Containerised Energy Storage — a Sizing Guide from 1 MWh to 1000 MWh

Power or capacity? MW and MWh are not the same

MW describes how fast the storage system can deliver energy, MWh — how much it can hold. A 1 MW / 2 MWh block discharges its full capacity in 2 hours. The same container with a PCS twice as powerful would do it in an hour, but the thermal load on the cells would be higher.

C-rate — what 0.5C and 0.25C mean

C-rate is the ratio of power to capacity. 1C means discharge in one hour, 0.5C in two, 0.25C in four. A lower C-rate means less degradation and a lower PLN/kWh cost, a higher one means more revenue from services that pay for power.

2h, 4h, 8h configuration — which one to choose

How to match scale to the application

System architecture

20 ft container — how many MWh it holds today

A 20 ft unit holds 5.0–6.9 MWh, depending on the cell generation. Dimensions 6.06 × 2.44 × 2.90 m, weight 30–38 t, footprint 15 m² plus a service zone.

Liquid cooling vs. air cooling

Liquid cooling keeps the temperature difference between cells below 3 K, versus 8–12 K in air-cooled systems. The result: even pack degradation, higher availability in hot weather, and the ability to operate at 0.5C without derating.

PCS, transformer, substation

On the AC side, the block is completed by a 1.25–2.5 MW PCS, a transformer matched to the voltage level, and an MV switchgear. Above 20 MW, projects use a dedicated on-site substation (GPZ) with an HV line bay.

EMS and SCADA integration

The EMS drives the entire revenue stream: it schedules charging and discharging, maintains the regulation band and reports availability. Protocols: Modbus TCP, IEC 61850, DNP3, REST API.

Cells: CATL, EVE, Hithium, BYD, REPT, CALB

How much does energy storage cost

CAPEX structure

How the price in PLN/kWh drops with scale

LCOS — the levelized cost of storage

LCOS covers CAPEX, cost of capital, service, augmentation and losses. For a 20 MWh project with one cycle per day over a 15-year horizon, it typically falls in the PLN 320–430/MWh range.

Scaling: from a single block to a 1000 MWh project

The architecture does not change with scale — only the number of blocks and the connection voltage level do. That is why a 20 MWh project can be expanded to 100 MWh without replacing the existing infrastructure, provided the design allowed spare capacity in the MV bay and on site.

Revenue models

Arbitrage on the TGE power exchange

The daily spread on the day-ahead market currently allows PLN 180–320/MWh per cycle at 250–300 cycles per year. This is variable revenue and does not finance a project on its own.

Capacity market — standby agreements

A capacity agreement provides a fixed, indexed payment per MW of obligation. A new storage unit can secure a multi-year contract, which forms the basis for debt financing.

Ancillary services and DSR

aFRR, mFRR and DSR use the same installation outside the hours of the capacity obligation. Shallow regulation cycles have little effect on degradation.

Peak shaving and the capacity fee

For an industrial off-taker, cutting 15–25% off the peak during peak hours translates directly into a lower capacity fee and no penalties for exceeding contracted capacity.

Permitting: building permit above 300 kWh

Installations above 300 kWh require a building permit. Grid-scale projects also need compliance with the local zoning plan (MPZP) or a zoning decision, fire-safety approval, and — above 10 MWh of capacity — a URE license for electricity storage.

Grid connection

The deadline for issuing connection terms is 120 days for MV and 150 days for HV from a complete application. For power above 5 MW, a deposit of PLN 30/kW of connection capacity is required.

Fire safety and approval by the State Fire Service (PSP)

The standard is flammable-gas detection at module level, a zoned fire-suppression system, a minimum of 3 m between containers, and design approval by a fire-safety expert before the PSP acceptance inspection.

Delivery schedule