Vintage Solar in Belgium: Timing, Behavior, and the Math Behind a 2009 Setup

I have been seeing a lot of posts on Hive lately about solar panels, electricity prices, and home energy strategies. It seems like a hot topic right now. Most of these posts focus on brand-new setups, battery integration, or perfect optimization.

I want to share a slightly different perspective: what happens when your system is already in place, inherited when you bought your house, and the "old" rules dictate your strategy.

We bought our house in 2016. The solar panels were already there: 16 panels, roughly 3.8 kWp. By today’s standards, that is nothing remarkable. But what came with the house was something you simply can't buy anymore: a pre-2009 Flemish solar installation with green energy certificates.

In hindsight, that specific timing mattered more than the hardware itself.

The Human Factor (and Covid)

We have had Electric Vehicles (EVs) for about five years now, and we switched to a dynamic electricity tariff (hourly prices) as soon as it became possible in Belgium.

That switch required a change in behavior. I definitely received some "feedback" at home in the beginning when I ran the dishwasher while prices were high! It took some time to adjust, but since the Covid pandemic, this has become much easier. Working from home more often means we can actually use appliances or charge the cars when the sun is shining, rather than pushing everything to the evening peak.

1. Production: The Solar Year 2025

Despite their age, the panels are still performing well. 2025 was actually a great solar year for us. Here is the breakdown of where that energy went:

The Story Behind the Numbers: We managed to use about 60% of our own power directly. That is decent for a setup without a home battery. The remaining 1,178 kWh was injected back into the grid.

Financially, that injection doesn't earn us much because market prices usually crash when the sun is shining brightest. However, in our specific situation, production is key. Even if we don't use the power ourselves, the total production count (2,939 kWh) is what triggers our green energy certificates.

2. The Cost: The Reality of the Bill

Belgium is known for high grid fees and taxes. Even with solar panels, if you consume from the grid (like we do for heat and cars in winter), the bill adds up.

The Story Behind the Numbers: This table shows the reality of the Belgian grid. The actual energy only costs about €1,240, but the grid fees and taxes add another €1,600 on top of that! Luckily, my wife works for a utility company, which grants us a 30% discount on the total bill (excluding VAT). Without that discount, the bill would have been much steeper. In the end, €2,082 is what actually left our bank account in 2025.

3. The Result: Are We Winning?

So we paid over €2,000. That sounds like a loss, until you look at the income side generated by the "Vintage" status of the panels and our EV charging strategy.

The Story Behind the Numbers: This is where the strategy comes together.

1. Certificates: Because the system is pre-2009, we get €450 for every 1,000 kWh produced. That is €900 cash.

2. EV Arbitrage: We get reimbursed a flat €0.25/kWh by my employer for charging the car. The trick here is the dynamic tariff. We strictly try to charge when the raw energy price drops below €0.10/kWh. In Belgium, that €0.10 is deceptive. Once you add grid fees, distribution costs, and taxes, that price roughly doubles to ~€0.24 per kWh for a standard consumer. That would barely break even with the reimbursement. However, thanks to our 30% discount on the total bill, our effective cost drops well below that level, while the reimbursement stays fixed at €0.25.

We don't necessarily aim for "profit" as the main goal—we just want to cover our costs. But managing to power a house and drive two cars for a year while ending up €779 in the green is a very nice bonus.

Future Plans: The Battery Dilemma

We are thinking about installing a home battery, but not yet.

If we modify our installation now to add a battery, we lose the right to those valuable green certificates. So, the strategy is simple: patience. We will wait until the 20-year certificate contract expires. Once that happens, we will upgrade to a modern setup with a battery. That will allow us to:

• Align EV charging even better with solar hours.

• Store cheap dynamic energy from the grid in winter.

• Increase that self-consumption well above 60%.

For now, the lesson is that solar optimization isn't always about the newest tech. Sometimes, it's about understanding the rules of the system you inherited and knowing when not to change a thing.