How to compare solar quotes in the Algarve: assumptions, evidence and red flags

Start by making the quotes comparable

Two installers can look at the same Algarve villa and produce very different savings because they are not modelling the same household. One may assume that the pool pump, water heating and laundry run at midday; another may use the existing timetable. One may count almost every generated kilowatt-hour as a saving at the retail import price; another may separate direct use from surplus. Before comparing prices, ask each company to state the consumption data, roof orientation, shading, system losses and appliance schedule behind the proposal.

PVGIS is the right independent starting point for solar resource and expected photovoltaic performance, but it is not a sales guarantee and it does not know how the home is occupied. Request the location, orientation, slope, installed power and loss inputs used. Then compare the installer’s monthly production table with PVGIS. A modest difference may reflect a better roof survey or equipment model; a large unexplained difference deserves a written explanation.

A homeowner method that survives the sales meeting

Begin with evidence you control: twelve consecutive electricity bills, occupancy dates, pool and hot-water schedules, major appliance ratings, and notes about unusual months. Photograph the meter board and usable roof planes, but do not open electrical equipment. Mark future changes such as an electric vehicle, a heat pump or longer rental seasons. This prevents a proposal from solving last year’s house while ignoring next year’s loads.

Ask for seasonal results rather than one annual percentage. The Algarve has strong solar potential, yet winter production, summer occupancy and shoulder-season loads are not interchangeable. A useful proposal shows at least monthly generation, expected direct self-consumption, surplus and remaining imports. Treat every result as a scenario with stated assumptions, not a promise that weather or behaviour will follow an average year.

A realistic Algarve example

Consider a year-round home near Loulé and a holiday villa near Lagos with the same annual bill. The resident household may use cooking, office equipment and hot water throughout sunny hours. The villa may be almost empty in spring and heavily occupied in August. The same array can produce similar energy on both roofs but deliver different self-consumption and savings. A credible quote shows both patterns rather than hiding behind a national average.

Turn technical output into a cautious financial case

Ask for a simple bridge from production to euros: generated energy; energy used instantly; energy shifted into sunny hours; remaining surplus; energy still imported; prices applied to each flow. Contracted power and fixed or regulated bill components should not silently disappear from the forecast. ERSE’s consumer material is the appropriate reference for understanding the bill, while your supplier contract provides the actual prices to model.

Use the household’s real energy prices and separate energy that avoids an import from energy sent away as surplus. Do not assume future tariffs, incentives or export arrangements unless the proposal identifies the current source and date. Ask for a base case and a conservative case with lower direct use. The comparison should still make sense without a temporary promotion or perfect appliance scheduling.

Compare lifetime responsibilities as well as purchase price. Inverters, communications hardware, consumption meters and batteries may have different warranty terms from modules. Access equipment, travel, diagnosis and labour can be treated differently by providers. Request the written warranty path, maintenance expectations, monitoring access and ownership of system data before accepting the offer.

Installation, handover and after-sales

A good handover leaves the owner able to understand the system. It should identify isolators and emergency contacts, provide equipment documents, record serial numbers and layout, create owner-level monitoring access, explain normal seasonal variation and set a process for reporting faults. For a holiday home, include the property manager and define who may authorise attendance.

Portugal-specific administrative and grid steps can depend on system characteristics and the current rules. DGEG is the official energy authority and ERSE is the energy regulator and consumer-information source. Ask the installer to list the steps applicable to this project, who completes each one and what evidence the owner receives. Avoid relying on an undated blog post or a verbal promise about incentives.

Common mistakes

• Comparing only total price or panel count
• Accepting an annual yield with no location, orientation or loss inputs
• Treating every generated kWh as an avoided retail-price kWh
• Ignoring scaffolding, switchboard work, monitoring meters or paperwork exclusions
• Choosing a long warranty without checking who handles a claim in Portugal

Questions to ask the installer

• Which 12 months of consumption did you model, and how did you treat missing bills?
• What PVGIS inputs and system losses did you use?
• What share is expected to be used directly in each season?
• Which protections, monitoring devices and electrical-board work are included?
• Who responds if production falls, and what evidence triggers a site visit?

Decision checklist

• Collect 12 consecutive bills and note occupancy
• Write down pool, hot-water, cooling and appliance schedules
• Request monthly PVGIS-based production with all inputs
• Separate direct use, surplus and remaining grid imports
• Confirm roof, shade, structure, access and electrical-board survey
• List every inclusion, exclusion, warranty route and monitoring account
• Keep a conservative case beside the sales case

Frequently asked questions

Bottom line

The strongest solar decision joins an independent production reference, measured household behaviour, a safe site-specific design and a support plan. Slow down where assumptions are hidden; move forward when the installer makes energy flows, responsibilities and uncertainties easy to see.

Sources consulted

Production modelling should be checked against the European Commission’s PVGIS. Portugal-specific energy, consumer and efficiency context should be verified with DGEG, ERSE and ADENE on the date of the decision.