IN Brief:
- Construction has started at Domokos on a 251.9MW solar plant paired with an expected 375MWh storage system.
- Tsakos Group owns 60% of the project vehicle, while METLEN holds 40% and is responsible for construction and energy management.
- The project has financing support from the EU Recovery and Resilience Facility, with the battery power rating and commissioning date not yet disclosed.
METLEN and Tsakos Group have begun constructing a combined solar and battery project at Domokos in central Greece. The development will incorporate a photovoltaic plant rated at 251.9MW and storage with an expected energy capacity of 375MWh. Construction follows a joint development agreement under which the two Greek groups will share ownership while METLEN takes responsibility for delivery and subsequent energy management.
The development is held through a jointly owned special purpose vehicle. Tsakos Group has a 60% interest and METLEN holds the remaining 40%. METLEN will undertake construction and retain responsibility for the plant’s energy and commercial management, placing delivery and subsequent market operation within the same organisation. The investment is supported by lending through the European Union’s Recovery and Resilience Facility, part of NextGenerationEU.
The two partners marked the transition to construction at a ceremony attended by regional and local representatives. Neither the completion date nor the budget was disclosed in the project information available on 12 November. The developers also have not specified the battery’s maximum discharge power, its supplier, the inverter configuration, or the voltage at which the combined installation will connect to the network. Those figures will be necessary to determine the storage system’s duration at its rated power and the detailed connection arrangements.
The partners have given the solar plant’s generating capacity in megawatts but described the battery in megawatt-hours. The latter measures stored energy rather than instantaneous output, and the battery’s discharge power has not been announced. Its duration at rated output therefore cannot be calculated: a 375MWh system would operate for different periods depending on whether its rated output were 100MW, 150MW, or another figure. The available project specification does not justify describing it as a two-hour or four-hour installation.
Pairing photovoltaic generation with a battery can permit energy captured in the middle of the day to be exported later, subject to operational losses, the agreed grid connection capacity, and applicable market rules. A storage system may also alter the net export profile at the connection point, although any specific provision of balancing or ancillary services depends on the installed controls, performance testing, and market qualification. None of those individual service commitments has yet been established for Domokos.
Electrical integration will determine how the photovoltaic and storage systems operate together once the site is energised. The panels generate direct current that must pass through inverters before electricity can be delivered to an alternating current network. Batteries also require power conversion equipment capable of controlling charging and discharge, alongside switchgear, transformers, electrical protection, and monitoring. The developers have not specified whether the two assets will share conversion or grid connection equipment, so their precise configuration remains open.
Electrical installation at Domokos must bring together photovoltaic strings, storage enclosures, cable routes, substation equipment, and monitoring and protection systems. The construction sequence must allow parts of the plant to be tested and isolated safely before they are energised. Coordination is especially important where a single connection point is used by equipment with different operating characteristics, although METLEN has not specified whether that shared arrangement will apply at the site.
METLEN will also manage the electricity produced and stored at Domokos once the plant is operational. The generation forecast, battery charging requirements, export limits, and market dispatch instructions will have to be reconciled by the site’s control systems. Operating choices will remain constrained by usable battery energy, inverter capability, thermal limits, and any reserve margins required under the applicable connection and market arrangements. Those physical limits define the range within which commercial optimisation can take place.
Tsakos Group’s investment extends its business beyond the maritime operations for which it is known, while METLEN’s responsibilities encompass both delivery and operation. The project is backed by loans through the European Union’s Recovery and Resilience Facility, although the developers have not put a figure on the financing. The start of physical construction moves the project into a phase in which equipment procurement, network arrangements, and the construction programme will begin to determine when generation and storage capacity can be brought online.
The location and connection design will have a direct bearing on how useful the battery is to the wider system. Storage can shift some solar electricity away from hours of high local generation, but it cannot exceed the available charging power, battery energy capacity, or grid export limit. Participation in balancing services would require compatible controls and the relevant market qualifications. Neither the plant’s export capacity nor any committed balancing products has yet been specified, leaving those functions to be confirmed as engineering and commercial arrangements develop.
Work at Domokos has now moved beyond project planning, but construction completion and grid energisation dates remain outstanding. The engineering programme must establish the storage discharge rating, equipment selections, cable and substation design, and commissioning sequence before the announced capacity can be brought into operation. Until those specifications and dates are confirmed, the developers’ substantiated project scale is 251.9MW of photovoltaic generation paired with an expected 375MWh of storage.
