What You Need to Know About Anchoring and Mooring for Floating PV



December 20, 2021

One of the areas that separates floating solar from ground mount solar is anchoring and mooring.

For developers with little or no floating solar experience, this is one area that often leads to many questions as it is unfamiliar ground - or water.

To shed light on some key considerations regarding anchoring and mooring, we spoke to Charles Gery from Seaflex, a Swedish anchoring and mooring company with global operations including for floating solar projects.

1. The anchoring and mooring system on a floating solar array is a vital component of the entire system. Can you explain the importance of mooring in ensuring the longevity of FPV systems?

“There are several environmental factors including wind, waves, current and water level variation that interact with the floating PV system. It is the job of the mooring system to keep these environmental forces in check and allow the floating PV to remain in one place for 25+ years.  Progressive elastic systems (like Seaflex), not only keeps these forces in check but actually reduces the forces by absorbing them in the movement of the elastic hawsers. This is one of the key elements to ensuring the longevity of the entire system, including the floats and anchors."

"Another element to ensuring longevity is to design the mooring system so that it evenly distributes the environmental forces around, both PV floats and anchors. Many suboptimal designs and materials cannot achieve this type of even distribution and thus allows for higher, unsafe forces which directly translates in shorter life spans for the FPV components.”

2. What is the most important data that goes into a proper anchoring and mooring assessment?

“The accuracy of the raw environmental data of the site is extremely important in determining the correct design specifications of the mooring system. For example, if the design max wind speed is stated to be 30 m/s and the actual max wind speed could be 40 m/s there is a risk that there can be failures over time in many components like the float attachments, interconnections, mooring lines, and anchors.”

3. What are the benefits of an elastic mooring system vs. a traditional mooring system? And in which cases will a non-elastic system suffice?

“An elastic mooring system, specifically a progressive one, safely reduces the forces placed on the anchors and floating system, and can be designed to evenly distribute the remaining forces across the floats and anchors. A non-elastic system utilizing static material like rope, cable or chain does not have the ability to dampen forces and is extremely difficult to achieve an even distribution of force. It may be easy to simulate an even distribution, but in reality it is extremely difficult and costly to achieve. Additionally, the characteristics of an elastic system allow for its design to utilize fewer mooring lines and anchors in comparison to a static system which in turn lowers the capex and opex costs for the elastic solution.”

4. How should solar developers consider the impact of climate change with regard to an installation?

“It is a very interesting question to ask if a 50, 100, 500 year return period for data sufficiently covers the potential environment changes of the upcoming “xxxx” number of years. I would like for someone else with more weather/climate education and experience to bring a perspective to this topic. I feel that it is very important and must be considered when designing in our time 25+ years into the future.”

5. How much does the cost change in relation to water level variation and other key site conditions? E.g. if there is 15 m variation, how much does this affect the cost?

“There are definitely different environmental factors that directly affect the cost of mooring and anchoring designs. The max wind speed is at the top of the cost driving list. Increasing the wind speed in design is not linear in cost increase. So, even just small increases in wind can greatly affect the number of mooring lines/anchors needed and thus increase the solution cost by 10%, 20%, even 30%. The second largest cost driver would be a combination of water level variation and depths. High water level variation, such as those often seen in dams, in combination with very deep water require the need for long mooring lines. The elastic portion of the mooring line must also be of significant length so together this translates to a higher material cost. This is another reason why it is so important to use solutions that can reduce the number of mooring lines and anchors, like progressive elastic ones. Interestingly, in inland bodies of water, waves and current do not significantly affect the cost of an elastic mooring solution. This is completely different for offshore environments as can be expected.”

Have you gathered the necessary climate and site data for your project? At Glint, we've unfortunately seen too many projects without the necessary site or climate data, parts of which are crucial input data into the correct anchoring and mooring analyses. Luckily, advanced satellite data can give multi-year analyses on the local site conditions to properly design the project and reduce the likelihood of catastrophic outcomes as seen e.g. on the Yamakura Dam in Japan.

Request a demo and see how Glint can help you and your team gather the right data for your FPV project.

Even Kvelland