Worked example. Two quotations for the same 1 MW / 2 MWh containerized system arrive on the same day. One is EUR 210,000. The other is EUR 233,300. The first is 11 percent cheaper as quoted, and 10.6 percent more expensive once both are pulled onto the same basis. The arithmetic that shows it takes about twenty minutes with a worksheet.
The two quotations, as they arrived
Both documents describe the same system, and neither is dishonest. They are simply written in different units, and the units are where the decision hides.
Line Quote A Quote B
Headline price EUR 210,000 EUR 233,300
Rated energy 2,000 kWh 2,000 kWh
Scope statement exclusions in an annex transformer, suppression and commissioning included
Warranty 5 years, capacity retention 70 percent 10 years, throughput guarantee 6,000 MWh
Efficiency 98.5 percent 98.5 percent, over 25 to 100 percent load
Figures and prices in this comparison are a worked example built to demonstrate the normalisation method. They are illustrative and not taken from a delivered project.
Two lines in that table are already comparable, and they are the two that tell you least. Rated energy is identical. Efficiency is identical until you read the qualifier attached to one of them. Everything that decides the project sits in the rows where the two columns are written in different units.
Why the price gap is the last thing to look at
Price is the only line that arrives pre-normalised, which is exactly why buyers anchor on it. Capacity arrives as rated or usable. Efficiency arrives at one load point or across a range. The warranty arrives in cycles, in years, or in throughput. Scope arrives as an inclusion list or as an exclusion annex. Comparing those directly is not a comparison, it is a preference.
If a quotation does not state the load range behind its efficiency figure, the efficiency line cannot be normalised, and any price difference it justifies is unknown. If the capacity figure does not state its depth-of-discharge convention, the capacity line cannot be normalised either.
The normalisation worksheet, line by line
The worksheet has one rule: no line is compared until both columns describe the same thing. Practically, that means starting with the scope statement, because scope is where the numbers are created.
Excluded item Quote A Quote B
MV transformer and switchgear excluded included
Fire suppression excluded included
Commissioning labour excluded included
Spares and first-year service excluded included
Four exclusions is not a defect in Quote A. It is a different offer. The comparison only becomes arithmetic once those items are priced and added to the column that omits them. Using the buyer's own budget figures for the same four items:
Quote A headline price: EUR 210,000
Transformer and switchgear: EUR 26,000
Fire suppression: EUR 9,000
Commissioning labour: EUR 7,000
Spares and first-year service: EUR 6,000
Comparable total for Quote A: EUR 258,000
Comparable total for Quote B: EUR 233,300
Quote A is EUR 24,700, or 10.6 percent, more expensive
The second normalisation is the one most buyers skip. Quote B attaches a throughput guarantee to its warranty. Quote A states a retention percentage and no throughput figure, so its warranty cannot be converted into the same unit at all.
Three lines where the gap is created rather than revealed
The efficiency line looks identical in both documents until the qualifier is read. One number is measured at rated load. The other holds across 25 to 100 percent of load. A commercial duty cycle built from peak shaving and solar self-use spends a large share of its hours at part load, so the two figures describe different machines doing the same job in the document.
The capacity line hides the same problem one level down. Rated energy is a nameplate. What the site can use is rated energy multiplied by the depth-of-discharge convention, and 90 percent against 95 percent on a 2,000 kWh nameplate is 100 kWh of deliverable capacity that never appears in either price. That is why the capacity line has to be normalised to usable energy before any cost per kilowatt-hour is quoted.
The warranty line is where the two quotations stop being comparable in principle. Quote B attaches a throughput guarantee. Quote A attaches a cycle count and a retention percentage, and if the warranty is written in cycles rather than throughput, a year of deep cycling costs the supplier nothing. Which raises a question that has to be answered before signature: if the warranty term is shorter than the financing term, the residual risk does not disappear, it simply moves to the party holding the asset. What makes the usable-energy line checkable is that both numbers belong on a published datasheet rather than in a sales reply, which is how the container units Ruibit supplies are presented before a purchase order rather than after it.
What the normalised numbers say, and what they leave open
Once both columns are on the same basis, two ratios decide most of the argument.
Quote A comparable total: EUR 258,000
Quote A usable energy at 90 percent depth of discharge: 1,800 kWh
Quote A cost per usable kWh: EUR 143.3
Quote B comparable total: EUR 233,300
Quote B usable energy at 95 percent depth of discharge: 1,900 kWh
Quote B cost per usable kWh: EUR 122.8
Quote B is 16.7 percent cheaper per usable kilowatt-hour
The throughput ratio points the same way and is more informative, because it is the only one the supplier has actually committed to.
Quote B guaranteed throughput: 6,000 MWh
Quote B cost per guaranteed MWh: EUR 38.9
Quote A cost per guaranteed MWh: not computable from the quotation
A number that cannot be computed is a finding, not a gap in the analysis. Quote A has priced a product; Quote B has priced a product plus an obligation. Those are different offers and the worksheet is what makes that visible.
What the worksheet still leaves open is the part no arithmetic settles. The excluded scope in Quote A has been added at the buyer's own budget prices, and whether those prices can be achieved depends on whether the buyer already holds three contracts that Quote B is consolidating into one. The efficiency qualifier needs a measurement condition before it can be warranted at all. The augmentation obligation is not stated in either document. And once the purchase order is signed, four of these items stop being negotiable: the exclusion list, because anything not written into the agreement becomes a variation order; the warranty start definition, whether that is delivery, energization or handover; the party performing commissioning, which fixes who owns the interface when a fault appears during the first energization; and the ownership of the transformer, which carries the grid-connection date with it and cannot be recovered during commissioning.
Questions to ask before you normalise anything
Three questions do most of the work, and each of them has a comfortable answer and an evasive one.
Ask which items the price excludes, and for the exclusion annex. A reply that everything needed is included, with no document attached, cannot be normalised, because exclusions live in annexes and the annex is the only place they can be priced.
Ask whether the efficiency figure is measured at rated load or across a load range, and under what measurement condition. A bare 98.5 percent is not an answer, and it is the number most likely to be quoted back at you when a savings model fails in year two.
Ask what throughput the warranty guarantees and what happens if the system never reaches it. A reply built from a cell datasheet cycle count describes a cell, not a contractual obligation.
If this describes your project Then this quotation wins
you already hold transformer, suppression and commissioning contracts and can beat EUR 48,000 Quote A
you want one party accountable for transformer, suppression and commissioning Quote B
your hold period is five years and the residual risk can sit with the operator Quote A
the asset is financed beyond the warranty term, or you intend to enforce throughput Quote B
your duty cycle is dominated by part-load operation neither, until the efficiency condition is normalised
Laid out this way, the decision stops being about which quotation is cheaper and becomes conditional. Quote A is the cheaper offer when the four excluded items genuinely cost less than EUR 48,000 inside your own contracts, and when a five-year retention guarantee matches the period you intend to hold the asset. Quote B is the cheaper offer when that scope cannot be consolidated for less, when the transformer lead time would otherwise sit on your critical path, and when the throughput guarantee is something you intend to enforce rather than file.
FAQs
1. How do I compare two BESS quotes fairly?
Normalise every line before comparing any. Price arrives in the same unit in both documents, which is precisely why it cannot mislead on its own. Capacity, efficiency, warranty and scope do not.
2. What does a BESS quote usually exclude?
Transformer and switchgear, fire suppression, commissioning labour, spares and first-year service are the common exclusions. They are listed in an annex rather than in the price table, so ask for the annex.
3. Should I compare BESS quotes on price per kWh?
Only after converting rated energy into usable energy. A 2,000 kWh nameplate at 90 percent depth of discharge is 1,800 kWh usable, and at 95 percent it is 1,900 kWh. The 100 kWh difference sits in neither price until you do the conversion.
4. Why does the efficiency figure matter in a quote comparison?
Because one number is measured at rated load and another holds across a load range. A commercial duty cycle spends many hours at part load, so a figure qualified over 25 to 100 percent load describes a different machine from a single rated-load number.
5. What warranty wording should I compare?
Compare the currency, not the term. A warranty written in cycles does not charge the supplier for deep cycling, while a throughput guarantee does. If the term is shorter than the financing term, the residual risk stays with the asset owner.
6. Does the cheapest BESS quote win?
Only under stated conditions. The cheaper offer wins when the excluded scope genuinely costs less inside your own contracts and the hold period matches the warranty. The higher offer wins when that scope cannot be consolidated for less and the guarantee will be enforced.
