The Development of New Technologies for Solar Cells

The Development of New Technologies for Solar Cells


The International Maritime Organization has continuously launched international conventions on energy conservation and emission reduction of ships, and the China Maritime Bureau has also put forward restrictions on the exhaust pollutants of inland ships, which has prompted the shipbuilding industry to accelerate the development of green technologies. Technologies such as air lubrication systems and lightweight materials are used in the design and construction of ships. The use of new energy technologies such as LNG, carbon neutral fuel, solar energy, wind energy, nuclear energy and fuel cells in the power system is the future development direction of green ship technology. Solar energy has become an important development direction of marine renewable energy due to its advantages of being inexhaustible and zero-emission.
 
1) Photonic crystals are composed of two or more materials with different refractive indices (dielectric constants) arranged periodically in space, which can provide different means of electromagnetic wave control and propagation. The spread and distribution of photons can improve conversion efficiency. At present, photonic crystal structures are mainly used in the research of ultra-thin crystalline silicon solar cells, DSSCs, QDSSCs and perovskite solar cells.
 
2) Graphene is a kind of two-dimensional thin-film material with a honeycomb lattice structure composed of a single layer of carbon atoms, which has excellent optical, thermal, electrical and mechanical properties. Organic polymer and graphene composite facilitate exciton diffusion and carrier migration in solar cells. The good intrinsic conductivity of graphene itself can be used as electron conduction and electric field emission material. Graphene Quantum Dots (GQDs) are nanoscale graphene with one or more layers of special structure, and also a new type of zero-dimensional carbon nanomaterials. GQDs have the advantages of good electrical and thermal conductivity, high mechanical strength and large specific surface area like ​​graphene materials; at the same time, they have excellent hot carrier injection and conversion luminescence capabilities based on quantum confinement, sizes and edge effects. At present, derivatives such as graphene and GQDs are mainly used to improve the conversion efficiency and stability of perovskite solar cells. Other high-efficiency solar cell technology routes include multi-junction solar cells, intermediate-band solar cells, multi-exciton solar cells, hot carrier solar cells, and thermal photovoltaic solar cells.
 
The development of solar on ships
With the innovation and industrialization development of various new high-efficiency solar cells, and the application of electric propulsion technology to ships has become more and more extensive; the research on the application of solar energy to ships has developed rapidly in recent years.
 
The working mode of the solar photovoltaic system
According to the proportion of the power supply capacity of the solar photovoltaic system in the total load of the ship, the ships equipped with the solar photovoltaic system can be divided into full solar electric ships powered by solar cell modules, and solar cell modules are only part of the solar hybrid ship. According to the different electrical systems of the ship's power system, the marine solar photovoltaic system can adopt two different integration methods: DC and AC. According to the difference in ship power load demand and operating conditions, the marine photovoltaic system can be designed into three modes: off-grid, grid-connected, and off-grid hybrid.
 
(1) Off-grid photovoltaic systems
The off-grid photovoltaic system is a self-contained system for the ship's power supply or independent load operation, and there is no power interchange with the ship's main power grid, which will not have a substantial impact on the safety and reliability of the ship's main power grid, and the transient stability of the main power grid depends only on the output characteristics and load characteristics of the generator set on the grid. Off-grid systems need to generate electricity efficiently according to the 24-hour power consumption of the load and the photovoltaic system due to fluctuations in the power generation capacity of marine solar photovoltaic systems. Under the premise of considering the power supply margin of the reserved load for a certain time, the set capacity of the energy storage system should be multiple of the total capacity of the solar cell to meet the dynamic balance between the photovoltaic power supply capacity and the average daily electricity demand of the load.
 
(2) Grid-connected photovoltaic systems
The grid-connected photovoltaic system does not directly run with load, but integrates the power output by the photovoltaic system into the main power grid of the ship, and is regulated by the ship's integrated power management system (PMS). The grid-connected system can be divided into two types: non-adjustable grid-connected types and adjustable grid-connected types. The difference is that the adjustable grid-connected type is equipped with an energy storage system equivalent to the total capacity of the solar cell, while the non-adjustable grid-connected system does not have this device. The adjustable grid-connected system can output the maximum power under any sunlight, which is beneficial to the peak regulation of the main power grid and increasing the stability margin, and the energy utilization efficiency is high. Generally speaking, the grid-connected system is an adjustable grid-connected system. The photovoltaic inverter in the grid-connected system cannot support the voltage of the main grid, and cannot resist the great disturbance impact of the main grid. The fluctuation of the ship's electricity load is completely balanced by the main power generation system.
 
(3) Off-grid hybrid photovoltaic systems
The off-grid hybrid photovoltaic system has the characteristics of both off-grid and grid-connected systems, and can switch between the two modes or be operated alone according to the solar lighting conditions, shipload conditions, energy storage system capacity and the operating status of the ship's main power grid. The off-grid hybrid system has good independence and applicability, and can help stabilize the system when the ship's integrated power system is in complex working conditions such as entering and leaving ports and severe sea conditions, output reactive power to help lift voltage when the main grid fails, and also be used as an emergency power supply.