Two quotes arrive for the same 120 kW charging site. One is priced materially above the other. The datasheets are almost word for word identical, both say CE, both say OCPP. What separates them is not on the page at all — it sits in the clauses that were never written: the derating condition, the module brand, who owns the payment terminal fee, whether the certificate is held by the seller or by the factory behind it. This is why procurement teams who compare prices first tend to end up comparing them twice. The list below is the one to send before prices are compared.
Why identical ratings can still produce quotes far apart
A charging station is not a single product; it is a stack of decisions that all get compressed into one number on a quote sheet. The power stack, the cable assembly, the meter, the payment terminal, the software licence and the warranty boundary are chosen independently by each supplier, and each choice moves cost in a different direction. A supplier optimising for a low headline price tends to take cost out of exactly the parts a buyer is least able to inspect from outside.
The consequence is a quote sheet that looks comparable and is not. The only reliable way to compare is to force the missing decisions to appear in writing — not as a brochure claim, but as an answer to a numbered question with a document attached.
The twelve questions worth putting in writing
Send these as a numbered list and require a numbered reply. Anything answered with a paragraph instead of a number is a non-answer.
Start with the conditions hiding behind the power rating
Every charger has a rated output. Almost none of them produce that output under the conditions your site actually runs in. A unit marketed as a 120 kW terminal is typically characterised at 25 °C or 35 °C ambient; at 45 °C inside a metal enclosure in direct sun, the same unit may cap itself well below its nameplate figure. Ask for the derating curve as a document, not a sentence — the curve shows power against ambient temperature and against input voltage, and it makes the summer performance of two shortlisted units instantly comparable.
The second condition is sharing behaviour. A dual-connector unit advertised at 120 kW can mean anything: 60 kW fixed per side, 120 kW to whichever vehicle arrived first with the second throttled, or a dynamic split that follows each vehicle's state of charge. For a highway site with high turnover the first model is fine; for a fleet depot with vehicles parked for hours it wastes capacity. This single answer can change the number of units your site needs, which is why it belongs in the same conversation as the 120 kW and 180 kW DC charging station selection itself rather than after it. Sites that expect to grow past a few hundred kW should also ask how the architecture scales — a host-and-terminal charging hub distributes power differently from a row of independent cabinets, and the two are not interchangeable later.
The third is efficiency. A two-point difference in full-load efficiency sounds trivial until it is applied to volume: across 1 GWh of delivered energy, two percentage points is roughly 20 MWh paid for and never sold, plus the cooling load needed to remove it. Combine that with standby draw — a charger that idles at 150 W instead of 40 W costs real money across a ten-year site life — and the cheapest quote stops looking cheapest. Multi-unit sites should extend this question to the distribution design, since the way power is shared between units determines whether the transformer you already own is sufficient.
Then ask what the hardware is actually made of
Questions four and five are the ones that decide year-three costs, and they are the ones most often answered with adjectives. Insist on a part list: power module manufacturer and model, module rating, and whether modules are field-swappable or require return to factory. A hot-swappable module replaced on site in under an hour and a module that travels back to the factory for six weeks are two completely different reliability propositions, and the spare-part price quoted today is the one you will pay without competition for the next decade.
On the cable assembly, ask for length, cooling method, connector brand, terminal plating and mating-cycle rating. Length is a layout question disguised as a specification — a 5 m cable reaches the far side of a parking bay that a 3.5 m cable does not, and re-pouring concrete to fix that later costs more than the difference between the two units. Cooling method decides whether the high-current sessions you are advertising are sustainable or a ten-minute peak, and the mating-cycle rating is the number that predicts when the cable becomes a recurring line item in your maintenance budget.
The meter deserves its own question because it has a legal consequence rather than a technical one. If you intend to charge drivers per kWh, the meter usually has to be of an approved type with a traceable certificate and a sealable enclosure. A supplier who answers "built-in energy meter" without an accuracy class or certificate number is telling you that billing by energy will be your problem to solve after installation.
Then ask who owns the software bill
Hardware is bought once. Software is rented. Question seven exists because the payment terminal is frequently a third-party device with its own acquirer relationship: someone pays a percentage of every transaction, and if the quote does not state who, assume it is you, at a rate you have not seen. Ask for the fee structure, the terminal supplier, and whether the terminal can be replaced without replacing the charger.
Question eight is where "compatible" and "certified" diverge. A claim of protocol compatibility means the charger can talk to a back office under the right conditions; a certification means an independent body tested it against the specification. Ask for the version number and the certifying body, and check the certificate directly rather than accepting a logo. The practical stake is migration: a site built on an uncertified implementation is difficult to move to another network operator later, which quietly converts a one-off purchase into a long-term dependency.
Question nine is the most common omission in an otherwise professional quote. First-year connectivity is often bundled; the second year onwards is billed per charger, per month, plus SIM traffic and sometimes per API call. Multiply that by the number of units and by ten years before comparing headline prices, and ask explicitly what happens to site data if you change platform provider.
Then ask what happens after handover
The last three questions are about the period when the sales conversation is over. Environmental ratings need to be read against your site rather than in the abstract: an IP54 enclosure in a coastal or de-icing-salt environment is a corrosion question, not a water question, so ask whether a higher corrosion-protection option exists and whether anti-condensation heating is standard or extra. Ask for the operating temperature range with the derating that accompanies it, because the two numbers are meaningless separately.
Certification is the question buyers most often get wrong. Ask who holds the certificate — the seller's brand, the manufacturing site, or an unrelated third party — and ask for the report number so the issuing body can be checked. Which test regime applies depends on the market and the product type, and the requirements of one do not satisfy the other. A unit certified under one scheme is not automatically acceptable under another, and subsidies and grid connections are commonly refused on exactly this point. A supplier that holds its own approvals can usually produce the documentation immediately rather than deferring it to the contract stage.
Finally, warranty scope and service terms. Ask which components are excluded — cables, fans, filters and contactors are the usual suspects — and ask for numbers rather than assurances: remote diagnosis response time, on-site arrival time, spare-part delivery time, and who performs the work when the site is three countries away. Then confirm what the Incoterms figure in the quote actually covers, because a delivered price that excludes unloading, foundations, commissioning and training is not a delivered price.
Three answers that should end the conversation
Red flag 1 — no derating curve exists
A supplier who cannot produce this document is unlikely to have characterised their own product. Whatever the datasheet claims, nobody in the conversation knows what the unit does at 45 °C.
Red flag 2 — certificates offered only as images
A screenshot cannot be verified. Request the certificate number and the issuing body, then look it up. If the holder name differs from the seller, that is not necessarily disqualifying — but it must be explained before contract, not after.
Red flag 3 — one total price, no breakdown
A single number gives you nothing to hold the supplier to. Every later change — an extra cable, a payment terminal, a software tier — becomes a negotiation with no baseline. A quote that cannot be itemised cannot be compared, and should not be signed.
Turn the answers into a single comparison sheet
The method only works if it is applied identically to every supplier. Build one sheet with the twelve questions down the left column and one column per supplier, and refuse to fill any cell from a brochure. Attach the same five inputs to every request so the answers are answering the same question:
• Site plan with bay count, bay dimensions and expected daily sessions
• Available transformer capacity and incoming supply voltage
• Target power per session and how many vehicles charge simultaneously at peak
• Destination market, and which approvals or subsidy schemes the project depends on
• Whether energy will be billed to drivers, and by which payment method
With those five inputs stated, a supplier has no room to answer a different question than the one you asked, and the twelve answers become a like-for-like table. From there the commercial comparison is straightforward: convert the recurring items — efficiency loss, software fees, transaction charges, cable and module replacement — into a ten-year figure, and compare it against the capital cost instead of next to it. That conversion is simple arithmetic, and it is worth doing once per supplier rather than once per project. Reference documents for the equipment types discussed here are usually available through the technical document library.
What this list changes
None of the twelve questions is unusual, and none of them requires technical expertise to ask. What they change is the sequence: instead of comparing prices and then discovering the differences during commissioning, you surface the differences first and let them price themselves. The outcome is not always a lower price, but it is a price with a traceable basis behind it, and fewer surprises once the units are on site.
For public network projects where uptime is contractually measured, the same discipline applies to availability guarantees and service terms, which is why the twelve answers are usually reviewed alongside the site's public fast charging solution design rather than in isolation.
Score every quote against the same twelve rows
One column per supplier, twelve rows, no cell filled from a brochure. If an answer only exists verbally, treat it as missing until it appears in the documents.
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