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A brief discussion on the types of solar cells
Solar energy was once the preserve of advanced spacecraft and some fancy gadgets, but that’s no longer the case. Over the past decade, solar energy has transformed from a niche energy source to a major pillar of the global energy landscape.
The earth is continuously exposed to approximately 173,000TW of solar radiation, which is more than ten times the global average electricity demand.
[1] This means that solar energy has the ability to meet all of our energy needs.
In the first half of 2023, solar power generation accounted for 5.77% of total U.S. power generation, up from 4.95% in 2022.
[2] Although fossil fuels (mainly natural gas and coal) will account for as much as 60.4% of U.S. power generation in 2022,
[3] But the growing influence of solar energy and the rapid development of solar energy technology deserve attention.
Currently, there are three major categories of solar cells (also known as photovoltaic (PV) cells) on the market: crystalline, thin-film, and emerging technologies. These three types of batteries have their own advantages in terms of efficiency, cost, and lifespan.
01 crystal
Most home rooftop solar panels are made from high-purity monocrystalline silicon. This type of battery has achieved an efficiency of more than 26% and a service life of more than 30 years in recent years.
[4] The current efficiency of household solar panels is about 22%.
Polycrystalline silicon costs less than monocrystalline silicon, but is less efficient and has a shorter lifespan. Lower efficiency means more panels and more area are needed.
Solar cells based on multi-junction gallium arsenide (GaAs) technology are more efficient than traditional solar cells. These cells have a multi-layer structure, and each layer uses a different material, such as indium gallium phosphide (GaInP), indium gallium arsenide (InGaAs) and germanium (Ge), to absorb different wavelengths of sunlight. Although these multijunction cells are expected to achieve high efficiencies, they still suffer from high manufacturing costs and immature research and development, which limits their commercial feasibility and practical applications.
02 film
The mainstream of thin-film photovoltaic products in the global market is cadmium telluride (CdTe) photovoltaic modules. Millions of such modules have been installed around the world, with a peak power generation capacity of more than 30GW. They are mainly used for utility-scale power generation in the United States. factory.
In this thin-film technology, a 1-square-meter solar module contains less cadmium than an AAA-sized nickel-cadmium (Ni-Cd) battery. In addition, the cadmium in solar modules is bound to tellurium, which is insoluble in water and remains stable at temperatures as high as 1,200°C. These factors mitigate the toxic hazards of using cadmium telluride in thin-film batteries.
The content of tellurium in the earth's crust is only 0.001 parts per million. Just like platinum is a rare element, tellurium's rarity can significantly affect the cost of a cadmium telluride module. However, it is possible to alleviate this problem through recycling practices.
The efficiency of cadmium telluride modules can reach 18.6%, and the battery efficiency in a laboratory environment can exceed 22%. [5] Using arsenic doping to replace copper doping, which has been used for a long time, can greatly improve the module life and reach a level comparable to crystal batteries.
03Emerging technologies
Emerging photovoltaic technologies using ultra-thin films (less than 1 micron) and direct deposition techniques will reduce production costs and provide high-quality semiconductors for solar cells. These technologies are expected to become competitors to established materials such as silicon, cadmium telluride and gallium arsenide.
[6]There are three well-known thin film technologies in this field: copper zinc tin sulfide (Cu2ZnSnS4 or CZTS), zinc phosphide (Zn3P2) and single-walled carbon nanotubes (SWCNT). In a laboratory setting, copper indium gallium selenide (CIGS) solar cells have reached an impressive peak efficiency of 22.4%. However, replicating such efficiency levels on a commercial scale remains a challenge.
[7]Lead halide perovskite thin film cells are an attractive emerging solar technology. Perovskite is a type of substance with a typical crystal structure of the chemical formula ABX3. It is a yellow, brown or black mineral whose main component is calcium titanate (CaTiO3). Commercial-scale silicon-based perovskite tandem solar cells produced by UK company Oxford PV have achieved a record efficiency of 28.6% and will go into production this year.
[8]In just a few years, perovskite solar cells have achieved efficiencies similar to those of existing cadmium telluride thin-film cells. In the early research and development of perovskite batteries, lifespan was a big issue, so short that it could only be calculated in months.
Today, perovskite cells have a service life of 25 years or more. Currently, the advantages of perovskite solar cells are high conversion efficiency (more than 25%), low production costs and low temperatures required for the production process.
Building integrated solar panels
Some solar cells are designed to capture only a portion of the solar spectrum while allowing visible light to pass through. These transparent cells are called dye-sensitized solar cells (DSC) and were born in Switzerland in 1991. New R&D results in recent years have improved the efficiency of DSCs, and it may not be long before these solar panels will be on the market.
Some companies infuse inorganic nanoparticles into polycarbonate layers of glass. The nanoparticles in this technology shift specific parts of the spectrum to the edge of the glass, allowing most of the spectrum to pass through. The light concentrated at the edge of the glass is then harnessed by solar cells. In addition, technology for applying perovskite thin film materials to transparent solar windows and building exterior walls is currently being studied.
Raw materials needed for solar energy
To increase solar power generation, the demand for mining of important raw materials such as silicon, silver, copper and aluminum will increase. The U.S. Department of Energy states that approximately 12% of the world’s metallurgical grade silicon (MGS) is processed into polysilicon for solar panels.
China is a major player in this field, producing approximately 70% of the world's MGS and 77% of its polysilicon supply in 2020.
The process of converting silicon into polysilicon requires very high temperatures. In China, energy for these processes mainly comes from coal. Xinjiang has abundant coal resources and low electricity costs, and its polysilicon production accounts for 45% of global production.
[12]The production of solar panels consumes approximately 10% of the world's silver. Silver mining occurs primarily in Mexico, China, Peru, Chile, Australia, Russia and Poland and can lead to problems such as heavy metal contamination and forced relocation of local communities.
Copper and aluminum mining also pose land-use challenges. The US Geological Survey notes that Chile accounts for 27% of global copper production, followed by Peru (10%), China (8%) and the Democratic Republic of Congo (8%). The International Energy Agency (IEA) believes that if global renewable energy usage reaches 100% by 2050, demand for copper from solar projects will nearly triple.
[13]Conclusion
Will solar energy one day become our main energy source? The price of solar energy is falling and efficiency is improving. In the meantime, there are many different solar technology routes to choose from. When will we identify one or two technologies and make them actually work? How to integrate solar energy into the grid?
Solar energy's evolution from specialty to mainstream highlights its potential to meet and exceed our energy needs. While crystalline solar cells currently dominate the market, advances in thin-film technology and emerging technologies such as cadmium telluride and perovskites are paving the way for more efficient and integrated solar applications. Solar energy still faces many challenges, such as the environmental impact of raw material mining and bottlenecks in production, but after all, it is a fast-growing, innovative and promising industry.
With the right balance of technological advancements and sustainable practices, the growth and development of solar energy will pave the way for a cleaner, more abundant energy future. Because of this, it will show significant growth in the U.S. energy mix and is expected to become a global sustainable solution.