Container BESS: What Ships in the Box and What You Still Have to Buy

A containerised battery system is a complete product when it leaves the factory and an incomplete project when it arrives on site. The gap between those two statements is where budgets go wrong. Typically six items sit outside the container price, and three of them are things buyers assume are included. This article draws the boundary precisely, so the comparison you run between two suppliers is a comparison of the same scope.

What Is Actually Inside the Container

A modern 20 ft or 40 ft BESS container is not a box of cells. It is a small electrical room, and the scope inside it is well defined.

The first six rows are the product. The last four rows are the project. The paperwork that travels with the container is a third category entirely — the five documents that decide whether it clears customs is a separate exercise from the scope question. Suppliers differ on exactly where they draw the line, and a quote that does not state the line is not comparable to one that does.

The Six Items That Are Almost Never in the Price

These are the ones that turn a tidy budget into a variation order. None of them is exotic — every project needs them. They are simply not part of what a container factory ships.

Add those up and the balance-of-plant is commonly 25–45% of the total project cost. A container quoted at a headline price per kWh that ignores this is not cheaper — it is a smaller number describing a smaller scope.

Two quotes are only comparable when they draw the boundary in the same place. Most do not, and that is why the cheap one wins the comparison and loses the project.

The Boundary Question That Decides Everything

Ask one question before you compare prices: where is the point of interconnection, and who owns each device up to it?

Utilities use several terms that sound interchangeable and are not. The point of interconnection (POI), the point of common coupling (PCC), the metering point and the ownership boundary can be four different physical locations on the same site. The protection scheme, the metering arrangement and the export limitation all hang off which one your project uses.

• If the container connects at low voltage, the transformer is the utility’s or the site’s, and the container scope usually ends at its own AC terminals.
• If the container connects at medium voltage, someone has to supply the step-up transformer and the MV switchgear. Sometimes that is packaged with the container, often it is not.
• If the site exports, the protection and metering must meet the utility’s specification, not the supplier’s. That specification is a document you should obtain before signing, not after.

A single-line diagram with the boundary drawn on it, signed by both sides, prevents most of the arguments that otherwise happen during commissioning.

Factory Test and Site Commissioning Are Not the Same Test

Every container is tested at the factory. That test proves the container works. It does not prove the project works, and the difference is where schedules slip.

The most common schedule failure is not a broken container. It is a container that passes its factory test and then cannot be energised because the protection settings were never coordinated with the upstream relay, or because the utility’s witness test was never booked. Both are project-scope items, and both are invisible in a container quotation.

Three Questions to Ask Before You Sign

1. “Send me the scope boundary on a single-line diagram.” Not a datasheet — a drawing with the boundary marked. If the supplier cannot produce one, the scope is undefined.
2. “Which grid code will this be certified against, for this country, and who files the application?” CE marking is not a grid-code certificate. The answer should name the standard and the party responsible for the utility submission.
3. “What is included in commissioning, and what is chargeable?” Site commissioning support, witness-test attendance and post-commissioning tuning are the three items most often assumed included and most often invoiced separately.

Frequently Asked Questions

Does a containerised BESS include the transformer?

Usually not. A standard container scope ends at its own AC terminals, at low voltage. If your site connects at medium voltage, the step-up transformer and MV switchgear are normally supplied by the EPC or the owner, and they are 8–15% of project cost. Some suppliers offer an MV-skid option; ask explicitly.

Is the fire suppression system in the container price?

Yes, but check which standard it is designed to. Aerosol, perfluorohexanone and water mist are all used, and local codes differ on which is acceptable for the occupancy and the country. “Fire suppression included” without a standard reference is not enough for a permit submission.

Who is responsible for grid-code compliance — the supplier or the EPC?

The equipment supplier certifies the equipment to a named standard. The project owner or EPC owns the interconnection application and the plant-level studies. No supplier can make a project compliant by shipping a certificate, because compliance is assessed at the point of connection, not at the factory gate.

How long does site commissioning take for a container project?

Typically one to three weeks for a single container including utility witness testing, and longer where protection coordination studies are still open when the container arrives. The commissioning duration is driven by the project’s paperwork more often than by the equipment.

Can the container be energised before the utility witness test?

Not for export-capable systems in most jurisdictions. The witness test is what authorises parallel operation. Energising for commissioning in island mode or behind an open breaker is usually permitted; exporting to the grid before the test is not.