The world wide thirst for electricity is absolutely immense. And with people like me opting to ditch natural gas in favor of heat pumps and driving electric cars, that demand is only going to increase. I talk about solar all the time, but global wind generation is about twice that of solar (according to our world in data in 2019) (link).
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Studies even suggest that offshore wind energy alone could power the entire world. In fact, 80 % of the world’s wind resource is offshore in deep waters. So why isn’t every country building off shore wind farms as fast as they can, and why aren’t they everywhere? [thinks to himself] Let’s find out!
Now when you think wind turbine, you’re probably picturing something like this. Massive horizontal axis wind turbines or HAWTs.
But a company called Hydro Wind Energy believes they have a novel solution to the offshore wind problem, by using these, vertical axis turbines with some very interesting properties. But before we get into that, let’s talk about conventional offshore wind turbines.
Here in San Diego, we have really mild weather and slow wind speeds. It doesn’t help that i live on a hill and have all these trees. [hold wind speed meter and show results, on the roof]. But out here near the ocean, you can just tell how much more active the wind is.
If we look at offshore wind speed data 70 km off the coast of Rona in Scotland, here’s what an hourly average for the entire year looks like. First of all it should be clear just how variable and intermittent the wind speeds really are.
But if we average it by season, we can get a little more clarity. Interestingly the strongest winds come in winter, which is good news, because that’s when solar energy is at its lowest. And before you think that wind speeds are super constant throughout the day, remember this is an average. If we instead look at one day August 1st 2020 for summer, and January 27th 2020 for winter, we can see how the offshore wind and solar potentials compare.
This is the first major issue of offshore wind, it’s unpredictable and varies throughout the day. There’s no way to increase or decrease production to match what people are actually using or even know what you can expect hour by hour.
Spanish-German wind giant Siemens Gamesa is preparing to deploy 60 of its SG 14-222 DD turbines of this variety by 2024. Each of the 60 turbines will produce 14.7MW, which is a new world record. (LINK) Feature blades that are 108M long, about the size of Football or soccer field, and a rotor diameter of 222 meters, about 45 Tesla Model S’s parked bumper to bumper, it’s pretty mind boggling.
There are issues though, as costs increase dramatically as the blade size increases. Both in larger molds and casts to create the blades, but also the logistics of larger support towers and anchoring them safely to the sea floor using monopiles. (LINK) A Monopile is a steel cylinder piled into the sea floor by a special hydraulic ram.
And as wind turbines continue to grow in size, these monopiles too will have to get bigger to support their massive size, and resulting moments of inertia. Now while there are some floating platforms being worked on, these turbines will largely be limited to about 50 meter sea depths which will restrict where it can be installed.
The second problem with offshore wind turbines, is that they aren’t really able to harness the entirety of the winds potential.
Large wind turbines like these, require around 5m/s airspeeds to start spinning, and have to shut down when wind speeds reach around 25m/s. Their ideal operating range is around 10-15m/s and thats where the gearing, generators and power electronics are sized to operate. More modern turbines like the Siemens Gamesa 14.7MW turbines, make use of a technology called High Wind Ride Through (HWRT) which help with this, but that’s a topic for another day.
Being so massive, these turbines actually affect the laminar flow of air, impacting other turbines down wind in a offshore farm. I had a chance to chat with Marc Spieler at NVidia, a company doing amazing work using digital twins, AI and computer simulations, to determine optimal turbine placement.
According to an article by the American Society of Mechanical Engineers, written by Michael Abrams, while horizontal wind turbines can be 50% efficient, turbines down wind can see their outputs decreased by about 40%. To avoid the turbulence of an 10MW upwind turbine with a rotor diameter of 150meters, a downstream turbine would need to be installed three kilometers away. And these large distances, means production density is lowered, maintainence times would be higher, not to mention all the cabling to connect them all. (link)
So massive conventional turbines, operate best in a small range of wind speeds, are costly to install and require more space. But as they get bigger and bigger, the cost per MW produced continues to drop making them cost competitive in more and more regions around the world. But what about those Vertical axis turbines, or VAWTs I mentioned earlier?
Well Hydro Wind Energy has created this, the Ocean Hydro Omni, and it functions in a completely different way than other horizontal or vertical axis wind turbines.
While HAWTs have efficiencies of 50%, VAWTs are only around 35-40% efficient. This is largely due to the fact that the wind hits both the collection side, as well as the other side turning back into the wind, slowing its spin. But unlike HAWTs, VAWTs generate a funnel-like wake that stretches like a contrail and the wind is less turbulent after it passes through, meaning they can be installed much closer together.
But that’s not what makes Hydro Wind Energy’s Omni turbines special. Unlike all other wind turbines, the Ocean Hydro Onmi doesn’t produce electricity directly from the wind. No, instead it uses the wind to lift a heavy mass. Then when energy is needed, the weight can be dropped, powering a generator. This has some very interesting benefits. For one, the omni can operate in a much winder range of wind speeds. (clip from interview with Lee talking about wind speed range). Because they don’t have delicate electronics and generators attached to the turbines, they can just lift the weights faster or slower through a much wider range of wind speeds. (interview of lee talking about how the energy of wind speed is a function of speeds cubed.)
Also unlike traditional wind turbines, the ocean hydro omni, can respond to grid needs, either storing or release energy on demand. If the winds are high and demand is low, they can lift the weights and stand by. When demand rises, they can release the weights at a set speed and create uniform power output.
The energy storage potential of the Ocean Hydro Omni, is a function then of the sea depth, and the weight of the mass. Mass of the weight? You know what I mean. For this reason, their first pilot plant scheduled for the second half of 2022, will be installed at a depth of 300 meters, far deeper than most traditional wind turbines.
The omni then isn’t just a off shore wind energy generator, it’s also a battery, and a smart grid enabled device. To see just how valuable this could be, let’s compare the omni to a traditional 10MW wind turbine over the course of a day.
Using our data for Rona from earlier, and factoring average and maximum wind speeds, we can approximate true wind speeds for a day. For a traditional turbine, power output will increase with wind speeds until about 15 m/s. From 15-25 m/s the traditional turbine will change its rotor pitch angle to slow down and maintain a constant output. When wind speeds rise above 25 m/s, the turbine has to do a safety shutdown, to prevent overspeeding and damaging itself. This is what I mean by not harnessing the entirety of the wind potential. Plus the traditional turbine can’t do anything about matching demand, it just produces whatever energy it can based on the wind.
In comparison the Ocean hydro Omni, can safely operate in windspeeds between 4 and 40 m/s which means this entire day, it is able to harness the wind speed to lift its weights. And it can lower them back down in a controlled way throughout the day in cycles. Now a single omni probably won’t be able to produce as much power as a traditional wind turbine, but because they can be grouped closer together, and cost less per turbine, they can still provide similar power outputs over an entire wind farm. And if built with the same surface area, they’d generate at least 4x as much energy.
But where this gets really interesting is when we look at power output as a function of grid demand. Again the traditional turbine can’t do much to vary its output, its just a function of wind speed. But Hydro Wind Energy’s Turbines can act as an on demand device, and the more you have in a farm, the more it can either charge by lifting its weights, or provide power by dropping them. Build enough omni’s and it could be possible to meet an entire grids demands, no matter the time of day.
A lot of the ideas they’ve employed aren’t new, vertical axis wind turbines, gravity batteries, but their unique packaging definitely has me excited.
But Hydro wind energy isn’t in the clear just yet. They have so far tested their technology on shore, and are preparing for their first offshore installation later in 2022. The data gathered there will feed back into their engineering design and eventual final production model.
They’ll need to prove the concept can withstand gale force winds out in the deep ocean, show that their systems can last 20-30 years like a conventional turbine, and come up with maintenance procedures and intervals to ensure their turbines reach full life. This data will be critical to determine its true levelized cost of electricity. If they can win on their strategy of smaller vertical turbines that can be build closer to gether in deeper waters, with energy storage, I think they have a winner on their hands.
So are we going to stop seeing bigger and bigger conventional offshore wind turbines? Not at all, in fact there is more interest in larger conventional wind turbines than ever. But the benefits of the Ocean Hydro Omni will be a new tool in our toolkit, allowing greater renewable energy generation, and greater flexibility. Their design will be a grid operators best friend, able to provide energy when needed, regardless of wind speeds.
If we’re to move away from stable but dirty forms of energy production like coal and natural gas, we’ll need every tool we can get. And if renewable energy’s achilles heal is predictability, on demand generation like the omni can provide will be huge to not only produce energy, but lower the need for grid storage.
But what do you think? Are you as excited for vertical axis wind turbines with gravity battery storage as I am? What percent of future offshore wind projects will use this approach? Sound off in the comments below.