Mobile network (4G/5G) and fibre: how to connect your wind turbine reliably

In the tower base, the router is blinking green, yet the display in the office has been showing the same value for days. The mobile network provider switched over a frequency band during the night; the router re-registered on the network and never re-established the VPN tunnel. The turbine was running perfectly the whole time – it is just that nobody could see it. Had a fault occurred in the meantime, nobody would have noticed that either.

The data connection is the most inconspicuous component of remote monitoring and, at the same time, the one on which everything depends: database server, live display, cloud, direct marketing, camera and shutdown systems all need a link that is up around the clock. Whether this link runs over the mobile network, fibre or a radio bridge is not decided at the desk, but on site.

We have been operating our own wind turbines since 1998, and we set up mobile network links (4G/5G) for single turbines and wind farms or lay fibre within the wind farm – manufacturer-independently. In this article, we show what matters when it comes to the router, antenna, SIM card, fibre ring, lightning protection and IT security, which mistakes can be avoided and how a project runs smoothly.

Why the data link has a say in how the turbine operates

A wind turbine (WTG) operates autonomously. Its controller does not need the internet to generate electricity. For everything that you as the operator want to see or influence from outside, however, it needs a connection: fault messages, operating data, remote acknowledgement, schedules from the direct marketer and the signals from external systems.

If the link fails, the turbine initially keeps running. The risk lies elsewhere: faults go unnoticed, curtailment instructions do not arrive, and gaps in the operating data are difficult to explain later on – for instance to the insurer, the direct marketer or the authorities.

Everything that runs over the line

Before we talk about technology, it is worth taking stock of the services. They determine the bandwidth, availability and security level of the link.

1. Operating data and fault messages: small data packets, but continuous and time-critical. They flow to the database server and to the live display.
2. Direct marketing: schedules and setpoints, for example via EMSYS. What counts here is that instructions reach the turbine reliably and without delay.
3. Remote access to the turbine terminal: service and technical operations management access the controller, acknowledge faults or read out parameters.
4. Camera: by far the largest data consumer as soon as live images or recordings are transmitted.
5. External systems: bird and ice detection, bat and sector shutdown exchange signals with the turbine controller and log shutdowns.

2G and 3G: check legacy equipment in good time

Many existing turbines still transmit using modems from the GSM era. The 3G networks (UMTS) in Germany have been switched off since 2021, and now 2G is following. Telekom has announced that it will completely shut down its GSM network by 30 June 2028 and use the freed-up frequencies around 900 MHz for 4G and 5G (Telekom, media information of 22 October 2024). Vodafone and O2 also intend to follow in 2028; for Vodafone, a possible transition period for M2M and IoT applications until 2030 has been mentioned (teltarif.de, June 2026).

Mobile network, fibre, microwave link, DSL: comparing the options

Four routes are available for connecting a wind turbine. None of them is the best across the board. The right solution depends on the location, the data volume and the required reliability.

When the mobile network is sufficient

For a single turbine in the field, the mobile network is usually the pragmatic route: no civil works, no cable route, and commissioning is quick if the coverage is right. According to the Federal Network Agency (Bundesnetzagentur), 4G reaches around 97.5 % of Germany's land area, and 5G in all its variants around 93.9 % (as of January 2025, mobile network monitoring by the Bundesnetzagentur).

Area coverage, however, does not mean that a stable signal arrives at the tower base. Wind farms are deliberately located away from settlements, often on hilltops or at the edge of forests. That is precisely where the network is thinner, and the radio cell shares its capacity with all other users.

5G brings higher data rates and, above all, more capacity. It is not necessary for operating data alone. It becomes interesting when several cameras are involved or when the LTE cell at the site is congested. A 5G-capable router automatically falls back to 4G (LTE) if 5G is not available at the site.

When fibre is the better choice

Fibre optics (i.e. optical fibre cables) transmit data as light signals. This makes the link immune to electromagnetic interference and galvanically isolates the turbines from one another – a major advantage in the event of lightning strikes. In a wind farm, fibre can be laid in the medium-voltage cable trench at the same time. The fibre then connects the turbines with each other and with the handover point, where a central internet connection serves the entire wind farm.

Fibre makes sense whenever several turbines work together, large volumes of data are generated or availability should not depend on the public mobile network.

Microwave link and DSL as special cases

A microwave link (point-to-point radio) connects two points via a focused radio beam. It requires a clear line of sight between both antennas and is worthwhile when a fibre connection is within reach but there is no cable route to it. DSL rarely plays a role in open countryside, because there is usually no telephone line at the turbine site. If there is one, for instance at an operations building, it can serve as a second route alongside the mobile network.

Mobile network in practice: router, antenna, cable

A mobile network connection consists of three building blocks: the router in the tower base, the antenna on the outside of the tower and the cable in between. Each of these building blocks can slow the link down.

The industrial router in the tower base

A router from the electronics store has no place in the tower base. What is needed are industrial routers for DIN rail mounting, with an extended temperature range, a 24-volt supply and functions for continuous operation. Manufacturers such as Insys icom, Phoenix Contact, Siemens, Teltonika or Welotec offer such devices. Which device is the right fit depends on the interfaces, management and existing infrastructure. These are the points we pay attention to:

• Two SIM slots for a second network operator.
• Antenna connections for MIMO, i.e. operation with several antennas simultaneously. This increases data rate and stability.
• VPN and firewall directly in the device.
• Connection monitoring with automatic restart in case the dial-in hangs.
• Digital inputs and outputs, for example for a door contact or a hardware reset.
• Central management, so that firmware updates and configuration do not have to be carried out on site for each turbine individually.

Why the antenna has to go outside

A steel tower acts like a Faraday cage: it largely shields radio waves. Concrete towers with reinforcement also attenuate the signal considerably. An antenna in the control cabinet or directly on the router is therefore practically useless in the tower base.

The antenna belongs on the outside of the tower or on a separate mast on the transformer or handover building. What matters is a clear line of sight towards the serving radio cell, distance from metal surfaces and a mounting height above vegetation and terrain edges. In difficult locations, a directional antenna aimed specifically at one mast achieves more than an omnidirectional antenna.

Pay attention to the frequencies: in rural areas, coverage is carried mainly by the low bands around 700, 800 and 900 MHz, because they have a long range. Higher bands such as 1800 or 2600 MHz provide more capacity but less range. The antenna must cover the frequency range that the network operator actually uses at the site.

Cable length and attenuation

A coaxial cable runs between the antenna and the router. Every metre costs signal – and the higher the frequency and the thinner the cable, the more it costs. The attenuation per metre is given in the cable data sheet. For long runs, low-loss cable with a larger cross-section is worthwhile, or the router is moved closer to the antenna.

Every connector and every surge arrester in the line adds further losses. Our rule of thumb: as short as possible, as few transitions as necessary, and all outdoor connectors sealed against moisture. Corroded connectors are a typical cause of reception that gradually deteriorates over months.

SIM, tariff, private APN and data volume

M2M tariffs instead of a mobile phone contract

M2M stands for machine-to-machine, i.e. communication between devices without people in between. Network operators and specialised providers offer dedicated tariffs for this: industrial-grade SIM cards that withstand temperature and vibration, data volume pools across several turbines and a management portal in which you can see the usage and status of each card.

A private mobile phone contract often works technically as well – until throttling kicks in, the card is blocked due to inactivity or, after a change of staff, nobody knows any more whose name it is registered in. For a turbine with an operating life of several decades, the SIM card belongs in a commercial framework agreement.

Private APN: your own network within the mobile network

The APN (Access Point Name) determines via which access point a SIM card enters the data network. By default, it ends up on the public internet, usually behind an address shared by the network operator. The router is then not directly reachable from outside.

With a private APN, the network operator sets up a closed access point: the routers receive fixed internal addresses, and the traffic runs separately from the public internet all the way to your data centre or your service provider. This makes remote access easier and reduces the attack surface. The alternative is a VPN tunnel that the router establishes itself. Both approaches can be combined.

Estimating data volume realistically

The volume results from the services, not from a flat rate. Calculate each service individually and plan a reserve for updates and fault analyses.

The table shows the pattern: operating data is rarely the problem, the camera almost always is. If you need live images, you should choose the resolution, frame rate and recording location deliberately – for example, local recording in the tower base and retrieval only when needed.

Availability: Dual-SIM, fallback and a monitored link

Remote monitoring is only as available as its weakest link. With the mobile network, this link lies outside your control: maintenance work on the mast, high network load, a power failure at the transmitter site. Resilience is therefore achieved through redundancy, i.e. a second, independent route.

Dual-SIM and a second network operator

The simplest form of redundancy is a router with two SIM cards from two different network operators. If network A fails or the signal becomes too weak, the router switches to network B. Important: both networks must deliver a measurably sufficient signal at the site, otherwise the second card is merely reassurance on paper.

Many Dual-SIM routers have only one radio module and switch between the cards. Depending on the device and its settings, this takes a while. For higher requirements, there are routers with two modems that maintain both connections simultaneously.

Fallback routes and local data buffering

In a wind farm with a fibre ring, a mobile network router as a fallback at the handover point is worthwhile: if the fixed-line connection fails, the router takes over. Conversely, a single turbine connected via the mobile network can be backed up by an existing DSL line at the operations building.

Just as important as the second route is a local buffer. If a database server or logger on site buffers the measured values, no gaps arise when the connection drops. As soon as the link is back up, the data is delivered retrospectively.

Monitoring the link itself

A silent turbine is the most treacherous signal remote monitoring can send – because it is no signal at all. You should therefore set up monitoring of the connection itself: if a router does not report in within a defined time, a warning is sent to technical operations management. In addition, log signal quality and network changes. This way, you will detect a misaligned antenna or a corroded connector before the connection drops out completely.

Fibre in the wind farm: ring, switches and media converters

As soon as several turbines come together, fibre plays to its strengths. A central internet connection at the handover point or substation serves the entire wind farm, and the turbines communicate with each other via their own closed network.

Ring or star?

In a star topology, a separate fibre runs from each turbine to the central point. This is easy to keep track of, but damage to one cable cuts off the affected turbine completely. In a ring topology, the turbines are connected one after the other, and the last turbine closes the loop back to the start. If the ring is interrupted at one point, for instance by an excavator, the data reaches all turbines from the other direction.

For a ring to work, the switches need a redundancy protocol that prevents data loops and switches over in the event of a fault. Common protocols are the Rapid Spanning Tree Protocol (RSTP), the Media Redundancy Protocol (MRP) and proprietary ring protocols. It is important that all switches in the ring speak the same protocol.

Industrial switches and media converters

Each turbine houses an industrial switch for DIN rail mounting, with fibre ports for the ring and copper ports for the controller, router, camera and shutdown systems. Where only a single device needs to be connected, a media converter translates between fibre and copper Ethernet. Pluggable modules (SFP) make the switches flexible: depending on the fibre type and distance, the appropriate module is inserted.

The choice of fibre is important: single-mode bridges long distances and is the norm in a wind farm, while multimode is suitable for short runs, for example within a building. Fibre, modules and switch must be compatible with one another.

Cable, route and documentation

Fibre in a wind farm is often installed as blown cable in microducts or as direct-burial cable in the medium-voltage trench. Plan for spare fibres: they cost little during construction and save you a second cable route later. After splicing, every link should be measured end to end and documented, with attenuation values and fibre assignment. These records are worth their weight in gold when a fault has to be traced years later.

Lightning protection, surge protection and equipotential bonding

Wind turbines are often the highest points for miles around and therefore preferred lightning targets. The communication equipment in the tower base is particularly at risk: it connects the turbine to the outside world via antenna cables and data lines, and it is precisely via these routes that surges can enter.

Which standards set the framework

For wind turbines, IEC 61400-24 “Lightning protection” applies internationally, currently as the consolidated 2019 edition with Amendment 1 from 2024. It explicitly also covers the protection of electrical systems and the control system against direct and indirect lightning effects (IEC Webstore).

For structures in general, the DIN EN IEC 62305 (VDE 0185-305) series of standards applies, previously known as DIN EN 62305. Its Part 4 deals with electrical and electronic systems and relies on earthing and equipotential bonding, spatial shielding, EMC-compliant cable routing and surge protective devices, combined in the lightning protection zone concept (DKE overview of lightning protection standards).

Protecting the antenna line and copper conductors

For the data connection, this means in practice:

• Where the antenna line enters the tower or building, it is fitted with a coaxial surge arrester connected to the equipotential bonding.
• The cable shield is earthed at the building entry so that lightning currents do not travel all the way to the router.
• It is better to avoid copper lines between buildings or turbines: here, fibre is the safer choice, because glass fibre does not conduct electricity. Metallic cable components such as armouring or strain relief must nevertheless be connected to the equipotential bonding.
• The power supply of the router is given its own surge protection.
• The router, switch and arresters in the control cabinet are connected to a common equipotential bonding bar.

Network segmentation and IT security

A grid-connected wind turbine is part of the energy supply. Anyone who gains access to the controller via remote maintenance can, in the worst case, shut down turbines or change parameters. The Alliance for Cyber Security (Allianz für Cyber-Sicherheit) of the German Federal Office for Information Security (BSI) points out that remote maintenance via public networks increases the attack surface of industrial plants. In its view, analogue or ISDN modems and connecting controllers directly to the internet are no longer considered state of the art (BSI-CS 108, remote maintenance in industrial environments).

VPN, firewall and segmentation

The basic rule is: no controller is connected directly to the internet. There is always a router with a firewall in between, which only permits the connections that are actually needed. A VPN (virtual private network) establishes an encrypted tunnel between the turbine and the control centre or service provider. No open ports are visible from outside.

Within the turbine, segmentation is worthwhile: the controller, camera and shutdown systems sit in separate network zones (VLANs). If a camera is compromised, the attacker does not automatically gain access to the controller.

Remote maintenance access with clear rules

1. Personal accounts instead of shared passwords, so that it remains traceable who accessed the system and when.
2. Enable access only when needed, for example via a key switch in the control cabinet or after approval by technical operations management.
3. Logging of all sessions.
4. Keep firmware up to date, for routers, switches and cameras alike.
5. Change default passwords before a device goes online for the first time.

Planning and measurement on site

Many connection problems can already be avoided at the planning stage. That is why every order is preceded by a site survey.

Checking network coverage: first the map, then the measurement

The mobile coverage map of the Federal Network Agency (Bundesnetzagentur) provides a first impression. It shows coverage across all network operators and technologies. The data is supplied by Telekom, Vodafone, Telefónica and 1&1; the Bundesnetzagentur checks it for plausibility using spot-check measurements by its testing and measurement service and results from its dead-spot app (Funkloch-App) (Bundesnetzagentur). In addition, the network operators publish their own coverage maps.

A map, however, is no substitute for a measurement. Measurements are taken at the planned antenna location, ideally with a router or measuring device that displays the values for each network operator and each band separately. Three key figures are decisive: RSRP (reference signal received power, i.e. how strongly the network arrives), RSRQ (received quality) and SINR (ratio of the wanted signal to interference and noise). Router manufacturers state guideline values in their manuals. Measure over several minutes, ideally at different times of day, and add a data test that shows the actual transfer rate.

Site survey checklist

These points belong in every survey report:

Typical mistakes and how a project runs

Seven mistakes that can be avoided

1. Antenna inside the tower: The steel tower shields the signal, and the connection keeps dropping out.
2. Map value instead of measurement: The coverage map shows coverage, but at the tower base it is barely enough for operating data.
3. Antenna cable too long and too thin: The signal is lost on its way to the router.
4. Private SIM contract: Throttling, blocking due to inactivity or an unclear contract holder bring the connection to a standstill.
5. Two SIM cards on the same network: The redundancy only exists on paper.
6. No surge protection on the antenna line: A lightning strike nearby can damage the router and connected control equipment.
7. Open ports and default passwords: The controller can be reached from the internet without anyone noticing.

How a project runs with us

Our projects follow defined steps:

1. Order confirmation and technical clarification: We clarify services, location and requirements and determine the expected delivery date.
2. Design and manufacturing: The components within the scope of delivery are planned and manufactured.
3. Readiness for dispatch and transport: Once readiness for dispatch has been notified, the equipment is shipped to the site.
4. Installation and commissioning: Mechanical and electrical installation as well as commissioning take place on site. For installation and service, we work with professional service companies.
5. Handover, training, documentation: We familiarise you with the system during the commissioning phase and hand over the documentation.

The necessary structural measures, such as supply lines and telephone connections, as well as the power supply, are to be provided by the client. After handover, remote administration is handled by our office during normal business hours. We offer maintenance and spare parts as required.

Frequently asked questions

Conclusion

A reliable connection for a wind turbine does not happen by chance. For a single turbine, an industrial router with an external antenna, an M2M tariff and a second network operator is usually the fastest route. In a wind farm, fibre in a ring topology creates a stable basis, backed up by a mobile network fallback. In both cases, the rule is: measure first, then order – and include lightning protection and IT security in the planning from the outset.

If you still have 2G modems in your fleet, you should not postpone replacing them until 2028. We support you manufacturer-independently – from technical clarification through installation and commissioning to remote administration from our office in Warburg. Get in touch if you would like to plan or renew your connection.