Can Floating Photovoltaic Solutions Become the Next Blue Ocean? 

What technological challenges exist in the development of floating photovoltaic solutions?

Apart from hydropower, wind energy, and onshore photovoltaics, the most worthwhile energy to study is the floating photovoltaic solution. According to relevant information, the coastline of mainland China is 18,000 km long, with a total nearshore area of over 4.7 million km ², of which over 3 million km ² can be utilized. Theoretically, it is capable of developing nearly 700 million kW (700GW) of floating photovoltaic solutions. In recent years, Zhejiang and other regions have also introduced relevant policies to support the development of floating photovoltaic solutions. However, currently, only a small amount of floating photovoltaic solutions are being constructed, and most are still planned in the future. Can floating photovoltaic solutions become the next blue ocean? What technical difficulties are there in the development of floating photovoltaic solutions? Recently, the editorial department of "Southern Energy Construction" interviewed Mr. Cai Shaokuan, President of the Offshore Wind Power Branch of the China Ocean Engineering Consulting Association, on the above issue. Below is President Cai's discussion on floating photovoltaic solutions. 

Apart from hydropower, wind energy, and onshore photovoltaics, the most worthwhile energy sources to study are floating photovoltaic solutions. In today's world, renewable zero carbon energy will inevitably become the main source of energy supply for the whole society. Renewable zero carbon energy includes hydropower, wind energy, solar energy, temperature difference energy, geothermal energy, etc. Among them, hydropower has been developed for more than 100 years and it is about to be fully developed. It is extremely limited due to resource scale limitations. From the current level of technology, temperature difference energy is difficult to achieve large-scale and market-oriented development. Geothermal energy, due to limited application scenarios, has a narrow scale of direct heat utilization, and it is also difficult to scale and market power generation utilization. 

Wind energy (land wind, sea wind), onshore wind energy is being market-oriented (affordable) and large-scale development, and offshore and shallow sea wind power has entered market-oriented development and large-scale development. At this stage, it will definitely be vigorously developed. 

Light energy (land light, sea light) 
Land based photovoltaics are undergoing market-oriented and large-scale development, while floating photovoltaic solutions have a huge potential but are only in the exploratory stage of scientific research and development and still need to be explored. In summary, renewable zero carbon energy sources that can be developed on a large scale. In addition to hydropower, wind energy, and onshore photovoltaics that have been concluded to be developed on a large scale and in the market, the most worthwhile target energy to study is floating photovoltaic solutions. 

Distribution of nearshore marine energy regions

From the perspective of China's energy development prospects, there are three aspects of non-hot but promising energy: floating basic offshore wind power, offshore energy island, and floating (including mudflat, the same below) photovoltaic. The current blind spot in offshore energy research and development is floating photovoltaic. 

We divide the offshore marine energy distribution area into five zones: mudflat, intertidal zone, subtidal zone with water depth below 5m (usually as the deep water area where construction ships are difficult to enter the site for construction), 5-70m (the critical water depth for economic development of offshore wind power fixed pile foundation and floating foundation), and 70m (possibly deeper) above. Shrink the focus, and take the prospect of large-scale and marketization as the constraints: mudflat, intertidal zone, subtidal zone with water depth below 5m (usually as the deep water area where construction ships are difficult to enter the site for construction), and 5-70m (the critical water depth for economic development of offshore wind power fixed pile foundation and floating foundation). 

Comparison of installed capacity and power generation with offshore wind power

Compare the installed capacity and power generation of floating photovoltaic systems in a water depth range of 5-70m. When offshore wind power in this area enters the era of 6MW or more, a representative array of wind turbines with a row spacing of 1000m and a column spacing of 800m will be analyzed and studied. The rectangular sea surface area formed by four wind turbines is 0.8km ². Considering various channel requirements and safety distance requirements, the photovoltaic installed capacity should be 40MW when only 50% of the photovoltaic panels are arranged and designed with a technical index of 100W/m ². 

Assuming that the photovoltaic index of the row and column matrix around each wind turbine tower is isotropic, the technical and economic parameters for wind power participation in the comparison should be included in 1/4. If the 6MW single unit capacity is still considered, the photovoltaic installed capacity should be 40MW. The comparative capacity of wind power participation is 6 × 4/4=6MW. The ratio of photovoltaic installed capacity to wind power installed capacity is 40MW/6MW=6.68 times. Assuming that the utilization hours of wind power are 4 times the utilization hours of photovoltaic power, the ratio of photovoltaic power generation to wind power generation is 6.68/4=1.67 times. Although the geometric distance between single machine capacity and wind turbine layout matrix is diverse. From a qualitative perspective, the installed capacity and power generation scale of photovoltaic power are larger than those of offshore wind power, and the prospect scale is considerable. The technical difficulties and research directions of offshore floating photovoltaic development.

We will enlarge our vision and roughly analyze the photovoltaic development prospects of three coastal sea areas, namely, mudflat, intertidal zone and subtidal zone with water depth below 5m. The technical difficulties of offshore floating photovoltaic development include mooring, wave resistance, wind resistance and slap resistance. Through research in the past two years, the direction of solving the four major problems can be preliminarily determined.

1) Mooring. For the water depth above 5m, the feasibility study on the combined force of wind power foundation as the auxiliary force and pile chain anchor as the main force shall be carried out. For the subtidal zone below 5m, the feasibility study on the combined force of pile chain anchor as the main force and floating body bottom as the auxiliary force shall be carried out. For the intertidal zone, the feasibility study on the combined force of floating body bottom as the main force and pile chain anchor as the auxiliary force shall be carried out. For the mudflat, the feasibility study shall be carried out on the final supporting structure for the adaptability of the specific geographical and geological characteristics of the mudflat.

2) Wave resistance. We will increase our efforts in technological innovation, adopt a new floating structure, and adopt the technological innovation concept of "following the waves and overcoming rigidity with flexibility". Feasibility research will be conducted from multiple perspectives, including materials, structure, force principles, anchoring systems, force reduction and energy dissipation methods, dynamic cables, and new concepts of operation and maintenance. Floating structures, flexible connections, flexible cables, flexible photovoltaic modules, and dynamic cables may be the focus of attention.

3) Wind resistance. With the main focus on minimizing wind load, research on the form and materials of floating structures is particularly important.

4) Anti-impact. Using flexible photovoltaic modules as a technological breakthrough, feasibility studies will be conducted to fundamentally change the structural mechanics principles, damage mechanisms, tolerance boundaries, probability determination, and maintenance treatment of photovoltaic modules. Phased understanding of offshore floating photovoltaic propulsion.
At present, there have been relevant empirical projects put into operation for offshore floating photovoltaic systems. Practice has proven that offshore floating photovoltaic solutions can be achieved technically, but the main challenge it faces is not whether it can be achieved, but whether it can be scaled, market-oriented (affordable grid connection), and adapted to the sea. From the current level of scientific research and development, we believe that the development stage of floating photovoltaic solutions is in the stage of "scientific research+engineering" that can already be tested and demonstrated. From the perspective of the development of the entire industry chain, it can be said that whoever dares to take the lead in practice and breakthrough will occupy the development high ground and industry leading position of floating photovoltaic solutions.

Research and Breakthrough Direction of New Offshore Energy

The research and breakthrough directions of new offshore energy include fixed pile foundation offshore wind power moving towards deeper sea areas, floating foundation offshore wind power research and practice, floating photovoltaic research and practice from mudflat to fixed pile foundation sea depth, research and practice of offshore energy island based on natural island (within 120km offshore), attempts to combine offshore energy development with marine ranching, tourism industry development matching the formed marine energy projects, etc. The comprehensive development and utilization of marine resources can achieve the goal of sharing part of the investment cost and making full use of resources, shorten the process from technically feasible to technically and economically feasible, and make greater contributions to social and economic development.