A continued expansion of the marine renewable energy sector will result in an increased demand in monitoring the natural marine environment. This may be due to a basic scientific interest but is foremost linked to the requirement of pre- and post-construction studies in relation to environmental impact assessments and consenting processes for marine renewable energy projects. With focus on wave and tidal power, but without attempting to provide a comprehensive list, we review methods, technologies and other scientific tools used for monitoring and predicting possible impacts from marine energy installations, on both population and behavioural levels. This includes traditional methods such as fishing gear, like nets and cages, modern technologies such as platforms with multi parameter equipment and the use of deterministic models. This paper is intended to serve as an overview for technology developers as well as authorities, regulators and decision makers with interests in general techniques, and naturally for scientists and consultants commonly being executors of studies and monitoring programs. By giving relevant and up to date references this paper may also be useful for finding more detailed information on study methods and variants. Finally, we give recommendations on where development of technologies is needed in order to face future requirements.

With the prospect to deploy hydrokinetic energy converters in areas with heavy boat traffic, a study was conducted to observe and assess the depth range of cavitating flow produced by ferryboats in narrow channels. This study was conducted in the vicinity of Finnhamn Island in Stockholm Archipelago. The objectives of the survey were to assess whether the sonar systems were able to observe and measure the depth of what can be cavitating flow (in a form of convected cloud cavitation) produced by one specific type of ferryboats frequently operating in that route, as well as investigate if the cavitating flow within the wake would propagate deep enough to disturb the water column underneath the surface. A multibeam and a dual-beam sonar systems were used as measurement instruments. The hypothesis was that strong and deep wake can disturb the optimal operation of a hydrokinetic energy converter, therefore causing damages to its rotors and hydrofoils. The results showed that both sonar system could detect cavitating flows including its strength, part of the geometrical shape and propagation depth. Moreover, the boat with a propeller thruster produced cavitating flow with an intense core reaching 4 m of depth while lasting approximately 90 s. The ferry with waterjet thruster produced a less intense cavitating flow; the core reached depths of approximately 6 m, and lasted about 90 s. From this study, it was concluded that multibeam and dual-beam sonar systems with operating frequencies higher than 200 kHz were able to detect cavitating flows in real conditions, as long as they are properly deployed and the data properly analyzed.

Environmental data is crucial for planning, permitting, execution and post construction monitoring of marine renewable energy projects. In harsh conditions in which marine renewable energy is harvested, integrated monitoring platforms comprising multibeam imaging sonar systems coupled with other sensors can provide multi-dimensional data of the marine environment surrounding marine renewable energy installations. The aim of this study was to test the possibilities of observing the occurrence of fish and marine mammals using a multibeam imaging sonar system deployed at a wave power test site. The results obtained from a ten-day data set proved the platform as suitable for long time underwater monitoring and also revealed that the occurrence of fish and marine mammals was distributed across characteristic time and space domains. Large fish [>0.4 m] frequently occurred at night-time and near the benthic zone. Small fish [<0.2 m] frequently occurred during daylight and within the pelagic zone. The occurrence of seals was periodically distributed along a daily cycle, with intervals of 1 – 2 hours between maxima and minima. In conclusion, the use of multibeam imaging sonar can be a reliable technique for the qualitative and quantitative observations of fish and marine mammals in general and at marine renewable energy sites specifically, including protected and economically important species.

Marine renewable energy is emerging as one of the fast-growing industry in the last decades, as modern society pushes for technologies that can convert energy contained from winds, waves, tides and stream flows. The implementation of renewable energy technologies impose high demands on both structural and environmental engineering, as the energy converters have to work under extreme conditions where parameters such as sea-bottom configuration, water transparency and depth, sea-states and prevailing winds are harsh. Constant monitoring of the marine environment is crucial in order to keep this sector reliable. Active acoustics is becoming a standard tool to collect multi-dimensional data from physical, geological and biological properties of the marine environment. The Div. of Electricity of Uppsala University have been developing an environmental monitoring platform based on sonar (Sound Navigation And Raging) systems. This platform aims to monitor the installation, operation and decommissioning of marine renewable energy converters. The focus will be given the observations of behaviours of marine animals in vicinity of energy converters but also structural inspection and monitoring of MRETs. This paper describes how this multifunctional environmental monitoring platform come to existence from the design to the deployment phase.

Marine renewable energy technologies have a great potential in supplying clean electricity to millions of people across the globe, if technical and economic conditions are in right. So far, ocean energy projects are commonly started by SMEs or educational institutions with limited budgets. Therefore, any effort to reduce expenses is of great value. One of the areas involving substantial expenses are the inevitable seabed inspection prior to deployment of marine renewable energy device. Detailed seabed inspections can also reduce the risk of associated with deployment of structures on uneven seabed, especially marine renewable energy devices with gravity foundations. By reducing the costs and risks of such surveys prior and during the installation phases, the feasibility of marine renewable energy projects can be more favoured and competitive. In this perspective, this study proposes a cost and time effective technique for seabed surveys. The proposed technique involves the use of high precision and inexpensive sonar systems and underwater optical cameras integrated into a versatile and compact subsea monitoring platform. It also involves simple and practical data acquisition and processing protocols that do not requires hi expertise for operation. The results obtained showed that high resolution bathymetric maps and detailed seabed inspections imagery can be acquired. This study concludes that a simple and inexpensive subsea monitoring platform comprising a multibeam, dual beam and video cameras can be effective for high resolution seabed inspection and bathymetric measurements for marine energy applications.

Environmental monitoring and visual inspections are indispensable tasks in the marine renewable energy sector. Today, acoustic and electromagnetic instrumentation are used to observe the underwater environment. However, depending on the application, both electromagnetic and acoustic instruments have limitations mostly due to signal attenuation. For visual inspections, electromagnetic instruments e.g. optical cameras provide the best method of observation enabling an easy identification and classification of targets. However, electromagnetic radiation is more attenuated in water than sound, limiting the use of optical cameras to nearfield observations. In murky and turbid waters, acoustic imaging sonar systems can be used to observe underwater objects at much longer ranges up to 100 m away. Presumably, underwater optical images are mostly appropriate in clear waters or at nearfield, and acoustic images are suitable for murky and turbid waters. This study aimed to find the optimal ranges in which optical and acoustic images can be acquired in In Situ conditions. A multibeam imaging sonar and several different optical cameras were used to acquire underwater images of the surroundings of marine renewable energy devices. The results from observation showed that optical images were significantly affected by the decreasing of luminosity, increasing depth and water velocity. And acoustic images were mostly affected by water column stratification, bubbles and reverberation. In summary, optical cameras had superior performance for nearfield and high accuracy image acquisition, while imaging sonar provided superior performance at acquiring images at mid to long range.

Techniques for marine monitoring have evolved greatly over the past decades, making the acquisition of environment data safer, reliable and more efficient. On the other hand, the exploration of marine renewable energy introduced dissimilar ways of exploring the oceans and with that arises the need for new techniques for environmental data acquisition, processing and analysis. Marine energy is mostly harvested in murky and high energetic places where conventional data acquisition techniques are impractical. Modern sonar systems, operating at high frequencies, can acquire detailed images of the underwater environment. Variables such as occurrence, size, class and behaviour of a variety of aquatic species of fish, birds, mammals, coexisting within marine energy sites can be gathered using imaging sonar systems. Although sonar images can provide high level of details, still in most of the cases they are difficult to decipher. Therefore, to facilitate the classification of targets through sonar images, this study introduces a framework of extracting visual features of marine targets that would serve as unique signatures. The acoustic measure of visibility (AVM) is here introduced as an indirect technique of identification and classification of targets by comparing the observed size with a standard value. This information can be used to instruct manual and automatic algorithms for identification and classification of underwater targets using imaging sonar systems. Using image processing algorithms embedded in Proviwer4 and FIJI software, this study found that acoustic images can be effectively used to classify cod, harbour and grey seals, and orcas through their size, shape and swimming behaviour. Data showed that cod occurred as bright, 0.9 m long, ellipsoidal targets shoaling in groups of up to 50 individuals. Harbour seals occurred as bright torpedo-like fast moving target, whereas grey seals occurred as bulky-ellipsoidal targets with serpentine movement. Orca or larger marine mammals occurred with relatively low visibility on the acoustic images compared to their body size which measured between 4 m and 7 m. This framework provide a new window of performing qualitative and quantitative observations of underwater targets, and with further improvements, this method can be useful for environmental studies within marine renewable energy farms and for other purposes.

The access and quality of electricity are key factors for sustainable development. Off grid areas across the globe, in particular the rural areas in Africa, are in the need of renewable energy technologies as reliable electricity providers. Dedicated investments and technical reforms are needed in the renewable energy sector in order to diversify, expand and proliferate technologies able to provide reliable and affordable electricity for all. A specific case is Ghana where the electrification rate is approximately 79 %, but the utilization rate is approximately 35 %. To improve the current situation, different renewable energy systems should be brought into the power generation mix, and wave power can substantially contribute to electricity generation in Ghana and other countries with wave power resources. The aim of this study was to evaluate the wave power resource availability in Ada, Ghana, where a 100 MW wave power farm is planned to be located, and estimate the quantity of electricity that can be generated using different capacity factors. The results show that the wave climate in Ghana is mild with annual mean values of significant wave height of ca. 1.3 m, energy period of ca. 12 s and wave power value of ca. 10 kW/m. The availability, capacity factors and electricity generation were estimated to be high during the most of the year with exceptions for May, November and December. Estimated annual electricity generation were 175 GWh, to 610 GWh, for capacity factors in the range of 25%, 50% and ca. 70%, respectively. This study conclude that the annual resource availability factor is ca. 80%, suggesting that a wave power farm would be able to produce electricity during the most of the annual cycle. If these result were to be confirmed, wave power will be considered a dependable technology for electricity generation in countries such as Ghana and possibly qualify as baseload in the electricity generation mix.

Freshwater scarcity is one of humanity's reoccurring problems that hamper socio-economic development in many regions across the globe. In coastal areas, seawater can be desalinated through reverse osmosis (RO) and transformed into freshwater for human use. Desalination requires large amounts of energy, mostly in the form of a reliable electricity supply, which in many cases is supplied by diesel generators. The objective of this work is to analyze the wave power resource availability in Kilifi-Kenya and evaluate the possible use of wave power converter (WEC) to power desalination plants. A particular focus is given use of WECs developed by Uppsala University (UU-WEC). The results here presented were achieved using reanalysis-wave data revealed that the local wave climate has an approximate annual mean of 7 kW/m and mode of 5 kW/m. Significant wave height and wave mean period are within 0.8-2 m and 7-8 s respectively, with a predominant wave mean direction from southeast. The seasonal cycle appeared to be the most relevant for energy conversion, having the highest difference of 6 kW/m, in which April is the lowest (3.8 kW/m) and August is the peak (10.5 kW/m). In such mild wave climates, the UU-WEC and similar devices can be suitable for ocean energy harvesting for water desalination systems. Technically, with a capacity factor of 30% and energy consumption of 3 kWh/m(3), a coastal community of about five thousand inhabitants can be provided of freshwater by only ten WECs with installed capacity of 20 kW.

Active acoustics monitoring (AAM) systems can play an important role in the inspection and survey of the subsea environment around marine renewable energy devices, especially in murky and deep waters. Alternative methods comprising a multifunctional platform based on multibeam (MBS) and Dualbeam (DBS) sonar systems are being developed. The aim is to monitor the environmental impacts during installation, operation and maintenance of wave energy converters, marine current turbines, subsea substations and other offshore renewable energy technologies. At this initial phase, one of the specific objective is to understand the functionality of AAM systems. Field tests were done using the MBS and DBS systems. A platform is being tested at the Lysekil Wave Power Project test site and at the Söderfors Marine Current Project test site. Preliminary results show that the MBS produces better acoustic images when the platform is steady, and when in slow-moving waters such as in harbours and shallow rivers. At near field, the MBS is able to track targets < 20 cm such as fish swimming close to hard structures. The DBS can detect isolated targets at far field. Target dimensions estimated using the sonar match the real dimensions of the same´targets.

This paper provides a summarized status update ofthe Lysekil wave power project. The Lysekil project is coordinatedby the Div. of Electricity, Uppsala University since 2002, with theobjective to develop full-scale wave power converters (WEC). Theconcept is based on a linear synchronous generator (anchored tothe seabed) driven by a heaving point absorber. This WEC has nogearbox or other mechanical or hydraulic conversion systems,resulting in a simpler and robust power plant. Since 2006, 12 suchWECs have been build and tested at the research site located atthe west coast of Sweden. The last update includes a new andextended project permit, deployment of a new marine substation,tests of several concepts of heaving buoys, grid connection,improved measuring station, improved modelling of wave powerfarms, implementation of remote operated vehicles forunderwater cable connection, and comprehensive environmentalmonitoring studies.