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| Solar Farm |
“One mind-blowing fact about solar energy is that in just one hour, the amount of solar energy available on the Earth’s surface is enough to fulfill global consumption needs for an entire year. And only half of the total energy is needed to achieve that.”
In the year 2023, everyone on the globe is familiar with solar energy and its role in sustainability. Rising emissions and rapidly changing climate conditions have made governments across the globe shift a certain amount of their energy generation from non-renewable sources to renewable sources. Solar energy has shown a promising result as a sustainable form of energy that is readily available in ample amounts on the Earth’s surface with no cost associated with the availability of sunlight. Additionally, people are aware of climate change and they are investing in solar panel installation in their homes.
The reason why everyone is showing trust in solar energy is that it provides an alternative source of renewable energy and does not emit any form of harmful greenhouse gases. But the drawback of solar energy is the efficiency of solar panel technology which is around 25 to 30 % and the lifespan of one solar panel is around 25 years. This technical article will provide you with an insight into the overview of solar energy and its application, solar panel technology, and how solar energy is available for household appliances.
What is Solar Energy?
Sun is a source of solar energy, and solar radiation travels from the Sun to Earth where before reaching the Earth’s surface, the radiation is filtered through the ozone layer, as shown in the figure below. Electromagnetic radiation in the range of ultraviolet to infrared spectra (200 -~3000nm), is considered solar energy. The intensity of solar radiation available before filtration is around 1353 watts per square meter, while after filtration the solar radiation intensity on the earth's surface is approximately 1000 watts per square meter.
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| Solar radiation travels from the sun to the Earth’s surface. (Source: Flickr) |
How is Solar Energy Harness for Use?
Solar energy available on the Earth's surface after filtration is captured using technologies that convert radiation into a useful form of energy. The photovoltaic effect phenomenon is utilized for the conversion of sunlight to electrical energy. Photovoltaics (PV) and concentrating solar-thermal power (CSP) are the two major types of technologies available for solar energy conversion.
What is the Photovoltaic Effect?
It is necessary to understand the working principle of the photovoltaic effect before understanding the operation of the technology utilized in harnessing solar energy. In simple words, the photovoltaic effect is the process that allows solar cells to capture sunlight and generate a useful form of energy such as electricity. Light is electromagnetic radiation and is composed of photons. The solar cells capture photons which excited the electrons and set them in motion. This movement of electrons results in current in the solar cell.
How Does Photovoltaics Work?
The basic component responsible for converting solar radiation through PV technology is solar cells. The elemental structure of any solar cell is a p-n junction which has an antireflective coating (ARC) along with metal contacts. Photovoltage is produced by exposing solar cells to the solar radiation reaching the Earth's surface, and the voltage generated is in the range of 0.5 to 1 volts, or even higher. The voltage generated is primarily dependent on the solar cell material composition. A solar panel available in the market is an assembly of several solar modules. Each solar module is made of a certain number of solar cells, as shown in the figure below.
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| (A) solar cell, (B) solar module made of solar cells, and (C) solar panel or array is an assembly of solar modules. (Source: Wikimedia Commons) |
The material commonly utilized for a solar cell is silicon and the solar cells are widely available in markets according to the requirements such as the quality level. The quality level of solar cells is categorized as high-quality, which is a single crystal or monocrystalline, average quality which is polycrystalline, and at the bottom are amorphous solar cells. Polycrystalline solar cells are cost-effective whereas amorphous solar cells are cheaply available.
What is P-N Junction?
A single solar cell is a p-n junction and compromises components such as ARC, emitters, absorbers, and metal contacts, as illustrated in the figure below. The photocurrent is produced when electron-hole pairs are formed after a certain amount of radiation is absorbed from ARC. In simple words, when sunlight strikes a solar cell, the electrons in the material are excited and they are set in motion which results in the flow of electrons, which is called electric current.
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| Schematic diagram of the p-n junction. (Source: ScienceDirect) |
Solar cells are semiconductors with silicon as a major contributor to material composition and p-type and n-type silicon regions. The junction is the boundary between the p-type and n-type and both of the types are in contrast to each other when it comes to electrical properties. The p-type silicon is a rich source of positive free carriers or holes, whereas the n-type silicon has an excess number of negative free carriers or electrons. There is diffusion across the junction when the p-type and n-type come in contact, and an electric field is generated which tries to avoid further diffusion. Due to this electric field, there is a potential difference over the junction which is later utilized to control the electron flow in the semiconductor.
Concentrating Solar-Thermal Power
The CSP system utilizes a mirror for reflection and the reflected sunlight is concentrated onto a receiver that captures solar radiation and then converts it into heat energy which is later then employed to generate electricity. The heat energy is utilized to heat water which then converts to steam that is used to rotate the turbine and then generate electricity.
Generally, utility-scale projects use CSP systems and there are multiple configuration ways, two of which are power tower and linear systems. The single mirror system is capable of generating 5 to 25 kilowatts of power. The figure below illustrates the use of CSP in a power plant.
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| Concentrated Solar-Thermal Power Plants. (Source: Wikimedia Commons) |
Solar Panel to Grid
Governments have initiated the creation of solar energy generation power plants to provide electricity to the available grid. Due to government awareness campaigns and available incentives, the public has taken advantage of the initiative to install solar panels in their homes. The working principle of solar panel installation is the same, whether it is done on an industrial or residential level, the working principle is the same. The figure below illustrates how solar energy is harnessed on the residential level.
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| Solar energy from panels to the grid. (Source: Wikimedia Commons) |
- Solar panels absorb solar energy available on the Earth’s surface and convert it into electrical energy using the photovoltaic effect.
- The output of solar panels is a DC current, but for actual use, an AC current is required. Therefore, an inverter is used for DC-to-AC conversion, which is then used for household appliances.
- Generally, households rely on electricity from the grid when solar energy is not available, but in the presence of solar energy, it is used instead.
- When using electricity provided by the government, the meter shows an increase in consumption, and the customer is charged accordingly.
- In the case of using solar energy, after consumption, any excess energy generated is supplied back to the grid, and the customer gets paid accordingly.
Environmental Impact of Solar Energy
Even though solar energy has shown a promising result with no emission of any greenhouse gases, there is a downside to solar technology. The lifespan of one solar panel is around 25 years, after which it is wasted. Now the problem arrives because solar panels are made with certain material compositions which are hazardous when disposed of and currently there are no recycling techniques that will 100% recycle the solar panel. Solar panels include adhesives which make it difficult to separate each layer of the solar panel. Lead which is hazardous in nature is also to be found in the solar panels. So researchers I trying to find out ways to 100% recycle the panel with zero damage to the environment.
Takeaways
Solar energy systems have become crucial in electrical energy generation in accessible as well as remote locations, along with heating applications. Although solar energy systems’ efficiency might be less compared to other available renewable energy, it is still a promising alternative source of renewable energy.
Advancements are being made to manufacture solar panels with environmentally friendly materials, ease of recycling, and improved efficiency. Solar panels are widely available globally and are the best source of electricity for residential usage