Renewable electricity production
At the Division of Electricity, we conduct research on wave, wind, hydro- and marine current power. We are at the forefront of wave energy research and have launched our own experimental facility in the study of marine current power.
Wave power
Ocean waves provide a renewable energy source with high potential to contribute to the global electricity production with minimal environmental impact. Uppsala University is at the forefront of wave energy research and has the largest group in the area.
Our research group is one of the largest worldwide and has developed and deployed full-scale wave energy converters since 2002. The research site at Lysekil on the west coast of Sweden is one of the few off-shore test sites for full-scale wave energy converters in the world.
The Lysekil project
The wave energy research group at Uppsala University test fullscale devices and technology solutions at a research test site outside the town Lysekil at the west coast of Sweden. At the site, not only the wave energy technology is studied, but also how a wave energy park may influence the local marine environment.
A Datawell Waverider wave measuring buoy was installed in 2004 and measures the waves at the site continuously. The first fullscale wave energy device was installed in 2006. Since then, a large number of wave energy generators, buoys, marine substations and various wave energy technology has been deployed and studied in a long series of experiments at the site.
From the gathered information on wave height and length, one can calculate something that may be thought of as a mean wave height, through a so called spectral analysis. This is called the significant wave height. The significant wave height is not only important for the knowledge of how large the waves are that fall in towards the coast, but it is also needed for the calculations of the amount of power flux that enters the research area, and for calculations on the amount energy that is carried by the waves.
For more information on the Lysekil wave energy project, please contact Jens Engström: jens.engstrom@angstrom.uu.se
Wave power concept
The Uppsala University wave power concept is based on simplicity and functionality to ensure a robust and effective system for converting wave energy to electricity in the grid. The main idea is simple: a buoy at the sea surface is moving due to the motion of the waves, and connects to a direct-driven, linear generator where the motion is converted to electricity.
Forces in waves can be very large, especially in storms, and survivability is a key issue in wave power technology. It has previously been recommended that, to shelter the wave power plant from the extreme destructive powers of the ocean, as much as possible of the wave power plant should be concealed underneath the surface. In view of this, placing the most critical component, namely the generator, on the sea bed is an important part of the Uppsala concept. The buoy, acting as power take-off, is a robust, cheap, and insensitive component, and together with the line it is the only part of the energy system directly affected by the extreme mechanical forces of the ocean surface. To prevent seawater from entering the system, a rod connects the rotor with the buoy line through a sealing device on top of the capsule. The system is designed to work at depths ranging from 20 to 100 m.
The wave power system is simple, in the sense that the amount of moving parts and expensive technology is minimized. This reduces the risk for failure and the costs for off-shore maintenance.
The first Uppsala University full-scale wave energy converter (WEC) was developed and deployed at the Lysekil research site in 2006, and twelve full-scale WECs have been developed since.
Wave power in the Baltic Sea (WESA-project)
WESA is a pioneering research project with the aim to study the potential of wave power in the Baltic Sea. The project is financed by the EU and is a collaboration between Uppsala University, Ålands Teknikkluster r.f. and the University of Turku. The goals of the project include finding optimal buoys that can withstand ice conditions during winters, and to study prospects and challenges of large-scale wave power in the Baltic Sea.
For information regarding the WESA project and wave power in the Baltic Sea, please contact Erland Strömstedt: Erland.Stromstedt@angstrom.uu.se
Environmental impact
All energy conversion, also from renewable energy sources, affects the environment in some way. The wave power plants may impact the local ecosystem, and the local environment may also affect the power plants with, for example, biofouling.
It is important to study the environmental impact at an early stage of the project and adjust eventuall negative impact on the ecosystem. In the Lysekil project, the environmental impact of the wave power park has been studied continuously since the start of the project. This has been done, for instance, by studying the artificial reef effect of 30 buoys attached to fundaments on the sea bed, and by studying the sound impact and changed sedimentation and water movements.
For more information on the environmental impacts of wave power, please contact Jan Sundberg: jan.sundberg@angstrom.uu.se
Research projects
SUrvivability and PERformance of wave energy FARMS (SUPERFARMS)
To produce electricity in the MW range, wave power devices will be deployed together in large parks. In a new research project financed by the Swedish Energy Authority, the performance and survivability of large-scale wave energy farms will be studied and improved.
The research project involves both analytical and numerical simulations and optimizations of the full wave energy farm, including hydrodynamical and electrical interactions, development of control methods for increased performance and experiments in wave tank and in full-scale off-shore.
Marine substation
The site is equipped with one subsea power cable and signal cable connected to the measuring station on shore. All the WECs connect through a low voltage marine substation (LVMS) at the seabed. To transmit the power and connect the WECs to the substation there are underwater connectors at the end of the cables from the WECs and at the substation. In the substation, the AC from each generator is first converted to DC in a diode rectifier and then connected together on a common DC bus to smoothing the power. The DC is inverted back to AC in an IGBT inverter, transformed and transmitted to shore through the subsea power cable to the resistive loads at the measuring station. The first marine substation was installed in 2009 and was able to connect three WECs. In 2015, a new, repaired substation was installed.
Tidal compensation system
To handle mean sea level variations due to tides, a mechanical device able to adjust the length of the connection line has been developed and mounted on a buoy. The goal of a compensation system for sea level variations is not only to optimize the power output of the generator during tides but also to compensate for the error due to misalignment of the center of the stator with the center of the translator during deployment.
Remotely Operated Vehicle (ROV)
The wave power devices designed at Uppsala University are small units that will be deployed in larger arrays in order to produce a significant power output. For this reason the number of connections is very large and need to be automated by an ROV to decrease cost and time of the installation operation. A docking and connection system for small ROVs are developed for the automatization of large scale deployment.
Marine ecological studies
Studies on eventual environmental impact on marine fauna from wave energy devices started in 2005. This has included marine biological studies such as artificial reef effects (e.g. by fish and crustaceans), biofouling and colonisation patterns on wave energy devices, effects on the nearby seabed invertebrate fauna and underwater noise. Presently ongoing are the developments of sonar systems for the monitoring of studies of fish communities and marine mammals around marine energy devises, such as wave energy generators. Further, mark and recapture studies on decapods (crustaceans) are performed in order to estimate differences in population size and growth rates around the wave energy devices and control areas. Also ongoing is a follow up study on motile macro fauna composition on the foundations that first was done 2007-2009, directly after initial deployment, for investigations on long term changes.
Measurement systems
To measure and evaluate key parameters during off-shore opreation is crucial to study and improve the construction, performance and life span of a wave energy converter. In a research project financed by the Vargö Foundation, the generators are equipped with measurement system designed to log their electricity production, movement and forces. From these measurements, the performance and efficiency of the generator can be determined, and the forces acting on the devices can be analysed. This can be used to determine the expected total electricity production from a wave energy farm, as well as life span and maintenance needs.
Equivalent circuit models
To make the wave power system modelling more efficient and less complicated, an equivalent electric circuit model has been developed. This modelling method enables the study of the buoy - power take-off interaction in one circuit framework. Main wave energy system performance indicators, like velocity, force or power, can be simulated and analyzed rapidly.
Offshore operations
Offshore operations such as deployment and maintenance of wave energy converters and marine current energy converters has been expensive, time-consuming and complicated processes raising safety issues. The offshore operations can be optimized by adapting existing offshore fleets, or by using new technologies, for example a new vessel designed for these specific operations. Various hull forms as well as the positions of the energy converters and cranes may influence the initial stability, hydrodynamic properties, seakeeping and towing ability. In an ongoing research project, different solutions for cost efficient and safe deployments are studied.
Wind power
Due to increasing global electricity consumption, climate change threats and decreasing oil resources, the interest for alternative energy sources such as wind energy is increased. The wind is both free of charge and renewable, it has no polluting discharges and is therefore a good complement to regulated energy sources such as hydropower.
At Uppsala University, we mainly study vertical axis wind turbines, where the blades are rotating around a vertical axis as opposed to a horisontal, as in conventional wind power plants. One of the advantages with a vertical axis is that the generator can be situated on the ground, which gives a better performance and cheaper construction costs.
To develop effective wind power plants, the aerodynamics must be modelled with good accuracy. This is a complex problem which is usually studied with different numerical methods.
A 2 kW vertical axis wind turbine of Uppsala University was constructed in 2005. In 2006, a 12 kW turbine was developed and built at Marsta outside Uppsala.
Vertical axis wind turbines
The generator of a vertical axis wind turbine can be placed on the ground which allows an optimization for price and performance. The system developed at Uppsala University uses a direct drive generator and therefore no gearbox, which is beneficial as gearboxes failure is a common cause of downtime for conventional wind turbines. The vertical wind turbine is instead controlled electrically by means of the generator. Elimination of the pitch system further reduces the risk of downtime and the need for maintenance.
The vertical axis turbine have certain environmental advantages over the horizontal axis. The turbine generally have lower rotational speed than the corresponding horizontal axis turbine which results in lower noise level. Ice throw from a vertical-axis turbine is not thrown, as far as there is no vertically component of throw. When the generator is placed on the ground, the design can be made more robust. In some places of the world there is a problem with relatively frequent collisions between rotating blades and birds or bats. A vertical axis turbine is probably safer for birds and bats. This is because a vertical axis turbine is easier to detect for a bird since it does not move in the vertical direction. Furthermore, compared to the horizontal axis turbine, it has lower blade speed which makes it easier to avoid collision.
For more information on vertical axis wind turbines, please contact Hans Bernhoff: hans.bernhoff@angstrom.uu.se.
Generator physics
The generator is, in addition to generating electricity, used for control and starter for the turbine. The turbine is not self-starting but when the turbine has reached a sufficiently high rotation speed the wind can drive the turbine. The energy spent in the start sequence corresponds approximately to the energy generated for 3 seconds nominal operation.
For a variable speed turbine, it is important that the generator has a high efficiency over a wide range of rotational speeds. The possibility for this has been examined for the 225 kW generator designed, constructed and installed in Falkenberg. The generator has a minimum efficiency of 96% at wind speeds of 6.5 m/s. The generator has the task of controlling the rotation of the turbine for optimal efficiency but also to act as a brake at very high wind speeds.
For more information on generator physics, please contact Sandra Eriksson: sandra.eriksson@angstrom.uu.se
Aerodynamics
A simulation tool has been developed to predict the aerodynamics of a vertical axis wind turbine. The goal was to better understand how a vertical axis turbine captures energy from the wind and thus be able to improve performance by optimizing turbine design.
Aerodynamic flows are complex and must in many cases be solved numerically. When the aerodynamics is simulated for the vertical-axis turbines, three different methods are generally used: the stream tube model, vortex models and finite element/volume method. Research at Uppsala University, focuses on the first two models.
The stream tube model allows for most rapidly numerically solution as it does not contain a time-dependent flow. The velocity field is approximated only on the turbine blades. Thanks to its speed, this model can be used to simulate the flow in three dimensions. It allows simulations of varying wind speed of the turbine area, and the impact of the blade support arms.
Studies of how various turbines affect each other must instead use the vortex method which is somewhat more complex. Vortex simulations are preferably done in two dimensions as these require more computational power. Higher power can be obtain for individual turbines if they are placed close to each other in a line while the flow direction is perpendicular to this line, according to simulations with the vortex method.
The model developed at Uppsala University can be used in the design of an H-rotor to optimize efficacy and/or minimize material-loads. With the help of wind statistics from a given location, the most optimal design for a turbine can be calculated iteratively.
For more information on aerodynamics of wind power plants, please contact Anders Goude: anders.goude@angstrom.uu.se
Hydropower
To handle a deregulated electricity market with a large penetration of renewable energy sources, old hydropower generators must be thouroghly characterized and improved. We also study the interaction of the generator with the adjacent grid and what transients and other main disturbances which can propagate into the generator and cause adverse effects. Using modern power electronics and magnetic actuators, investigate how the electrical and magnetic properties of the generator can be controlled.
One of the main goals of the research is to use computer based models to draw conclusions about operation properties, which can be used as a basis for future decisions on the operation and investment. Through our involvement in the Swedish hydropower center (SVC), we get the opportunity to verify our FEM models with measurements on real units.
For more information about our research on hydropower, please contact Urban Lundin: Urban.Lundin@angstrom.uu.se
Marine currents
Marine currents in rivers, straights and the oceans constitute a renewable energy source with good potential. At Uppsala University, research is primarily focused on the generators of marine current energy converters. The goal is to have a power plants that generate electricity with high efficiency at slow water movement.
In March 2007, the first prototype generator adapted to these low velocities was completed at the Ångström Laboratory. 2013 the first experimental facility was launched at Soderfors in the Dal river. The next step in the research is to connect the power plants to the grid and to develop and scale up the technology so that it is suitable for tidal applications.
Söderfors marine current power plant and experimental station
We deployed the first marine current power plant in the river Dal outside Söderfors 2013. The purpose of the project is to run a small-size experimental station for marine currents in realistic settings.
- Studies of the potential/resource - development of models based on short series of measurements to compute current speeds, which can then be used for energy forecasts and to calculate the maximum loads.
- System simulations - computational models of the total system for electricity generation from the flowing water, from a description of the flowing water via conversion to electricity in the turbine, generator and electrical system to the power grid.
- Fluid dynamic simulations of flow control and protection of turbines.
- Slow-moving permanently magnetized generators - the development of the generator.
- Experimental validation of the generator and the control system - Through the experimental facility in Soderfors the generator technology and monitoring and control systems are evaluated and developed in a real environment.
Research on the interaction between fish and turbines
In 2015 initial test fishing was done in order to investigate the common fish community in the waters. In 2017 experimental studies were started. Smaller salmon and trout (smolt) was released in the waters around the turbine. With the help of sonar recordings fish behaviour was documented including rotating and still (control) turbine conditions. This study continued during 2018. In 2018 an experimental laboratory study started using the facilities of Swedish Univ. of Agricultural Science in nearby Älvkarleby. In their brook aquarium smolt behaviour around turbines will be tested using turbine models. With the focus on different turbine models, varying rotation speeds, velocities and light regimes aiming to finding the tidal/current stream concept and technologies with the least environmental impact.
Research projects
Project SWERM (Swedish Wave Energy Resource Mapping)
In the project the conditions for offshore-based wave energy conversion technology in Swedish seawaters with respect to a variety of selected parameters and variables has been mapped.
Ocean Energy Scale-up Alliance (OESA) project
OESA aims to accelerate the development of marine energy technologies through strategic partnerships and international collaboration.
