What Is a PCS Skid? Inside the PCS Container and How It Differs from a Battery Container

A PCS skid is the power conversion system (PCS) of a battery energy storage system packaged with its medium-voltage step-up transformer. Housed in a container-type enclosure, the package is a PCS container. On discharge, the PCS converts the batteries' DC output to AC and the transformer steps it up to medium voltage for the site's MV collection system; on charge, power flows the other way.

The examples below come from Richborough Energy Park in Kent, UK, where ETENZ manufactured the 20 PCS containers for NR Electric: eighteen 40 ft high cube units and two 20 ft high cube units. The project is described in the UK BESS PCS containers case study.

What is inside a PCS container

The main equipment is the PCS and the step-up transformer. The PCS, also called the battery inverter, is bidirectional: it converts DC from the batteries to AC on discharge and AC from the grid back to DC on charge. In this kind of unit the PCS delivers low-voltage AC, and the transformer raises it to medium voltage. The equipment supplier decides the combination, and some PCS containers also carry an LV panel and an MV ring main unit.

Cooling and maintenance access decide how the doors are laid out. At Richborough, each 40 ft unit has four mesh ventilation doors in the middle of the long side, facing the transformer compartment. They ventilate it in service and open fully for maintenance; the other doors are solid.

PCS container vs battery container

A battery container holds battery racks and the battery management system (BMS) and is sized by energy, in MWh, like the 143 BESS enclosures of 5 MWh built for Zhongwei, Ningxia. A PCS container holds no batteries and is rated by power, in MW: each 40 ft unit at Richborough houses a 5.5 MW power conversion and step-up set.

Their cooling differs. Batteries are sensitive to temperature, so a battery container is sealed and holds them in a narrow temperature band with liquid cooling or air conditioning; the enclosure side is covered in BESS enclosure design requirements. In a PCS container the heat comes from the PCS and the transformer, and the transformer compartment is ventilated through mesh doors or louvers. A liquid-cooled PCS also needs a PCS inverter liquid cooling unit, whose mounting, pipe penetrations and auxiliary supply are designed together with the enclosure.

Two other pieces of equipment are often set beside it. An enclosure that holds only the step-up transformer and MV/LV switchgear, with the PCS placed elsewhere, is a step-up substation enclosure, such as the ‎20 ft BESS step-up substation enclosure with its HV, transformer and LV rooms. The substation sits at the grid connection: the PCS containers across a site each step up to medium voltage, and the collected power reaches the high-voltage grid through a substation.

‎40 ft or 20 ft: matching the container to the power rating

The enclosure follows the equipment. The PCS and transformer supplier sets the rating and the layout, and the enclosure manufacturer builds to that supplier's technical requirements. The PCS containers at Richborough use two high cube container sizes:

The 20 ft unit houses half the power of the 40 ft unit in roughly half the length. Both are 2,438 mm wide and 2,896 mm high, share the same cross-section and carry standard corner castings and container numbers. Specifications and delivery scope for the 40 ft unit are on the ‎40 ft BESS PCS container product page.

What the enclosure manufacturer supplies

The equipment supplier provides the PCS, the transformer and the technical requirements; the enclosure manufacturer builds the enclosure and its auxiliary systems. For Richborough, ETENZ completed the following at its factory to NR Electric's technical requirements:

• Enclosure: the 40 ft and 20 ft high cube structures, the mesh ventilation doors of the transformer compartment, door locks and seals.
• Lighting: CE-marked LED lighting and 90-⁠minute emergency lighting.
• Fire detection and egress: smoke detectors and exit signs.
• Environment and power: heaters, temperature and humidity controllers with an English interface, and UK-standard sockets.
• Exterior: painted in the project's livery, so every container arrived on site in the station's common look.

NR Electric supplied the PCS and transformers. PCS and transformer manufacturers and BESS integrators can hand ETENZ the enclosure manufacturing and auxiliary fit-out and have it built around their own equipment and brand; see BESS enclosure manufacturing and integration.

PCS skid, MV skid or PCS container

PCS stands for power conversion system. A skid is the steel base frame on which equipment is pre-assembled and moved as one piece, so a PCS skid is the PCS and its step-up transformer built as one package. Inside a container-type enclosure the same package is a PCS container, the term ETENZ uses.

Suppliers use these names in different ways. One MV skid includes the PCS, another carries only the MV transformer and switchgear. The equipment list shows what a given unit contains more reliably than its name.

Richborough Energy Park: 20 PCS containers

Richborough Energy Park in Kent, UK, is a 100 MW / 100 MWh battery energy storage system connected to the transmission grid through National Grid's 400 kV Richborough substation. ETENZ manufactured its 20 PCS containers for NR Electric: eighteen 40 ft high cube units, each housing a 5.5 MW power conversion and step-up set, and two 20 ft high cube units of 2.75 MW each.

The containers were delivered in July 2022 and reached site in October 2022. The station was connected to the grid in December 2023 and is in commercial operation. Delivery and enclosure details are in the Richborough case study.

Frequently asked questions

What is the difference between a PCS container and a battery container?

A battery container holds battery racks and the BMS, is sized in MWh and controls temperature and humidity inside. A PCS container holds the PCS and the step-up transformer but no batteries, is rated in MW and ventilates its transformer compartment.

What does PCS stand for in BESS?

Power conversion system: the bidirectional converter between the batteries and the grid. A PCS container is the enclosure that houses it together with the step-up transformer.

Is a PCS container the same as a step-up substation enclosure?

A step-up substation enclosure holds only the step-up transformer and MV/LV switchgear, with the PCS placed separately. A PCS container houses the PCS as well.

What size container is used for a PCS skid?

The size follows the equipment. At Richborough Energy Park, each 40 ft high cube (12,192 × 2,438 × 2,896 mm) houses a 5.5 MW power conversion and step-up set, and each 20 ft high cube (6,058 × 2,438 × 2,896 mm) houses 2.75 MW.

Is a PCS skid the same as an MV skid?

It depends on the supplier. Some MV skids include the PCS; others carry only the MV transformer and switchgear, with the PCS placed separately. The equipment list shows which.

To have an enclosure built around your PCS and transformer, send the equipment layout and technical requirements to ETENZ and request a quote.