The tax return gives part of your solar back, if the papers are right

The state deduction: up to 40 percent

The state deduction for energy-efficiency improvement works is alive, with its current legal basis in Royal Decree-law 2/2026 and a horizon of 31 December 2026. For a solar installation, the bracket that applies in practice is the 40 percent one on a maximum base of 7,500 euros a year, because self-consumption reduces the home's non-renewable primary energy use, which is exactly what that bracket requires you to prove.

The key word is prove: you need two energy performance certificates for the home, one from before the works and one from after, signed by a qualified professional, and the later one must demonstrate the improvement and be registered in time. Without that pair of certificates there is no deduction, however real the installation.

The Valencian regional one: stackable

The Valencian Community also keeps its own deduction for self-consumption installations in the main home, at 40 percent on a maximum base of 8,800 euros, and 20 percent for second homes. It requires the installation's entry in the self-consumption register and the certificate issued by IVACE, and if your tax bill is too small to use it all, the excess can carry over to the next four tax years.

Both deductions are compatible with each other, each with its own rules. And both share the same Achilles heel: they are won or lost in the paperwork, not on the roof.

The mistakes we see repeated

When someone loses the deduction, it is almost always for one of these reasons:

• Skipping the before certificate: without the prior snapshot, there is no way to prove the improvement. It is the most expensive mistake and the most common.
• An installation left unlegalised or missing from the self-consumption register: the regional deduction expressly requires it.
• Cash payments: the deductions require traceable bank payment.
• The after certificate registered late: the register has a deadline and does not wait.

How we tie it down

In our files, the certificates are not an optional extra: the before, the after, the full legalisation and the register entry are part of the job. When tax season arrives, you have the whole folder with what your advisor needs, without hunting for year-old papers.

One honest note: we are engineers, not tax advisors. The exact amounts and requirements of your return are confirmed by your advisor with your case in front of them; our job is that no paper is missing when they ask.

The car charger: the deduction that gets left in the drawer

If you install a charging point for an electric car alongside the panels, there is a separate deduction of its own: 15 per cent on a maximum base of 4,000 euros. With MOVES III having ended on 31 December 2025, this is the tax incentive left for the charger, and even so it is the deduction we most often see go unclaimed. People fight for the panel deduction, which is the big one, and the charger stays in the drawer as if it did not exist.

Our advice is to treat charger and panels as a single electrical job with separate paperwork. One intervention on the consumer unit, one visit from the installer to protect and wire both, and at the same time separate, clear invoices, because they are different deductions with different bases and every euro should sit in its own box. A charger invoiced as a lump within the solar installation is harder to defend in a tax check than one with its own invoice, its own electrical certificate and its own identified payment.

The underlying requirement is the same spirit as with the panels: a legalised installation and payments that leave a trail. A charger hanging off a socket any old way is not just an electrical risk: it is deduction money lost for not having done things with the proper certificate.

Two owners, a small tax bill and works that straddle the year

A house in both names: it is the most common case and the one that raises the most doubts. If you file separate tax returns, the split of the deduction has to line up with ownership and with who actually pays the invoices. The boring, correct solution is to decide before paying, not the following May: whose name goes on the invoice, which account the payments leave from and how each deduction is shared. A conversation with your tax adviser before signing the quote saves arguments later.

A tax bill that is too small: it happens more than you would think with pensions and modest incomes. The Valencian regional deduction allows for it: whatever does not fit in one year's tax can be carried over to the following four tax years. The state deduction plays by different rules, which is exactly why it pays to run the numbers before installing, while you can still choose when to pay, rather than afterwards, when all that is left is regret.

And works that straddle the year: the state deduction requires the energy performance certificate from before and the one from after, and the current window runs until 31 December 2026. An installation signed in autumn and paid across two years needs payments and certificates lined up in time, because which tax year each amount belongs to depends on those dates. It is a calendar detail that costs nothing to get right early and causes plenty of headaches when sorted late.

Frequently asked questions