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Selling Surplus Solar Electricity in Portugal: What Homeowners Should Check First
A practical Portugal and Algarve guide to direct self-consumption, batteries, grid injection, selling surplus and the DGEG and E-REDES questions to put in a solar quote.
A rooftop system creates several energy flows during the day. The panels may be producing, the house may be using some electricity, and the balance may be available for a battery or the grid. At night the direction reverses: the home may buy electricity or discharge a battery. A quote that only shows annual panel production leaves out the part of the design that determines how much value the household actually keeps.
For an Algarve homeowner, surplus can change from one week to the next. A villa near Tavira may have the pool pump and air conditioning running while guests are present, then sit empty for ten days. A permanent home in Lagos may have regular daytime demand but a high evening cooking load. Similar annual production does not mean similar direct self-consumption. Treat the calendar, not just the roof, as part of the system design.
Understand the four energy quantities in the forecast
Ask the installer to use the same words throughout the proposal. PV production is what the array generates. Direct self-consumption is the part used by appliances at that moment. Stored energy is production sent to a battery and later returned, after conversion losses. Export or injection is the remainder sent to the network. Grid imports are electricity bought when the house needs more than the solar system can provide. Confusing these quantities can make a good-looking annual percentage meaningless.
| Number | Plain meaning | Why it matters |
|---|---|---|
| Annual and monthly PV production | What the array is expected to generate | Shows seasonality and reveals whether the forecast matches the roof and location |
| Direct self-consumption | Solar used by the home at the time of production | Usually relates more closely to avoided purchases than total production |
| Battery charge and discharge | Energy shifted to a later period | Shows whether the battery has a real job rather than being a default add-on |
| Export or injection | Energy sent to the network | Needs a clear commercial and metering arrangement before it is valued |
| Grid import after solar | Electricity still bought from the supplier | Prevents a claim of zero bills from hiding night and winter demand |
The figures should be based on your occupancy, equipment and roof assumptions. They are a model, not a guarantee.
The Portuguese process belongs in the quote
E-REDES explains that an individual autoconsumer can use renewable production at the installation and, when there is an excess, store it, inject it into the network or sell it to a retailer. The same guidance says registration with DGEG is required when the customer wants to inject or sell surplus or when installed power is above 700 W. DGEG’s registration page separately describes a Mera Comunicação Prévia up to 30 kW of installed power and a UPAC registration above 30 kW. These are current official instructions, so the proposal should identify which route applies to your exact project.
Ask who completes each step and what evidence you will receive. The installer should name the responsible technician, confirm the information needed from your electricity contract, and explain any meter or production-meter requirement. If the project includes export or sale, do not assume that switching on the inverter is the same as being ready to inject commercially. Keep the DGEG record, E-REDES communications, meter details and retailer agreement with the system documents.
Compare value without guessing an export price
The value of electricity avoided at the home is not automatically the same as the value of electricity exported. Retail offers, contract terms, fees, taxes and metering conditions can change, so a current quote should state the commercial assumptions and the date they were checked. Ask the retailer or installer for written terms rather than copying a number from a calculator. If the export offer changes, the household should still understand how the system performs without it.
| Route | Potential benefit | Question to ask |
|---|---|---|
| Shift flexible loads | Uses more production directly | Can the pool pump, hot water or laundry move safely into the solar window? |
| Store in a battery | Makes some production available later | What usable capacity, power limit, round-trip assumptions and warranty apply? |
| Inject or sell to the network | Provides an outlet for energy not used at home | What registration, meter, retailer contract and settlement process are active? |
| Do a mixture | Avoids relying on one outlet | Does the model show the order in which direct use, storage and export happen? |
Make the meter and monitoring part of the handover
E-REDES says customers can consult information about consumption and energy injected through its digital service. Your installer’s monitoring app may show PV production, battery state and inverter status, but that is not necessarily the same as the grid meter’s record. At handover, ask how to distinguish production, household use, export and grid import. Test the access while the installer is present, and record the meter readings and commissioning date.
Questions for the installer and retailer
- Which DGEG route applies to this installed power, and who submits it?
- Will the design export surplus, store it, or do both under normal operation?
- What monthly production, direct use, battery discharge and export did you model?
- Which meter and CPE details are needed, and who confirms that the meter is suitable?
- If I want to sell surplus, which retailer contract is assumed and what is excluded from your quote?
- What happens to surplus during a vacant week when the pool pump is off?
- Can I see production, consumption, battery and export separately after handover?
- What documents prove that the installation is ready to operate and, where relevant, inject or sell?
Surplus mistakes that are easy to avoid
- Calling all panel production savings without separating direct use and export.
- Using an export rate in a payback calculation without a dated written commercial offer.
- Assuming a battery is always better than moving a pool pump or hot-water load.
- Starting export discussions after installation instead of putting registration and metering in the scope.
- Comparing two quotes that use different assumptions about occupancy, battery cycling or retailer terms.
- Treating a monitoring app as proof that the grid meter has recorded export correctly.
- Forgetting that a vacant holiday home can create surplus when there is little household demand.
- Promising a zero bill when the property will still have night, winter and fixed charges.
Frequently asked questions
Can I sell every kilowatt-hour my panels produce?
No. The home normally uses some production first, and the remaining flow depends on the system, meter, registration and commercial arrangement. Ask for the forecasted split and the exact steps required before sale.
Is exporting surplus the same as saving money?
No. Direct self-consumption avoids a purchase at the home, while exported energy is valued under a separate arrangement. The commercial terms should be current, written and kept with the quote.
Do I need a battery before I can export?
Not necessarily. E-REDES describes storage and network injection as alternative ways to handle excess. Whether a battery is useful depends on the property’s timing, vacancy, evening demand and backup requirements.
What does DGEG registration have to do with a small home system?
The applicable route depends on the project. E-REDES says registration is required in stated circumstances including wanting to inject or sell surplus or installed power above 700 W; DGEG sets out the MCP and UPAC routes by installed power. Have the installer confirm your case.
What should I keep after commissioning?
Keep the signed scope, equipment list, layout documents provided, DGEG and E-REDES records, meter details, retailer terms, monitoring access and warranty contacts. These make a future fault or contract question much easier to resolve.
Use the free estimate or send a question to get more practical guidance.
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