Most people asking for a solar quote ask about price and output. What actually decides whether the system is legal is something else: the installation file and the surplus compensation contract. This guide explains which documents make up that file, who signs them, and how the contract with the electricity retailer is closed.
What the installation file contains
The file is the set of documents proving the system was designed and built according to the Spanish low-voltage regulation (REBT) and RD 244/2019. It is filed with the regional authority and stays attached to the supply for the life of the installation.
Technical memorandum or engineering project
Up to 10 kW of inverter power a technical memorandum is enough: single-line diagram, cable and protection calculations, datasheets for panels, inverter and battery. Above 10 kW a full engineering project signed by a qualified engineer is required, with a production study and, where applicable, a health and safety study.
CIE, the electrical installation certificate
The CIE is issued by the authorised installer who carried out the work. It records installed power, protections, earthing and measurement results. Without a CIE there is no commissioning: it is the document the Junta de Andalucía requires to register the installation.
Supporting documents
The file also holds equipment conformity certificates, an updated supply-connection certificate when the connection is modified, and the planning paperwork (responsible declaration or municipal licence, depending on the town hall).
How the export contract is closed
Once commissioning is registered (PUES or TECI) and the CAU code requested, the regional authority notifies the distribution company. From there two different companies are involved, and they are easy to confuse:
- The distributor (Endesa / e-distribución across most of Málaga) manages the meter and the access contract. It does not bill you.
- The retailer is the company that issues your bill. You sign the self-consumption and surplus compensation contract with them.
The contract sets the rate at which exported kWh are credited. Simplified compensation has a legal cap: within one monthly bill the surplus credit can never exceed the value of the energy you consumed. You are not paid cash — it is deducted from the bill.
Realistic timelines
From a finished installation to compensation appearing on the bill usually takes 4 to 8 weeks. Delays typically come from the distributor (access-contract change) and from the retailer switching the tariff scheme, not from the regional register.
And if the system is off-grid
A genuinely off-grid system has no CAU, no bidirectional meter and no export contract. Its file ends with the CIE and the commissioning registration. Our Loja project (28 Aiko 610 W panels, a 15 kW Deye hybrid inverter and 32 kWh of MTS storage with ATS and EPS) was legalised exactly that way.
Frequently asked questions
Who signs the installation file?
The authorised installer signs the CIE; the technical memorandum is signed by the installer or an engineer, and a project above 10 kW by a chartered engineer.
Can I switch retailer after signing the export contract?
Yes. Switching retailer means signing a new compensation agreement with the new company; the CAU and the installation file stay the same.
What does the paperwork cost?
On a residential system the legalisation is included in our turnkey quote. Files needing an engineering project above 10 kW are quoted separately.
What happens if it is never legalised?
Without the file there is no surplus compensation, and the installation can lead to a penalty and to problems when selling the property.
Read the full legalisation guide: RD 244/2019, ATS, EPS and batteries →
Source: MiTechoSolar.com, Premium solar energy on the Costa del Sol
Installed by Mi Techo Solar · Professional solar panels, batteries & EV chargers · mitechosolar.com