# Greenvolt Power Breaks Ground on 600 MW / 2,400 MWh Siedlce BESS in Poland, Central Europe’s Largest Grid Storage Hub

> Greenvolt Power has officially broken ground on the 600 MW / 2,400 MWh Siedlce utility-scale battery energy storage project in eastern Poland, representing Central and Eastern Europe’s largest standalone grid storage installation.

- **Publish Date:** 2026-09-20
- **Category:** energy-storage
- **Reading Time:** 5 min
- **Original Source Citation:** [Greenvolt Power & Polskie Sieci Elektroenergetyczne (PSE)](https://greenvoltpower.com/news/groundbreaking-siedlce-600mw-bess-poland-september-2026)
- **Tags:** Greenvolt Power, BESS, Poland, PSE, Capacity Market, 400 kV, Grid Storage
- **Canonical URL:** https://voltformer.com/news/greenvolt-power-breaks-ground-600mw-2400mwh-siedlce-bess-poland
- **Markdown Source:** https://voltformer.com/news/greenvolt-power-breaks-ground-600mw-2400mwh-siedlce-bess-poland.md

## Direct High-Voltage Interconnection to PSE 400 kV Transmission Grid

Awarded a 17-year capacity agreement under Poland’s state capacity market auction, the 4-hour Siedlce BESS facility is situated adjacent to PSE’s 400 kV Siedlce Ujrzanów substation.

The plant incorporates three dedicated 250 MVA 400/33 kV step-up transformers, containerized lithium iron phosphate (LFP) energy storage enclosures, and centralized liquid thermal management systems engineered for continental winter temperatures.

## Stabilizing the Synchronous Continental European Connection

With the Baltic States recently desynchronizing from the Russian IPS/UPS grid to synchronize fully with Continental Europe (ENTSO-E), the Siedlce battery facility will provide critical fast frequency response (FCR) and automatic frequency restoration reserve (aFRR).

Commercial operation is targeted for late 2027, unlocking multi-gigawatt onshore and offshore wind integration across the Polish electricity network.

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