Collective self-consumption in a block of flats: sharing the roof's solar power among the homes

A shared roof that can work for everyone

The idea is simple to tell: a single photovoltaic installation on the building's communal roof, whose energy is shared among the participating flats through fixed percentages. Each home keeps its own electricity contract, tariff and supplier; there is no need to run new cables to every flat or fit extra meters. The sharing is administrative: the distribution company applies each neighbour's share of the generation, hour by hour, and the effect shows up directly on each individual bill.

Scale is the strong argument. According to APPA's 2025 sector data, the average residential installation in Spain is around 5.5 kW; the roof of a block of flats allows considerably more than that, and sharing one larger installation among many flats usually works out better than multiplying small ones. The roof, which in many buildings has spent decades merely holding up aerials, becomes the community's most productive asset.

The split by fixed coefficients, explained without jargon

Each participating flat is assigned a coefficient: a fixed percentage of the output. Fixed means exactly that: the same at midday as at midnight, in January as in August. All the coefficients together cover the whole installation, and the split is officially registered with the distribution company.

Hour by hour, your share of the generation is subtracted from your consumption. If in that hour you use more than your share, you buy the rest from your supplier as usual. If you use less, the remainder is credited on your bill as surplus, under the terms of your contract. That is why habits matter: whoever runs the washing machine at midday squeezes their coefficient; whoever is only home at night gets rather less out of it.

As for output, the local reference is clear: PVGIS estimates between 1,350 and 1,500 kWh per year for each kW installed in this area, with optimal south-facing arrays near the top. On flat roofs it is common to mount panels east-west to make the most of the surface; that yields somewhat less than due south, around a factor of 0.82 to 0.85, in exchange for spreading production more evenly between morning and evening.

What the owners' association has to agree

The installation sits on a communal element, so the owners' association must approve it at a general meeting. Spanish horizontal property law provides specific majority rules for renewable energy installations, and unanimity is not always required; the exact rules applying to each case should be confirmed by the administrator or a lawyer before the meeting is called. What common sense does require is that the agreement tie down several points in writing:

An extra half hour of the meeting spent on these points saves years of misunderstandings. It is the moment to think unkindly, in the best sense: imagine the awkward cases now, while everyone agrees, rather than once money and bills are involved.

• Who takes part and with what coefficient, with names and signatures, not word of mouth.
• Who pays for the installation and in what proportion, which need not match the energy split exactly.
• How maintenance is funded each year and who contracts it.
• How a neighbour who says no today can join in a few years' time, and at what price.
• What happens to the coefficient when a flat is sold: whether it goes with the home or is renegotiated.

How the saving reaches each flat's bill

The saving does not arrive as a cheque or a separate receipt: it appears within each neighbour's usual bill. The distribution company applies your coefficient to each hour's generation; what you consume of your share is no longer bought from the grid, and what is left over is credited against the energy term under your contract. Each flat remains free to change tariff or supplier without affecting the rest.

It helps to set expectations with one figure: on a typical household bill, network charges and levies account for around 40%, and that part does not disappear because the roof generates. The saving works on the energy you consume and on the surplus that is credited. As a sector reference, APPA puts the typical payback of a residential installation in Spain at around 6 to 7 years before tax deductions.

And the deductions do exist, each with its requirements. The state one allows 40% off a base of up to 7,500 euros per home (RDL 2/2026, in force until the end of 2026, requiring an energy performance certificate from before and after the works, registered within the deadline). The Valencian regional one reaches 40% on a base of up to 8,800 euros, with 20% for second homes, can be carried forward for four tax years, and requires self-consumption registration and the IVACE certificate. Every case needs looking at calmly, because the requirements forgive no oversights.

The property administrator: the piece that keeps it all oiled

In a scheme of this kind, the property administrator is the piece that keeps everything running smoothly. They call the meeting, draft and keep the minutes recording the agreement, channel the payments or the special levy, hold the paperwork and remain the stable point of contact as neighbours change, which over the years they always do. An administrator who understands the project speeds up everything that depends on the building.

What is not the administrator's job is the technical and administrative side of the installation itself: sizing, legalisation, self-consumption registration or notifying the coefficients to the distribution company. That is the engineering firm's work. The combination works when each does their part and, above all, when they talk to each other from the start and not only when something goes wrong.

What if the penthouse wants to go it alone? Collective versus individual

Sometimes the question comes from the penthouse: I have a terrace, why not fit my own and skip the meetings? It is a legitimate option. An individual installation on a private surface is simpler to decide and the energy belongs to one household alone. That said, if the terrace is for private use but the element itself is communal, the association's agreement is still needed, and the best surface in the building is usually precisely the communal roof.

The collective route shares that good surface among more people and benefits from scale; the individual route is nimbler to govern but leaves the rest of the building without its share of the roof. Where roof space is tight, the two options compete for the same square metres, so the sensible thing is to decide once, and together. In either case, the installed equipment carries the statutory three-year conformity guarantee.

Typical mistakes worth dodging

The stumbles in these projects are hardly ever technical. They repeat themselves so often that they deserve their own list:

Almost all these mistakes are avoided the same way: working out the split with real bills on the table, putting the agreements in writing and having someone keep an eye on the installation every day once it is running. That last part is precisely the trade of an engineering firm that does not leave when the works end: set it up properly, leave it legal and stay watchful that it produces what it should.

• Coefficients shared out by eye, equal for everyone, across very different consumption: the retired neighbour on the second floor squeezes the midday sun while the empty flat on the fourth gives its surplus away.
• Not writing down how a latecomer joins: those who paid at the start feel the newcomer is jumping on the cart at no cost, and that thorn poisons meetings for years.
• Signing the agreement without a word about maintenance, as if the panels cleaned and watched themselves.
• Treating the installation as finished on commissioning day, with nobody watching production or raising the alarm if an inverter stops in the middle of July.
• Leaving the arrangements verbal: buildings change neighbours, and what is not in the minutes does not exist.

Frequently asked questions