Introduction
As alluded to in a previous article, there is a fundamental difference between fossil fuels being used for energy production and renewable energy production notwithstanding the ecological and climate benefits. This difference is point of generation (PoG). Fossil fuels must be recovered from the earth and transported to where they can be used. For connectivity providers and communication satellite operators, this implies lots of traffic for crews and machinery generally far from society and its networks.
This is not the case for offshore renewables which are mostly unmanned and have generation at the point of production. A wind turbine can have as many as one thousand sensors reporting, less in a solar farm or wave generator but offshore nuclear facilities could have tens of thousands reporting back to shore-based monitoring and management systems. Given that high tension cabling has to be installed from the PoG to the network, it is feasible (difficult but not impossible) to send all the data points down the high voltage cable. There are a host of acronyms to describe this depending on the end-user; including Broadband over power lines (BPL), Power Line Communication or Power Line Carrier (PLC) and HD-PLC (High-Definition Power Line Communication).
Many people will be familiar with this using signal repeaters, often plugged into their household circuit. If they have a smart meter, that uses communication over power lines. However, sending signals over high tension lines is an order of magnitude more difficult. Utility companies have been using frequencies in the range of 24 to 500 kHz on the same line as the electrical current to monitor the performance of their own power grids and to switch equipment on or off for years. This is called a PLCC system (powerline carrier communication system) where high frequency in the order of 50 –500 kHZ signals (voice/video/data) is modulated and sent in the power line of system frequency 50Hz.
Discussion
Nothing is as easy as it seems. There have been several attempts in Australia, the UK, France, Japan, Italy and the US to implement access BPL. The results would seem to show that BPL is so difficult that it is not viable. The main problems are attenuation, low bandwidth, noise and electromagnetic interference which cannot come close to the speeds available with ADSL, Wi-Fi, or even 5G mobile. But, of course, with IoT, speed may not be the most significant factor. The benefits are security (difficult to hack a power line), cost, bounded latency (the total delay for data travelling the network is fixed between two predetermined values) and relatively low power consumption.
There are some differences with existing systems that would be required for offshore renewable communication over power lines. Existing systems tend to be relatively short distances – metres or a few kilometres depending on band, but offshore generators might be as far as 370 kilometres (230 miles) offshore, and the cables are underwater (so much less likely affected by environmental interference and network hazards). Such systems need devices to modulate, filter, amplify and repeat the data stream – there are other components, but we’ll gloss over them. These devices will fail and will need to be replaced or repaired so maintenance might be an issue. However, once the system is in, there are no subscription costs.
HD-PLC (High Definition Power Line Communication), a technology that complies with the international standard IEEE 1901-2020 (IEEE Standard for Broadband over Power Line Networks: Medium Access Control and Physical Layer Specifications) is coming on leaps and bounds and in 2021, MIRAIT Corporation, MMD inc, NURI Telecom Co Ltd and Socionext Inc obtained communication verification results for a distance of over 1 km and expect to enable communication for a total distance of 10 km with the multi-hop function. It is not 370km but is heading in the right direction.
Satellite connectivity, however, is a well-established technology, easy to implement and simple to operate if the correct service provider is selected. The only drawback is the continuing subscription charges. This a problem for a cost accountant and financial director and depends on selected payback length – a modern offshore wind turbine may have an expected life of 25 years.
It would not be untoward to install both types of communication and use the existence of each other to drive down prices. A likely scenario is using satellite as an initial primary method of data transfer and back-up with a BPL hybrid.
For example, modern offshore wind turbines may seem like leviathans but depend on sensors to control and monitor their operation as they face incredible stresses, vibration, and sea-borne movement (even those anchored to the sea-floor). These sensors produce immense amounts of internal operating data such as rotor and gearbox temperatures, as well as blade stress and tower flex with corresponding climate data such as wind speed, heave, yaw angles, precipitation, temperature (both dry and wet), and others to monitor and predict performance and life expectancy continuously. This allows operators to schedule maintenance and replacement. Wind turbines are complex and typically have more than 8,000 components.
Figure 1: The basic components of a wind turbine within the nacelle and some of the types of sensors and where they’re placed.
The diagram illustrates sensor components within a wind turbine.
(Source: TE Connectivity brochure)
Wave energy generators would require a fewer number of sensors as the structure is more compact. Offshore solar farms probably need more environmental sensors and sensors measuring the output of individual panels to ascertain replacement requirements.
Small modular offshore nuclear fission plants, the design of which has already achieved design certification exceeding NRC “safety goals by several orders of magnitude” and small modular nuclear fusion plants, whose time is surely fast approaching, would all require many thousands of continuous sensor data uploads.
Of course, for near-shore offshore wind farms, cellular networks are available also on a subscription basis. Many current wind farms are within cellular reach. 4G/LTE services previously extended to around 12 nautical miles from the coast depending on tower height. With the launch of new technologies and products, this is now much greater.
An ideal candidate for offshore windfarm IoT communication is the LoRaWAN® specification, which is a Low Power, Wide Area (LPWA) networking protocol designed to wirelessly connect sensors and to operate correctly designed equipment to the internet in national or global networks, and targets key Internet of Things (IoT) requirements such as bi-directional communication, end-to-end security, mobility and localisation services. This has become especially pertinent since October 2023 when EchoStar, which operates 13 Hughes Communications satellites in ‘geosynchronous’ orbits joined the LoRa Alliance® (the global association of companies espousing the interests of open low-power wide-area networks (LoRaWAN®) standard for IoT) board of directors. It is arguable that high altitude satellites are not the ideal solution for IoT.
Combining a Wide Area Network and satellite means that each single turbine does not need hardware to communicate to the satellite network. A central server for the farm and gateway reports exceptions and daily summaries from all the turbines thus lowering data transmission costs.
Conclusion
IoT data transmission for offshore renewables is an essential requirement and both satellite connectivity and data transmission over power lines are acceptable responses. Satellite connectivity and cellular connections are already installed in windfarms offshore China, the UK, the USA, Japan, South Korea, India, Germany, the Netherlands, Denmark and Belgium.
For example, Iridium has significant business in this area with its IoT midband services. By simply including its Iridium Core and 9600 series, turbines on smaller offshore farms existing in France, Portugal, Spain, Ireland, Sweden, Norway, Finland and Italy have satellite IoT links. It is worth noting that the majority of these farms are installed around inshore waters and may also be within cellular reach.
There are estimates that satellite connectivity can be as little as a tenth of the cost of running separate communication cabling, but communication over powerlines can bring this cost down considerably. Because of the strategic value of wind power, it is unlikely that any wind farm would depend on a single method of communication and satellite communication links are generally secure and trusted by governments and militaries worldwide.
An additional benefit is for maintenance vessels and technicians, who have access to the farm gateway and communication to the shore base. Direct data from the turbines and meteorological forecasts allow sensible programming of work on-site.
Finally, Lacuna Space (based in Harwell Campus, Oxfordshire) uses low-cost cubesats (about the size of a shoe-box) that fly in a 500km altitude orbit, circling the Earth fourteen times each day which is ideal for IoT transmissions although of less help for maintenance and service personnel transmissions.