Solar power is a renewable and readily available source of energy. Solar power is attractive because it is readily available and renewable. 2018 solar energy accounted for less than 2% of global significance. Solar energy harvesting was expensive and inefficient historically. Solar energy harvesting has been costly and inadequate for the past two decades. However, even this modest solar usage is an improvement compared to the previous 20 years since solar power worldwide increased by over 300 times from 2000 to 2019. This increased solar use is due to technological advancements that have reduced costs over the past 20 years. New technological developments will continue to decrease costs and expand solar panel efficiency.
Solar Cells – Costs, challenges, and design
In the last 20 years, the costs of solar cells, which are structures that convert light energy to electricity, have steadily decreased. The National Renewable Energy Laboratory (NREL), a US government laboratory that studies solar technology, estimates the factors contributing to solar’s increasing affordability. The National Renewable Energy Laboratory estimates that the hard costs are the hardware costs for solar cells, and the soft prices include the labor costs or the cost of getting the required government permits. Soft costs are down because more people want to buy solar cells, and there are more experts in installation. This allows companies to produce them in large quantities and install them easily. The hard costs have decreased by more than half since 2000. This is mainly due to reduced material costs and increased efficiency of solar cells. It was necessary to consider the physics of solar capture and innovative design to design more efficient and cost-effective solar cells.
Solar cells are less expensive if the materials and labor used to make them decrease in price or if they convert more light into electricity.
Solar cells convert light energy into electricity. They must therefore be made of a material good at capturing light’s energy. The material is sandwiched between metal plates that carry the electricity generated by light energy where it’s needed, such as the lights in a home or the machines in a factory. The difference between the two energy levels, the valence and conduction bands, is used to select the best material for capturing light. The lower-energy band of the valence band contains many electrons. However, the higher-energy band is mostly empty. When electrons are struck by photons (light particles), they can absorb sufficient energy to jump into the high-energy band of the valence. The electron’s extra power can be converted into electricity once it reaches the valence bands. The electrons would be like those at a mountain’s bottom (conduction band), and a photon would give them the energy they need to jump to the top.
The material type determines the energy required for electrons to jump into the valence bands. The size of this metaphorical hill depends on the material properties. This energy gap is significant because it affects how well solar cells convert sunlight into electricity. If electrons hit photons at lower energy than what is required to jump from the valence to conduction bands, then none of the power in the light will be captured. If, however, the energy of the light is greater than the energy needed to bridge the gap, the electron will grasp the point it needs and waste the rest. These two scenarios can lead to inefficient solar harvesting, making the solar cell’s material essential.
Figure 2 shows that silicon is the most common material used for solar cells. This popularity is due to the large gap between silicon’s conduction and valence band. The energy of light particles is very close to what silicon’s electrons need to jump this energy gap. A silicon solar panel can convert about 32% of light energy to electric power. It may not sound much, but the silicon solar cell is more efficient than other materials. Silicon is also very cheap. The cost of refining silicon has dropped dramatically since 1980. It is one of the most abundant elements in the universe. Solar cell and electronics manufacturers have been responsible for the reduction in the cost of purification. They have developed better bulk purification methods to meet the increasing demand for solar cells and consumer electronic products.
The light hitting a solar panel causes the electrons to jump to a conduction region, allowing light energy harvesting. Yellow electrons (labeled Si) move through silicon atoms when a photon hits the solar cell.
The efficiency of silicon-based solar cells is being pushed closer to its theoretical maximum by clever engineering tricks. The photons must first collide against an electron to convert photons into energy. To increase the probability of a photon/electron collision, solar cells can be patterned in the shape of microscopic pyramids. The light absorbed by a pyramid travels farther, increasing the likelihood of a clash between the light and the silicon electrons.
Chemists and material researchers have developed anti-reflective surfaces to be applied to the front of solar panels to stop proper light from being reflected into space without ever reaching an electron within the solar cell. A reflector placed on the back allows more light to enter the cell. The light that makes it to the solar cell without hitting an electronic is bounced back to the front, giving it another chance to collect the light.
The cost of solar cells based on silicon continues to fall, despite predictions that it would not. Silicon solar cells’ popularity will likely continue for the next couple of years. Other alternatives to silicon solar panels have been developed, but they have yet to be commercially viable.
The Future of Solar Cells
To surpass current solar cells, the new design must be able to capture more light and convert light energy into electricity more efficiently. It also needs to be cheaper to manufacture than current designs. Solar power is more attractive to consumers and energy producers if it’s more reasonable or equal to other forms of electricity.
Solar cells can be improved by adding hardware to the cell. This does not require us to abandon our current designs. The solar cell can be fitted with electronics that track the sun’s movement through the sky during the day. Solar cells always pointing at the sun will receive more photons than those pointing only towards the sun during midday. The challenge of designing electronics to accurately and consistently track the sun’s position over several decades at an affordable cost is a constant one. However, innovation continues on this front. Mirrors can focus the light onto a cheaper, smaller solar cell instead of moving it.
Solar cells can be improved by increasing their efficiency. This will allow them to convert more sunlight into electricity. Solar cells that have more than one layer can capture more photons. Recent lab tests have shown that four-layer solar cells can charge up to 46% of incoming light energy. The cells are too expensive and complicated to manufacture for commercial use. However, ongoing research could one day allow them to be used.
Solar cells can be made more efficient by lowering their price. Although processing silicon has become cheaper in the last few decades, the cost of solar cell installation is still significant. Material costs are reduced by using thinner solar cells. The “thin-film” solar cells harvest light energy with a thin layer of material 2-8 micrometers thick. This is less than 1% of the thickness of a conventional solar cell. Thin-film solar panels are difficult to make, just like multilayer cells. This limits their use, but research continues.
Costs of silicon solar cells will continue to fall, and they will be installed in more significant numbers shortly. These cost reductions in the United States are expected to increase solar power production by 700% or more by 2050. During this time, the research will continue on other more efficient and cheaper solar cell designs. In a few years, we will likely see silicon replaced by other materials on solar farms and roofs to help provide renewable energy. The bulk production of solar cells and the development of new technologies to make them cheaper and more efficient have made and will continue to make these improvements possible.