How to size solar panels for self-consumption in Portugal in 2026

Solar quotes often begin with a single number: annual consumption in kilowatt-hours. That number matters, but it hides the decision that determines how much value the system can create. A house in Albufeira may use most of its electricity during the day because a pool pump and air conditioning are running. A smaller home in Monchique may use less overall but have a larger evening load. The two homes should not automatically receive the same system.

For a homeowner, sizing means balancing four things: the roof’s usable area, the property’s production potential, the timing of demand and the way surplus will be handled. A technically large system can still be a poor fit if much of its output arrives when the house is empty. A modest system can be very effective when its production is consumed directly by flexible daytime loads. The objective is a design you can explain and operate, not the biggest array that fits on the roof.

Start with the shape of your electricity use

Collect twelve months of electricity bills if you can, and mark unusual periods rather than averaging them away. Note whether the property is occupied every month, whether summer guests arrive, and whether heating or cooling changes the winter pattern. Then list large loads separately: circulation pumps, air-conditioning units, water heaters, ovens, induction hobs, laundry, irrigation controls and an electric car. A bill tells you how much you used; it does not tell you which load created the demand at 11:00 or 22:00.

The next useful detail is timing. A dishwasher that can run at lunchtime is different from an immersion heater that only runs overnight. A pool pump may be flexible, but its operating schedule must still protect filtration and water quality. Air conditioning can be partly shifted by pre-cooling, while a holiday home may have a sharp demand peak when guests arrive. Give the installer these facts in writing so the proposal models your home rather than an anonymous average.

What the Portuguese process means for a homeowner

DGEG’s current autoconsumption guidance describes the UPAC framework and links to registration, legal and FAQ material. E-REDES explains the practical journey for an individual autoconsumer, including checking the installation, the meter and the information needed when surplus is injected or sold. The exact administrative route depends on the installation and its power, so a quote should identify who is responsible for each submission and what is included.

Do not let a salesperson turn a regulatory threshold into a universal promise. The DGEG registration page distinguishes a Mera Comunicação Prévia up to 30 kW of installed power from UPAC registration above 30 kW, while E-REDES also describes a registration requirement in circumstances such as exporting surplus or installed power above 700 W. These are official process details, not a substitute for checking your exact project. Ask the installer to state the applicable route, the documents they will provide and the point at which you may operate the system.

Use PVGIS as an independent sense check

The European Commission’s Joint Research Centre provides PVGIS, a public tool for estimating photovoltaic production by location and system assumptions. Put your approximate Algarve location into the tool and compare the result with the installer’s annual and monthly forecast. The purpose is not to produce a perfect engineering model from a browser form. It is to notice an unexplained gap: if two forecasts differ materially, ask whether the cause is orientation, tilt, shading, temperature, system losses, clipping or a different solar-data set.

Record the assumptions with the result. A south-facing roof with clear sun is not the same as an east-west array behind a parapet. A flat roof may need spacing between rows that reduces usable area. A coastal property can have salt exposure and wind considerations even when its solar resource is strong. Use PVGIS to ask better questions, then let a qualified installer verify structure, cabling, protection and the distribution-board work.

Compare the design against the property profile

Plan for surplus before you buy equipment

Every rooftop system will sometimes produce more than the home is using. E-REDES explains that surplus can be stored in batteries or injected into the public network, and that a customer may sell surplus to a retailer when the required process is in place. The value of exported energy depends on the arrangement and current commercial terms; it should never be treated as identical to the value of avoiding a purchase from the grid. Ask for the forecast split between direct use, storage and export.

A practical design can leave room for future changes. If you expect an electric vehicle, a pool heat pump or a larger family, tell the installer now. That does not automatically mean installing a larger inverter or more panels today. It means checking cable routes, protection, monitoring, spare roof area and whether a later addition would be technically compatible. Future-proofing is a written design question, not a vague promise that the system is ‘expandable’.

Sizing mistakes that are easy to avoid

• Choosing a panel count from the monthly bill without checking when the energy is consumed.
• Using annual average consumption that hides summer guests, pool equipment or a long vacant period.
• Treating a calculator’s production estimate as a guarantee instead of recording its assumptions.
• Ignoring roof shade from chimneys, parapets, trees or neighbouring buildings.
• Assuming that a battery automatically fixes a poor match between production and demand.
• Accepting a forecast with no monthly figures, system losses, degradation assumption or self-consumption explanation.
• Letting the installer handle the DGEG or E-REDES process without stating what documents and fees are included.
• Sizing for a future electric vehicle that may never be bought while under-sizing the loads already present.

Questions to put on every quote request

• What annual and monthly production did you model for my exact roof orientation, tilt and shade?
• Which hours of my consumption did you assume are directly covered by solar?
• Did you use my bills, interval data and equipment labels, or only a generic household profile?
• What part of the output is expected to be direct self-consumption, stored energy and export?
• Which DGEG and E-REDES steps apply to this installation, and who completes them?
• What monitoring will I receive, and can I see production, household consumption and export separately?
• What would change if I add an EV charger, pool heat pump or battery later?
• Which work is excluded: scaffolding, roof repairs, board upgrades, meter changes, permits or communications?

Frequently asked questions