Technical terms on PV inverters, grid connection and plant control, briefly explained and related to REFU.
Function that detects series arcs on the DC side, for example caused by loose connectors or damaged cables, and shuts the system down. AFCI reduces the fire risk, especially on rooftop systems.
At REFU: AFCI is integrated in the utility models and optionally available for the C&I models. The 250K-5T and 360K-6T are tested to IEC 63027.
Protection function that detects a grid failure and disconnects the inverter. This prevents voltage being fed into a de-energised grid and protects technicians working on the grid.
At REFU: Anti-islanding is integrated in all REFUsol inverters.
PID is a loss of performance in PV modules caused by high voltage between the cells and earth potential. PID recovery reverses the effect at night by applying a counter-voltage.
At REFU: PID recovery is integrated in the 110K-10T and 125K-10T and optionally available for the 250K-5T and 360K-6T.
PV systems on commercial and industrial buildings or sites, often with high self-consumption of the electricity generated.
At REFU: For C&I systems, REFU offers compact string inverters from 20 to 50 kW as well as the 110/125K-10T for larger rooftop and ground-mounted systems.
Control over where plant data is stored and who can access it. For operators of critical infrastructure, this is increasingly a regulatory question too.
At REFU: With REFUview, plant data is hosted and processed in Germany.
Ratio of installed PV power (DC, in kWp) to the inverter's rated AC power. A higher ratio makes better use of the inverter; during rare peak periods, output is limited.
At REFU: REFUsol inverters allow a DC/AC ratio of up to 150 %, helping to reduce system costs.
Automatic reduction of output power at high temperatures or high altitudes to protect components. What matters is up to which temperature full power is available.
At REFU: The 250K-5T delivers full power up to 50 °C, the 360K-6T 363 kVA up to 30 °C and 330 kVA at 40 °C. Altitude-related derating starts at 3,000 m or 4,000 m depending on the model.
Step-by-step specification of feed-in power, e.g. 0, 30, 60 or 100 %, usually via the grid operator's ripple control receiver. The term originates from the Australian standard AS/NZS 4777; in German-speaking countries it is usually called feed-in management.
At REFU: REFUlink implements DRM setpoints at the levels 0, 30, 60 and 100 % on all connected inverters; REFUstix can be extended for this.
Maximum efficiency is the best value under ideal conditions. European efficiency weights several partial-load points according to typical Central European irradiation and is therefore closer to the actual annual yield.
At REFU: REFUsol inverters reach a maximum efficiency of up to 99.01 % (250K-5T, 360K-6T). The values for each model are listed in the technical data on the product pages.
Device that connects the inverters of a plant with monitoring, control system and grid operator, and collects, processes and forwards data.
At REFU: REFUlink is REFU's gateway for entire plants and can also be operated in slave mode under gateways such as Solar-Log, meteocontrol or Smartone. REFUstix connects individual inverters directly to REFUview.
Protective device that disconnects a generating plant from the grid in the event of impermissible voltage or frequency. In smaller plants it can be integrated in the inverter; in larger ones (from 30 kVA in the low-voltage grid) a central grid and plant protection is required.
At REFU: Evidence of grid and plant protection for each model is available in the download centre.
Grid codes are the technical conditions for grid connection. The network code “Requirements for Generators” (EU Regulation 2016/631) sets uniform minimum requirements across Europe.
At REFU: REFUsol inverters are certified to EN 50549, the European standard that specifies the NC RfG requirements for generating plants connected to the distribution grid. Declarations of conformity are available in the download centre.
Measurement of the current-voltage curve of individual strings directly by the inverter. This makes it possible to detect shading, soiling or defective modules without on-site measuring equipment.
At REFU: The IV curve scan is integrated in the 250K-5T and 360K-6T.
Open communication protocol used in industry. Modbus RTU runs serially via RS485, Modbus TCP via Ethernet.
At REFU: REFUsol inverters have an RS485 interface; the utility models communicate via Modbus. REFUlink provides data and power control via Modbus TCP/IP.
Continuous recording and analysis of the operating data of a PV system in order to secure yield, detect faults early and deploy service in a targeted way.
At REFU: REFUview is REFU's monitoring platform with real-time data, user and access management and remote configuration of the inverters, hosted in Germany.
Control method that continuously adjusts the operating point of a PV string so that the maximum possible power is drawn. Several independent MPPTs allow strings with different orientation or shading to be optimised separately.
At REFU: Depending on the model, REFUsol inverters have 2 to 10 independent MPPTs, e.g. 2 on the 20K-2T, 6 on the 360K-6T and 10 on the 110/125K-10T.
EU directive on cybersecurity that also obliges companies in the energy sector to manage risks and report security incidents. In Germany, it is transposed by the NIS2 Implementation and Cybersecurity Strengthening Act.
At REFU: REFUlink and REFUview support operators with the requirements for controlled access and a traceable system architecture. Hosting and data processing take place in Germany.
Controller that implements the grid operator's specifications for active and reactive power at the grid connection point of a plant. For connection to the medium-voltage grid under VDE-AR-N 4110, it is usually required.
At REFU: REFUlink implements power setpoints centrally on all connected REFUsol inverters and works with higher-level plant controllers and control systems, including in slave mode under devices such as Solar-Log or meteocontrol.
Data transmission via the existing AC cables. Separate communication cables between inverter and data logger are not needed, which saves effort, especially in large solar parks.
At REFU: The 250K-5T and 360K-6T support PLC.
The protection rating describes how well an enclosure is protected against dust and water: IP65 and IP66 are dust-tight and protected against water jets, IP66 also against powerful water jets. According to ISO 12944 (1998 edition), C5-M denotes very high corrosive stress in a marine atmosphere, for example near the coast; the current edition groups this under C5.
At REFU: The C&I models have protection rating IP65, the utility models IP66. The 250K-5T and 360K-6T are designed for corrosivity category C5-M.
Residual current monitoring in the inverter. It monitors differential currents and disconnects the inverter from the grid in the event of a fault.
At REFU: The RCMU is one of the integrated protection functions of all REFUsol inverters.
Reactive power oscillates between grid and plant without doing work and is needed to maintain grid voltage. The power factor cos φ indicates the ratio of active to apparent power. Grid operators often specify how much reactive power a plant must provide.
At REFU: REFUsol inverters can be set to a power factor from 0.8 inductive to 0.8 capacitive.
Replacement or modernisation of components in existing PV systems, usually the inverters, to increase yield and extend operating life.
At REFU: The 25K/33K-3T and 50K-4T are designed for repowering. REFUlink and REFUstix integrate new and existing generations of REFU inverters into shared monitoring and control.
Ratio of the grid's short-circuit power at the connection point to the connected power of the plant. A low SCR indicates a weak grid, in which voltage fluctuations and stability problems occur more easily.
At REFU: The 250K-5T and 360K-6T are designed for operation in weak grids down to an SCR below 1.1.
Inverter to which several series-connected module strings are connected directly. Unlike a central inverter, the power is distributed across many units, so a failure only affects part of the system.
At REFU: All REFUsol inverters are string inverters, from 20 kW for commercial rooftops up to 360 kW for solar parks.
Devices that protect against overvoltages. Type I discharges lightning currents from direct strikes and is required where external lightning protection is installed; type II protects against overvoltages from distant strikes or switching operations.
At REFU: All REFUsol inverters have type II surge protection on the DC and AC side. For the C&I models, type I + II on the DC side is available on request together with AFCI.
Proof that an inverter type meets the electrical requirements of VDE-AR-N 4110 or 4120. It is a prerequisite for the plant certificate when connecting to the medium- or high-voltage grid.
At REFU: Unit certificates for REFUsol inverters are available in the download centre.
Large ground-mounted PV systems feeding into the medium- or high-voltage grid. The focus is on cost per kWh, grid compliance and central controllability.
At REFU: For solar parks, REFU offers string inverters from the 110/125K-10T up to the 360K-6T with 360 kW, combinable with REFUlink and REFUview.
Application rules for grid connection in Germany: 4105 for low voltage, 4110 for medium voltage, 4120 for high voltage. They define which properties generating plants connected to the grid must have.
At REFU: According to their certification: the 20K-2T to VDE-AR-N 4105, the other C&I models and the 110/125K-10T to 4105 and 4110, the 250K-5T and 360K-6T to 4110 and 4120.
A technical question about your plant? We advise you personally, directly with our engineers.
Or directly+49 7121 145 1888info@refu.com
Request a project