3 types of renewable offshore power generation
When we think of offshore wind power, the first image that pops up is probably wind turbines just off the shore, slowly spinning in the breeze. Wind turbines are in the news around the world, especially in the United States where new wind farms are being planned on the East Coast, West Coast, and even the Gulf of Mexico (watch out for hurricanes). But while wind farms are getting most of the press, wave power and floating solar are quietly advancing. This Fun Fact Friday, we’re going to take a look at wind power, wave power, and floating solar as the biggest opportunities for offshore power generation.
This is the one everyone knows, wind power! Wind turbines are a common sight onshore, offshore, and even in deep water. How do they work? Energy.gov explains, “Wind turbines work on a simple principle: instead of using electricity to make wind—like a fan—wind turbines use wind to make electricity. Wind turns the propeller-like blades of a turbine around a rotor, which spins a generator, which creates electricity.” They are basically the opposite of a regular fan that takes electricity to generate wind, turbines instead use wind to generate electricity. The blades work like an airplane wing, creating a pressure differential that pushes the blade in one direction, driving the rotor which is connected to a generator. Wind is a great renewable resource, but is dependent on weather conditions which makes it more unpredictable than other sources of energy. Wind intensity depends on how the sun heats the atmosphere, topography, and the Earth’s rotation. Bodies of water, trees, and terrain all affect wind output, so wind farm locations are well studied for consistency before anything is built. Constant, strong wind is best for reliable, maximum power generation.
Hornsea 1 wind farm. Image from renews.biz.
The search for optimum turbine conditions has driven wind developers from onshore to offshore, and eventually deepwater. Over land, wind can vary greatly, but farther offshore, wind speeds are stronger and more consistent. Even the increased cost of building farther offshore is easily offset by the increase in power generation, as well as the freedom to build wind turbines as large as possible. Many people view wind turbines as an eyesore, especially off the coast, but go far enough and offshore turbines are no longer visible from land. After all, there are no complaints about a 264 meter tall turbine like the MySE 16.0-242 if it’s out of sight. These turbines are usually installed directly onto the seabed, which you can learn more about in our article about how offshore wind turbines are installed. However, with deeper waters providing the double benefit of more power generation and no direct line of sight, there is a lot of focus on floating wind technology. Instead of a rigid installation system like a monopile, floating turbines are usually moored to the seabed so they stay in one place, like a ship dropping anchor. Since they float over deepwater, some developers are investigating the opportunity to get some wave power and wind power from one unit. Projects like the 2 GW floating offshore wind project off South Korea are becoming more common as floating wind technology improves with innovations like float out and sink substations.
Most of the recent innovations in wind turbines have been to simply make them larger and more efficient. With the optimal number of blades set at three and the thin blade shape set, the question has been how to make more power with a three-bladed turbine. More recently, research into vertical wind turbines has found that they may be better suited to power generation. They can feed off of each other in wind farms, generating more power in pairs as opposed to horizontal turbines that decrease in power when placed near other turbines. They are also omnidirectional, meaning they don’t have to be oriented in any way to capture maximum wind energy. We haven’t seen any large scale installations of these types of turbines yet, but they look really cool!
Vertical wind turbines. “Mike vanBavel | 42795”. Image from Energy.gov.
Wave power is capturing the motion of the waves to generate power, usually electricity. As with wind power, you have to go where the waves are to get the most bang for your buck. According to Conserve Energy Future, these places are the West Coast of North America, as well as Africa, Scotland, and Australia. Although limited to specific areas, wave energy is quite predictable and doesn’t rely as much on solar or wind, although those can be a factor. The oceans are always moving, so waves continue to move - all that is needed is a way to convert that kinetic energy into electrical energy we can use. From our previous article about wave power, “The machine that does this is called a wave energy converter (WEC), and there are many designs for these converters.” Waves are strongest at the surface of the water, so most wave energy converters are at the surface or may float just below the surface.
“Mocean Energy Blue X in operation at EMEC Scapa Flow wave energy test site, (photo Colin Keldie)”. Image from Offshore Engineer.
The first patent for wave energy technology was filed in 1799 (over 220 years ago!), but it still lags behind wind, solar, nuclear, hydro, and most other forms of renewable energy. However, with the increased interest in green energy comes a greater focus on wave energy. We now have point absorber buoys, oscillating converters, pressure differential WECs, and more. These units capture the flexing motion, up and down bobbing motion, pressure differentials, or use turbines to produce power. Waves can even be directed into a tapered channel at the shore to power a turbine, similar to hydroelectric dams. Total potential wave energy is massive, and while individual installations only capture a tiny fraction of that energy, they are still useful. Wave energy converters are a viable alternative to large wind turbines and the huge coverage of solar panels, especially for the right areas like islands or places where the waves are especially strong. The biggest detriment still looming over wave power is the lack of investment - it’s just not a big focus when wind and solar are so popular, and produce so much energy. It will be exciting to see where wave power goes and if more investment changes the landscape of renewable offshore energy.
“This floating solar array, the largest in the world, produces enough electricity to power 15,000 homes in China. There are 166,000 panels included on the structure.” Image from Energy Sage.
Floating solar describes solar panels that are attached to a buoyant structure. The best place is usually calmer bodies of water, such as lakes and reservoirs, where they won’t be disturbed. Compared to wave and wind power, floating solar is in its infancy with commercial installations just ramping up. Why float the panels? Some areas just don’t have the space, rooftop or otherwise, to mount enough panels. Solar hasn’t been very viable for powering a house or business up until the last 10-20 years, but with efficiency improving and cost dropping rapidly due to technology and manufacturing advancements, it makes a lot of sense. According to Sunrun, “The cost of solar has dropped significantly in the past several years. A decade ago, an average 6 kilowatt hour residential solar system could cost more than $50,000. Now, the outright cost of a typical home installation ranges from $16,200 to $21,400.” As you can see from the chart below, the cost has dropped from around $7.7 per watt to around $2.6 in ten years. If you’re short on space, you can always float the solar panels, which is exactly what Singapore is doing. This summer 2021, Singapore built one of the world’s largest floating solar farms the size of 45 football fields. It is a 60 megawatt peak photovoltaic (PV) system that powers the island’s five water treatment plants. The panels are expected to operate 5-15% better than rooftop panels due to cooling from the water. Singapore has four other floating solar farms in the plans.
Graph of the cost of residential solar energy from 2008 to 2018. Image from Sunrun.
The advantages of “floatovoltaics” are that they don’t take up valuable land space and, as mentioned above, perform better from the cooling effect of the water. They can also help prevent evaporation and reduce algae blooms, which is important for sources of drinking water. One of the disadvantages of floating solar panels is the increased cost, especially since this type of solar installation is quite new. Another disadvantage is that it is only useful for calm waters and large, industrial installations. Nevertheless, floating solar combined with hydroelectric power can help produce electricity when the water is low and make more use of the open water real estate on huge reservoirs.
Green hydrogen is the next step in offshore power generation after wind, wave, and solar. This describes the production of hydrogen fuel from renewable sources of power. Instead of simply producing electricity for use in the grid, the energy sources above can be used to create hydrogen on-site. Offshore, this could be used to fuel vessels transported to shore via pipeline or ship for any purpose. Siemens Gamesa already has plans to use large wind turbines to produce hydrogen. There are different types of renewable fuels like hydrogen, ammonia, and e-methanol that are being researched. If you’d like to learn more about that frontrunner in the race to decarbonize shipping and the differences between gray, blue, and green hydrogen, check out our article Is hydrogen the next fuel in shipping?
The future of offshore energy
Offshore is the place to be if you want to make big power - more wind, more waves, and (depending on the location) bright sun. Renewable energy will probably continue to move offshore with the benefits of those technologies being off land and with greater power potential. The technology in offshore renewables is evolving fast, so keep an eye on it!
If you’d like to learn more about some of the world’s largest wind farms, or how wave power works, check out the links below. Happy Friday!