The dependency chain
Each decision below constrains everything under it and is only weakly constrained by anything above. Changing something near the top after the design is underway is what turns a quotation into a revision cycle; changing something near the bottom is routine.
| Order | Decision | What it locks downstream |
|---|---|---|
| 1 | Operating objective, in one sentence | Everything. Cycle count, C-rate, cell selection, warranty basis and controls all follow from it. |
| 2 | Power and energy, as two separate numbers | PCS rating, cell chemistry and format, DC current path, cooling class, footprint. |
| 3 | Grid connection point and its available capacity | Transformer, switchgear, protection scheme, whether the design is even permissible at that point. |
| 4 | Voltage architecture and cluster split | BMS topology, contactor and fuse sizing, rack count, parallel behaviour. |
| 5 | Cooling class | Cabinet density, footprint, auxiliary power, maintenance regime, acoustic profile. |
| 6 | Fire strategy and the authority that approves it | Spacing, enclosure rating, detection and suppression, and often the site layout. |
Why the objective has to be a single sentence
“Peak shaving, and also backup, and maybe arbitrage later” is three projects with incompatible requirements. Backup wants the pack full and rarely cycled; arbitrage wants it cycled hard every day; peak shaving wants power available at unpredictable moments. Cell selection and warranty basis pull in different directions for each.
Write the primary objective as one sentence, then list the secondary ones explicitly as subordinate, with the state of charge each is allowed to claim. That sentence is what a supplier prices against, and a system sized for the sizing method behind peak shaving looks quite different from one sized for daily arbitrage.
The demand-bill arithmetic behind the first case is worked through in the peak-shaving sizing note.
Power and energy are not one number
A cabinet described only in kWh has not been specified. The same 200kWh can be built to deliver 50kW for four hours or 200kW for one, and those are different cells, different thermal designs and different prices. State both, then state the duration they apply at, and the three together define the duty.
Check the implied C-rate before going further. A high rate against a modest energy figure narrows cell choice sharply, and it is better to discover that at the specification stage than after a layout exists.
The grid connection can veto the design
This is the item most often deferred and least often deferrable. Available capacity at the connection point, the existing transformer rating, the protection scheme it was built with, and the utility process for adding storage behind it can all constrain the project before any equipment is chosen.
Start that conversation in parallel with the technical work rather than after it. A utility study that returns a lower export limit or requires a protection upgrade changes the economics, and it is the one input with a lead time nobody controls.
What can safely stay open
Not everything needs an answer before a quotation. Trying to close these too early produces false precision and slows the parts that matter.
- Enclosure colour, finish and branding
- Exact cable routes and gland positions inside the cabinet
- The monitoring platform and dashboard layout, so long as the protocol is agreed
- Spare-parts list and quantity, once the responsibility for holding them is settled
- Training scope and documentation format
- Commissioning date, provided the dependency on the grid process is understood
Who owns each interface
The BMS reports limits, the PCS converts power, the EMS decides what the system should be doing, and the site controller and metering tell it what the site is doing. Each works on its own. The project risk lives at the four boundaries between them.
Name the responsible party for each boundary in writing before ordering. Specifically: who resolves a disagreement between the BMS current limit and the PCS behaviour, who owns the protocol revision when one side updates firmware, and who attends site when a fault is not attributable on the first visit. The sourcing note covers how that ownership changes what a quotation is worth.
Cooling and fire are coupled decisions
Cooling class sets cabinet density, and density sets spacing, and spacing is frequently what a fire authority has an opinion about. Choosing liquid cooling to shrink the footprint and then discovering that the required separation restores it is a common and expensive sequence.
Take the heat estimate and the local fire requirement together. The method for the first is in the cooling note; the second belongs to a qualified professional in the installation country, and no supplier can answer it for you.
What to send for a configuration review
The JKESS C&I ESS Cabinet listing covers configurable project capacities from 64kWh to 2.09MWh with air-cooled or liquid-cooled options. The written quotation defines the equipment and services actually supplied.
- The objective in one sentence, with any secondary objectives marked subordinate
- Usable energy and charge and discharge power, with the duration they apply at
- Measured load profile at the meter interval, where demand charges are involved
- Grid connection point, voltage, available capacity and existing transformer
- Existing PV, generator, switchgear and metering
- Site: indoor or outdoor, ambient range, altitude, and the space available
- Cooling preference, or the constraint that will decide it
- Protocols and monitoring expectations for the PCS, EMS and site controller
- Country, applicable certification target, and who is handling fire approval
- Delivery scope, quantity and the date the system must be operational
Fix the top three, then ask for a price
Objective, power and energy, and the grid connection. With those settled the rest of the design converges instead of looping.