19 JULY 2026

12 Smart Questions to Choose the Right Solar Panel Installer

Choosing a solar installer in Spain isn’t a “who has the best price per panel” decision. You’re buying an electrical installation that must be safe under the REBT (Reglamento Electrotécnico para Baja Tensión), produce what the proposal promised, and leave you with paperwork that works for warranties, grid connection, and (if you want) compensation for exports.

TL;DR: before you sign, ask questions that force documented proof authorizations, technical memory, equipment data sheets, and a clear scope for legalisation and after-sales. If they can’t show it, you can’t audit it.

Done well, these questions let you compare instaladores placas solares confianza without guessing who “seems more professional” on a sales call.

What accreditations and qualifications should you require from an installer in Spain?

In Spain, you should require an installer to be an instalador autorizado en baja tensión and to prove their authorization is valid and appropriate for the work they will perform. That authorization is what ties the installer to REBT responsibilities: design compliance, testing, and issuing certificates.

Instalador autorizado en baja tensión: a person or company authorized to build, maintain, or repair low-voltage electrical installations under the REBT after obtaining the corresponding official authorization.

If a company says “we’re trained” or “we have a course,” treat that as marketing until they show the authorization that lets them sign and certify the electrical installation. Under the REBT framework (ITC BT-03), the official authorization has requirements (technical means, qualified staff, insurance, tax/Social Security obligations) and validity (renewed every 5 years).

Ask for proof you can keep in your project folder:

Authorization / registration number as instalador autorizado en baja tensión (so you can verify it in official registers).
Applicable category: IBTB (básica) or IBTE (especialista), and why they chose it for your project scope.
Validity / renewal date: the authorization runs on a 5-year cycle; you want it current at signing and during commissioning.

A common real-world scenario: a homeowner in Valencia gets a “solar specialist” crew on the roof, but the company outsources the legal sign-off to a third party later. If that third party delays, the system may run but the paperwork lags meaning extra friction for grid-related steps and any future warranty claims that ask for the CIE/boletín.

Also ask for risk and liability coverage that matches a contractor touching your roof and your main electrical panel:

Civil liability insurance (Seguro RC): minimum coverage under REBT guidance is €600,000 for IBTB and €900,000 for IBTE ask for a certificate showing coverage and validity.
Occupational risk prevention plan (Prevención de riesgos laborales) for the on-site works (roof access, fall protection, electrical isolation).
Manufacturer certifications (when applicable): if they sell a specific inverter brand and claim “certified installer,” ask for the credential because it changes who handles certain support cases and how fast.

What questions should you ask to validate the technical design and your expected production?

o validate the technical design and your expected production, ask questions that force the installer to show their sizing logic, site study method, exact equipment models, and an annual estimate with explicit assumptions and realistic losses. You’re not shopping for optimism; you’re shopping for a design you can defend on paper.

"What power and why?"

An informed installer sizes for your actual consumption pattern, your near-term changes, and constraints from your roof and the grid connection approach. Ask them to base the answer on:
Your consumption profile (monthly bills + if you have hourly/quarter-hour data, even better).
Future loads you plan to add (a heat pump, EV charger, pool pump) and the timeline.
Roof and electrical limits: available surface, orientation, safe setbacks, and whether the main panel and wiring path make the layout sensible.

Concrete scenario: a household in Seville adds an EV within 12 months. An installer who sizes only to last year’s bills may underbuild by a few modules. That forces either a second mobilization later or a system that exports midday power while buying at night both outcomes change the economics.

“What are you studying?”
You want a site study that covers more than “we looked at your roof on Google.” Ask what they do on-site (or with precise tools) to check:

Shading and obstacles (chimneys, nearby buildings, antennas) and how they model partial shade.
Orientation and tilt choices, plus the trade-off between maximum kWp and better annual yield.
Structural and waterproofing approach: how they mount, seal, and route cables without creating leak risk.
Cabling and protections: where they run DC and AC, how they keep cable lengths under control, and where protections sit relative to the inverter and main panel.

Named frameworks matter here: tell them you expect the design to be consistent with REBT practice and documented as part of the project file, not held in someone’s head.

"What exact equipment?”
“Tier 1 panel” is not a model. “Hybrid inverter” is not a spec. Ask for exact make/model and the documents you can read yourself:

Panel model(s) with data sheets and product warranty terms.
Inverter model(s) (string inverter, microinverters, optimizers if proposed) and warranty terms.
Compatibility statement: how they ensure the chosen inverter, protection devices, and monitoring work together.
Monitoring platform: what you will see (production, consumption if included, alarms) and who gets access installer, homeowner, both.

A practical test: ask them to place the model numbers in the quotation and to attach manufacturer PDFs. If they resist, you’re signing blind.

“What is the annual estimate?”
A serious production estimate includes assumptions and losses, not a single heroic number. Ask them to show:

Input assumptions: orientation/tilt, shading factors, temperature/soiling approach.
Losses and margin: wiring, inverter conversion, mismatch, and a buffer that reflects reality.
Degradation: how they account for performance decline over time in a way consistent with the product warranty language.
Best / expected / conservative cases: even a simple range tells you they’ve thought about uncertainty.

Quantified context you can demand: they should explain how they land on a number you can sanity-check against your own goals e.g., “this design should cover X% of your annual consumption” and what conditions must hold for that to be true (daytime loads, exports, battery/no battery).

"Quality signal: they hand you a memoria técnica with unifilar diagrams (esquema unifilar), equipment list, and a written justification of sizing choices. If they can’t produce that, you can’t verify what they installed later especially if you sell the home or need warranty support."

What should a solar panel installation budget include and what to review?

A good solar installation quote in Spain includes enough detail to audit equipment, labor, legalisation, timelines, and warranties so you can compare offers on scope, not on slogans. If the quote hides key line items, expect change orders.

Presupuesto desglosado: a quote broken down into verifiable line items (equipment, materials, labor, legalisation, timelines, and warranties) so a third party can confirm what you’re paying for and what you’ll receive.

If you’re comparing three offers, force them into the same columns. This avoids the classic problem: one quote looks cheaper because it omits legalisation, scaffolding, or post-install support.


Checkpoint	Quote A	Quote B	Quote C
Equipment (exact models)	Panels + inverter model numbers + monitoring included?
Labor & materials	Mounting, cabling, protections, panel upgrades included?
Legalisation scope	CIE/boletín + autonomous registry + grid steps included?
Timeline	Install days (often 1–3 days for residential) + admin lead time (2–8 weeks, varies)
Warranties	Installation warranty (2–10 years is common) vs equipment warranties separated

Then go hunting for “small print” that becomes big money once your roof is open:

Scaffolding / lift / roof access: extra charges if they can’t use a ladder safely.
Structural reinforcement: if they discover weak roof zones or need different anchoring.
Travel / displacement: especially for rural sites.
VAT (IVA): confirm what rate and whether the quote includes it.
Administrative fees and taxes: municipal fees, registry fees, and who pays/advances them.

Now tie price to outcome with concrete metrics your installer can compute from your design:

Price per Wp (€/Wp): use it only after you confirm the same scope (models + legalisation + protections). A lower €/Wp with missing paperwork isn’t cheaper.
Estimated self-consumption: ask for a % estimate and the assumptions (daytime loads, scheduling, whether you’ll add a battery).
Exports and compensation: if you choose “con excedentes,” ask how the quote treats the steps for compensation with your retailer (commercializadora).
Financing: if they offer it, ask for the exact structure and what happens if commissioning/legalisation takes longer than expected.

Concrete scenario: two quotes in Madrid differ by €1,200. Quote B includes scaffolding and a panel upgrade; Quote A doesn’t mention either. If your roof requires scaffolding for risk prevention, Quote A becomes Quote B after the first site day plus delays.

How do you confirm paperwork, legalization and after-sales support before signing?

You confirm legalisation and post-sales support by naming the exact documents, who files them, which self-consumption modality you’re choosing under RD 244/2019, and what response times the installer commits to in writing.

Start with legal responsibility: if they “help” but don’t own the process, you carry the risk of unfinished paperwork.

“¿Quién legaliza?”: name the person/company who issues the CIE/boletín and files the registro autonómico.
“¿Qué modalidad de autoconsumo registras?”: sin excedentes (with antivertido) or con excedentes (with simplified compensation or sale, depending on your plan).
“¿Quién gestiona contratos?”: if you want compensación simplificada, confirm who coordinates with the distribuidora and your comercializadora.

Autoconsumption details change hardware and paperwork. “Sin excedentes” usually means an anti-export (antivertido) system that prevents injection to the grid. “Con excedentes” means you may inject and then decide whether you’ll use simplified compensation (no tax obligations per the KB summary) or go into selling energy, which brings fiscal steps.

Then get specific about support after handover:

Monitoring: what platform you’ll use, what data it shows, and who receives alarms.
Response times: a written SLA-style commitment for diagnosing faults (even if it’s “within X business days” in the contract).
Maintenance options: preventive visits, cleaning, and how they price incident callouts.
Warranties split: installation warranty (workmanship) versus equipment warranties (panels/inverter/monitoring), and who manages the claim.

A practical outcome to aim for: you finish with a folder (digital or paper) containing the CIE, memory/diagrams, equipment warranties, and proof of registry/filings so any future electrician, insurer, or buyer can audit the system without chasing your installer.

Making Your Final Choice

The right choice comes from four things you can verify: baja tensión authorization, a design you can justify on paper, a quote you can audit line-by-line, and a closed plan for legalisation and post-sales support under RD 244/2019.

If they don’t document it, it doesn’t count.
If they won’t name exact models, don’t compare prices.
If they can’t explain legalisation steps and who owns them, walk away.
If insurance and authorization aren’t current, don’t sign.

Next action: request three offers, then run this checklist in the same order every time. You’ll notice fast which installer behaves like a contractor who can sign, certify, and support an electrical installation and which one behaves like a lead-generation funnel.

References

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