1. Request in writing what you are going to compare
Before comparing percentages, ask each provider for four documents: the method for measuring savings, the wording of the guarantee on your bill, the draft contract and a description of who operates the system day to day. If any of them does not exist in writing, you already have a difference between proposals.
A savings percentage without a measurement method is an estimate. A percentage with a method, with identified meters and with your tariff’s formulas, is a figure that can be audited month by month.
2. Measurement: two meters and your tariff’s formulas
BESS savings do not appear as a line on the CFE bill: you have to calculate what you would have paid without the system and subtract what you paid. For that calculation to be verifiable, it needs two things.
- Two certified meters. One in parallel with CFE’s meter, which reproduces your bill, and another on the BESS side, which measures what the system delivers to you. Class 0.1S (IEC 62053-22) is more accurate than CFE’s meters.
- Your bill’s formulas and tariffs. Both figures are calculated item by item, with the tariffs CFE publishes for your division that month, VAT included, so the comparison is like for like.
Also ask how the forecast is reconciled against the actual bill. At ENEGRIN, the average match between the forecast bill and the actual bill is 99.98%, measured over the last three billing months. That figure shows the calculation reproduces CFE’s. How we measure and reconcile
3. Which guarantee protects your bill?
The key question is what happens in a bad month. If the system saves less than expected, do you pay less? And if it saves nothing, do you pay anything? The guarantee that protects your bill fits in one sentence: you never pay more than you would have paid without the system.
Ask for that sentence to be in the contract and to apply under both models, whether the system pays for itself out of the savings or you buy it. At ENEGRIN it is written that way, and it is why the monthly payment under shared savings is always a percentage of measured savings. The two contracting models
4. The contract: term, exit and who answers for the system
A shared-savings BESS contract usually runs 10 to 15 years. Over that term your plant may grow, relocate or be sold. Check that the contract says what happens in each case and who answers for the system while it lasts.
- Term and exit. How long it runs, whether you can buy the system before it ends and how it is settled if the plant closes or relocates. A BESS integrated in a cabinet or container can be relocated.
- Who is responsible for the system. Who installs, operates, maintains and insures the equipment. Under the no-investment model, all of that should be on the provider, and you should not have to take on debt or tie up credit lines.
- Permits and filings. Who files the CENACE study and handles Grid Code compliance. Which permit a BESS requires
5. Continuous operation: who watches the system every day
A BESS saves because it decides every day when to charge and when to discharge, using your tariff’s time bands and charges. That decision is made by an energy management system (EMS). Ask whether it is programmed for Mexico’s tariffs or follows fixed schedules that are the same in every country, and who supervises it.
Also ask for access to the platform where you will see the system’s status and the month’s savings, and confirm that your auditor can log in with a read-only user. If the provider cannot show you a system operating in Mexico, ask to see one. Come see a BESS operating in Mexico
6. Checklist for your committee
| Criterion | What to request in writing | How ENEGRIN meets it |
|---|---|---|
| Savings measurement | The method, identifying the meters and your tariff’s formulas | Measured. With two certified class 0.1S meters and your tariff’s formulas. The bill we forecast matched the actual bill by 99.98% on average in August, September and October 2026. The full method is given in writing to your auditor or finance team at signing. |
| Guarantee against your bill | The guarantee clause in the contract | By contract, under both models, you never pay more than you would have paid without the system. |
| A month with lower savings | What you pay if the system saves less, or nothing | You pay less. With BESS, everything you pay ENEGRIN each month is a percentage of the measured savings. |
| Debt and credit | Whether the contract is a loan, a fixed rent or a financial guarantee | Under shared savings you invest nothing, sign no debt and post no financial guarantees, and your credit lines remain available. You do not pay a fixed rent either. |
| Contract and exit | Term, early purchase and what happens if the plant closes or moves | BESS contracts of 10 to 15 years. You can buy the system at any time, and it can be relocated if the plant moves. |
| Operation and filings | Who operates, maintains and insures the system, and who handles the filings | ENEGRIN, under both models. It installs, operates and maintains the system and handles the filings with CFE, CENACE and the CNE. Under shared savings, it also insures the system. |
| Verification | Seeing a system in operation and the reconciliation platform | We will take you to see an ENEGRIN BESS operating in Mexico and the Ollin Platform, where savings are reconciled every month. Monthly PDF reports for your accounting team and your auditor. |
- Is the savings measurement method in writing, and does it identify the meters and the formulas?
- Does the contract say you will never pay more than you would have paid without the system, under both models?
- What happens if there are no savings one month, if the plant closes, or if you want to buy the system early?
- Who operates, maintains and insures the equipment, and who handles the filings?
- Can you see a system operating in Mexico and the platform used to reconcile every month?
With those five answers in writing, proposals are compared on the same criteria, and your auditor can verify each one after signing.
Use the Ollin Simulator to estimate what a BESS would save your plant.
The simulator asks you to create an account with your company email. Actual savings are measured every month once the system is running at your plant.