General information about electricity generation

Any potential network reinforcement measures must be considered already during the planning of electricity generation. Confirm the connectivity of generation equipment over 10 kW to the electricity network with us before purchasing the equipment. The generation capacity includes all production connected behind the point of connection and is determined by inverter capacity if the plant is inverter-connected.

The recommended maximum capacity of the generation equipment depends on the short-circuit current at the point of connection. If the generation equipment is located farther from the point of connection, the recommended maximum capacity decreases according to the short-circuit current.

The voltage change caused by generation equipment connected to the low-voltage network or by generation equipment connected to the same point of connection must remain within permissible limits. Power quality must always remain within the limits of standard SFS-EN 50160 at the point of connection. Connection to the distribution network must be implemented so that the starting or switching current is limited to approximately the nominal current.

Generation equipment must be connected to the network using fixed connections in accordance with electrical installation standard SFS 6000. For single-phase generation equipment (max 16 A), Caruna must be informed of the phase to which the single-phase generation is connected, and Caruna reserves the right to influence the phase selection. Caruna recommends using three-phase generation equipment.

Before connecting generation to the network, the customer must always make an electricity contract for the purchase of surplus electricity with their chosen electricity supplier before connecting the generation equipment, in accordance with section 2.5 of the Network Service Terms (VPE 2024).

A usage point for the surplus electricity contract is created during the processing of the general information form.

Small-scale generation refers to electricity generation equipment with a production capacity of up to 1 MW. The connectivity of small-scale generation over 10 kW must be confirmed with Caruna before purchasing the equipment. Note that for solar power plants, the nominal production capacity is determined based on inverter specifications rather than the calculated panel capacity.

Equipment up to 10 kW

As a rule, solar and wind power plants with a maximum capacity of 10 kW can always be connected to Caruna’s network when 3x16 A or larger fuses are in use.

If the site’s fuse size or network device is single-phase, the connection capacity can be a maximum of 3.7 kW.

Equipment 10–100 kW

Confirm the connectivity of generation equipment over 10 kW to the electricity network with us before purchasing the equipment. Connectivity requires that the starting current and production capacity of the generation equipment do not exceed the peak current value specified in the connection agreement and that the production does not cause disturbances to the network.

The connectivity check also determines whether network reinforcement is necessary.

Over 100 kW – max. 1 MW

The size, type, and future location of the generation equipment in Caruna’s network significantly affect the network connection. The connectivity review must consider all generation equipment connected under the same electricity connection, such as multi-meter sites in commercial buildings and offices where different operators have their own generation equipment.

Typically, power plants with a capacity of up to 300 kW can be connected to Caruna’s low-voltage network (voltage level 0.4 kV), in which case we install the metering in the customer’s metering cabinet. For plants over 300 kW, connectivity to the low-voltage network must be checked separately. When connecting to the medium-voltage network, Caruna defines the connection point at the nearest technically connectable point in the medium-voltage network, where the customer connects using a connection cable they construct. Energy metering for the connection is located in the customer’s switchgear.

It is advisable to contact us well in advance regarding connectivity, as possible network construction can take a considerable amount of time.

Professional electricity generation refers to power plants with a capacity of over 1 MW, an independent 20 kV or 110 kV generation connection, such as a wind farm.

In addition to other technical requirements, professional electricity generation plants must comply with Fingrid’s System Technical Requirements for Power Plants (VJV2018 document). Electricity generation solutions are always reviewed and planned on a case-by-case basis.

If you are planning to connect small-scale generation to the medium- or high-voltage network and/or generation capacity over 1 MW, please contact our contractor service.

For small-scale generation plants, Caruna follows the Energy Industry’s network recommendation “Connecting small-scale generation to the electricity distribution network YA 9:23,” which is based on the European standard for small-scale generation SFS-EN 50549-1:2019. The protection settings presented in Appendix 1 of the network recommendation YA 9:23 (effective 2 June 2025) are recommended for all newly installed generation plants. These protection settings must be followed for generation plants whose binding purchase agreement is made after 1 July 2025. In exceptional cases, protection settings valid at the time of the connection agreement may be used. The protection settings defined in the previous network recommendation (YA 9:23 dated 29 November 2023) are shown in the 2023 settings table.

In addition, all generation plants above 800 W must comply with Fingrid’s System Technical Requirements for Power Plants (VJV2024 document).

All electricity storage systems with a rated power of at least 800 W in production mode must comply with Fingrid’s guideline “System Technical Requirements for Electricity Storage” (SJV2024).

For generation plants connected to medium-voltage connections, the requirements of the small-scale generation standard SFS-EN 50549-2 must also be considered.

The generation equipment (including the grid device) must be equipped with a separate lockable disconnection switch that can, if necessary, prevent electricity from being fed into the public network. Information about the location of the disconnection switch must be provided to Caruna. The switch must be located in a place where Caruna’s representative has free and unobstructed access, such as near the main switch of the main switchboard or the metering cabinet. If the disconnection switch is in a locked space, such as a technical room, the customer must arrange unobstructed access according to our instructions.

The disconnection switch must be clearly marked with labels and signs so that it is easily and unambiguously identifiable. In addition, the connection’s switchboards must have warning signs about back feed hazards and instructions for disconnecting the equipment. If small-scale generation can only be disconnected via the main switch, the consumption connection will also lose power.

Caruna’s representative has the right to disconnect the generation equipment if required for network maintenance or repair work. The generation equipment may also be disconnected from the network if it does not meet the requirements set for the equipment or the connection or causes disturbances to the distribution network. Caruna will always aim to inform the producer separately about disconnection from the network.

For electrical safety, the generation equipment must be equipped with protection devices that disconnect the generation equipment or the island supplied by the generation equipment from the public network if the network supply is interrupted or if the voltage or frequency at the connection point deviates from normal network values. The operation of the protection must be verified for the entire installation if the system consists of several separate generation units with their own or shared grid connection protection devices.

If the generation equipment has a production capacity of 50 kW or more, an additional requirement is a separate centralized protection and prohibition of using ROCOF protection (rate of change of frequency).

After a network fault or disturbance, the network voltage and frequency must remain at normal values for at least 60 seconds before the generation equipment can reconnect to Caruna’s network. Automatic synchronization must be used when reconnecting the generation equipment to the network. In addition, the protection system must ensure that the short-circuit and earth-fault protection of the generation equipment and the public network are compatible and meet network protection and safety requirements.

The structure and protection of the generation equipment must withstand network operation disturbances without damage, such as short-circuit and earth-fault faults with automatic reclosing, voltage dips, and frequency disturbances. 

Caruna is responsible for measuring electricity taken from and fed into the network. The producer is responsible for any necessary measurements of production and self-consumption. If Caruna requires information on self-consumption for its own billing purposes, Caruna will handle the measurement (usually for generation plants over 1 MW).

In Caruna’s network areas, the electricity meter usually does not need to be replaced when commissioning generation equipment. We activate bidirectional metering on the electricity meter at the usage point during connection approval and provide the measurement data to the electricity supplier chosen by the customer, who purchases surplus production fed into Caruna’s network.

Caruna’s electricity meters use the Ferraris measurement method. The meter instantly nets electricity taken from Caruna’s network and electricity fed into Caruna’s network (i.e., surplus production) across all three phases.

Example of the Ferraris measurement method

At a given measurement moment, one phase of the property feeds 100 W into Caruna’s network, while the other two phases take a total of 60 W from Caruna’s network. The electricity meter sums the results across phases, so at that moment, the net result is 40 W fed into Caruna’s network, and this is recorded in the meter’s production register. At the next measurement moment, electricity consumption from Caruna’s network may be significantly higher, and the netting result between phases is recorded in the meter’s consumption register. Instantaneous netting occurs in real time within fractions of a second.

When production is connected to an existing usage point, consumption and production are measured through the same electricity meter. The measurement period is 15 minutes, during which the electricity produced and consumed by the customer is netted, i.e., summed for the same quarter-hour. Netting applies when the generation equipment capacity is a maximum of 100 kW. In this case, Caruna does not charge for transferring production to the distribution network, but the small-scale producer needs an agreement for selling surplus production.

During the quarter-hour, surplus production transferred to the distribution network and not used reduces the small-scale producer’s transfer invoice by the same amount.

If more electricity is produced than consumed during the same quarter-hour, the electricity supplier credits the customer for the netted surplus production.

If consumption is greater than production during the same quarter-hour, the customer pays for the difference between consumption and production for that quarter-hour.

Without netting, both consumption and surplus production could accumulate in the same quarter-hour if they do not occur at the same time. More information on the effects of netting for small-scale producers can be found in the Own Electricity Generation section.