Offshore wind power plant operations are most common in Europe, but technology advancements on the renewable front are leading experts to believe they will soon become just as prevalent in other regions of the world, including the United States.
There are many benefits and challenges to offshore windfarms. Due to the strong, steady wind gust over the ocean, wind turbines off the coast are able to generate electricity more efficiently and produce more reliable power. However, they are much more expensive to build, require larger turbines that produce delivery logistics issues, and they are farther from land requiring longer submarine transmission lines to be laid under the sea floor.
There are also regulatory roadblocks that stand in the way. Everything from how offshore turbines will affect the fishing industry, commercial vessel routes, sea life, and military testing operations to creating an eyesore for costal residents. There are many hurdles to overcome.
One simple way to overcome some of these challenges is by using High Voltage Direct Current (HVDC) rather than High Voltage Alternating Current (HVAC).
The History of HVDC & HVAC
The DC transmitting system was developed first and used to bring electricity from power plants to customers. The challenge was that there was no way to adjust the voltage level of DC power and the farther the power had to travel through the transmission lines, the more the voltage dropped.
The AC transmitting system was developed shortly after as a solution to this problem. Using a transformer, it is easy to adjust the voltage of AC power, allowing for electricity to travel much longer distances with less voltage loss. Once AC power reaches the end of the transmission line, it can easily be adjusted for utilization. For this reason, HVDC power has been used less often.
HVDC For Offshore Wind Power Plant Operations
New technologies and the emerging offshore wind market have made HVDC power a highly efficient alternative. HVDC transmission lines require fewer conductors than HVAC transmission lines. HVDC cables cost less and cables with XLPE insultation are lighter. The lighter weight allows for easier transportation and the ability to use longer cable sections reducing the installation time, amount of cable joints, and risk of failure when building an offshore wind farm.
Additionally, HVDC lines have considerably lower power loss over longer distances and offer better voltage regulation because they do not cause inductance.
The Break-Even Point
All of the advantages of HVDC come at a cost. While less conductors and less expensive cables do tip the price point in favor of HVDC, terminal converters are very expensive and needed for HVDC, but not HVAC. The cost-benefit of using HVDC over HVAC is dependent on a break-even point that is related to the distance of the transmission lines.
When using overhead lines, anything longer than 600km is more affordable with HVDC than HVAC. When using submarine lines, which all offshore windfarms do, anything longer than 50km is more affordable with HVDC than HVAC.
As companies, cities, and countries continue to push harder for renewable energy, offshore wind power plant operations will become more popular around the world. HVDC power and transmission lines offer an affordable and reliable option as a way to overcome some of the obstacles it will take to get approval for their development.
As a leader in load bank testing, Comrent has extensive knowledge in wind farm commissioning and maintenance for both onshore and offshore wind power plant operations. Read our recent case study to get an inside look at how we load tested 100+ wind turbines without a grid connection.