An off-grid solar system for a Mallorca finca is designed around December, not June. Winter days produce about a third of a summer day's energy, so the panels, the battery and a backup generator have to carry a year-round home through a run of cloudy days. Done well, it gives normal modern living with no grid, no standing charges and no dependence on a weak rural line. This guide walks through sizing, equipment, costs and the paperwork isolated systems still need.
Grid connection or independence?
Start with the connection quote from the distributor. Beyond a few hundred metres of new line, connecting a rural property routinely costs €15,000 to €30,000, sometimes more, and takes months. A complete off-grid system for a year-round finca costs €20,000 to €35,000, and a weekend house far less. When the connection quote passes €15,000, independence usually wins on cost alone, and you keep the money you'd otherwise pay in standing charges every month for decades.
A hybrid is also possible: a grid-connected home with a large battery and a backup circuit behaves almost like an off-grid system during cuts, which matters on rural lines.
Start with the loads
Off-grid sizing begins with a load list, not a roof. For a typical year-round finca for two to four people:
| Load | Daily energy (winter) | Notes |
|---|---|---|
| Fridge and freezer | 1.5 to 2.5 kWh | Efficient A-class units matter |
| Lighting, electronics, router | 1 to 2 kWh | LED throughout |
| Washing machine, dishwasher | 1 to 2 kWh | Run them at midday |
| Well or booster pump | 0.5 to 2 kWh | Short, heavy loads; size the inverter for the start-up |
| Water heating | 2 to 5 kWh | Heat-pump water heater or gas cuts this a lot |
| Heating | varies | Wood or pellet stove is the off-grid norm; heat pumps only with a big system |
| Air-conditioning (summer) | 5 to 15 kWh | Fine in summer when production is high |
A frugal house lands at 6 to 8 kWh a day in winter; a comfortable one at 10 to 15. Moving water heating and cooking to gas or a heat-pump water heater is the single biggest saving in battery size.
Panels: size for winter
In December a south-facing panel in Mallorca produces about 2.5 to 3 kWh per kWp a day; in June, 7 to 8. To cover 10 kWh a day in winter with some margin for cloudy weather, you need about 5 to 6 kWp. Summer surplus is large and free: that's when the air-conditioning and the pool run.
Where to put them: on the finca roof if it faces anywhere near south, on a barn or outbuilding, or on a ground frame. Ground mounts on rustic land need a municipal licence and depend on the plot's classification; roof mounts on an existing legal building are normally admitted with a licence. See the permits page.
Battery: two to three days of autonomy
The battery bridges nights and dull days. The design point is usually two to three days of winter consumption: for 10 kWh a day, a 20 to 30 kWh lithium bank. Lithium (LiFePO₄) has replaced lead-acid in almost all new systems: it can be discharged deeply, lasts 10 to 15 years, needs no maintenance and takes up less space. It costs more up front and pays for itself in lifetime.
Put the battery and inverter in a cool, ventilated room: a store room or garage, not a sun-baked shed.
Generator: backup, not a crutch
A well-sized system runs its generator a few dozen hours a year, during the longest winter stretches of cloud. The key is automatic start: the hybrid inverter starts the generator when the battery falls to a set level, charges it, and shuts it off. Systems without this end up with the owner nursing the battery by hand, which is how fincas end up with tired batteries and a generator running every evening.
Diesel or petrol, 5 to 10 kVA, with an auto-start panel. Budget €2,500 to €6,000 installed.
Inverter and monitoring
A hybrid off-grid inverter (5 to 10 kW for a home) manages panels, battery, loads and generator. Choose one sized for your biggest simultaneous load, including pump start-ups. Remote monitoring over the mobile network lets you and the installer see the system from anywhere, which matters when the house is empty.
Costs in 2026
| System | Typical installed price |
|---|---|
| Weekend house: 2 to 3 kWp, 10 kWh, small generator | €10,000 to €16,000 |
| Year-round finca: 5 to 8 kWp, 20 to 30 kWh, auto-start generator | €20,000 to €35,000 |
| Upgrading an old lead-acid system to lithium with a new hybrid inverter | €8,000 to €15,000 |
The battery is usually half the cost. FACTOR's 45% battery grant applies to storage in general for residents, including off-grid systems, as long as the technical conditions are met; confirm with the installer before counting on it.
Paperwork
Isolated systems are outside the self-consumption register, but they're still electrical installations under the low-voltage regulations. The installer issues the electrical certificate (CIE) and files a memoria técnica (up to 10 kW) or an engineer's project (above 10 kW) with the Balearic authority. If you plan to sell or apply for a tourist licence, this documentation will be asked for. Older systems without it can be legalised; see How to Legalise an Existing Solar System in Mallorca.
Common mistakes
- Sizing on summer production and running the generator all winter.
- Lead-acid batteries bought on price, dead in four years.
- No automatic generator start.
- An inverter too small for the well pump.
- Panels on the ground on rustic land with no licence.
- No monitoring, so nobody notices a fault for weeks.
Getting quotes
Off-grid is a specialism. We match finca owners with installers who design and maintain isolated systems regularly, not as a sideline. Describe the property, the loads and whether there's an existing system on the request form form.
Common questions
How many days of autonomy should the battery give?
Two to three days of winter consumption is the usual design point, with the generator covering anything longer.
Can I run air-conditioning off-grid?
Yes, in summer when production is highest. Size the inverter for the start-up load and use inverter-driven units.