How to choose a solar installer: the checks that actually matter

A good solar installer inspects your roof before writing a quote, can prove the licence or qualification their country requires, and itemises every component and every task separately. Everything else is negotiable; those three things are not. The reason is simple: a photovoltaic system is not a product you buy but a building work you commission, and the company that carries it out is the one you will be dealing with for the next two decades.

Start with the licence, not the price

Across Europe, connecting a generator to the grid is regulated work, and the specific credential differs from one country to the next. What does not differ is that the credential is checkable, usually free, usually online, and always before you sign rather than after.

• Austria: the electrical work may only be carried out by a business holding the regulated Elektrotechnik trade licence. Anyone can look up a company in the public GISA register, which gives the name, location and the exact wording of the trade licence.
• Switzerland: an installation permit from the federal inspectorate ESTI is required, and photovoltaic systems are named explicitly among the installations that need the restricted permit for work requiring special knowledge. ESTI publishes the permit registers.
• France: for public support and for the surplus purchase tariff, the use of a qualified company is compulsory, and the panels must be installed by an RGE certified professional. Qualit'EnR and Qualibat both run public directories searchable by company registration number.
• Italy: the company needs the abilitazione under ministerial decree 37/2008 covering electrical systems, and must have filed the corresponding notification with the business register or the register of craft businesses.
• Spain: the company must have filed a declaración responsable with its autonomous community and hold professional liability cover of at least 600,000 euros for the basic category and 900,000 euros for the specialist category, which is the one self-consumption work requires.

What a complete quote contains

Quotes only become comparable once the same line items appear in all of them. Ask every bidder for the same list, in writing, and refuse to compare totals until you have it.

• Every component with manufacturer and model: modules, inverter or micro inverters, mounting system and, where applicable, the battery. Branded modules is not a specification.
• All labour, including scaffolding, cable routes, surge protection, earthing and reinstatement of the roof covering.
• Any consumer unit or meter cabinet work. This is the single most common change order on a residential installation.
• Who files the grid connection paperwork, and who files it with which body.
• The tax rate applied and the rated power used, stated explicitly, because both change how the headline total should be read.
• A payment schedule tied to construction milestones rather than a large deposit on signature.
• The handover pack: circuit diagram, layout plan, datasheets and a commissioning report.

Compare on price per kilowatt, and distrust published ranges

The only figure that makes two quotes comparable is the price per kilowatt of installed capacity, at identical scope. Larger systems are almost always cheaper per kilowatt, because the travel, the scaffolding and the paperwork are spread over more capacity. A small system is therefore not a bad deal simply because its price per kilowatt is higher.

Be careful with published market averages, including ours. In Italy, for example, one energy utility's own guide puts a residential system at 2,500 to 3,500 euros per kilowatt while other market surveys place the range at 1,300 to 2,500 euros per kilowatt. Both figures are honestly reported; they measure different scopes and different periods. The practical consequence is that no published range can tell you whether your quote is expensive. Three quotes for the same specification, from companies in your region, can.

How long the installer stays liable

This is where the difference between a warranty and a guarantee becomes money. Statutory defect liability is owed by the company you contracted with. Manufacturer guarantees on modules and inverters are voluntary, usually longer, and owed by the manufacturer, who will rarely pay for the labour of removing and refitting the part.

Read the table as a question to put to the installer rather than as reassurance. In every one of these countries the period runs against the contractor, which means it is only worth what the contractor is worth. A company that will still exist in year seven is a materially better bet than one offering a longer paper guarantee today.

Payment terms tell you more than references

A payment schedule is the clearest single signal of how a company is financed. Staged payments against milestones, with a meaningful balance due only after commissioning and handover of documents, mean the company can fund its own work. A large deposit on signature means you are funding it, and it puts you in the weakest possible position if anything goes wrong. Keep a retention until the paperwork is in your hands, not just the panels on your roof.

Never buy at the door

Solar is one of the most heavily canvassed home improvements in Europe, and several countries have legislated against it directly. France has prohibited telephone canvassing in the energy renovation sector since 2020 and extended the ban to electronic canvassing, meaning emails, texts and social media, from 1 July 2025. An unsolicited approach there is itself an offence, which makes it the most reliable quality signal you will ever get.

Withdrawal rights exist as a safety net, and they are useful, but they are not a decision method. In EU member states the withdrawal period for an off premises or distance contract is 14 days, and Italy extends it to 30 days where the contract was concluded during an unsolicited visit to the consumer's home. Switzerland is the outlier: its withdrawal right is narrower, applies to doorstep type situations where the customer's payment exceeds 100 francs, and its application to a contract for a fixed roof installation is not settled.

Questions worth asking out loud

1. Which licence or qualification do you hold, and in which register can I look it up?
2. Will you visit the roof and open the consumer unit before quoting?
3. Which components exactly, by manufacturer and model, and why those?
4. Who files the grid paperwork, and by when?
5. What is your payment schedule, and what is due only after handover?
6. If the inverter fails in year eight, who removes it, who ships it, who refits it, and who pays for that labour?
7. Can I speak to two customers whose systems you commissioned in the last year within twenty kilometres of here?

System size follows your consumption, not your roof area

A good installer asks about your annual consumption, your load pattern and whether a heat pump or an EV charger is coming, before saying a word about modules. Sizing from free roof area sells you kilowatts; sizing from consumption sells you self consumption, and self consumption is what pays. Bring your last electricity bill to the site visit and ask which self consumption share the payback calculation assumes and where that assumption comes from. A homeowner who cannot answer that question has not been sold a system, only a price.

Maintenance, monitoring and subcontracting

Installation takes days; operation takes twenty years. Ask what happens after commissioning. Is there monitoring that will tell you a string has failed, or will you discover it on next year's bill? Does the company offer a maintenance agreement, what does it cost, and what does it cover: visual inspection, fixings and torque checks, inverter firmware? How fast do they respond to a fault in November, when yield is low and the pressure to come out is lower still?

Then ask who actually does the work. Subcontracting is normal and not a red flag by itself, but you should know which company will be on your roof, which one holds the electrical credential, and which one your defect claim runs against. That is the company that issues the invoice, whatever the crew's van says. Get it in writing whenever more than one business is involved.

Reviews, references and the national versus local question

An average star rating tells you very little; the pattern inside it tells you a great deal. Read the bad reviews first and look for the same complaint repeating: dates moved, grid paperwork left unfiled, output below forecast, an inverter replacement that took months. One angry customer is normal. The same failure in five reviews is a finding. Then ask for two or three reference installations from the past year within a short drive, and call them: not to hear that it went well, but to hear what went wrong and how the company handled it.

National companies often win on price and financing options; local ones usually win on the thing that decides your next twenty years, which is whether someone answers the phone in year eight. Where statutory liability is short, as in Austria and Germany, that argument is stronger still, because a paper guarantee is only worth the company standing behind it.

Warning signs

• A quote produced without a site visit, or from satellite imagery alone.
• An unsolicited call, message or doorstep visit offering solar.
• A large deposit demanded on signature.
• A twenty year return calculation built on selling electricity to the grid rather than on using it in the building.
• A subsidy or tariff cited without a date or a source you can check.
• Documentation, commissioning reports or compliance certificates presented as paid extras rather than as part of the job.

Where to go next

The checks above hold everywhere; the registers, tax rates, tariffs and deadlines do not. Rules on who may connect a system, what the grid operator requires and which subsidies are open change by country and sometimes by month, so use the myosolar edition for the country the roof is in, and take three quotes from installers in your own region before you compare anything at all.