An Aerial View of Floating Solar Farms Causing Safety Concern

An Aerial View of Floating Solar Farms Causing Safety Concern

Recently, a group of Google photos went viral in the floating solar circle at home and abroad. The photos presented the aerial view of a floating solar farm under construction in Huainan, Anhui.

According to these photos, the power plant encountered an unexpected situation in the construction process -- there was a collision between the adjacent floating islands and some parts of the islands had been scattered around. Because the responsible contractor was not available, we turned to exchange ideas with experts, and eventually came to a conclusion. It was very likely that the situation was caused by a strong wind.

In recent years, floating solar power plants have emerged as new type of photovoltaics. They are now in vogue on account of not taking up valuable real estate, high density construction and speedy installations. In 2017, floating photovoltaics (FPV) had delivered about 350MW of installations in China. With the rapid development of floating solar, investors, manufacturers and contractors swarmed to the market, going after those promising prospects. However, some manufactures did not have an in-depth knowledge of material selection and production process of the buoys, and even rushed to launch the products that did not pass a long-term system test. In addition, some contractors attached too much importance to project cycle and grid connection nodes and did not do enough to design and select suitable materials. As a result, various flaws of the projects would be revealed in the spotlight, which would also cause trouble for later operation and maintenance.

Without doubt, it is a systematic job to design floating islands for the power plants, with two factors should be taken into account. First, on the whole, for the overall design of a floating island, it is essential to take the location, shape, size as well as the anchoring system into full consideration. Second, focus should be paid on those basic "parts" that make up the floating island, including floats, fixed supporting systems and anchoring materials. These two factors also affect each other. Only after fully understanding the characteristics of floating solar, can a reasonable design be made to ensure that the floating solar farm can be operated safely during the service period.

Specifically, concerning the overall design of a floating island, it is necessary to achieve the following objectives: rational use of water area, optimization of power station wiring, ease of operation and maintenance, less impact on waterway traffic, convenient for anchoring and construction, guarantee of mooring safety and so on. As for the size, it depends on the overall planning of the floating island on the one hand, but on the other hand it depends on the strength between the wind load of the floating island and the engaging lugs of the pontoon. The first point is easy to understand thus there is no need to explain. Then why the size of the floating island depends on the strength between the wind load and pontoon lugs?

Usually, the anchor system is installed on the periphery of the floating island, with anchor ropes connected to a circle of pontoons around the floating island. On the pontoons are solar pontoons, which when it's windy, will be subjected to the wind load in the same direction as the wind. In order to maintain the position of the floating island, the anchor system will resist the corresponding wind load. As a result, the floating island is affected and torn by the wind load as well as the anchor force. Such being the case, it is conceivable that the larger the area the floating island occupies, the larger the wind load is, which exceeds the maximum force tolerance of the engaging lugs, thus the floating island is torn more violently. In other words, the size of the floating island should be controlled in a proper range. Therefore, under settled environmental conditions, to enlarge the floating island, the overall strength of the pontoons,particularly the engaging lugs, must be enhanced. Only in this way can we ensure the stability of the island. At the same time, with respect to the design of the anchor system, it is also necessary to increase the number of anchor points or enhance the strength of a single anchor point to ensure that the system can withstand the corresponding wind load.

With the above analysis, it is concluded that the size of the floating island, the anchor system and the strength of pontoons are correlated and interact with each other. In the actual design process, in addition to the design the floating island itself, the design of the anchor system is also crucial. If the system is ill-designed, it cannot effectively withstand wind load, which leads to the floating island deviating from the right position. Or when the horizontal stiffness of the system is too low, the floating island will displace drastically so as to cause collisions between pontoons and destroy modules. Furthermore, changes in water level must be taken into account. If the surrounding environmental condition is much more complicated, apart from the wind, we should also take water current and waves into consideration to work out a more comprehensive design.

According to relevant statistics, the engineering design process makes a big difference for the project cost. We must take the design of floating PV seriously and keep our nose to the grindstone to guarantee satisfactory operation and convenient maintenance. All floating PV developers and contractors should keep strict requirements for the work in the design stage and make adequate preparations for various possible technical problems. In this way, there will be less risks and accidents in floating PV power plants. (Editor: Claire Jeawin)