Ask every installer for the same thing
Two quotes only compare well if they start from the same data. Give each installer your 12 months of CFE bills, photos of the roof, your location and any equipment you plan to add.
Ask in writing for exact models, system size, month-by-month production, total cost, scope, exclusions and warranties. If someone won't put it in writing, that tells you something too.
Compare system size, not number of panels
Eight 550 W panels add up to 4.4 kWp, the same as ten 440 W panels. Counting panels doesn't tell you which proposal delivers more. To compare prices, divide the total by the kWp.
A table to fill in
Copy this table and fill it in for each proposal. Mark each row as included, excluded or to be confirmed.
| What to compare | What to ask for |
|---|---|
| Total system size | kWp of the panels and kW of the inverter |
| Equipment | Brand, model and data sheet |
| Structure | Type, material and how it attaches to the roof |
| Protections and panel board | What's included and whether the board needs replacing |
| Production | kWh per month, with the data source and losses |
| Savings | Your bill with and without panels, on your tariff |
| Cost | Total including IVA, and price per kWp |
| CFE paperwork | Who handles it and whether it's included |
| Schedule | Start, work and switch-on dates |
| Warranties | Panels, inverter, labor and roof leaks |
| Service | Monitoring, maintenance and who answers for it |
| Exclusions | What isn't included and what it would cost |
Ask for production by month
A serious estimate needs location, orientation, tilt and shade. If two proposals predict very different production at the same size, ask them to explain what they assumed.
Ask what losses they considered and where the sun data came from. A yearly figure with no breakdown doesn't show what happens in your highest-usage months.
Source: Department of Energy: technical criteria and solar savings factors (technical reference; its U.S. incentives don't apply to Mexico) ↗Separate production from savings
Generating a kWh doesn't take your average cost off your bill. In subsidized homes, panels first remove the most expensive kWh and the cheap ones last. Charges such as street lighting also stay.
Ask for your estimated bill with and without panels, based on your history and tariff. Ask which arrangement it assumes, usually net metering (medición neta), and what happens if you overproduce: credits last 12 months and anything left over is paid at a wholesale price, far lower.
Source: Diario Oficial: Resolution RES/142/2017 on distributed generation and compensation ↗Review the paperwork and the installation
The proposal should say who handles the CFE process and what happens if CFE requires work. The official maximum is 13 to 18 business days, not counting works, so be wary of anyone promising an immediate connection.
Ask whether the inverter has the IEEE 1547 and UL 1741 certifications, which the rule recognizes. Also ask them to confirm shade, cable routes and roof condition on site. A photo doesn't certify a structure.
Source: Diario Oficial: Resolution RES/142/2017 on distributed generation and compensation ↗Read each warranty separately
A long warranty only helps if you know who stands behind it, what it covers and how to claim it.
- Panels: manufacturing defects and output over time.
- Inverter: how long it lasts and who replaces it if it fails.
- Labor: installation faults.
- Leaks: who pays if they appear at the roof penetrations.
- Monitoring: whether it costs anything and what happens if the provider disappears.
- Conditions: whether they depend on maintenance or a specific installer.
Red flags
None of these alone proves an offer is bad, but all of them deserve a question.
- They promise your bill will reach zero.
- They give a savings percentage without seeing your bills.
- They skip the technical visit or don't explain what happens if something changes later.
- The price is much lower with no explanation of equipment or scope.
- They leave out the CFE paperwork or take it for granted.
- They pressure you to sign today.
- They offer power for several homes: collective net metering is still awaiting regulation.
Before you sign
Make sure the contract includes the following.
- Exact models, and what happens if they change because of stock.
- Payment terms, with part due when the work ends and part at switch-on.
- Schedule, and what happens in case of delays.
- Who pays for any work CFE requires.
- Delivery of the diagram, data sheets, warranties and monitoring access.
Sources and scope
The numerical examples are hypothetical. Tariffs and conditions can change and depend on the service; check your bill and current sources before making a decision.
