Development Reasons and Types of Floating Solar Systems 

Development Reasons and Types of Floating Solar Systems

This news is about the development reasons and types of floating solar systems.

1. Under the policy promotion, the offshore photovoltaic has a highlight moment.
1.1. Under the background of "dual carbon", the coastal areas should increase the development of new offshore energy.

Driven by national policies, China's coastal provinces actively respond to the CPC Central Committee's goal of realizing "dual carbon". They successively focus on the development of the marine photovoltaic industry. 
The main reasons are: 

1) Power consumption in coastal areas is large, and the development of new energy sources is limited by land resources (centralized power stations involve land acquisition, and distributed photovoltaic contribution is insufficient).

2) Coastal provinces and cities are rich in marine resources. The collaborative development of marine photovoltaic and marine wind power can effectively optimize investment costs (submarine cables, power transformation facilities, etc.).

3) Marine photovoltaic can also be combined with aquaculture, which can improve the overall return on investment.

4) The power generation efficiency of marine photovoltaic has more gain compared with that of ground-based photovoltaic under the same lighting conditions.

1.2 Shandong Province is at the forefront of offshore photovoltaic development

In the past two years, Shandong Province has taken the lead in the direction of offshore photovoltaic development and construction. In December 2021, Shandong Provincial Oceanic Administration issued the Guiding Opinions on Promoting the Management of Three-dimensional Use of photovoltaic Power Generation Sea Areas (Draft for Comments), which stipulated the planning and project site selection, examination and approval, right confirmation, paid use, supervision and management of complementary use of fishing and light sea areas. In April 2022, the Shandong Provincial government released the List of High-quality Development Policies of "Seeking Progress while Maintaining Stability" in Shandong in 2022 (Batch 2), implementing the policy of actively promoting the offshore PV pilot demonstration. 
In March 2022 and July 2022, Shandong Provincial Energy Bureau issued the Guiding Opinions on Provincial Energy Work in 2022 and the Action Plan of Shandong Offshore Photovoltaic Construction Project respectively. The latter stated that:

1) Build a double 10 million kilowatt offshore photovoltaic base "around the Bohai Sea and along the Yellow Sea" with advanced technology, ecological friendliness and wisdom integration. The "Bohai Rim" offshore photovoltaic base has 31 offshore photovoltaic sites with a total installed capacity of 19.3 million kW. Among them, there are 20 photovoltaic sites, with an installed capacity of 14.1 million kW. There are 11 sites with "the same scenery", with an installed capacity of 5.2 million kW. There are 26 offshore photovoltaic sites along the Yellow Sea with a total installed capacity of 22.7 million kW. Among them, there are 9 photovoltaic field sites, and the installed capacity is 9.5 million KW. There are 17 sites with "the same scenery", with an installed capacity of 13.2 million watts. 

2) It is necessary to accelerate the development and construction of offshore photovoltaic systems on pile foundations. By 2025, about 13 million KW will be started and about 11 million KW will be connected to the grid. 
3) Actively and steadily promote the development of the floating photovoltaic systems, and strive to start construction of 2 million watts and complete grid connection of 1 million KW by 2025.

2. The offshore photovoltaic: the main battlefield of floating power stations

2.1 Surface photovoltaic systems are divided into two categories: pile-based fixed photovoltaic systems and floating photovoltaic systems.

Photovoltaic is a new type of power generation technology that converts solar energy directly into electricity. In general, large-scale onshore photovoltaic projects require a large amount of land area and land resources to be occupied, while offshore photovoltaic power generation is a new way of energy utilization and resource development mode, which is to move "photovoltaic power station" from the land to the sea and establish a power station on the sea by using photovoltaic technology. It has the characteristics of high power generation, less land occupation, and it is easy to combine with other industries. Compared with land-based photovoltaics, marine photovoltaics have natural environmental advantages: open water surface without shielding, longer sunshine and full utilization (reflected light from the water surface), which can significantly increase power generation. Water surface photovoltaic systems are divided into two categories: pile foundation fixed photovoltaic systems and floating photovoltaic systems. Both of them have their own application scenarios. In general, if the water depth is less than 5m, the pile driver can be installed in the high type, and the water depth above 5m can be installed in the floating photovoltaic systems.

(1) The pile foundation fixed (scaffolding type) marine photovoltaic systems

Pile foundation fixed water surface photovoltaic systems. It is also known as a high-water surface photovoltaic power station. It is often applied to shallow water levels, no site subsidence and other geological disasters. The water level change is small, such as aquaculture ponds, salt farm drainage ponds, etc. Prestressed reinforced concrete pipe piles are generally used for the photovoltaic support foundation of the high-height surface photovoltaic power station, which is usually built in water with a depth of less than 5m. The foundation form is the combination of a PHC pipe pile heated galvanized steel bracket, and the pile top height is more than 0.4m above the water level. In order to facilitate the passage of ships, the lower end of the photovoltaic module should be more than 1m away from the highest water level. The module should be installed at the best angle. This kind of power station mostly adopts the construction mode of "complementary fishing and light", that is, the development and construction of the photovoltaic power generation projects by using the pond and ocean resources in the concentrated area of aquaculture. The mode of ocean power generation and underwater aquaculture, so as to realize the complementary development of productive industries.

(2) The floating surface photovoltaic systems

Floating photovoltaic systems refer to making photovoltaic modules, inverters and other power generation equipment float on the ocean to generate electricity by means of floating body materials and anchoring systems. It is suitable for water with a depth of more than 5m. It is little affected by the typhoon. It is mainly divided into floating tube type and floating tank type. Among them, the floating pipe type includes HDPE floating pipe + bracket, thin-wall steel pipe + inner caulk + outer anticorrosive coating + outer anticorrosive rubber + bracket, stainless steel + inner caulk + bracket and other forms; the floating tank type includes HDPE standard floating tank, HDPE floating tank + support, stainless steel floating tank + support, high strength composite concrete floating tank + support and other forms.

1) The floating tube-type photovoltaic system

The "Floating tube + support" floating surface photovoltaic system is a floating system composed of floating tube material and metal support. The floating body is connected in rows with high-density polyethylene pipe or thin-wall galvanized steel pipe with external anticorrosive coating. The buoyancy of water is used to support the load of the upper photovoltaic system. The front and back photovoltaic mounting support form a whole through connecting rods. They are finally fixed with the anchoring system. This type is suitable for water with relatively deep water depth and relatively stable water levels. When the water level changes greatly, it is necessary to consider the redundancy of the array anchored and cable laying.

2) The floating tank-type photovoltaic system

The "Floating tank + support" floating surface photovoltaic system is a marine floating system. It is composed of pure floating tank or floating tank materials and metal support. According to its material and structure form, it can be divided into standard high-density polyethylene float tank form, high-density polyethylene float tank and metal bracket combination form.

(1) Standard high-density polyethylene float tank form

This type of floating system uses a high-density polyethylene special floating tank as the floating body. The floating tank is made into the corresponding angle according to the angle of component inclination. The bracket system only uses a small number of steel connecting pieces, without the design of a steel bracket. The weak link of the system is the connection earrings. It needs to go through detailed internal force calculation and mechanical tests. If you are not to meet the force requirements, you should carry out local node strengthening. The component support system and floating body system are the same systems, which are greatly affected by ocean fluctuations. Therefore, measures to enhance the durability of high-density polyethylene materials need to be taken.

(2) Combination forms of the high-density polyethylene float tank and metal support

This type of floating solar system uses a high-density polyethylene float box as the floating body. The upper part of which is set up with metal support, and the upper part of which is fixed with photovoltaic modules. This kind of floating form is derived from the weak link of the standard high-density polyethylene floating box. This type of floating tank can only bear the buoyancy force and the pressure of the upper support system. The large horizontal force is generated by wind load. The water flow force and wave forces are borne by the metal support with strong bearing capacity, which can give full play to the advantages of each component. It is a kind of floating system widely used in marine floating photovoltaic systems. Similarly, measures should be taken to enhance the durability of the high-density polyethylene float tank. They are used in the system to ensure that it can meet the requirements of the design service life of the photovoltaic systems.

(3) Other materials float tank and metal bracket combination form

This type of floating solar system is made of stainless steel or high-strength composite concrete floating tank as the floating body. The upper frame is equipped with metal support. The upper side of the support is photovoltaic modules. Because the pile-fixed offshore photovoltaic system is fixed in the offshore or tidal flat area, it is mainly applicable to the shallow sea area. It will face greater pressure in technology and the economy when moving to the deeper sea area. Floating marine photovoltaic systems can overcome the above problems better. The corresponding application range is wider. It will become the mainstream form of marine photovoltaic systems in the future.