LiDAR stands for Light Detection and Ranging and is very similar in concept to RADAR and SONAR. In its simplest form, a laser beam is emitted which hits an object and the reflection is recorded by a circuit. The time difference between the sending of the laser beam and the reception is used to determine the distance to the object. If the laser beam is quickly scanned around the surrounding environment, then a simple map of the surrounds can be made.
LiDAR has taken off in popularity over the last several years. It's been integrated into robotics, astronomy, as well as archaeology and security when paired with drones. It's also been instrumental in the burgeoning autonomous vehicle industry (where proprietary LiDAR research has caused dramatic legal battles). Once requiring thousands or tens of thousands of dollars, LiDAR costs have been dropping, which means that we'll likely see this technology appear in more and more unique applications.
One such application is FLiDAR, or Floating LiDAR, which aims to present solutions to problems in wind energy that have proven difficult and costly to solve.
Scouting Offshore Wind Farm Locations: A Riddle of Logistics
Offshore wind farms take advantage of the fact that wind speeds are higher and more consistent in the sea than they are on land, primarily due to the lack of hills, mountains, and buildings which can break wind up. But not all offshore sites are created equal. Before a wind farm is installed, a lot of research and wind speed measurements are needed to determine the cost-effectiveness of the potential farm (only cost-effective locations are granted funding).
Typical site scouting practices for getting wind data rely on a wind speed gauge called an anemometer which needs to be installed on tall masts. They need to be away from the surface of the water because wind speed varies with height and the measurements need to be taken at the height that wind turbines will operate at. (These wind speed and direction variations at elevation also dictate that hot air balloons use different layers in the atmosphere to move around.)
Obtaining wind data on masts on shorelines and inland is relatively easy since erecting these structures has little difference from constructing a typical tower. Off-shore, however, is a different matter as not only is planning difficult but the costs are significantly higher. According to some estimates, the cost of installing an inland anemometer mast is approximately $50,000 but the cost for an off-shore mast is $15 million with a year wait for a permit and up to six months construction time. Off-shore masts also face the issue of water depth which is one of the factors for the price tag (300m of water is not a trivial depth at which to install a mast).
So how do you remotely measure wind 500 feet above the surface of the ocean five to 15 miles offshore without needing to build a $15 million tower?
Set LiDAR afloat!
Measuring Atmospheric Variation with LiDAR
How does LiDAR measure the wind? Unlike the anemometer, LiDAR systems do not need to be mounted on a mast to the altitude that the wind turbine will operate at. Instead, the LiDAR system merely needs to be located on the surface (land or water), where the planned farm is to be built and measurements can be taken remotely.
According to ZephIR, a LiDAR sensor developer involved with multiple FLiDAR applications, LiDAR systems can be used to detect incredibly small variations in the atmosphere which directly translate to wind speed. Their validation of measurement literature claims that this measurement from a ZephIR LiDAR sensor can yield wind data "at least the same standard as a met mast".
Image from ZephIR
A similar method that uses a form of LiDAR is the use of artificial stars by astronomers. One of the biggest challenges for land-based telescopes is the atmospheric wind shear and thermal convection currents which make stars appear to shimmer and wobble. To overcome this, an artificial star is made in the atmosphere using a high powered laser which is specifically designed to excite sodium atoms. The result is a star in the sky next to the star that is being viewed which also exhibits the same fluctuations. Since the unaffected appearance of the artificial star is known, a simple subtraction can be used to change the appearance of both the artificial star and the distant so that the fluctuations are removed.
Creating an artificial star with a LiDAR laser at the Starfire Optical Range on Kirtland Air Force Base, New Mexico. Image from the US Air Force
LiDAR's capacity for giving precise data on wind patterns makes it suitable for remote monitoring applications like the "floating laboratories" now tethered around the world's oceans.
LiDAR Takes to the Seas
Floating LiDAR buoys are being used to remotely monitor ocean environments for scouting offshore wind farm locations, but also for scientific studies and other commercial applications. Through additional sensors, many these buoys also have the capability to measure other metocean data. Metocean (a portmanteau of meteorological and oceanographic) data refers to environmental data including measurements of waves, currents, tides, sea levels, and weather. While the value of this data extends across many industries, it also makes it even easier for wind farms to determine build locations and maintenance schedules.
Here's a look at some of the FLiDAR rigs floating our seas.
AXYS Technologies FLiDAR WindSentinal
Canadian-based AXYS Technologies was founded in 1974 with a focus on remote environmental monitoring. In April of 2015, AXYS partnered with ZephIR, utilizing their ZephIR 300 in a dual arrangement on their FLiDAR WindSentinal buoy (acquiring a Belgian company called FLiDAR in September of that same year). The buoy can float on the water (tethered to an anchor) and uses solar panels for power and batteries for power storage.
The system has multiple sensors for roll, pitch, yaw, and translation. Image courtesy of AXYS
Each sensor and data acquisition system on the WindSentinal can record data independently but the sensors are synchronized using GPS. This is important since all the data is combined to produce a more true wind speed (if, for example, the buoy experiences are large wave the data will need to be adjusted for this). The system has seen 20 commercial deployments worldwide with 16 locations meeting mast validations, most recently earlier this month when a WindSentinal was deployed off the coast of New Jersey to determine the optimal location for an upcoming wind farm dubbed Ocean Wind.
EOLOS Solutions EOLOS FLS200
The EOLOS FLS200 from EOLOS
Back at home base, engineers may view the real-time data gathered from the data via the EOLOS 2.0 SCADA system.
RPS is an international energy and resources company based in the United Kingdom. This month, RPS announced that it has partnered with Norwegian energy company Equinor to develop FLiDAR systems for US offshore wind farm research.
This image can help demonstrate the scale of these FLiDAR systems. Screencap from RPS
Below, you can see a short video that follows a "sea trial" of RPS's floating LiDAR rig by RPS's Australia and Asia Pacific division on June 29th:
LiDAR Gust Protection
LiDAR technology, as seen in the FLiDAR system developed by AXYS, can dramatically help with determining the best locations for wind farms without having to incur large costs. But the use of LiDAR goes beyond planning of wind farms; it can also protect wind turbines. One problem that wind farms face is storms, which can bring winds so powerful that the turbine is damaged through sheer force. The turbine can also become disengaged, allowing the turbine to spin too fast (which can result in catastrophic failure).
Strong winds can be detrimental to wind turbines. Image courtesy Geograph
Strong winds can be prepared for with the use of forecast models so that engineers can disable turbines as a storm approaches. Wind gusts, however, are particularly dangerous as they are impossible to predict (in terms of weather forecast) and are very hard to prepare for. LiDAR sensors could be used to measure the wind speed several hundred meters in front of a wind turbine, allowing the turbine precious moments to react to the oncoming gust.
LiDAR has many applications such as mapping of the environment and autonomous control but it can also be used in more unusual ways such as measuring wind speed from a distance. Now that AXYS are using their FLiDAR systems in a commercial environment, we may see more wind farms being produced now that wind data can be economically gathered.
Featured image courtesy of AXYS Technologies.
Read More on LiDAR
- The Affordable LiDAR Movement—Researchers Aim to Drastically Reduce Sensor Costs
- Tesla vs Google: Do LIDAR Sensors Belong in Autonomous Vehicles?
- Saturating and Spoofing LiDAR Attacks Cast Doubt on the Safety of Driverless Cars
- What Is Solid State LiDAR and Is It Faster, Cheaper, Better?
- Light Sensors: The Absorption Spectrometer, LIDAR, and Thermal Cameras on Display at CES 2018