In recent years, the environmental damage caused by the excessive use of traditional energy has gradually attracted people’s attention. Therefore, there is an urgent need to find a renewable clean energy that can be used on a large scale and will not cause damage to the environment. In recent years, the utilization forms represented by solar photovoltaic and wind power have developed rapidly, and China has a vast territory and abundant solar photovoltaic resources. Therefore, centralized grid connected photovoltaic power stations or small-scale distributed photovoltaic power generation can be constructed on a large scale. The emergence of solar photovoltaic agricultural greenhouses provides a way to solve the problem of land use shortage caused by the large-scale development of solar photovoltaic power generation systems. While generating clean electricity, it also provides cooling and heating energy for agricultural planting and animal husbandry, and modern technology and new energy support for agricultural development. It is an innovative model for the development of solar photovoltaic power generation. Therefore, the application of solar photovoltaic power generation technology in agricultural greenhouses has extraordinary significance for supporting modern agriculture and promoting China’s agricultural transformation.
At present, China’s application of solar photovoltaics in combination with agriculture is relatively limited. At present, the level of agricultural technology and equipment in China is not high. To change this situation, it is necessary to increase the utilization rate of unit land resources and reduce land resource waste. Therefore, the development of solar photovoltaic agriculture is necessary. It can not only achieve complementary advantages between green power generation and agricultural production, but also combine agricultural production and green energy, and provide important ways for the development of efficient and recyclable ecological agriculture.
In summary, solar photovoltaic agricultural greenhouses are a win-win model that not only benefits the development of new and renewable energy, but also promotes the new development of modern agriculture. As an effective way of targeted poverty alleviation, solar photovoltaic poverty alleviation has generated good economic and social benefits in various parts of China in recent years. The electricity generated can be uploaded to the power grid not only to increase farmers’ income and alleviate poverty, but also has important significance for protecting the rural ecological environment and sustainable energy development.
The design and implementation of the 10MW agricultural photovoltaic complementary project in Peixian County, Jiangsu Province is a typical case of the combination of solar photovoltaic and agricultural applications. The technical difficulties in the combination of solar photovoltaic power generation and agricultural greenhouses, such as the array layout of the greenhouse roof, the design of the spacing between the array front and back, and the comprehensive simulation using PVsyst, including shadow shading simulation, detailed losses, and calculation of annual theoretical power generation, are discussed. Similar research will be widely applied in future agricultural and fishery light complementarity, with positive practical significance and engineering value.
Extending to other large-scale solar photovoltaic power plants, there are still key areas for further research in array occlusion analysis and power balance compensation for solar photovoltaic power plants, which are of great significance for real-time and accurate prediction of power generation and optimization of economic benefits.
1. The development status and trend of solar photovoltaic power generation
1.1 Current research status in China
In the process of grid connection, the current key technologies mainly include solar photovoltaic DC grid connection technology, anti islanding protection, and solar photovoltaic grid connected inverter technology.
With the changes in China’s subsidy policies for grid connected solar photovoltaic power generation in the past two years, relying solely on wasteland and mountainous areas to build large-scale centralized solar photovoltaic power stations is clearly not the optimal solution. This is because there are fewer and fewer available development sites, and it cannot be guaranteed whether the electricity generated can be fully consumed by the local power grid. Therefore, a new type of agricultural photovoltaic complementary power station suitable for agricultural and forestry applications has emerged in people’s vision. It can achieve the dual utilization of solar photovoltaic resources. The upper layer is for solar photovoltaic power generation, and the lower layer is for crop cultivation. The installation method of the solar photovoltaic array can achieve good transparency, not only will it not affect the crops in the greenhouse, but it can also use the generated energy to improve on-site electricity for daily lighting, temperature and humidity control in the greenhouse, truly achieving the goal of killing two birds with one stone and intensive development.
Overall, China has abundant solar photovoltaic resources, with most regions having an annual daily radiation of over 4kWh/m2. Thanks to China’s strong support and policy guidance in recent years, coupled with market demand, solar photovoltaic power generation has experienced rapid and vigorous development in the past decade.
The current main problem is grid connected consumption, and the problem of abandoned light is becoming increasingly prominent. In the northwest region, the construction of solar photovoltaic power stations has a large available area and abundant solar photovoltaic resources, but the demand for electricity is small. In contrast, the central and eastern regions have a large demand for electricity but limited solar photovoltaic resources. Therefore, while accelerating the construction of corresponding supporting facilities, the current focus is to consider how to improve the consumption of electricity generated by solar photovoltaic power by the power grid and promote the vigorous development of the new energy development market, including solar photovoltaic.
1.2 World research status
One of the current research focuses on grid connected technology, and the conversion efficiency of solar photovoltaic inverters is constantly improving with the application of new semiconductor materials and new topology structures. In addition to improving conventional MPPT technology, there are also many breakthroughs in improving inverter efficiency and voltage levels.
The technical solution of solar photovoltaic grid connected inverters has gone through a development process from centralized to series. With the increasing maturity of technology, the cost of distributed photovoltaic power generation continues to decrease. Guided by relevant technologies, inverter manufacturers have made various innovations and breakthroughs in power station construction methods. Currently, various solar photovoltaic grid connection technology solutions have emerged, including centralized photovoltaic grid connection, string photovoltaic grid connection, distributed solar photovoltaic grid connection, and DC integrated modular photovoltaic grid connection technology solutions.
The solar photovoltaic high-voltage DC grid connection technology among them is particularly suitable for centralized solar photovoltaic power stations with large installed capacity in remote areas in the west. Its unique advantages will be more evident, and the corresponding topology structure and DC grid connection equipment will be the focus of research in the next stage.
1.3 Future development trends
The main trends of future solar photovoltaic grid connection technology are as follows: the power of inverters mainly composed of series, centralized, and distributed inverters will continue to increase, which can reduce DC line loss during transmission and continuously reduce investment costs; Component level products, mainly micro inverters, will continue to be enriched to meet the market demands of different installation locations; The adaptive ability of the power grid will also continue to improve, such as the continuous improvement of functions such as low voltage ride through and high voltage ride through, to make its reliability higher.
Meanwhile, high-voltage direct current grid connection will also be a research focus in the future. This structure can achieve medium and high voltage direct current output with low losses, improve the power of solar photovoltaic arrays, and achieve long-distance transmission; Its voltage level is relatively high, which can achieve transformer free transmission at this voltage level, reduce losses and lower costs; Having the optimal power regulation output for each string unit, it can achieve the series connection of solar photovoltaic string power units with different powers. It can solve the problem of inconsistent power of installed components and periodic obstruction of components by fixed objects due to different roof areas in building rooftop solar photovoltaic power stations. It can fully utilize limited space to maximize the power generation of solar photovoltaic power stations; At the same time, this structure abandons the commonly used DC and AC combiner boxes in traditional centralized and string structures, reducing transmission losses and lowering costs.
2. Research content
The design scheme and simulation simulation of a 10MW photovoltaic agricultural greenhouse photovoltaic power station in Peixian County, Jiangsu Province were studied in the following aspects:
(1) This article introduces the research background, significance, latest research status at home and abroad, and future development trends of photovoltaic agricultural greenhouses that combine solar photovoltaic technology with agriculture.
(2) Introduced the design conditions of a complementary solar photovoltaic power station for agriculture and solar energy, including a summary of the power station, analysis of local solar photovoltaic resources, geological conditions of the factory area, and the necessity and feasibility of project construction.
(3) This article introduces the overall scheme design of solar photovoltaic power plants, mainly including the selection of solar photovoltaic modules, inverters, DC combiner boxes, layout schemes of solar photovoltaic arrays, comparison of advantages and disadvantages between fixed and single axis installation methods, design of front and rear spacing of solar photovoltaic arrays under different terrains, and calculation of 25 year power generation.
(4) Through the PVsyst simulation software, detailed simulations were conducted on various factors that affect the output of solar photovoltaics, including reflectivity, different installation methods, detailed losses, shadow shading, line losses, and voltage drops. Finally, complete simulation results were provided through specific data.
(5) Introduced the electrical system design of solar photovoltaic power station system, mainly including primary and secondary electrical design, including the main electrical wiring of the booster station, selection of distribution equipment, layout of electrical equipment, calculation of reactive power of transformers, etc.