20 Questions to Ask Your Solar Installer in Spain Before You Sign
Solar panels can be a brilliant investment in Spain, but only if the system is designed around your real electricity usage, your roof, your battery needs, your legal paperwork and your electricity tariff. Before you sign a solar quote, ask these questions so you know whether the installer is designing the right system, or simply selling the biggest one they can.
This guide is written for homeowners in Spain who want to understand the quote before committing. It covers solar system sizing, batteries, inverter choice, legalisation, export compensation, virtual battery credit, warranties, monitoring, aftercare and realistic tariff savings.
UswitchSpain does not install solar panels. We help you check the electricity tariff and savings side using your real bill.
Quick answer: what should you ask a solar installer in Spain?
Before signing a solar installation quote in Spain, you should ask how the system has been sized, what annual consumption data was used, whether a battery is genuinely needed, which inverter is included, whether legalisation and surplus compensation paperwork are included, what export rate has been assumed, and whether your electricity tariff will need changing after installation.
The most important questions are:
- What annual kWh usage did you use to size the system?
- What percentage of the solar production will I use directly?
- What happens to excess solar production?
- Is legalisation included in the quote?
- Who handles the surplus compensation paperwork?
- What inverter and battery model are included?
- What is the battery discharge power, not just the kWh capacity?
- Does the battery provide backup during a power cut?
- What tariff assumptions are used in the savings calculation?
- Should my electricity tariff change after installation?
Do not judge a solar quote from panel count alone
A good quote should explain expected production, self-consumption, export compensation, tariff assumptions, battery logic, legal paperwork and aftercare. If it only shows a system size and a total price, ask for more detail.
Check my solar savingsWhy these questions matter before installing solar in Spain
Solar in Spain is often sold as simple: add panels, reduce your bill, enjoy free electricity. In reality, the savings depend on several moving parts. Your roof orientation, shading, daytime usage, battery size, inverter limit, export compensation rate, virtual battery rules, contracted power and tariff all change the result.
A larger system is not always better. A bigger battery is not always worth it. A quote with a high annual saving may be using optimistic assumptions about electricity prices, export rates or how much solar you will use directly.
The goal is not to catch out a good installer. A professional installer should be able to answer these questions clearly. The goal is to separate a properly designed system from a sales quote that looks impressive but leaves too much unexplained.
For a wider overview of solar panels in Spain.
System sizing questions
1What annual consumption figure have you used to size the system?
A solar quote should be based on your real annual electricity usage where possible, not just a rough monthly estimate or the amount of roof space available. In Spain, electricity use can vary heavily between summer and winter, especially if you have air conditioning, electric heating, pool pumps, holiday rental guests or an electric vehicle.
We used your annual kWh consumption from your electricity bill or usage history, then checked how that usage changes by month.
We sized the system based on the roof space (or) this is the package most people choose.
2Have you looked at my usage pattern by month?
Monthly usage matters because solar production and household demand do not always match. A home with heavy summer air conditioning may benefit differently from a home with winter heating, pool heating or seasonal rental occupancy.
Yes, we reviewed your monthly consumption and designed around when you actually use electricity.
The annual total is enough (or) monthly usage does not really matter.
3Are you sizing the system for self-consumption, export or battery charging?
A solar system can be designed with different priorities. Some systems are designed to maximise direct self-consumption. Others produce more surplus for export compensation or virtual battery credit. Others are designed to fill a physical battery. The installer should explain the design goal.
The system is sized to cover your daytime base load first, then useful battery charging/export after that.
More panels always means more savings.
4What percentage of my solar production do you expect me to use directly?
Direct self-consumption is usually the most valuable use of solar energy because every kWh used directly avoids buying electricity from the grid. Exported energy is normally compensated at a lower value than the import price.
We estimate X% direct self-consumption based on your usage profile, and the rest as export or battery charge.
All production is treated as saving the full import price.
5What happens to excess solar production?
Surplus solar can be exported for compensation, used to charge a battery, credited through a virtual battery, or wasted if the system is not set up correctly. The answer should include both the technical and tariff side.
Surplus will be exported once the system is legalised, and your supplier/tariff will determine the compensation or virtual battery treatment.
You get paid full price for everything you export (or) the bill will simply go to zero.
Panels, inverter and battery questions
6Why have you chosen this solar panel brand and size?
The installer should be able to explain why a particular panel has been chosen. The answer should cover warranty, degradation, panel efficiency, roof fit, availability and support, not just wattage.
These panels fit the available roof area, have a strong product/performance warranty, and suit the mounting layout.
These are the best panels (with no detail).
7Why have you chosen this inverter size?
The inverter is one of the most important parts of the system. It controls how much solar power can be converted and used at a time. Sometimes panels are oversized compared with the inverter, which can be acceptable, but the installer should explain why.
The inverter size is matched to your expected production and usage. We may oversize the panels slightly because real-world output is usually below the panel rating.
The inverter size does not matter (or no explanation of clipping).
8Is the inverter hybrid, battery-ready or grid-tied only?
If you might add a battery later, this matters. A grid-tied inverter may work well for panels only, but it may not support batteries without additional hardware. A hybrid inverter can often support battery storage, but compatibility still needs checking.
This is a hybrid inverter and supports these battery models (or) this is grid-tied only, so adding a battery later would need extra equipment.
You can add any battery later.
9What is the battery discharge power, not just the kWh capacity?
Battery capacity is measured in kWh, but discharge power is measured in kW. A 10 kWh battery does not necessarily mean it can run all heavy household loads at once. The discharge limit determines how much power the battery can provide at a given moment.
This battery stores X kWh and can discharge at Y kW continuously, with a peak of Z kW.
It is a 10 kWh battery, so it will run the whole house.
10Can the battery provide backup during a power cut?
Many customers assume that solar plus battery means the house will keep running during a power cut. That is not always true. Backup usually requires specific inverter support, backup hardware and often a dedicated essential-loads circuit.
Backup is only included if we add the backup box/essential loads circuit. Otherwise the system shuts down for grid safety.
All batteries work during power cuts.
Important: Battery backup and normal solar self-consumption are not the same thing. Always ask exactly what will happen during a grid outage.
Roof, shading and installation quality questions
11Have you done a shading assessment?
Even partial shade from a chimney, tree, aerial, neighbouring building or roof feature can reduce production. Shading also changes by season, especially in winter when the sun is lower.
Yes, we checked shading by roof area and designed the string/optimiser layout accordingly.
There is some shade, but it will not matter.
12Which roof orientation and tilt are used in the production estimate?
In Spain, south-facing panels usually produce the strongest annual output, but east/west or south-east/south-west arrays can still work very well. A split array may even suit households that use energy in the morning and late afternoon.
The estimate uses your actual roof orientation, tilt and local production assumptions.
This is the standard production figure for Spain.
13How will the panels be fixed to the roof?
A cheap or poorly explained mounting method can cause problems later. Ask about the mounting system, waterproofing, roof penetrations, wind loading and whether the installer has experience with your roof type.
We use this mounting system for your roof type, with proper waterproofing and wind-rated fixings.
We just screw the rails down (with no detail).
14Where will the inverter and battery be installed?
Inverters and batteries need suitable locations. Heat, ventilation, weather exposure, WiFi signal, cable runs, noise, access for maintenance and manufacturer requirements all matter.
The inverter/battery will be installed here because it is shaded, ventilated, accessible and within manufacturer limits.
We will decide on the day.
Legalisation, paperwork and export questions
15Is legalisation included in the quote?
In Spain, solar installations need proper paperwork. The exact requirements can vary by region, system type and installation details, but the quote should clearly state what legalisation, registration and documentation are included.
Yes, the quote includes legalisation and the required installation paperwork.
You can sort the paperwork yourself later.
16Who handles the grid registration and surplus compensation paperwork?
Installing panels is only part of the process. To receive surplus compensation, the installation usually needs to be registered and accepted correctly. Some customers start producing solar quickly but wait longer before export compensation appears on the bill.
We handle the registration process and provide the documents needed for your supplier.
The panels work, so the paperwork is not important.
17How long does the paperwork usually take after installation?
The installer should give a realistic answer. Physical installation can be quick, but registration, legalisation and surplus compensation can take longer depending on the distributor, supplier and paperwork flow.
Installation usually takes X days, but export compensation/legalisation can take longer. We will keep you updated.
Everything is instant.
18What documents will I receive after installation?
You should receive clear documentation for the installed system. That may include panel and inverter datasheets, warranties, electrical certificates, legalisation documents, monitoring access and user instructions.
You will receive the system documentation, warranties, certificates and monitoring login.
You do not need any paperwork.
Tariff, savings and aftercare questions
19Which electricity tariff have you used in the savings calculation?
This is one of the most important questions. A solar quote can look very different depending on the assumed import price, export compensation, standing charges, virtual battery rules and annual consumption. If the quote assumes high electricity prices or full-value export, the savings may be overstated.
We used your current tariff and showed import, export and self-consumption assumptions separately.
We assumed electricity prices will keep rising (or) all solar production saves the full import price.
20Will my electricity tariff need changing after the system is legalised?
Often, yes. The best tariff before solar is not always the best tariff after solar. Once your system is legalised, your tariff should be reviewed for import rates, export compensation, virtual battery rules, fixed monthly fees and potencia costs.
Yes, once the system is legalised you should compare solar tariffs based on your real import and export pattern.
Your tariff does not matter once you have solar.
Good answer vs red flag: solar quote checklist
Use this table as a quick way to judge the quality of a solar quote. A good installer should welcome clear questions. If the answers are vague, rushed or based only on headline savings, be careful.
| Question area | Good answer | Red flag |
|---|---|---|
| System size | ✓Based on annual kWh usage and monthly pattern | ✕Based only on roof size or a standard package |
| Self-consumption | ✓Shows direct use, export and battery charging separately | ✕Treats all solar production as full-price savings |
| Battery | ✓Explains capacity, discharge power and backup limits | ✕Only mentions battery kWh size |
| Inverter | ✓Explains inverter size, hybrid capability and clipping | ✕Says inverter choice does not matter |
| Shading | ✓Includes shade, roof angle and orientation | ✕Uses generic production figures |
| Legalisation | ✓Included and clearly explained | ✕Left for the customer to sort out |
| Export compensation | ✓Explains supplier/tariff dependence | ✕Promises full-price export |
| Virtual battery | ✓Explains credit rules and limits | ✕Says it makes the bill zero automatically |
| Power cuts | ✓Explains whether backup hardware is included | ✕Claims all batteries work in outages |
| Tariff | ✓Uses real import/export rates | ✕Uses optimistic assumptions with no detail |
| Aftercare | ✓Monitoring, documentation and warranty support included | ✕No clear handover process |
Check the numbers before you sign
Upload your electricity bill and tell us the proposed system size, inverter, battery and quote price. We’ll help you understand whether the tariff and savings assumptions make sense.
What a proper solar quote in Spain should include
A proper solar quote should be more than a total price and a panel count. At minimum, ask for enough detail to understand what you are buying and how the savings have been calculated.
If a quote does not show the tariff assumptions, the savings figure is incomplete.
Should you compare electricity tariffs before or after installing solar?
You should understand your current tariff before installing solar, then compare again after the system is legalised. Before installation, your bill tells you how much electricity you use, when you use it and what you currently pay. After installation, the question changes: you need the best balance of import price, export compensation, virtual battery terms, fixed fees and potencia.
For example, a household with high daytime use may benefit most from direct self-consumption. A household that exports heavily may need a tariff with better export compensation or virtual battery credit. A household with a battery may care more about cheap import periods and how the battery is charged. There is no single best solar tariff for every home.
Already have a solar quote? Let us sanity-check the savings
UswitchSpain does not install solar panels, so we are not trying to sell you a bigger system, extra panels or a battery. Our role is different. We can look at your electricity bill and the quote assumptions from the tariff side.
If you send us your latest bill and the basic details of the quote, we can help check whether the estimated savings look realistic based on your current import price, potencia, likely self-consumption, export compensation and post-solar tariff options.
Final advice before signing a solar contract in Spain
A good solar installation should be designed around your home, not around a standard sales package. The right system depends on your annual consumption, roof, shading, daily routine, air conditioning, pool pumps, EV charging, battery needs, legal paperwork and electricity tariff.
If an installer can explain the design clearly, show realistic assumptions and include the paperwork, that is a good sign. If the quote relies on vague savings, full-price export assumptions or pressure to sign quickly, slow down and ask for more detail.
Before signing:
- Check the system size against annual usage
- Understand direct self-consumption vs export
- Ask whether a battery is genuinely needed
- Confirm inverter and battery specifications
- Confirm legalisation is included
- Confirm who handles surplus compensation paperwork
- Check the tariff assumptions
- Compare your post-solar tariff options
- Keep all documentation and warranties
- Do not assume the biggest system gives the best return
Frequently Asked Questions
Q. What should I ask before installing solar panels in Spain?
Q. Is legalisation included in a solar quote in Spain?
Q. Is a bigger solar system always better?
Q. Should I get a battery with solar panels in Spain?
Q. Can a solar battery run my house during a power cut?
Q. What is solar export compensation in Spain?
Q. What is a virtual battery?
Q. Should I change electricity tariff after installing solar?
Q. What documents should I receive after a solar installation?
Q. Can UswitchSpain check my solar quote?
Make your solar quote work with the right tariff
Solar panels reduce the energy you buy from the grid, but your tariff still matters. Upload your bill and use our solar analyzer to understand the savings before and after installation.
Upload your billRelated Guides
See all guidesBest Tariff for Solar Owners in Spain in 2026 | Feed-In, Battery or Lower Import Rates?
Are solar tariffs in Spain really worth it? Honest guide to feed-in rates, Octopus Solar, batteries, self-consumption and lower real bills.
Plug-In Solar Spain: Costs, Savings, Balcony Solar & How It Works
Plug-in solar in Spain costs €400–€650 and saves €300–€450/year. How it works, real costs, sizing, legality, and whether it suits your home. Full guide.
How to save money by using electricity during solar hours
Electricity savings do not always come from using less power. In many Spanish homes, savings come from using electricity at better times.
Electrical Certificate (CIE) for Solar in Spain
Every grid-connected solar installation in Spain requires a CIE. Learn what the solar CIE covers, how RAIPRE registration works, and how Uswitch can help.