HEDNO Announcement on the Submission of Requests to Add Energy Storage to Existing and New RES Plants via a Common Inverter
19.01.2026
The Network Operator announces that, pursuant to Article 11G of Law 4685/2020, as in force, the online RES platform has been updated to enable the submission of requests for the addition of an energy storage system via a common inverter to RES plants of independent producers. Requests fall into two categories:
- A request to add an energy storage system that increases the plant’s short-circuit contribution, compared to the Final Connection Offer (FCO) that has been issued.
- A request to add an energy storage system that does not increase the plant’s short-circuit contribution, compared to the Final Connection Offer (FCO) that has been issued.
Requests under case (a) can be submitted only during the first 10 days of the application cycle, as they reserve extra electrical capacity. Requests under case (b) can be submitted at any time throughout the month via the “Add energy storage system” option, as they do not require any additional electrical capacity.
An increase is deemed to occur when the following condition is met:
1.1 × rated apparent power of the new common inverter > total short-circuit power allocated to the plant under the issued FCO
Example:
Assume a PV plant with an installed capacity of 400 kW.
If the rated apparent power of the new common inverter is up to 400 / 1.1 = 363.6 kVA, the request falls under case (b). If it exceeds this value, the request falls under case (a).
Documents required for connection requests:
- A) Supporting documents
For case (a) — request to add an energy storage system (new request) — the online platform requires the applicant to submit the supporting documents listed in the form “Supporting documents for a new connection request for a RES or CHP or storage station”, available at the link below, updated to include the energy storage system:
For case (b) — request to add an energy storage system (producer action) — a dedicated field is provided at the final stage of the application on the online platform, where the applicant must upload the supporting documents submitted with the initial connection request for the RES plant, updated to include the energy storage system:
- A Certificate or a Producer Certificate for Special Projects, or an Electricity Production License issued by RAAEY, accompanied by a topographic sketch indicating the boundaries of the proposed installation site (where the plant is subject to the relevant permitting requirement).
- Environmental Permit / Environmental Approval Decision
- A single-line electrical connection diagram, stamped and digitally signed by a suitably qualified engineer (in the case of converting a RES plant into a plant under para. 11A of Article 10 of Law 4685/2020, the diagram must also show the directional sensors relating to the prohibition on the storage system absorbing energy from the Network).
- A site / floor plan, including the coordinates of the property polygon and an indicative layout of the plant’s electromechanical installation (where the plant is subject to the requirement to obtain a Producer Certificate from RAAEY).
- A site plan for the layout of the installation area (where required for an exempt plant).
- A technical description of the plant’s electrical installation.
- The technical manuals and certificates for the plant equipment.
In addition to the above, in the case of an exempt plant where the energy storage system is to be installed at a location different from the RES plant site, the following must also be submitted:
Solemn Declaration under Law 1599/1986, issued online via https://www.gov.gr/
, declaring (a) the installation location of the energy storage system, and (b) that this location is different from the RES plant installation site, and
- Legal/authorizing documentation evidencing the right to use the installation site of the energy storage system.
For the above supporting documents, the clarifications and requirements set out in the form “Supporting documents for a new connection request for a RES or CHP or storage plant” apply, available at the following link:
- B) Letter of Guarantee
In both case (a) and case (b), the addition of an energy storage system requires the submission of a letter of guarantee, in accordance with para. 5(c) of Article 11G of Law 4685/2020, as supplemented by Article 56 of Law 5261/2025, which provides as follows::
- For the purpose of calculating the amount of the letter of guarantee for the addition of energy storage systems to existing PV plants, as well as to new PV plants under paragraph 11A of Article 10, the “requested capacity” is deemed to be the plant’s Maximum Output Power.
- For the purpose of calculating the amount of the letter of guarantee for the addition of energy storage systems to existing PV plants, as well as to new PV plants under paragraph 11B of Article 10, the “requested capacity” is deemed to be the plant’s Maximum Injection Power. (Pursuant to point (e) of paragraph 1 of Article 19A of Law 4685/2020: “The Maximum Injection Power of a RES and CHP generation plant with storage systems may not exceed the Maximum Output Power of the RES and CHP plant and the Maximum Injection Power from the plant’s storage systems, whichever is higher.”)
Example:
Assume a PV plant with an installed capacity of 400 kW and a maximum output of 400 kW.
- For the addition of an energy storage system and conversion of the plant into a plant under paragraph 11A of Article 10 of Law 4685/2020, the amount of the letter of guarantee will be calculated based on the plant’s Maximum Output Power, i.e. 400 kW.
- For the addition of an energy storage system and conversion of the plant into a plant under paragraph 11B of Article 10 of Law 4685/2020, where the storage system has a Maximum Injection Power of 500 kW, the amount of the letter of guarantee will be calculated based on the plant’s Maximum Injection Power, i.e. 500 kW.
The above letter of guarantee must be submitted to HEDNO’s Network Customer Department at the following address: 23, Syggrou Ave., Athens.
- C) Annex with technical equipment specifications
In both case (a) and case (b), the submission of Annex Ι or Annex ΙΙ with the technical specifications of the plant equipment is required.