Nameplate energy is not the number you are buying
The headline kWh figure is usually cell nameplate capacity at beginning of life under laboratory conditions. What the site gets is that figure reduced by the permitted state-of-charge window, by temperature derating in the actual ambient, and by degradation to whatever point the warranty guarantees.
Ask every supplier for usable energy at end of warranty, at the site ambient, at the intended rate. Quotes that looked ten percent apart often move by a great deal more once they are all expressed that way.
Warranties measure different things
One warranty counts years, another counts full equivalent cycles, another counts energy throughput, and each guarantees a different retained-capacity percentage at the end. They are not versions of the same promise and they cannot be compared side by side until they are restated against your duty cycle.
Check what voids them as well: operating temperature bounds, depth of discharge, rate limits, connectivity requirements for remote monitoring, and whether a missed maintenance visit is a breach.
The line items that quietly sit outside the quote
A quotation is comparable only once the excluded work is priced by someone. These are the items most often left to the buyer without being stated as exclusions, and several of them are large.
- Transformer, switchgear, protection relays and the utility interconnection study
- Civil works: foundation, bollards, drainage, fencing, access road
- Fire detection and suppression, and the local approval process for it
- Freight, import duties, unloading equipment and site handling
- Commissioning, grid compliance testing and witness testing
- Communications: the site link, SIM or fibre, the cloud platform and what happens when its term ends
- Spares holding, response times and the cost of a service visit outside warranty
- Training, operating documentation, and as-built drawings
Who owns the boundary between the parts
The battery, the PCS, the EMS, the cooling, the fire system, the switchgear and the site controller each work correctly on their own bench. The risk lives where they meet, and it is real whenever no single party has written down that they own the whole set.
Ask directly who is responsible when the battery and the PCS disagree about a current limit, who resolves a protocol version change, and who attends site when the fault is not attributable on the first visit. A quotation that is cheaper because that ownership is unassigned is not cheaper.
Custom means four different things
Separating these before asking for a price is what stops a lead time from doubling after the order. A supplier should be able to sort your requirements into these four buckets during the first conversation.
- A configurable option that already exists -- no engineering, no schedule impact
- Integration work against existing hardware -- engineering hours and a test cycle
- New mechanical or electrical design -- prototype, validation and tooling
- A new certification target -- test-house time, and usually the longest item on the schedule
Send one specification to every supplier
Quotes come back comparable when they were all answering the same question. Write the requirement once, send it unchanged, and ask each supplier to price exclusions explicitly rather than omitting them.
- The objective, and the measured load profile behind it
- Usable energy and power required, with the duration and the ambient they apply at
- Grid connection, transformer, existing solar or generator, and metering arrangement
- Cooling preference or the constraint that decides it, plus the site environment
- Controls, protocols, monitoring and cyber-security expectations
- Certification target, delivery scope, destination and the date it must be operational
Custom enclosure work follows the electrical design
Where the scope includes bespoke lithium battery enclosures, the mechanical drawing is an output of the electrical design rather than an input to it. Current path, insulation distance, thermal behaviour, lifting points and rack loading all set dimensions, so a shape agreed before those are fixed gets revised.
Questions this raises most often
Because the kWh figure is nameplate capacity, and the quotes differ in usable energy, warranty basis, and how much of the surrounding scope each includes. Normalise all three before comparing.
Usable energy at end of warranty at the site ambient and rate, the warranty basis restated against your duty cycle, and an explicit exclusion list covering grid equipment, civil works, fire approval, freight, commissioning and service.
An unassigned integration boundary. The individual products usually work; the failures happen where the battery, PCS, EMS, cooling and site controller meet and nobody owns the whole set.
It depends which of four kinds it is: an existing configurable option adds nothing, integration work adds engineering and testing, new mechanical design adds prototyping and validation, and a new certification target usually adds the most.
Take it to a part number
Ratings vary between codes that read almost the same, so settle the decision here and then confirm the figures on the product page for the exact code.