As the worldwide energy industry strives to move away from fossil fuels and towards clean and renewable energy sources, wind energy can be considered among the most crucial technologies to develop. While civilizations have been harnessing the ubiquitous power of winds for millennia, in the form of sail boats and water-pumping windmills, creating electricity from wind has really taken off over the past twenty years. Over that time, U.S. wind generation went from barely a blip on the radar to recently surpassing hydroelectric power as the most prominent source of renewable energy generation in the country.
The explosion in wind energy prominence came from two different fronts, though, with a burgeoning onshore wind energy sector that’s becoming increasingly prevalent and important across the Midwestern United States on one end and a nascent offshore wind energy field looking to take hold in coastal states.
While it would perhaps be simple to assume that the only difference in onshore and offshore wind technology is the location, the reality is that the two different types of wind power have different advantages and disadvantages, unique considerations, and independent future projections. Understanding these differences is key to recognizing the manner in which wind power will upend the U.S. power industry.
When it comes to building up renewable energy generation, cost is always a key factor to consider because these sources must ideally be even more economical than fossil fuel sources in order to get wide buy in. Regarding wind energy specifically, cost is a huge difference between offshore and onshore generations, so it’s worth talking about first.
Offshore turbines require many more considerations in terms of construction than do onshore turbines because the entire platform supporting the wind turbine must first be accounted for before the costs of the turbine itself is even factored in. Additionally, because offshore wind farms are often miles out at sea they require more extensive transmission cables in order to connect them to the grid than do onshore turbines that are more likely to be built near existing grid infrastructure.
Additionally, all of these higher-cost items for offshore wind turbines also bring with them greater required construction times. The longer the construction process, the more expensive they are to build and the longer it takes before they can generate electricity and start making their owners money. Not only that, but being sited offshore amidst waves, storms, and salt water leads to greater wear and tear on offshore turbines and necessitate more frequent and costly maintenance.
Put together, the difference in costs for onshore and offshore wind energy sources are quite significant. According to the U.S. Energy Information Administration, offshore wind capacity additions cost almost three times more than onshore wind capacity additions on a dollar per megawatthour basis, exceeding the costs for even new fossil fuel generation. Meanwhile, onshore wind farms are often cited as the cheapest form of clean energy to install.
However, those increased costs of offshore wind turbines bring with them some advantages. Chiefly, offshore wind turbines are able to be built much larger and taller, which inherently comes with greater energy production– not only because the turbines are larger but because wind speeds at greater altitudes (and further out to sea, where buildings or hills aren’t blocking wind) are faster and can thus transfer more energy to wind turbines. In contrast, onshore wind turbines are typically built shorter, so they can’t access the faster wind speeds at greater heights. This difference also results in onshore turbines producing energy in a more intermittent manner than offshore turbines because of poor wind speed and environmental surroundings blocking wind.
On the other side, though, offshore wind turbines suffer when compared with onshore wind turbines due to the previously mentioned distance the cables must travel to connect the turbines to the grid. The longer these cables are, the greater the voltage drop and thus the power losses over the transportation process.
In the end, offshore wind turbines are still more efficient than onshore turbines. Because these offshore turbines can access the higher wind speeds that will blow more consistently, they are a better long-term solution to provide reliable and efficient energy than onshore turbines. Especially as manufacturers and utilities climb up the learning curve in installing offshore wind turbines, the difference in costs will decrease (although offshore will always be somewhat more expensive than onshore) and the improved efficiency will become more critical.
Another factor to consider when analyzing onshore wind turbines vs. offshore wind turbines are the impacts on the surrounding environment– both on communities of people in the surrounding areas and on nature.
Opponents of wind turbine installations often attempt to convince the public that they are unsightly, loud, and take away from the natural landscape. Opinions on that conclusion differ depending on who you ask, but wind turbines that can be placed miles out to sea are less likely to be considered intrusive and are thus more likely to receive necessary approvals while onshore wind farms tend to be more scrutinized and contested by those who live nearby. Of course, many people in coastal communities will still be anxious about the idea of their water views being ‘clogged’ by offshore wind turbines– no matter how deep at sea they are placed– so engaging with the communities when planning and building the turbines remains important.
Offshore wind turbines must be sited and built carefully because communities and industries that rely on the natural ecosystems of the water, such as for fishing and shipping, could be disrupted. Such concerns are a common hurdle for offshore wind farms before they can actually be permitted. These concerns exist for onshore wind farms, notably with more concerns about how turbines might affect the habitats and survival of local endangered bird or bat species.
Current installation capacity and future projects
Based on all these competing considerations for onshore wind turbines vs. offshore wind turbines, analyzing the existing and future installations of each provides some intriguing insights. Onshore turbines have had longer to be built up, for companies to learn how and where to site them, and have been profitable for much longer. In fact, construction on the first commercial-scale offshore wind farm in the United States is expected to begin in 2019 with an 800-megawatt project 15 miles off the coast of Massachusetts. Meanwhile, the United States has a combined capacity of 90,550 megawatts of wind power installed– all onshore.
However, globally offshore wind capacity has reached a cumulative 17 gigawatts. While this value is still dwarfed by onshore wind, accounting for less than 5% of global wind capacity, offshore wind is still coming on strong. Moving forward, both onshore and offshore wind capacities are expected to continue to grow globally and displace dirtier and carbon-intensive sources of electricity. However, according to a recent report from Navigant Research:
While the onshore wind market is larger in terms of total megawatt capacity added manually, offshore wind is growing more quickly. It is forecast to grow at an 11.1 percent annual growth rate between 2017 and 2022, compared to single-digit growth rate for onshore wind.
So onshore wind will remain king for now, thanks to its lower cost and ease of installation, but the massive efficiency advantages of offshore wind will continue to disrupt the renewable energy sector and eventually bring offshore wind out of the shadows and into prominence. Taken together, though, the wind energy sector looks to be an unstoppable force in the clean energy transition.