Recently, my country's water photovoltaics have once again ushered in a highlight moment.

Just on March 31, my country's first three-dimensional photovoltaic sea use project - Binzhou New Energy 850,000 kilowatt photovoltaic power generation project was successfully connected to the grid at full capacity. The project is located in the north of Binhai Town, Zhanhua District, Binzhou City, Shandong Province, occupying 15,800 acres of sea tidal flats. It adopts the circular economy model of "water photovoltaic power generation + underwater aquaculture", while taking into account seawater salt and bromine extraction. Through three-dimensional layered rights, the three-dimensional development and comprehensive utilization of the sea space have been realized.

It is understood that after the project is put into operation at full capacity, it can generate 1.286 billion kilowatt-hours of electricity and reduce carbon dioxide emissions by 917,700 tons per year, showing good economic benefits, social benefits and environmental benefits.

In recent years, as the land resources available for photovoltaics have become increasingly scarce, water photovoltaics have received widespread attention due to their various advantages, and have been successfully applied in various scenarios such as lakes, rivers, tidal flats, and offshore.

In particular, offshore photovoltaic power generation projects have opened up a vast ocean space for the development of photovoltaic green energy, filling the gap of increasingly scarce land photovoltaic resources.

Relevant data show that as of now, more than 60 countries and regions around the world are actively promoting the development of offshore photovoltaic power stations, of which more than 35 countries and regions have more than 350 floating photovoltaic power stations. As a major photovoltaic country, my country's coastal provinces such as Shandong, Jiangsu, Zhejiang, Liaoning, Guangdong, etc. are also actively deploying offshore photovoltaics and carrying out their own offshore photovoltaic projects.

However, with the rapid development of water photovoltaics, more and more people are beginning to worry about a question-will water photovoltaics affect water quality? What is the impact on the ecological environment? And, does the fish-light complementary model really have no impact on fishery farming?

Will photovoltaic power stations on the water affect water quality?

Will setting up photovoltaic power stations on the water surface affect water quality? In fact, foreign scientific research teams have already conducted systematic research on this issue.

Since 2020, BayWa r.e., Europe's leading provider of surface photovoltaic solutions, has conducted an environmental impact survey of a 27.4MW surface photovoltaic power station located in a quarry in the Netherlands for more than a year with the help of Hanze University of Applied Sciences, University of Groningen and research institute Buro Bakker / ATKB. In May 2021, the first batch of survey results released by BayWa r.e showed that surface photovoltaic power stations will not affect water quality.

According to the report, the oxygen content in the water under the solar panels changes little within a year, wind and sunlight can still easily reach the water surface under the modules, and the measured deviations are mainly caused by changes in weather conditions. The water quality under the floating system is still at the same level as the adjacent waters.

At the beginning of 2021, the International Journal of Low Carbon Technology also published a related report. By setting up water surface photovoltaic modules with different coverage and tilt angles and monitoring the water quality parameters of the water bodies below, the results showed that there was no adverse effect on water quality; on the contrary, the data showed that the concentrations of nitrate and chlorophyll in the water bodies also improved, with the highest nitrate concentration falling by 14%, and the average chlorophyll concentration in surface water falling by 17.5%. This is because the photovoltaic modules cover the water surface, reducing the evaporation of the water surface and lowering the water temperature, thereby inhibiting the reproduction of algae.

A study in the UK found that surface solar power stations can in turn improve the water quality of rivers and lakes. This is based on the discovery that when the water body is heated by sunlight and divided into two layers with different temperatures, the bottom water body will be deoxygenated and the water quality will be reduced. After the photovoltaic array is set up on the surface, the duration of the "stratification" of the water body will be shortened, which can play a role in protecting the water quality to a certain extent. This discovery points out at least two aspects of the value of water-based photovoltaics:

1. Reducing the impact of global warming on water bodies in the coming months and years;

2. Protecting the water quality of drinking water sources.

In fact, many water-based photovoltaics have been applied to drinking water sources. For example, the Singapore Tengger Reservoir Photovoltaic Project, which was completed and put into operation in 2021, is currently the world's largest drinking water reservoir photovoltaic project. The electricity it generates can power five local water treatment plants, meeting about 7% of the Singapore Water Authority's annual energy needs, and providing a demonstration for the protection and innovative development of drinking water sources around the world.

What impact will water photovoltaics have on the ecological environment?

Large photovoltaic panels are installed on the water surface for a long time. In addition to considering their impact on water quality, the changes in the underwater ecological environment must also be considered.

The paper "Analysis and Countermeasures of the Impact of Water Surface Photovoltaic Power Stations on the Ecological Environment of Water Areas" published by the Three Gorges Ecological Environment Monitoring in 2018 pointed out that the main objects of the ecological environment affected by water surface photovoltaic power stations during operation are plankton and fish.

For plankton, the main impact of water surface photovoltaic power stations is the long-term blocking of sunlight, which weakens the photosynthesis ability of phytoplankton and hinders its growth and reproduction to a certain extent; and the reduction in the number of phytoplankton will lead to a decrease in the number of zooplankton that feeds on phytoplankton.

For fish, the long-term operation of water surface photovoltaic power stations will not have a direct impact on fish, but may lead to a decrease in the bait organisms of fish, that is, a decrease in the number of zooplankton.

However, with the continuous innovation and development of water surface photovoltaic technology, the awareness of protecting the water ecological environment in the engineering design stage of the project is also increasing. When developing water bodies with relatively mature ecosystems such as large lakes and reservoirs, from the proportion of the surface area covered by water photovoltaic modules to the specific layout methods, they are all moving towards maintaining the healthy and sustainable direction of the water ecosystem.

Is "fish-light complementarity" really feasible?

Since for fish, setting up a water surface photovoltaic power station will only lead to a reduction in fish bait organisms, how do farmed fish perform under the water surface photovoltaic array? Let's take a look at some actual cases.

The Jinshan 100MW fish-light complementarity project of Huadian Zhaoqing Company, located in Gaoyao District, Zhaoqing City, Guangdong Province, has a fish pond of about 1,200 acres, with rows of four or five-meter-high photovoltaic panels neatly arranged. Photovoltaic power generation can be used on the top, and fish and ducks can be raised on the bottom.

It is understood that the project was not recognized by the villagers at first, and everyone was worried that setting up photovoltaic panels on the fish pond would affect breeding. But after the first batch of fish and ducks were put into breeding, the advantages of "fish-light complementarity" soon emerged. In previous summers, due to the continuous high temperature, farmers often suffered heavy losses in fish and duck fry, and there was no good solution. Today, the 4-meter-high photovoltaic "umbrella" in the fish pond brings a shade. Whether it is the fish in the water or the ducks on the water, the survival rate has increased, which has become the most direct benefit brought by the "fish-light complementarity" model.

Some farmers have calculated that the profit per mu of fish pond used to be about 1,000 yuan, but now the profit per mu can reach 2,000 yuan or even 3,000 yuan under photovoltaic panels, which can increase the income by hundreds of thousands of yuan a year.

Fangchenggang Xinrun Breeding Co., Ltd., located on the Beibu Gulf of Guangxi, also embarked on the development path of "fish-light complementarity" in 2017. A photovoltaic power generation panel with a total capacity of 80MW is installed above the breeding base. The annual power generation has brought considerable economic benefits to the company. In 2022 alone, the power generation will be nearly 100 million kWh, with an income of about 70 million yuan.

Fish and shrimp continue to be raised under the photovoltaic panels. With the help of photovoltaic brackets, the base has equipped each breeding pond with a steel greenhouse, which is covered with insulation boards and waterproof films. The water temperature reaches about 25°C, truly realizing the photovoltaic greenhouse shrimp farming "cooling in summer and keeping warm in winter". By adopting a stepped factory-based breeding model, the temperature and humidity of the breeding pond can be effectively adjusted to create a good growth environment for shrimp. The breeding output of white shrimp in South America has reached more than 10 times that of traditional earth pond breeding.

Looking around the world, there are extremely rich resources such as oceans, rivers, lakes, and reservoirs. Water-based photovoltaic power stations are undoubtedly the third front to remove the constraints of land resources and expand photovoltaic power generation. However, as the scale of water-based photovoltaic power generation expands, the impact of non-"fish-photovoltaic complementary" water-based photovoltaic power generation projects on the ecological environment still needs to be paid attention to. How to maintain the healthy development of the water-based photovoltaic industry with more ecological and environmentally friendly design solutions and materials has become an important "test" facing the industry.