One environmental concern regarding offshore renewable energy is the potential effects of electric and magnetic fields on the marine environment. The importance of this issue has been identified in several studies and in some countries it is mandatory to describe the potential impact from EMF in an Environment al Impact Assessment (EIA) to meet the statutory requirements of the permit process.
There are marine organisms that are able to detect the natural geomagnetic field for navigational purposes (such as whales, turtles, and fish) and others (mainly fishes as sharks and rays) that can also respond to the biological electric fields emitted by all organisms. This enables them to find prey, mates and possible potential predators. One concern is that when more anthropogenic sources of magnetic and electric fields are present in the marine environment there is a potential that those organisms will be affected.
The aim of this study was to provide an up to date knowledge base concerning environmental effects in the marine environm ent due to EMF and underwater cables from wave power farms and off shore wind power farms. A better knowledge base will aid permit processes, contacts with authorities, the general public and other stakeholders. The aim was also to identify potential ongoing R&D projects and practical studies, summarise gaps in knowledge and provide recommendations on potential future actions that can be taken to fill these.
Within the study, modelling of the magnetic field was performed for five different AC power cables (10 – 145 kV, 100 – 500 A), as well as induced electric fields. The modelling results showed that:
- The maximum strength of the magnetic field produced by the cable is from 2 – 35 μT, depending on the cable setup and current load.
- The magnetic fields produced by the generating units (wave energy converters) are negligible compared to the fields from the cables. An induced electric field of 0.3 – 4 mV/m depending on cable setup and current load will be generated by an AC cable.
- The field strengths decrease rapidly with the distance from the cable. For example, a maximum of 35 μT immediately above the cable will be reduced to 2.2 μ T at a distance of 2 meters from the cable.
The main conclusion of the literature study was that the current amount of information on the subject is very limited. Still, no research results were found that suggested that present sub-sea power cables posed as a threat to marine environment due to EMF. Although limited amounts of research have been conducted within the field a few other important conclusions can be drawn.
- Electric and magnetic fields within the magnitude of what is to be expected from marine renewable energy lies within the detection range for some electroreceptive marine organisms and within the assumed detection range for magnetoreceptive marine organisms.
- Behavioural effects have been shown in experiments both for species that use the magnetic field for navigational purposes (eel) and for species using electric fields for detecting prey (elasmobranchs). However the noticed effects have been considered to be small or the results have not been possible to use for evaluation of potential negative or positive environmental impacts.
- Comparing the thresholds identified in the literature study with the modelling results shows that magneto- and electro-receptive species may encounter detectable EM fields emitted by a power transmission cable in a range of a up to a few hundred meters, depending on the species and the cable characteristics.
- Within the project no research results were found that suggested that present sub-sea power cables posed as a threat to marine environment due to EMF.
- There is no information available from research on effects on marine mammals, and also no information suggesting that EMF from marine installations is an issue.
- There is not a sufficient amount of informat ion to evaluate differences between AC and DC transmission regarding environmental effects from EMF.
- There are currently studies undertaken in the U.S., aiming to identify detection thresholds for a number of species from alternating (AC) fields.
In environmental impact assessment and consen t processes, EMF-related impacts are treated differently in different countries in Northern Europe. While the environmental authorities in the U.K. and the Netherlands in many cases demand both analysis of potential impacts and monitoring programs dur ing the operation phase, countries like Germany and Norway consider the EMF-related impacts to be negligible. This gives another indication that the mechanisms and impacts of electric and magnetic fields are not fully understood.
Based on the results in this study the main strategy within Vattenfall for EMF and sub sea installations is suggested to be to follow research performed externally within the field, and follow the development on what authorities and interest groups find important regarding EMF impacts. When an environmental statement fo r a planned wave or energy project is prepared, EMF should be properly analysed but the findings of this study does not motivate for Vattenfall to conduct further research, field surveys or studies on the subject.