installation with more panels will therefore be cheaper per Watt Crete installed, and therefore more profitable.
  • Panel type
  • Inverter type
  • The distance between the inverter and the panels: if the panels are placed outside your home (e.g. a ground structure in the back of the garden), trenching work will have to be taken into account. And the greater the cable distance, the greater the cable diameter. This increases the price per Watt-peak.


2. The orientation and inclination of the panels, as well as their geographical location.

A south-facing panel produces more than an east- or west-facing panel. It makes perfect sense. Depending on the orientation and inclination of a panel, a 'producible' can be determined. Productivity is the number of kWh produced per kWp installed. In Brussels, this can vary from +/-1,050 kWh/kWp for an optimal situation at 30° South, to 850 kWh/kWp for a situation at 30° East-West. A loss of only 20% in the worst case.

3. The region

This is the most important criterion, along with the size of the installation. In fact, the region in which you carry out your project has a direct influence on the grants you receive.

  • Brussels: 3 to 6 years return on investment and 12 to 25% annual financial return
  • Wallonia: 5 to 10 years' return on investment and 10 to 20% annual financial return.
  • Flanders: 7 to 10 years' return on investment and 7 to 15% annual financial yield.

How can I control my production?

How can I monitor or control my production?


Whether you opt for a SMA or SolarEdge inverter system, you can benefit from a tool for controlling and monitoring your installation. They allow you to view your panel production in real time and access detailed information. It looks like this:

residential solar panel production dashboard

Here's a dashboard of a residential solar panel installation located in Brussels-North in production during the year 2022 with 23 panels.


These technologies are available on most inverters, so don't hesitate to ask us for more information.


What if I have a dual time meter?

Do you have a bi-hourly meter and are wondering about its impact on your photovoltaic system?


In the case of an installation linked to a meter that runs back wards (in the Walloon region for installations of -10kVA), two situations may arise:

  1. Your installation produces less than your annual consumption on your day meter. In this case,
    there's no point in changing your two-hour meter
    . The balance on your Jour meter will be positive at the end of the year, meaning that you will have benefited from 100% of the green electricity you produced. What's more, you'll still benefit from a reduced rate for the Night phase of your meter.
  2. Your installation produces more than your annual consumption on your day meter. In this case, the balance on your day meter will be negative at the end of the year, earning you nothing. What's more, your Night meter will always count your consumption positively, with no transfer between the two meters.
    It's in your interest to install a single-hour meter.

In the case of a meter that does not run in reverse (in the Brussels and Flemish regions for -10kVA installations and in the Brussels, Walloon and Flemish regions for +10kVA installations) :

  1. Your meter is working properly. That is, it will turn positive if you consume electricity from the grid (when your panels produce less than you consume). But it will never turn negative when you inject electricity into the grid. This electricity will be sold to your energy supplier at a lower price than the electricity purchase price.
    So it's in your interest to keep a two-hour meter
    to benefit from the reduced rates of the Night meter. Since your panels don't produce when the sun is down, you'll be using electricity from the grid in any case.

SIBELGA, the Brussels electricity grid operator, is now mandatorily installing the new digital meters in the Brussels region.


What are the main photovoltaic units of measurement?

The main units of measurement in photovoltaics are the watt-crete (Wp) and the kilowatt-hour (kWh).


Watt-peak (W p): the maximum electrical power that can be produced by a photovoltaic device under standard sunlight conditions. These conditions correspond to:

  • An irradiance of 1,000 W/m2
  • A spectral distribution of radiation known as AM 1.5, corresponding to solar radiation reaching the ground after passing through an atmosphere with a mass of 1 kg at an angle of 45°.
  • The panels are positioned to capture the maximum amount of radiation (their plane is perpendicular to the direction of the source of direct radiation).
  • A panel temperature of 25 °C


Kilowatt-hour (kWh ): this corresponds to the energy consumed by an appliance with a power of 1 kilowatt that has been in operation for one hour (1 kilowatt × 1 hour).

How do I size the inverter for my system?

The optimum inverter load (power in kWp of the panels/power in kVA of the inverter, in %) is between 100 and 130%.


  • Below this level, the inverter won't start if the panels don't produce a defined minimum output. System losses are therefore to be deplored.
  • Beyond that, clipping begins to occur.

Do I have to change my electricity meter before installing panels?

The answer depends on the region you're in.


In Brussels, the law specifies that a meter cannot be turned upside down. Self-generation plants therefore require a bidirectional meter, also known as an A+ A- meter, to measure separately the energy taken from the grid and any surplus reinjected. Changing your meter has been free since January 2020.


In Wallonia, your meter must be able to turn backwards. Check this information with your grid operator. In most cases, no modifications are required.


In Flanders, from January 1, 2021, the meter will no longer run backwards. It will therefore be necessary to change the meter when you install panels.

What types of roof can I install panels on?

Most roofs are suitable for photovoltaic panels.


You will find below a table summarizing the feasibility according to your type of roof:


Roof type Feasibility
Steel tray yes
Tile yes
Zinc roofing yes
Corrugated sheets yes
Slate yes
Flat roof yes
Ground structure yes
Pitched roofing no


Warning: it is forbidden to work on roofs containing asbestos!

What is a green certificate?

Green certificates are one of the sources of income generated by your photovoltaic installation.


When you produce solar-generated electricity, you generate securities called 'green certificates'. These securities can then be resold to various players. These players include energy suppliers, who are obliged to purchase a certain number of green certificates each year.

An analogy would be a stock market share, because the green certificate is saleable but can vary in value according to the prevailing market price.

It's also important to understand that the green certificate doesn't take away from your electricity production. So it's still true that :

  1. You consume your own electricity, reducing your dependence on the grid.

  2. You can resell your surplus energy to suppliers (Total Energie, Luminus, etc.).

For private customers, only the Brussels region still grants green certificates for new installations, for a period of 10 years from the date of commissioning. A downward revision of the scheme comes into force on January 1, 2021, and will see the introduction of facility categories (based on size) with a different regime depending on the category. After 01/01/2021, the scheme will be slightly less attractive, but will still make your installation very profitable.



We've written a much more detailed article with the latest news on green certificates in 2023 and 2024. There was a balancing act. We invite you to read it without moderation!


h ttps://soltis.be/news/certificats-verts-bruxelles-2023-2024/


What is the prosumer rate?

What is the prosumer tariff?

The prosumer tariff is a charge designed to make solar panel owners contribute to the cost of managing the electricity distribution network. Previously, the system passed on these charges to users who didn't have solar panels, or to those whose solar-generated electricity didn't cover their overall consumption.

The new government announced that the new 'prosumer' tariff (producers/consumers) would be postponed until 2025. This was without taking into account the intervention of the CWaPE, which challenged this political decision.

However, an agreement seems to have been reached between the partners of the government majority. The Walloon government will take over the prosumer tariff in 2020 and 2021. Then, 54% of the amounts linked to compensation in 2022 and 2023. In addition, the Walloon government, wishing to encourage self-consumption by households, should cover the cost of changing to a dual-flow meter.

Prosumer rates by region

  • Brussels: No prosumer tariff applies, as the network costs associated with the purchase of electricity are already covered.

  • Wallonia: The prosumer tariff applies.

  • Flanders: The prosumer tariff will no longer apply from January 1, 2021.

How does it work and how profitable is it in different regions?

The profitability of your photovoltaic panels is generated by different sources of income, depending in part on the region in which the installation takes place.

Please read the article we've concocted with our engineers to give you a clearer understanding of profitability: