Floating PV plants
Floating photovoltaics (FPV) is a new technology in which a solar photovoltaic (PV) system is placed directly on the surface of a body of water rather than on land or on the roofs of buildings. Floating solar power plants solve the problem of large areas to place and overheating of modules in hot climates, which contributes to a drop in electricity generation. In densely populated countries, which are often also characterized by hot climates, placing solar installations on the surface of reservoirs saves land resources on the one hand and provides cooling for the PV panels on the other. In addition, as practice shows, the economics of floating solar plants can be quite acceptable.
In May 2008, the Far Niente winery in Oakville, California (USA) became the world's first operator of a floating photovoltaic system by installing 994 solar PV modules with a total capacity of 477 kW on 130 pontoons and floating on the winery's irrigation pond. The main advantage of such a system was that it avoided sacrificing valuable land area that could have been used for another purpose.
Figure 1. Floating photovoltaic system Far Niente Winery, California, USA
According to data reported in the scientific journal Nature Sustainability [4], globally the highest regional potential is concentrated in parts of the United States, eastern Brazil, Portugal, Spain, northern South Africa, Zimbabwe, India and eastern China.
In some countries, such as Brazil, Ethiopia, Laos, Zimbabwe, and Brazil, the generation of floating solar power plants may overlap national electricity consumption.
In 2022, the world's largest floating solar power plant with a capacity of 340 MW was built and commissioned in the PRC. The power plant was built by a division of Huaneng Power International [1].
Figure 2. The world's largest floating solar power plant with a capacity of 320 MW in China
Photovoltaic modules have been installed on the surface of the reservoir next to the 2.65 GW Dezhou coal-fired power plant. The designers of the floating power plant expect it to have a lifespan of 25 years.
The project features also include integration with a nearby 100 MW onshore wind farm and an 8 MWh energy storage system.
Advantages and disadvantages of floating solar power plants
The demand for floating solar power plants is growing every year. What is the secret of the increasing popularity of floating solar power plants?
The following advantages of floating solar power plants can be noted [2]:
1) It does not occupy land suitable for cultivation of crops or construction of other important facilities, which is especially important for countries with high population density and limited land area.
2) The surface of the water reflects sunlight, thus increasing the insolation of the solar cells. This increases the efficiency of the panels and maintains the ability to generate electricity even in cloudy weather.
3) Solar panels need cooling when they are in operation. The temperature above the water surface is usually lower than above the ground, so heat exchange processes are more intensive. Studies have shown that the energy efficiency of floating solar panels is 11% higher than that of land-based panels.
4) No need to transport electricity over long distances, such a power plant can be deployed close to the consumer.
5) Floating solar power plants are easy to integrate into various infrastructures, they allow for placement on drinking water reservoirs and irrigation systems, even sewage treatment plants.
6) Floating solar platforms are kept at a lower temperature than on land, resulting in higher solar energy conversion efficiency. In addition, the floating PV array reduces the evaporated surface area of the water body mirror, preventing water loss, which is very important for arid regions, and inhibits algae growth.
However, it is also worth mentioning the disadvantages of floating solar installations. These include significant environmental risks such as:
1) The impenetrability of the sun's rays affects microorganisms, algae and living creatures living in water bodies. The effect on water ecology and biodiversity is still not fully understood. Lack of sunlight can lead to the decline of algae and aquatic plants, which in turn provide food for many fish species.
2) Solar panels also help to reduce surface water evaporation. On the one hand, this helps to conserve water resources and create a more favorable environment for fish farming. On the other hand, in arid climates, such as the Central Asian region, this can lead to climate change, as well as land degradation, increased dust storms and salinization of irrigation water, which has a negative impact on public health. Exactly with excessive salinity is associated with an increase in the number of patients with gastrointestinal, cardiovascular, oncological diseases, respiratory diseases, etc.
3) The presence of a solar park reduces the impact of wind on the water surface, which leads to less erosion of the water body's shores, as well as to the growth of vegetation on the water surface. At a weak gust of wind near the shores, algae are able to form a dense layer, the thickness of which can reach up to 15 cm. Under the influence of sunlight, they begin to decompose, while releasing the pigment phycocyanin, which gives the water a blue color. It is worth noting that warm-blooded animals die due to the use of "colored" water, and a person eating freshly caught fish, which absorbed these algae, can get severe poisoning of the organism.
Floating PV plants in hybrid systems
It is quite common practice in the world to combine two or more RES into one energy system. For example: Wind farms + Solar plants, Wind farms + HPP (or mini HPP) + Solar plants, or Solar plants (floating) + HPP.
As world experience shows, the installation of floating solar panels on the reservoirs of hydroelectric power plants has the technical potential to meet a significant part of electricity demand.
Fig. 3. Scheme of connection of the hybrid system "floating PV + HPP" to the grid
Researchers estimate that more than 379,000 freshwater hydropower reservoirs around the world could host combined floating solar installations with existing hydropower plants, but more research is needed to confirm their power generation potential, especially on their environmental, water ecology and water resource impacts.
Potential of Uzbekistan in the development of floating PV plants
In Uzbekistan, the main waterways are the Amu Darya and Syr Darya rivers, which in turn feed the country's system of water resources (lakes, reservoirs, ponds, etc.). Uzbekistan has more than 50 hydroelectric power plants with an installed capacity of about 2 GW. Also, there are 25 reservoirs with a total volume of basins of more than 180,000 million m3. As an example, consider the Charvak HPP with a reservoir volume of about 2 km3 and an installed capacity of 666 MW, with an average annual output of more than 2 billion kWh.
Figure 4. Charvak reservoir
The Charvak reservoir is located in Bostanlyk district of Tashkent region of Uzbekistan, situated on the Chirchik River slightly downstream of the confluence of the Pskem and Chatkalrivers between the spurs of the Ugam and Chatkal ranges of the western Tien Shan. The reservoir is formed by a 168-metre-high stone-fill dam of the Charvak HPP. The volume of the reservoir is approximately 2 km³. The water surface area of the reservoir is more than 37 km², the length of the coastline is about one hundred kilometres [3].
The above-described hybrid system "floating PV power plant + hydropower plant" could have a positive effect on the share of electricity generation from renewable energy sources. In turn, the use of solar energy together with hydropower plants would reduce transmission costs by connecting to a common substation, and solar energy would also provide recharge during dry seasons when water levels are lower and, consequently, electricity generation is lower. Surplus solar energy from these plants could also be used to cover the own needs of the hydropower plant itself.
Conclusion
The advantage of a floating solar plant is that it does not occupy land that can be used for agricultural work. Such a plant is able to generate more electricity than a land-based plant: water cooling and low dust concentration provide increased efficiency in energy generation. Also, another great advantage is the possibility of hybridization of floating solar power plants, using wave, tidal and wave energy in parallel with solar energy to generate electricity (only for countries with access to seas and oceans). Undoubtedly, this opens up great opportunities for the prospects of developing new areas of renewable energy in general.
But on the other hand, the impacts on water ecology and biodiversity have not been fully studied, and the construction and operating costs are much higher than in the case of land-based plants.
The use of floating solar power plants is applicable to regions where the need for inexpensive and clean electricity is higher than the need for irrigation and water use for drinking and domestic purposes. In the Republic of Uzbekistan, first of all, the need for water use for irrigation is expressed, and only then for energy.
Taking into account all possible environmental risks, as well as the peculiarities of the arid climate of the Republic of Uzbekistan, the issue of using this type of power plants requires a number of additional studies to assess all the risks and benefits in the long term.
List of used sources
1. https://renen.ru/v-kitae-vvedena-v-stroj-krupnejshaya-v-mire-plavuchaya-solnechnaya/
2. https://rotomo.ru/services/plavuchie-solnechnye-elektrostantsii/
3. https://ru.globalconnect.uz/enciklopediya-uzbekistana/ch/charvakskoe-vodohranilishche
