Highlights from Energinets new grid code on energy storage and V2G

Energinet new technical grid connection requirements for energy storage (TF331) are now sent in public hearing.

Grid connection requirements for production units are the same throughout Europe as it is governed by the European Commission Regulation: Requirements for Generators (RfG). Energy storage is explicitly not covered by the RfG and each TSO therefore make their own grid code on them.

That makes it quite challenging for the BESS suppliers that needs special controller functions in Denmark.

1. More alignment with the RfG

Most of the requirements for a 1 MW energy storage are made the same as they are for a 1 MW PV plant except the requirements are made symmetrical, so they apply both in consumption mode and in production mode. That was not specified in the old TF331 and most DSOs therefore only required the functions during production as in the RfG.

It is strict to make the requirements apply during consumption, considering there are no requirements for stand-alone consumption units of the same size.

It does not matter if a small energy storage unit is placed behind the meter of a large consumption and newer is able to export to the grid. The requirements are based on the nameplate power capacity of the energy storage unit.

2. Standardization of the type of online communication

The most important change is about the requirements for online communication for energy storage >1 MW where Energinet has listened to our feedback.

Energy storage above 1 MW must connect with online communication to the DSO and give access to control and measure power factor, reactive power and limit active power. Even if the DSO is not able to utilise the signals.

Previously TF331 didn’t specify the communication protocol but required that it could withstand outage (loss of voltage). It was not specified if it was for a local outage or a total system wide blackout (no internet). That has led to very different interpretations in the projects we have worked on.

Some of the DSOs in Denmark require a simple 4G modem set up while other Danish grid companies require a dedicated black fiber cable connected to their main station several km away from the battery with backup UPS in both ends.

Additionally, some Danish DSOs today require analog signals from 4-20 mA while others just require TCP based communication such as IEC-104.

Energinet is putting an end to this inconsistency by requiring that the communication is done with the IEC 61850-standard, which can be exchanged over the internet. This, however, only takes place in 2025 so projects coming online in the meantime are still covered by the existing regulation.

3. Energinet does not recognize co-location of assets.

All the requirements in TF331 are defined in the point of connection (POC), where the energy storage meets the DSO grid. The problem comes if the energy storage is installed behind the same meter as a consumption or production unit and therefore is unable to control the power factor, reactive power or active power in POC, because it only can add a minor contribution.

A significant part of the grid connected energy storage units will be installed together with production and or consumption but most of the requirements in TF331 does not make any sense if they are defined in POC. Any co-location of energy storage >1 MW therefore requires a specific agreement with the local DSO and Energinet.

Another problem is that e.g. a PV plant and an energy storage co-located on a grid connection both needs to produce pull power if there is an under frequency according to LFSM-U. Each asset is not allowed to consider the grid connection capacity limits in their power response.

The power ramp limit of 20% of the rated power per minute is per asset type so by not recognizing co-location the result is that a BESS is not allowed to be faster to compensate for e.g. a fluctuating PV production.

4. Big problems for V2G

The main reason for updating TF331 is to include V2G chargers which are expected to significantly grow in numbers in the coming years.

The new TF331 will introduce the same grid connection requirements for V2G chargers as for all other types of energy storage (e.g. household batteries).

4.1 How can a V2G charger be approved?

All the requirements are to the inverter control, but it is the permanent installation that is approved. That means it should be easy to get a DC V2G charger on Green Power Denmarks positive list and approved for household installations, but it makes it almost impossible to approve onboard AC V2G in Denmark.

The reason is that the inverter can drive around to different locations and connect to different grid companies with different requirements. More specifically there are different requirements for flicker and for LFSM-O in DK1 and in DK2, so the EV would need to flip a switch when it crosses the Great Belt Bridge.

Another problem for onboard AC V2G is that grid connections with less than 125 kW of energy storage capacity have one set of requirements and grid connections with more than 125 kW have other requirements.

Each EV in parking lot with multiple EVs would need to know how many EVs that are grid connected and what the others are doing.

4.2 Charging speed ramp limit

Another general complication is that the technical requirements from the RfG are applied both during production and consumption. That means that the EVs would need to limit its charging speed ramp to 20% per minute so it would take 5 minutes to reach full charging speed every time.

4.3 Expensive hardware requirements

A result of the TF331 requirements is that the onboard or offboard charger needs to be equipped with an expensive frequency meter that measures the grid frequency with an accuracy of minimum 10 mHz. A high-resolution frequency meter has a hardware cost similar to an full AC charger.

Another new requirement for V2G chargers is that they must be able to receive stop and hold signals from the local DSO, which also requires extra hardware.

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