What happens to the solar energy you don't use?

On a sunny day, your panels often produce more electricity than your home is using. So where does it go? It goes to the grid, and its value is discounted from your electricity bill. In Spain this is called compensación simplificada de excedentes, simplified surplus compensation, and it's the usual option for homes.

It's a good system, but it has a few rules that surprise people, especially if you're used to how things work in another country.

How does surplus compensation work?

During the day, your panels first power whatever is running in your home. Whatever is left over goes out to the grid. At night, or when there isn't enough sun, you buy electricity from the grid as usual.

At the end of each bill, the value of the energy you exported is subtracted from the value of the energy you bought. You don't need to do anything each month: once it's set up, it happens automatically on your bill.

Who sets it up?

Two companies are involved, and it helps to know which is which. The distribuidora runs the local grid and updates your access contract once the installation is registered. Your comercializadora, the company that sends you the bill, activates the compensation. For homes in Catalonia, the regional government sends your installation's data to the distribuidora, so you don't need to visit anyone's offices. We handle the paperwork for the installation.

What are the limits I should know about?

• It's settled every month. The billing period can't be longer than a month, and under the rules any surplus left over in one month doesn't carry over to the next.
• Only the energy part is discounted. The fixed power charge (término de potencia), the meter rental and taxes aren't compensated, so your bill never goes below zero. Surplus isn't paid out as money.
• What you export is worth less than what you buy. On the regulated tariff (PVPC), surplus is valued at the wholesale market price. On the free market (mercado libre), it's valued at the price set in your contract. Either way, it's usually quite a bit less than what you pay for the electricity you buy.

What's a "virtual battery"?

You may see some electricity companies offering a batería virtual. It isn't something defined in the regulations: it's a commercial service that lets you store, as money, what normal compensation can't discount. Each company sets its own conditions, so read them carefully before signing.

Can I use more of my own solar energy?

Yes, and it's worth it, because every kWh you use at home saves you more than every kWh you export. A few ways to do it:

• Shift your consumption to daylight hours where you can: the washing machine, the dishwasher, the air conditioning.
• Add a battery, if you use a lot of electricity in the evening and at night. It stores what you'd otherwise export and lets you use it after dark. If you mostly use electricity during the day, you can start without one and add it later.
• Charge your electric car with the sun. A charger with a solar mode adjusts its charging speed to the surplus you have at each moment. See our EV charging page.

Who can use surplus compensation?

Renewable installations of up to 100 kW that sign a compensation contract and don't receive any other payment for their energy. That covers practically every home and most small businesses.

In our experience, it takes around a month from switch-on until compensation is active. In the meantime, your panels already power your home; we simply limit exports to the grid until everything is registered.

How do we size your system?

That's why we don't simply fill the roof with panels. A system that's too big sends a lot of energy to the grid at a lower value; one that's too small leaves savings on the table. We design around how and when you use electricity:

• An indicative quote to start with.
• A free technical visit to check your roof and consumption.
• A final quote, with or without a battery, depending on what makes sense for you.
• Installation, and we handle the permits and legalisation paperwork.

Send us your bills and get in touch. We'll tell you honestly whether a battery makes sense in your case.