Castor
Operating, 31 MW · 63 MWh, in Vlissingen, owned by Return (formerly SemperPower). Every fact below is as a published source states it, with the address beside it; a field not shown is one no source gave, and nothing is guessed.
The battery
| Power | 31 MW |
| Capacity | 63 MWh |
| Duration | 2.0 hours |
| Status | Operating, as of 20 October 2026 |
| Stated date | November 2023, delivered, operations taken over late Nov 2023 |
| Municipality | Vlissingen, Vlissingen-Oost, Zeeland |
| Placed on the map | at the site itself, as mapped on OpenStreetMap (Castor) |
| How sure | A dated source confirms it |
Who is behind it
| Owner | Return (formerly SemperPower) |
| Traded by | Return |
| Built by | Rolls-Royce (mtu) turnkey |
What the sources say
Conflict: Rolls-Royce order (ESN 10 November 2022) said 30 MW / 63 MWh; RVO report (April 2026) says 30 MW / 60 MWh each for Castor and Pollux; Return gives 60 MW / 120 MWh for Castor & Pollux combined. Same site as Pollux.; Owner figure used: Return gives 60 MW / 120 MWh for Castor and Pollux together (locations page read 20 October 2026, 'Operational'); RVO (April 2026) splits this as 30 MW / 60 MWh each. Earlier figures: 30.7 MW / 62.6 MWh on delivery (November 2023), 30 MW / 63 MWh in the Rolls-Royce order (November 2022). Confirmed: dated sources say it runs.
Evidence and sources
- source: solarmagazine.nl/nieuws-zonne-energie/i35940/grootste-batterij-v…
- source: energy-storage.news/semperpower-starts-operations-on-62mwh-rolls-ro…
- source: return.energy/locations
- position: openstreetmap.org/way/1183962439
From the owners’, developers’ and builders’ own releases, grid operators’ and permit notices and the trade press, read by Vitreous. No Dutch body publishes a meter, an instruction or a payment for a named battery, so this page carries none. List id NL-B02.