How to choose a solar company for your business in Spain

Before comparing prices, check four things: that the company is a registered electrical installation company in the category that covers generation plants, that it has delivered plants like yours you can visit, that its warranties and insurance are in writing, and that it sized the plant from your hourly consumption rather than your roof. Then compare quotes on the same basis and ask who handles permits, grid paperwork and maintenance.

Who designs and builds business plants in Spain?

Several kinds of company sell commercial solar, and they are paid in different ways. Knowing which one you are talking to tells you where its incentives lie, so ask each how it is paid and by whom.

• Installers and EPC contractors (engineering, procurement and construction) design and build the plant and are paid for the build. Their income depends on the build going ahead, so an independent check of the sizing is worth having.
• Utilities and energy retailers sell plants to their customers, often with financing, and may tie the offer to their supply contract.
• PPA providers and leasing companies finance and own the plant and are paid through your PPA price or lease instalments over many years.
• Independent engineering firms work for a fee: they design, tender and supervise on your behalf, and the builder is chosen separately.
• Energy companies that structure the whole project, such as Aeternus, study the site, bring in the builder and the financing and oversee the work.

What should you check first?

Price matters, but compare it last. Check these first:

• Registration. Electrical installation companies must be enabled by the regional industry department through a responsible declaration. For low-voltage generation plants of 10 kW or more the installer needs the specialist category, and high-voltage work needs its own qualification. Ask for the registration number and category.
• Plants actually delivered. Ask for three references of similar size and type, with a contact you can call, and visit one that has run for at least a year. Ask to see its real output against the estimate.
• Insurance. Ask for civil liability cover and construction all-risk cover for the works, with the amounts and the policy dates.
• Warranties in writing: module product and performance warranties, the inverter warranty and its extension options, the battery warranty if any, and the builder’s own workmanship warranty, with who you call if something fails.
• Financial standing. A warranty is only as good as the company behind it. Spanish companies file their accounts at the Mercantile Register, where anyone can request them.
• The roof. If it is asbestos cement, any work on it needs a company registered for asbestos work and a work plan approved by the labour authority (Royal Decree 396/2006), and the roof is often replaced first.
• Permits and grid paperwork. Ask who prepares the project, the municipal permit, the grid permits if you export, the electrical certificate and the registration, and who pays the fees.

Which questions should you ask every company?

Ask each company the same questions, in writing, so the answers can be compared:

• Which hourly consumption data did you use, what share of the output will my site use, and what share of my consumption will it cover?
• Which arrangement do you propose, zero export, compensation or selling surplus, and why?
• What yearly output do you expect per kWp, from which source, and with which losses assumed?
• Has the roof structure been checked, and what does my insurer say about the layout and fire safety?
• Is the grid connection or my transformer a constraint?
• What exactly is included, such as monitoring, maintenance, cleaning and insurance, and for how many years?
• Who makes the modules, inverters and batteries, and is any part of the work subcontracted?
• Who pays you, and does what you earn depend on what I choose?

Which red flags should make you slow down?

None of these proves bad faith, but each is a reason to ask more questions:

• A quote without your consumption data, or a plant sized to fill the roof rather than to what you use.
• Savings promised with no assumptions shown, or the word ‘guaranteed’ with no contract clause behind it.
• ‘Tier 1’ offered as the only proof of quality. BloombergNEF builds that list from which makers’ modules went into bank-financed projects; it does not test the modules.
• Grants presented as certain. Spain’s large EU-funded self-consumption grant programme stopped taking applications at the end of 2023; any current call has its own rules and deadlines.
• Pressure to sign quickly, or most of the price requested before the permits are in hand.
• Vague answers on who handles permits, or warranties that exist only in a brochure.
• For a PPA, a price described as fixed when the contract has a yearly increase, or an end-of-term purchase price left at ‘market value’.

How do you compare quotes like for like?

Put each offer on the same basis. A cheaper quote that assumes a higher output or leaves out the grid paperwork is not cheaper. Check the expected output yourself with PVGIS, the European Commission’s free solar tool: a quote well above its figure for your location and tilt needs explaining. As a reference, APPA puts a typical 180 kW industrial plant in Spain at about €126,000 in 2025, roughly €700 per kWp; smaller plants cost more per kWp.

Why the contract matters more between businesses

Spanish consumer law protects people acting outside their business, so a company buying a plant for its premises has no consumer withdrawal right or consumer guarantees. What is not in the contract is hard to claim, so write in the output the builder commits to, or how it will be tested; an acceptance test before handover; penalties for delay; the scope and length of each warranty; and the share of payment held back until acceptance.

Installer or independent adviser?

If you have an engineering team and the time to run a tender, going straight to two or three vetted builders works well. If you do not, an adviser can size the plant, run the tender and oversee the work. Advisers are paid either by a fee from you or by a commission from the builder or financier chosen. Both can work, as long as you know which.

Aeternus Power is one option. We are an independent energy company based in Madrid. We work out what your site can produce and the best way to pay for it, bring in a vetted builder (we check licences, warranties and the plants it has actually delivered) and the financing, and oversee the work until the plant is switched on. We never own plants. We are paid a commission by the builder or financing partner we bring in, only if the project goes ahead, and you pay us no fee. For a first figure, try the free preview on our business page; for a study with your bills, contact us. We reply within two working days.

Questions

Do solar installers in Spain need a licence?

Electrical installation companies must be enabled by the regional industry department through a responsible declaration, and for low-voltage generation plants of 10 kW or more the installer needs the specialist category. Ask for the registration number and check it with the region.

How many quotes should I get?

Two or three detailed quotes from vetted builders are usually enough, if they use the same consumption data and the same arrangement. More quotes on different assumptions are harder to compare, not more useful.

Should I choose the cheapest quote?

Only once the quotes are comparable. Check output per kWp, the share used on site, what is included and the warranties; a low price can hide a higher output assumption or missing permit work.

How can I check a solar company’s financial health?

Spanish companies file annual accounts at the Mercantile Register, and anyone can request them. Look at turnover, results and how long the company has been trading, because its warranty is only as good as the company.

Sources

• Real Decreto 842/2002, Low Voltage Electrotechnical Regulation, ITC-BT-03 on installation companies (BOE, consolidated text): https://www.boe.es/buscar/act.php?id=BOE-A-2002-18099
• Real Decreto 770/2025 amending the staffing requirements for installation companies (BOE, 3 September 2025): https://www.boe.es/buscar/doc.php?id=BOE-A-2025-17507
• Real Decreto 337/2014, High Voltage Regulation and its technical instructions (BOE, consolidated text): https://www.boe.es/buscar/act.php?id=BOE-A-2014-6084
• Energías Renovables (August 2026): the new bottleneck in self-consumption, installers for plants of 10 kW or more: https://www.energias-renovables.com/autoconsumo/el-nuevo-cuello-de-botella-del-autoconsumo-20260827
• IDAE: Guía Profesional de Tramitación del Autoconsumo, v.6 (July 2024): https://libreria.miteco.gob.es/ebook/416/free_download/
• Real Decreto 244/2019, administrative, technical and economic conditions of electricity self-consumption (BOE, consolidated text, last updated 22 March 2026): https://www.boe.es/buscar/act.php?id=BOE-A-2019-5089
• Ley de Sociedades de Capital, article 281: anyone may obtain information on accounts filed at the Mercantile Register (BOE, consolidated text): https://www.boe.es/buscar/act.php?id=BOE-A-2010-10544
• INSST, NTP 815: asbestos work plans under Real Decreto 396/2006: https://www.insst.es/documentacion/colecciones-tecnicas/ntp-notas-tecnicas-de-prevencion/23-serie-ntp-numeros-786-a-820-ano-2008/nota-tecnica-de-prevencion-ntp-815
• BloombergNEF: Tier 1 reports, a list based on project and asset finance data: https://about.bnef.com/tier-1-reports/
• Real Decreto Legislativo 1/2007, consumer protection law, article 3: who counts as a consumer (BOE, consolidated text): https://www.boe.es/buscar/act.php?id=BOE-A-2007-20555
• Real Decreto 477/2021, self-consumption and storage incentive programmes, article 4: applications closed on 31 December 2023 (BOE): https://www.boe.es/buscar/act.php?id=BOE-A-2021-10824
• European Commission, Joint Research Centre: PVGIS 5.3 photovoltaic output tool: https://re.jrc.ec.europa.eu/pvg_tools/en/
• Energías Renovables (23 February 2026): APPA figures for typical home and industrial installations in 2025: https://www.energias-renovables.com/autoconsumo/el-autoconsumo-solar-dom-stico-en-espa-20260223

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