Energy Storage

How a storage plant is connected

A storage plant connects to the grid through its PCS and a step-up transformer, cycling daily between charging, discharging and standby with power flowing in both directions. Unlike a conventional load, the transformer remains energised during standby, so its no-load loss is charged directly to auxiliary consumption and affects round-trip efficiency and project returns.

Electrochemical storage is usually built from prefabricated enclosures or containers, with battery units, PCS and step-up equipment lined up along the site — compact, and installed on a tight schedule. The equipment has to run outdoors through temperature swings, humidity and dust while keeping site wiring and later maintenance to a minimum.

What storage sites have to cope with

Equipment choices are driven by round-trip efficiency and by the pace of construction: every kilowatt-hour of auxiliary consumption dilutes the return, and every day of site work delays grid connection.

• Bidirectional operation with long standby periods, so no-load loss is charged to auxiliary consumption
• Harmonic content on the PCS side, which the vector group and winding arrangement have to keep away from the grid
• Compact container layouts that limit the footprint and transport dimensions of the step-up equipment
• Outdoor humidity, dust and temperature swings, calling for sealed construction and a high degree of protection
• Largely unattended sites, which require long maintenance-free intervals

In short, a storage site needs primary equipment that is frugal in standby, simple to wire and unlikely to be opened again once it is running.

Coreda's approach for storage sites

For PCS step-up units and the LV circuits inside the enclosures we build around fully sealed amorphous-alloy transformers, with compact substations and withdrawable LV cubicles to cut installation and maintenance work.

Recommended configuration:

• SBH15-M sealed amorphous-alloy transformer: fully oil-filled sealed design, no-load loss 70% below the group I values of GB/T 6451 and load loss 15% below the standard values, built to JB/T 10318—2002.
• ZGS11 compact pad-mounted substation (American style): fully sealed tank and fully insulated design, small and compact, suitable for both ring-main and terminal supply, with good short-circuit withstand.
• GCS withdrawable LV switchgear: rated up to 4000 A, with busbar, functional-unit and cable compartments separated from one another, covering incoming, feeder and reactive-power compensation duties.
• Dyn11 vector group: reduces the effect of harmonics on the grid and improves power quality at the connection point.

Equipment is delivered in groups that follow the container rows: one step-up circuit and one LV feeder per PCS, with the substation lifted into place so that only MV cable and communication connections remain on site.