The contract for work is the document that counts in an emergency – not the quote and certainly not the sales pitch. Three things are important: a precisely described scope of services, a payment plan that is linked to construction progress instead of advance payment, and clearly regulated warranties – which come in three different versions with three different debtors. This article is a checking guideline, not legal advice. (As of: July 2026)
Key points in brief
- A solar order is legally a contract for work – the provider owes a functioning work, not just the delivery of parts.
- The scope of services belongs literally in the contract: What is in the quote must be adopted as binding by the contract.
- A payment plan according to construction progress is standard; a high advance payment is a risk and a warning sign.
- Separate three types of warranty: Product warranty (manufacturer), performance warranty (manufacturer), work/installation warranty (your provider).
- Acceptance and documentation are your most important means of pressure – the final payment only flows after defect-free acceptance.
Why the contract for work – and not the quote – counts
The quote advertises, the contract for work obliges. In Swiss law, the installation of a solar system is typically a contract for work: The provider owes you a specific, functioning result – the finished, ready-to-operate system – and not just the delivery of modules. That is favourable for you, because it clearly shifts the responsibility for the overall work to the provider.
However, for this advantage to take effect, the contract must also describe the work. The most common error: People negotiate carefully over the quote and then sign a contract that only refers to it in blanket terms or – worse – deviates from it. Rule number one is therefore: The contract must literally contain the agreed scope of services or explicitly make the quote a binding component.
What belongs in the scope of services
The contract should have the same substance as a complete quote – the twelve technical minimum details are the benchmark here too. Pay particular attention to the items that tend to remain vague:
| Item | What the contract should record |
|---|---|
| Components | Modules and inverters with type designation; replacement only «equivalent or better», defined |
| Scope | Scaffolding, electrical work, meter space adjustment expressly included or clearly excluded |
| Registrations | Connection request, Pronovo, guarantee of origin, notification procedure, incentives – who submits what |
| Performance/Yield | assured power (kWp); yield specifications with assumptions, not to be misunderstood as a guarantee |
| Dates | Guideline date and regulation in case of delay |
| Acceptance | how and when acceptance takes place, what counts as a defect |
This overview does not replace a contract check in individual cases – in case of doubt, a look by a specialist is worthwhile, especially for larger projects.
The payment plan: according to progress, not according to trust
A fair payment plan links your payments to visible progress – this way your money always remains roughly where the service is. Staggering in a few instalments is standard in the industry: a moderate advance payment at the start of the order, a larger instalment upon delivery of materials or start of installation, and a noticeable final instalment only after defect-free acceptance.
The final instalment in particular is your most important means of pressure: As long as a relevant part is only due after acceptance, the provider has a tangible interest in rectifying defects quickly. If, on the other hand, the majority or the full sum is demanded in advance, the relationship is reversed – your money then secures the provider's liquidity instead of your project. A high advance payment is therefore not only a financial risk, but one of the most reliable warning signs of all.
Warranties: three terms that do not mean the same thing
«25 years warranty» is the most common smokescreen in solar sales – because the phrase mixes three completely different things. Separate them cleanly:
1. Product warranty (manufacturer): covers material and manufacturing defects of the component. For modules often 12–25+ years, for inverters shorter (often 5–12 years, extendable). The debtor is the manufacturer. 2. Performance warranty (manufacturer): guarantees that the module still delivers a certain percentage of its initial power after years – it concerns the gradual loss of performance, not the defect. Also a matter for the manufacturer. 3. Work/installation warranty (your provider): is liable for the installation, planning and interaction of the system – i.e. for everything that is not due to the component itself. The debtor is the company that built the system for you.
The third is the most important in everyday life – and the one that stands or falls with the provider. A manufacturer's warranty is of little use if no one on site removes, sends in and replaces the defective device. Clarify in the contract: How long does the company's warranty last, what does it cover, and – the crucial question from the consultation – who will come in the event of a service and within what timeframe?
Acceptance and documentation: Your moment of control
Acceptance is not a formal act, but your contractually strongest moment. Take it seriously: Have the system explained to you, check the documents and document visible defects in writing before you confirm acceptance and release the final instalment.
A complete handover includes, among other things, the safety certificate (SiNa) of the electrical installation, the commissioning or measurement protocol, the accesses to monitoring, the warranty documents for the components and the confirmation of the completed registrations. If any of these are missing, this is a legitimate reason to declare acceptance with reservations – the proper project flow explicitly provides for this handover.
The contracts that interested parties present to us for a second opinion rarely fail because of nasty clauses – they fail because of missing ones. Not a word about scaffolding, «registrations by customers», a payment plan with 90 percent before the start of installation and a warranty line that does not say who is actually liable. None of this is illegal, but all of it silently shifts risk to you. Our recommendation is unbureaucratic: Place the quote and the contract next to each other and check whether the contract keeps what the quote promised – item for item. Where the contract is vaguer than the sales pitch, it should be renegotiated before signing. A reputable provider is happy to write in what they will deliver anyway.
Frequently asked questions
Is a solar system legally a purchase or a contract for work?
As a rule, a contract for work – the finished, functioning system is owed, not just the delivery of parts. This strengthens your position in the event of defects, because the provider is liable for the overall work.
How much advance payment is normal?
A moderate advance payment at the start of the order is standard; the larger sum follows staggered according to progress, with a relevant final instalment only after acceptance. If someone demands 80–100 % in advance, you should question this critically.
What is the difference between product and performance warranty?
The product warranty covers defects of the component, the performance warranty covers the assured residual yield over the years despite normal ageing loss. Both are provided by the manufacturer – the installation is covered separately by your provider's warranty.
Can I withhold the final payment if there are defects?
You may document defects found during acceptance and withhold an appropriate part until they are rectified – this is exactly what the final instalment is for. The specific arrangement depends on the contract and the law; in the event of a dispute, professional advice is worthwhile.
Should I have the contract checked legally?
For standard systems, a careful comparison with the quote based on these points is usually sufficient. For larger projects, ZEV or unusual clauses, a professional check is money well spent.
Free initial consultation
A contract that delivers what it promises.
At ecoEn, the contract for work adopts the quoted scope of services item for item – with a payment plan according to construction progress and clearly regulated warranties. We explain it to you before you sign.
Want to calculate yourself first? Solar calculator with official roof data →
Prefer to talk? +41 78 830 83 35
Have a photovoltaic system installed →
Swissolar-certified specialist company · ESTI installation authorisation (Art. 14 NIV) · in Zurich since 2017 · over 150 systems completed · a personal answer from the specialist company, no call centre
Sources: Code of Obligations (contract for work, Art. 363 ff.; defect rights); Swissolar (recommendations on contracts and performance warranties); empirical values from practice. This article does not replace legal advice.
Last updated: 9 July 2026 · Author: ecoEn editorial team
