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What is Solar Energy?

Solar energy is the light and heat that are generated from the Sun and is harnessed applying a range of technologies. Some of the technologies are photovoltaics (PV), solar heating, solar thermal energy, solar architecture, molten salt power plants, and artificial photosynthesis.

In simple words, solar energy is the conversion or transformation of the light and heat energy from the sun into electricity. This energy has been used for thousands of years in various ways by people in different parts of the world. Humans in the earlier ages used solar energy for heating, cooking, and drying, and it is still used in the modern era to make electricity in the absence of other power supplies, such as in remote locations and in space. Solar energy is getting cheaper to make electricity, and in many situations, it is now competing with traditional energy sources such as coal or oil. 

Sunlight is an important source of renewable energy, and its relevant technologies are broadly classified into active or passive solar depending on their method of capturing and distributing solar energy or convert it into solar electricity. Active solar techniques include photovoltaic (PV) systems, solar water heating, and concentrated solar power to harness the energy. On the other hand, passive solar techniques include orienting and optimizing energy in a building, selecting materials with favorable thermal mass or properties that disperse light, and designing spaces where the air circulates naturally.

Solar energy is an abundant source of energy, and its optimum usage can pave the way to a fully energy-efficient lifestyle. The sunlight that comes from the sun, once captured and converted by solar systems into energy, is free and is not dependent on the fluctuation of energy markets. Solar power has no emissions and does not leave any carbon footprint. It is a clean alternative to fossil fuels. Due to unlimited solar energy in most places on earth, it has a huge potential to play a crucial role in our energy needs.

The amount of sunlight that hits on Earth’s surface is enormous, and just 20 days’ sunshine is more than the cumulative energy stored in Earth’s reserves such as coal, oil, and natural gas. Outside the Earth’s atmosphere, the sun’s energy comprises nearly 1,300 watts per square meter. About one-third of this light goes back into space, and the atmosphere absorbs the remaining. 

By the time sunlight falls on Earth’s surface, the total energy that comes down is around 1,000 watts per square meter at noon on a clear day. Considering an average of the entire surface of the planet is 24 hours per day for a year, each square meter saps energy that is equivalent to almost a barrel of oil every year or 4.2 kilowatt-hours of electricity per day. The northern latitudes receive less energy from sunlight received because of the shape of the planet. Due to the slightly oblong shape of the Earth, northern climates are relatively distant from sunlight than places located on the equator. For example, in December, Seattle, Washington in the US, receives only around .7 kilowatt-hours per day. 

The statistics mentioned above represent the maximum availability of solar energy that can be captured and used. However, solar collectors capture only a part of this, depending on their efficiency. For example, In Arizona, the USA, a one square meter solar panel with 15 percent efficiency, will be able to produce nearly one kilowatt-hour of electricity per day. 

On the other hand, in Alaska, due to its high latitude, there will be much less solar energy than the rest of the United States. Some other places, like Barrow, Alaska, receive no sunlight at all during the winter and sunlight every day during parts of the summer. Due to this unique and natural schedule throughout the year, the efforts of developing solar energy in Alaska face unique challenges and is limited when it comes to producing cheap and clean energy.

Inexhaustible solar energy makes it an attractive source of electricity. In 2000, the United Nations Development Program, through its World Energy Assessment, found that the annual potential of solar energy generation was 1,575–49,837 exajoules (EJ). The amount of energy is several times higher than the total world energy consumption, which was 559.8 EJ in 2012.

Earlier, In 2011, the International Energy Agency stated that producing affordable, unlimited, and clean solar energy technologies will yield significant long-term benefits. The energy generation will increase the energy security of countries through dependence on an indigenous, abundant, and sustainable source. Solar energy will further reduce pollution, bring down the costs of mitigating global warming, and keep the prices of fossil fuel lower to stay competitive.

The History of Solar Energy

The history of generating solar energy dates back to the 7th century B.C., to all the way down to the 2000s.

During the 7th Century B.C., magnifying glasses were used to concentrate the sunlight to make fire and to burn ants.

In the 3rd Century B.C., Romans used burning mirrors to light torches for religious events. 

In the 2nd Century B.C., the Greek scientist, Archimedes, used the properties of bronze shields to focus sunlight and light fire to wooden ships of the Roman Empire that were besieging Syracuse. 

From the 1st to 4th Century A.D., the Roman bathhouses had large south-facing windows to receive the sunlight. 

In the 6th Century A.D., sunrooms on houses and public buildings were common, and the Justinian Code stated “sun rights” to ensure individual access to the sun.

During the 1200s A.D., ancestors of Pueblo people, called “Anasazi” in North America lived in south-facing cliff dwellings that could capture the winter sun.

Historically, the real development of solar energy began the 1800s. In the summer of 1839, a French scientist, Edmond Becquerel, first invented the photovoltaic effect. His theory was that certain elements on the periodic table, for example, silicon, unusually reacted to the exposure of sunlight. Solar power is generated when solar radiation is converted into heat or electricity.

In 1876, William Grylls Adams and Richard Evans Day discovered that selenium generates electricity when exposed to sunlight. Although selenium solar cells could not convert enough sunlight to provide power to electrical equipment, they were able to prove that a solid material could change light into electricity without heat or moving parts. 

Between 1873 and 1876, English electrical engineer Willoughby Smith discovered that exposure to selenium sunlight could produce a high amount of electricity. The use of selenium was not an ideal method. However, it proved Becquerel’s theory that light could be converted into electricity by using various semi-metals on the periodic table, which were later labeled as “photo-conductive material.”

In 1953, Calvin Fuller, Gerald Pearson, and Daryl Chapin discovered that using silicon solar cells was quite efficient and generated a net charge that surpassed selenium. These days, solar power has many uses, starting from heating, electrical production, thermal processes, water treatment, and storage of power that are common and part of the renewable energy revolution.

During the 1960s, solar power was the standard for providing energy to space-bound satellites. In the early 1970s, solar cell technology became economical and more available ($20/watt). Between 1970 and 1990, solar power became more commercially available and was used at railroad crossings, microwave towers, oil rigs, space stations, aircraft, and more. Now, residential and commercial buildings all over the world use solar panels to power electrical devices for a wide range of applications. Solar power is predominant in the renewable energy field, mainly because of its high efficiency and cost-effectiveness. 

In the early 1990s, photovoltaic conversion reached a new height. During that decade, scientists used solar cells designed with highly conductive photovoltaic materials such as gallium, indium, phosphide, and gallium arsenide, which increased the overall efficiency by more than 30%. By the end of the century, scientists developed a special type of solar cells that were capable of converting more than 36% of the sunlight it collected into usable energy. These developments gave a huge boost to not only solar power but the entire renewable energy technologies around the world.

In 2000, the following major events sparked more advancement in the field of solar energy:

First solar panels began production in Perrysburg, Ohio, at the world’s largest photovoltaic manufacturing plant. The plant had an estimated capacity of producing enough solar panels each year to generate 100 megawatts of electricity.  

Astronauts started installing solar panels at the International Space Station, which is said to be the largest solar power array deployed in space. Each “wing” of the array comprised 32,800 solar cells. 

Sandia National Laboratories develops a new inverter for solar electric systems that could improve the safety of the systems during a power outage. Inverters could convert the direct power (DC) output from solar systems into alternating current (AC), which is the standard current for wiring at households and for the electrical lines that supply power to homes. 

During the same era, BP Solarex developed two new thin-film solar modules that broke the previous performance records. The company’s 0.5-square-meter module achieved 10.8% conversion efficiency, which was the highest among thin-film modules. Its 0.9-square-meter module achieved 10.6% conversion efficiency and a power output of 91.5 watts, which was again the highest power output for any thin-film module in the world. 

A family in Morrison, Colorado, installed a 12-kilowatt solar electric system at their home. It was the largest residential installation in the USA to have been registered with the U.S. Department of Energy’s “Million Solar Roofs” program. The system produced most of the power for the 6,000- square-foot home and the family of eight. 

Again, in 2000, Home Depot started selling residential solar power systems in three of its stores in San Diego, California. A year later, the company’s sales increased through 61 stores nationwide. 

In 2001, NASA’s solar-powered aircraft, “Helios” had set a new world record for non-rocket powered aircraft, which was 96,863 feet, and more than 18 miles high.

Solar Technology and Types

Energy technologies that directly use the sunlight are termed as solar energy technologies. These technologies may be applied heat or light living space, to supply energy to a heat storage system, or to generate electricity.

Using solar energy is an attractive option for many residential consumers, businesses, and organizations that seek to generate greener energy and save on their energy bills. Mostly, people are aware of what photovoltaic panels look and also know how the system generates solar energy from sunlight that hits the photovoltaic panels.

There are, however, more aspects of solar energy in terms of different types of technologies. Solar energy technologies have been designed to convert sunlight into usable energy. Though, it can be done in various ways in order to provide heat, light, electricity, hot water, and even cooling to residential/commercial buildings or even industrial complexes.

Many of these technologies have been developed to use solar radiation. Some directly use solar energy for providing light, heat, and so on, while others produce electricity.

The following are the solar technologies:

  • Photovoltaic (PV) System 
  • Solar Power Plants
  • Solar Electricity
  • Thin-Film Solar Cells
  • Passive Solar Heating
  • Solar Process Space Heating and Cooling

Photovoltaic (PV) System

Photovoltaic (PV) is one of the most commonly used solar energy technologies. They are also known as “solar cell systems,” which generate electricity directly from sunlight.

The principle behind this technology is similar to solar clocks or calculators that get their energy from the sun.

The application of semiconductor materials in this solar technology absorbs sunlight, which creates a reaction and subsequently generates electricity. In simple words, the solar energy knocks electrons loose from their atoms that makes them go through the semiconductor materials and generate energy.

These days, solar PV technology can absorb and convert into energy from most of the visible light spectrum and also nearly half of the ultraviolet and infrared light spectrum.

Typically, solar PV panels are combined into modules that have around 40 cells and can measure up to several meters on the side. These photovoltaic panels have adjustable size, can be mounted at a south-facing angle, or can be mounted on a tracking device that follows the sun. This way, the panels can capture the most sunlight throughout the day. 

Several of photovoltaic panels may be required to provide enough power for a residential building. However, for a large utility or industrial applications, hundreds of panels would be required and would have interconnection to create a single, large photovoltaic system.

Solar Power Plants

Installing solar plants is another way or technology to harness the sunlight for generating solar energy. Solar power plants are common in industrial applications. Still, most industrial power plants use non-renewable fossil fuels to boil water.

Electricity is produced from the steam that comes from the boiling water and makes a large turbine rotate, which activates the generator. This method of producing electricity is hazardous for both the environment and people’s health; considering the emission of greenhouse gases and air pollutants from the burning of fossil fuels.

The positive news is, however, that many modern power plants that rely on solar power. These plants use the sunlight as a heat source, and they can do so in three different ways — parabolic-trough system, dish/engine system, and a power tower system.

The parabolic-trough system captures energy from the sunlight using long rectangular, curved mirrors that are tilted toward the sun. In this way, they help concentrate sunlight on a pipe that has oil. The oil is then heated and used to boil water in a traditional steam generator to produce electricity.

A dish/engine system works through a mirrored dish that resembles a large satellite dish which collects and concentrates the sun’s heat onto a receiver. After absorbing the heat, the receiver and moves it to the fluid within the engine. The heat makes the fluid to expand against a turbine or a piston and produces machine power. This power works to run a generator or alternator to generate electricity.

Finally, a power tower system uses a large number of mirrors to concentrate sunlight on the top of the tower, where a receiver that contains molten salt. The salt’s heat is used to produce electricity through a traditional steam generator. Molten salt can retain heat efficiently, so it can be stored for days before converting into electricity. It means it is possible to generate electricity even on cloudy days or even several hours after sunset.

Thin-film Solar Cells

The thin-film solar cells technology use layers of semiconductor materials that are only a few micrometers thick. This is the reason why thin-film solar cells are also known as “Thin-film Photovoltaic Cell.” The thin layers of these solar cells are usually 300 – 350 times smaller than the layers of standard silicon panels.

Thin-film solar cells are developed by assembling the cells. Typically, these solar cells are created by depositing several layers of photon-absorbing materials layers of photovoltaic or PV materials on a substrate, including plastic, glass, or metal. Thin-film solar cells have much commercial use in various technologies such as copper indium gallium selenide (CIGS), cadmium telluride (CdTe), and amorphous thin-film silicon (a-Si, TF-Si).

A large number of solar cells are used as rooftop shingles, roof tiles, building facades, or the glazing for skylights, and maximizing the use of the available space from where sunlight is captured.

Passive Solar Heating

Passive solar heating or daylighting is another technology through which solar power can be harnessed. This concept has been in practice since the ancient civilizations such as the Anasazi Indians in Colorado, who had developed a passive solar design in their houses.

The sunlight has its impact when it comes to energy. Just like stepping outside on a warm day, we feel the energy, with proper design and optimization, buildings can get the energy as well. 

For example, windows that are south-facing, receive more sunlight. Also, incorporating materials such as sunlit floors and walls enable to absorb and store the sun’s heat.

The mentioned materials collect heat during the day and gradually release it at night when the heat is needed the most. Other design features like sunspace, which resemble greenhouses, concentrate plenty of warmth, which can be used for ideal right ventilation to heat a building. Features like these maximize the direct benefits from the sun’s heat as well as from the sunlight itself. Particularly, on warm days, there are ways to make sure that these features do not overheat buildings.

Solar Process Space Heating and Cooling

Residential and commercial buildings may use the same solar technologies such as solar PV, daylighting, passive heating, and water heating. Industrial buildings can also apply solar technologies that would not be practical for a household, including solar process heating, ventilation air preheating, and solar cooling.

Many buildings may require ventilated air to maintain indoor air quality, especially large industrial buildings. In cold climates, heating can consume a lot of energy. A solar ventilation system can preheat the air and save both energy and cost. A system like this typically uses a transpired collector, comprising a thin, black metal panel mounted on a wall that is facing the south to absorb the sun’s heat. Air passes through numerous tiny holes in the panel. A space behind the perforated wall let the air streams from those to mix. Subsequently, the heated air is sucked out from the top of the space into the ventilation system.

The design of solar process heating systems can provide a significant amount of hot water or space heating for nonresidential buildings. A typical heating system has solar collectors that work along with a pump, a heat exchanger, and one or multiple large storage tanks. The two major types of solar collectors used are an evacuated-tube collector and a parabolic-trough collector, which can operate efficiently at high temperatures. An evacuated-tube collector is a shallow box full of many glass, double-walled tubes, and reflectors to heat the fluid inside the tubes. 

Using the heat from a solar collector to cool a building is a common application. In this process, the cooling system uses solar energy as the main energy source instead of regular energy source, electricity, to create cool air. Solar absorption coolers have a similar process, which is combined with some complex chemistry, to create cool air from solar energy. Another application of solar energy is on evaporative coolers (also known as “swamp coolers”), which are useful in more humid climates. They use another chemistry technique called “desiccant cooling.”

Net Metering

Net metering or net energy metering (NEM) is a process through which utility customers using small generators can purchase energy from a utility when required and sell any excess energy back to the utility company.

Net metering is actually a solar incentive that allows consumers to store energy in the electric grid. When the solar panels generate excess electricity than consumers need, they can sell that energy to the grid in exchange for credits. In some other times, if their solar panels do not produce enough energy, they can pull energy from the grid and use their credits to offset the energy costs. 

Net metering allows consumers who, fully or partially generate their own electricity to use it anytime. This is a particularly effective method with renewable energy sources such as wind and solar, which are non-dispatchable (when not coupled to storage). Monthly net metering let consumers use solar power produced during the day at night. Annual net metering provides a net kilowatt-hour (kWh) credit to the next month, which allows them to use solar power that was produced in one month to be used in another. 

Net metering policies can vary drastically from one country to another or even from one state to another. There are several aspects of net metering that may vary. For example, how long consumers can retain the bank credits, how much the credits are worth. Most net metering policies involve monthly roll over of kWh credits. A small amount is required as the monthly connection fee, require a monthly payment of deficits, and annual settlement of any residual credit. For net metering, generally a single, bi-directional meter is used that can measure the flow of current in two directions. Net metering may also be implemented solely as an accounting procedure and requires no special metering or even any arrangement or notification beforehand.

With an ideal size of the solar energy system, consumers can generate enough electricity to match their residential electricity use for a whole year. However, the amount of electricity the solar panels produce is likely to vary throughout the year. Net metering helps them account for these differences by crediting the excess electricity that their panels produce so that they can use it later.

Even though net metering is not the only way through which utilities compensate consumers for going solar, it is so far the most common. For example, in Washington DC, net metering is available to residential and commercial customers with systems that are powered by renewable energy sources. The policy is for the sources of heat and power (CHP), fuel cells and microturbines, with a maximum capacity of 1 megawatt (MW).

Net metering is a policy that has been designed to encourage private investments in renewable energy. However, a 2014 report funded by the Institute for Electric Innovation revealed that net metering creates an excessive subsidy for maintaining the power grid, and shift the maintenance costs to residents without distributing energy generation.

Solar Energy vs. Traditional Energy

According to the Environmental Protection Agency, almost 40 percent of all energy consumption in the United States is used for generating electricity. For applying every process to produce power, from traditional non-renewable methods to renewable sources like solar, there are some environmental and economic factors that need to be considered.

All over the world, traditional energy sources such as oil, coal, and natural gas are still the predominant resources on which the global economy depends. On the other hand, renewable resources such as solar and wind contribute only two to three percent of global energy capacity. 

In this context, one common question is, how does solar energy fare compared to traditional energy sources in terms of environmental impact, cost, and other aspects? The comparisons are below:

Consumption of Resources

Most of the electricity produced all over the world, including the US is by coal-powered steam turbines. One of the reasons behind using this resource as many countries have an abundant supply of coal reserves. Other commonly used sources are natural gas and petroleum, which are mainly used by power plants. Burning all of these resources produce combustion gases, which pass through a turbine to generate electricity. In hydroelectric plants, water is used in place of combustion gases.

Solar energy, on the other hand, is produced by installing solar panels, solar plants, thin-film solar cells which do not consume any additional energy. These systems produce energy from direct sunlight, which is abundant.

The sun offers the most abundant, reliable, and pollution-free power in the world. However, problems with solar energy, namely the expensive cost and inconsistent availability, have prevented it from becoming a more utilized energy source.

Environmental Impact

Traditional ways of generating electricity using turbines that are powered by burning coal and other fuels cause pollution and climate change. These sources are also limited resources, which means once burned, they cannot be replaced. The water used in hydroelectric plants is renewable due to natural rainfall. However, these plants can only be placed where there is enough water to power the turbines. The same is true for wind-powered turbines as well, which need to be in areas where weather conditions are ideal. 

Production of solar energy through solar plants, solar panels, and other methods, hardly leave any carbon footprint. It means, compared to traditional energy generation methods, solar energy does leave any negative impact on the environment. It is safe to install solar panels and produce energy at households.   

Energy Alternatives

Solar power plants generate electricity by concentrating solar energy and using it to heat fluids, which produce clean, non-polluting power. In the coal plants, turbines produce electricity. Solar energy accounts for less than one percent of the electricity generated. The reason being, there are locations where solar plants cannot be placed due to inconsistent sunlight or the large surface area needed to capture the sun’s energy. In these locations, energy alternatives could be traditional energy sources like coal or gas, or other forms of renewable energy such as wind and hydro. So, the bottom line is none of the energy is completely replaceable due to certain limitations such as geographic locations and availability.

Future Potential

Even though currently the overall amount of solar-powered electricity is relatively small, its future is rather bright. In warm countries that get plenty of direct sunlight, such as Australia,  Spain, and Italy, electricity from solar panels is cheaper than commercially-generated electricity. In the US, however, solar is relatively expensive than other types of renewable energy as well as non-renewables. Improve technology, vast reach, and improved efficiency are likely to make solar energy more widely used in the near future and may gradually phase out traditional energy usage.

Challenges in Solar Energy

Solar power is promising renewable energy with great potential, which allows producing electricity from free from the abundant sunlight. Many homeowners all over the world have already adopted solar electricity. In the case of large-scale power generation facilities in many regions, solar energy offers advantages to thousands of consumers. However, solar still has a number of challenges that are coming in the way and preventing this renewable energy from becoming a true alternative to traditional energy sources. The major challenges are:

Inconsistent Solar Energy

One of the major obstacles to the widespread adoption of solar energy is variances in solar intensity or inconsistent solar availability in various regions. According to the National Renewable Energy Laboratory, the sunlight provides nearly twice as much energy in the desert areas as it does to relatively colder regions. Because the output of solar panels depends on the amount of direct sunlight, it receives. For example, solar is a much better source of energy source in Southwest deserts in the US than in other regions. Despite the fact that solar panels can provide free electricity anywhere, the investment will be much higher in regions that do not have intense solar coverage.

Solar power, for example, is a small fraction of all power produced in North America, even though there are vast regions in the continent where sunlight is abundant. To harness more of the free solar energy, authorities need to find new materials, invent new production techniques, and solve the problem of energy storage when there is no sunlight. By developing large energy storage systems, it will be possible to have a constant and reliable source of electricity during cloudy days or at night when there is no sunshine. 


Another factor that is pulling back solar power from becoming more popular is the cost. It is five to eleven times more expensive to generate electricity by installing solar panels compared to coal, hydro, or nuclear sources. The first problem lies with the cost of technology:

  • Solar panels are made using expensive semiconductor material to generate electricity from sunlight. Semiconductor factories require ‘clean’ manufacturing environments, which are expensive to build and maintain.
  • Currently, the efficiency of solar cells is nearly 20% up to a top range of around 40%, although this continues to improve. The rest of the sunlight that hits the panel is wasted as heat. More efficient photovoltaic cells have been discovered that can produce more energy at significantly lower costs.

It may take many years’ of research to discover new materials and methods that make solar panels less expensive. How long it will take depends on the time and money is invested in solar energy research by the government as well as private industry.

Even if the fundamental obstacle related to the cost the technology is resolved, there are still other issues:

  • Installing solar panels for residential purposes is expensive and needs experienced handling. Still, most of the solar panels are fixed systems, and installing them would be too expensive for average homeowners. The initial investment amount is a major factor, where consumers feel discouraged due to a lack of support from the authorities. 
  • Large solar farms that have been built in desert regions and have brought down the installation cost as a larger economy-of-scale is created (e.g., parts, material & installation people all are in one location). However, these large, inexpensive lands are mostly far away from the cities where the power is required. Expensive transmission lines are required to supply the power to a distant market.
  • Maintenance costs and time can add-up to make expenses even higher as a solar panel must be kept clean and clear of debris to operate at the optimum level. Their efficiency drops drastically even when a small portion is blocked by fallen debris or a film of dust.

Lack of Energy Generation

Another obstacle that is preventing solar electricity from becoming widespread is that energy generation is still not up to the mark. Consumers who live in warm regions that get direct sunlight, a single square meter of the solar panel could receive as much as 6 kilowatt-hours of energy during the day. However, a solar panel cannot convert that entire amount of energy to electricity. It means energy gets wasted in the process. The efficiency of a solar panel determines how much solar power is usable, and most commercial solar panels on the market have efficiency ratings around 25 percent or less. The more efficient a panel is, the more costly it is to produce. Unless any major leaps in technology, achieving efficiency ratings more than 33 percent are unlikely in the near future.

Potential Solution

Scientists need to research and invent more efficient semiconductors for electricity production. Increasing the efficiency of a panel will reduce the size of the array, which will further result in lesser space required to produce the same amount of power.

Also, engineers need to develop more advanced and efficient energy production techniques. Mass production of panels will help bring down production costs and make it more affordable for consumers. 

In terms of technology, new transmission technology is required to bring clean energy to market. Energy storage systems will also help to sort out the production issues due to environmental interruptions. 

Unless all of these problems with solar energy are resolved, the potential to create and use pollution-free energy from the sun will remain an ambition. 

Solar Energy Conversion

Solar energy conversion is about applying technologies to transform this energy into other forms of energy, such as heat, electricity, and fuel. It also covers technologies that harness sunlight, including conventional semiconductor photovoltaic devices (PVs), solar fuel generation, emerging photovoltaics, artificial photosynthesis, and related forms of photocatalysis that directed for generating energy-rich molecules.

Basic electro-optical aspects in various emerging solar energy conversion technologies for generating both electricity (photovoltaics) and solar fuels form an active area of current research.


Silicon cells are used in photovoltaics (PV) to convert the energy of sunlight into electricity. PV operates under the photoelectric effect that leads to the emission of electrons. Concentrated solar power (CSP) has lenses or mirrors and tracking devices to focus on a large area of sunlight into a small beam. It is anticipated that solar power is going to be the largest source of electricity in the world by 2050. For instance, solar projects with more than 1 GW (1 billion watts) capacity are under development and thought to be the future of solar power in the US and other countries.

Thermal Energy

The heat that the sun collects is highly intensive and radioactive. The sun hits the earth with billions of charged nanoparticles with a massive amount of energy stored in them. It is possible to use this heat for water heating, space heating, space cooling, and process heat generation. Many steam generation systems have integrated ways to use sunlight as a primary source for heating drinking water. It is a development that has significantly increased the overall efficiency of boilers and various other types of waste heat recovery systems. Solar cookers use sunlight for cooking, pasteurization, and drying. Solar distillation is used for water treatment processes to make potable drinking water, which has been an effective element for providing relief effort to countries in need through using the advancing technology.

Economic Development

Converting solar energy has the potential to be quite cost-effective technology. Solar installations are getting cheaper and more easily available to countries where energy demand is high, but supply is low due to poor economic conditions. A solar plant with 1GW capacity can produce nearly 10 times as much power as a fossil fuel power plant that is likely to cost twice as much to set up. It has been projected that solar power plants would be leading the way in terms of energy production by 2050.

Solar Energy Conversion in Rural Areas

Conversion of solar energy in rural areas has the potential to have many positive social impacts, particularly in the areas that never have access to grid-based energy. In many off-grid areas, conversion from solar to electricity conversion is the fastest-growing form of energy procurement. This is especially true at the places with latitudes within 45° north or south of the Equator, where sunlight is more consistent throughout the year and where most of the developing world’s population live. 

From a health point-of-view, solar home systems can replace traditional lamps, which may cause fires and emit pollutants like carbon monoxide (CO), nitric oxides (NOx), and sulfur dioxide (SO2). Such emitting pollutants may create health hazards by adversely affecting the air quality that can further impair lung function and increase the cases of tuberculosis, asthma, and cancer risks. In such areas, it has been shown that access to solar energy can save rural residents time and money, and increase their day-to-day productivity.

Besides access to energy, communities in rural areas can gain energy independence. It means they do not have to depend on a third-party electricity provider. The concept of energy independence is relatively new. It is mainly because most of the energy analyses in the 20th century primarily focused on technical or financial aspects, and did not include social impact analysis. A study carried out in 1980 study revealed that that access to renewable energy is likely to promote values that favorable to larger societal benefit. Historically, many researchers argued that the parties in control of energy sources are the ones who create social hierarchies. However, this type of analysis became more mainstream after the development of technologies that made solar energy conversion possible.

Solar Conversion through Community Solar

Conversion of solar energy can have an impact not only on individual consumers but on whole communities. For example, in an increasing number of neighborhoods across America, the traditional model of independent, rooftop installations is getting replaced by community-sized solar microgrids. The concept of “community solar” became popular due to issues related to energy storage. As of 2018, the wide-scale production of lithium-ion battery and other storage technologies slowed down the progress of rooftop PV installations. However, the main issue that has been preventing a nationwide shift to rooftop solar energy production is the lack of a reliable, single-home storage system that would be useful during contingencies. Some examples of contingencies are a requirement of energy at night, cloud cover, curtailments, and blackouts. In addition, getting finance for solar installations for single homes may be more challenging to secure, considering a smaller project scope and lack of funds. 

A viable alternative is to connect a community is installing a community microgrid that can be used for more proven large energy storage. In some areas, a microgrid “web” is made by connecting each independent rooftop PV system for a greater storage facility. Other designs, mainly where rooftop installations are not possible, place a large combined solar array plus a storage facility located on an adjacent field. This type of installation makes solar energy economically viable for multi-family homes and, historically low-income neighborhoods, and overall will have more social impact.

Grid Defection

Solar energy conversion has a potential socioeconomic drawback, which is a disruption to the electric utility business model. In the US, the economic viability of regional utilities depends on a large number of local customers who balance out each other’s variable energy load. This is why the installation of rooftop solar systems that are not connected to the grid poses a threat to the stability of the utility market. This is called “Grid Defection.” 

The pressure on electric utilities gets worse by the aging grid infrastructure that is not equipped to adapt to the new challenges that renewable energy poses. However, some analysts have made a point that with the steady increase in natural disasters that often destroy vital grid infrastructure, installation of solar microgrid may be necessary to ensure emergency energy access. Such emphasis on contingency preparation has expanded the off-grid energy market substantially in recent years, particularly in areas that are prone to natural disasters.

Solar Energy and Climate Adaptation

For communities to adapt to climate change need solutions to accelerate the process. The need for mitigating greenhouse gas emissions is a critical factor that has been a driving force behind this concept. The objective of climate adaptation is to analyze the role of decentralized solar power supply to prepare for climate change. This is why fieldwork has been carried out in various parts of the world that are vulnerable to natural disasters. For example, there are many states in the US, where residents are continually struggling with climatic challenges, such as tornadoes, hurricanes, cyclones, floods, excessive heat, and heavy snowfall. Due to this decentralized electricity production is required in the communities to deal with the challenges posed by the lack of electricity. It should be a combined effort by the state and private enterprises, along with the local community. 

Also, for uninterrupted energy supply, the production of energy should be off-grid, which makes the solar power plant a standalone system and not connected to the national power grid. Rather, the plant will supply electricity to a mini-grid, which will distribute power to the local community. Climate-friendly solutions are crucial for implementing a full-fledged adaptation process. Earlier, adaptation to climate change was not part of the strategy in most of the solar energy solutions. 

Later, it was realized that to have a mass reach; it is important to provide supply to communities in batches rather large-scale projects that can cover a large part of the population in a region but does not guarantee to reach communities that are far off from the plant. Decentralizing the power supply makes it easier to target all the consumers in a community and provide them support to be ready for climate changes. 

Here, it is important to keep in mind solar generation may have its side effects. Despite the fact that solar generation is emission-free, the manufacturing of solar panels and relevant technologies use substances that may not be environment-friendly. For example, nitrogen trifluoride is a common byproduct of electronics manufacturing, which is used in solar cells. The resulting greenhouse gas due to this is 17,000 times more toxic than carbon dioxide. 

Also, many solar cells come with small amounts of the toxic metal cadmium, and the batteries that store electricity can contain various heavy metals and dangerous substances. With the advancement of solar technology, manufacturers may be able to shun these potentially dangerous substances. Though, for now, they are the blemishes in the otherwise impressive ecological benefits of solar energy. 

The summary of climatic and emission challenges are below:

  • Greenhouse Gas Emission: Greenhouse gases will continue to emit, and the temperature is likely to increase by 4 degrees. To deal with it, financial resources for adaptation can be as
  • Energy Production: There could be uncertainties with hydrology, temperature, and other weather patterns, which may affect solar energy production.
  • Transmission: Energy transmission may get interrupted due to a lack of infrastructure and efficiency.
  • Increased Demand: Due to more heating, less cooling, and pumping, the demand for electricity may go up. 
  • Assessment of Climate Risk: With the increase of emission and natural disasters, an increasing number of people will be vulnerable. This is why frequency climate assessment needs to be carried to understand the risk and how to increase security. During contingencies, constant production and storage of solar may prove to be handy. During the assessment, short-, medium- and long-term implications need to be gauged.
  • Cost: Cost is another crucial factor in climate adaptation. Cost of installing individual rooftop solar panels is likely to be expensive. Instead, a micro-grid for each community will distribute the cost among all the consumers, and energy distribution will be even as well.  

In order to deal with the mentioned challenges, decentralized renewable energy (DRE) can provide electricity that can help prepare for and recover from natural disasters. Also, it can provide additional income and livelihood opportunities, and significantly reduce dependency on natural resources.

Solar Energy Efficiency

The solar panel or solar cell efficiency is about the conversion rate of sunlight into electricity via a photovoltaic system.

The efficiency of the solar cells that are used in a photovoltaic system, along with latitude and climate, determines the yearly energy output of the system. For example, a solar panel that has 20% efficiency and an area of 1 m2 can generate 200 W at Standard Test Conditions (STC). However, it can generate more when the sun is at the peak position during the day and produce less in cloudy conditions. In central Colorado, for example, which gets annual insolation of 2000kWh/m2/year, such a solar panel is expected to generate 400 kWh of energy annually. However, in Michigan, which receives only 1400kWh/m2/year, annual energy output will come down to 280 kWh for the same solar panel. In more northern European latitudes, the output will be significantly lower, for example, 175 kWh energy output per year in southern England.

There are various factors that affect the conversion efficiency of a solar cell, such as its thermodynamic efficiency, reflectance efficiency, charge carrier separation efficiency, charge carrier collection efficiency, and conduction efficiency values. As these parameters can be difficult to measure directly, instead other parameters are measured, including open-circuit voltage (VOC) ratio, quantum efficiency, and fill factor. 

In simple words, solar panel efficiency is stated as a percentage, which quantifies a solar panel’s capability to convert sunlight into electricity. The same amount of sunlight hitting for the same duration of time on two solar panels may have different efficiency ratings. The more efficient panel will generate more electricity than the less efficient one.

In the case of two solar panels with the same size, if one has a 21% efficiency rating and the other has a 14% efficiency rating, the panel with 21% efficiency will generate 50% more kilowatt-hours (kWh) of electricity in the same conditions than the other panel. Due to this reason, maximizing energy usage and saving on the electricity bill is heavily dependent on having a high-level of solar panel efficiency.

Many consumers and experts in the solar industry consider solar panel efficiency as the most important factor when evaluating the quality of a solar panel. Although it is an important factor, it is not the only one to consider while deciding on installing a particular solar panel. Solar panel efficiency is related to the ability of a panel to convert energy at a low cost and high supply rate.

How efficient are today’s solar panels?

Currently, most solar panels that are available in the market have an efficiency range between 15% and 20%. The efficiency of high-quality solar panels can go over 22% or more in some cases, whereas the majority of PV panels are not above 20% when it comes to efficiency.

The most efficient solar panels on the market that are available today have maximum efficiency ratings 22.8%, whereas most panels are quite a few notches below that mark. The most efficient panels usually come with a high price tag, which is not affordable for most consumers. This is a major factor that pulling the solar industry back.

Solar Energy Applications

Energy received from sunlight can be categorized based on their various applications, particularly in the form of heat and light. Solar energy has been in use in different ways. For example, clothes are being dried under the direct sunlight, or certain food items are kept under the sun’s heat to get rid of insects. Also, fossil fuels are actually the result of solar energy stored millions of years ago.

In this modern era, solar energy has a range of applications in both residential and industrial usage. Major applications are below:

Heating Buildings with Solar Energy

Solar energy is used for space heating of buildings in different ways:

(a) Collecting sunlight by designing buildings in certain ways. For example, by making large south-facing windows, sunlight is allowed to enter buildings to provide natural heating.

(b) Using separate solar collectors that may heat water or air or stor­age devices for accumulating the collected solar energy to use at night or during cloudy days.

When buildings need heat from solar collectors or storage devices, the heat is transferred by traditional equipment such as fans, ducts, radiators, air out­lets, and hot air registers to warm up the living spaces.

When a building does not need heat, the heated air or water from the solar collector can be moved to a storage device such as an insulated water tank. During overcast weather conditions, an auxiliary heating system can be used that runs through gas, oil, or electricity.

Solar Water Heating

A solar water heating unit consists of a flat plate metal collector along with a metal tubing that faces towards the direction of the sun. Above the plate collector, there is a transparent glass cover and a layer of thermal insulation under it.

The metal tubing of the collector is connected using a pipe to an insulated tank that stores hot water during overcast days. After absorbing the solar radiation, the collector transfers the heat to the water through the tubing either by a pump or by gravity.

This hot water moves to the storage tank through the attached metal tubing. This water heating system is commonly used in hospitals, hotels, guest houses, tourist bungalows, cafeterias, and also in domestic and industrial units.

Solar Cooking

Over many decades humans have been using various combustible elements for cooking such as coal, cooking gas, kerosene, firewood, dung cakes, and agricultural wastes. Over the years, due to the energy crisis, the supply of coal, firewood, and cooking gas have become precious and more expensive. The usage of solar energy has provided an easy and affordable alternative for cooking, and thus solar cookers started getting popular. A solar cooker looks like a simple flat plate, which makes cooking a simple task, and that too, without any emission. 

A solar cooker comprises an insulated metal or wooden box which is blackened from inside. The solar radiation that enters the box is of short wavelength. As higher wave­length radiation is not able to pass through the glass covers, the re-radiation is minimized through the two glass covers from the blackened interior to outside the box, which further minimizes the heat loss.

When a solar cooker is placed under the sun, the solar rays get through the glass covers and are ab­sorbed by the blackened surface, which results in an increase in tempera­ture inside the box. 

The uncooked food gets cooked with the produced heat energy due to in­creased temperature of the solar box. The area that collects the heat in a solar cooker can have increased temperature by providing a plane reflector mirror. When this reflector is ad­justed to reflect the sunlight into the box, the temperature inside the cooker box rises to by 15°C to 25°C.

A solar cooker neither needs fuel nor attention while cooking food and also there is no pollution, charring or overflowing of food. Another major advantage is that the cooked food keeps its nutritional value such as vita­mins, and also natural tastes of the food remains intact. 

The cost of maintaining a solar cooker is negligible. The main drawback of solar cookers is that the food cannot be cooked at night, during overcast days, or at short notice. The cooking time is more compared to other ways of cooking. 

Solar Pumping

The power generated through solar energy is used for pumping water for irrigation purposes. The need for water pumping is maximum in the hot summer months, which increase solar radiation during this period, and thus this method is ideal for irrigation. During the cloudy weather, when solar radiation is low, the requirement of water pump­ing is also relatively less as the transpiration losses from the crops are also low.

Solar Distillation

In dry and coastal areas where potable water is scarce, the abundant sunlight can be useful for converting saline water into drinkable distilled water by the method of solar distillation. In this method, solar radiation goes through a transparent airtight glass cover into a shallow blackened basin that contains saline water.

Solar radiation passes through the covers, gets absorbed, and converted into heat in the black­ened surface, and causes the water to evaporate from the brine or impure saline wa­ter. Subsequently, the produced vapors get condensed to form purified water in the cool interior of the roof.

The condensed water flows down the sloping roof and is deposited in the troughs at the bottom and from there into a water stor­age tank to supply potable distilled water in areas with a shortage of water, in schools/colleges, hospitals, laboratories, and pharmaceutical industries. The cost per liter distilled water obtained by this system is cheaper than distilled water obtained through other electrical energy-based processes.

Solar Energy for Drying Agricultural and Animal Products

This is a conventional method of using solar energy for drying agricultural and animal products. Agricultural products are dried in a simple cabinet dryer which comprises a box insulated at the base, painted black on the inside and covered with an in­clined transparent sheet of glass. At the base and top of the sides, there are ventilation holes to facilitate the airflow over the drying material which is placed on perforated trays inside the cabinet. These perforated trays or racks are designed to provide controlled exposure to solar radiation.

Solar drying, particularly drying fruits using the sunlight improves the fruit quality as the sugar concentra­tion increases on drying. Usually, soft fruits are vulnerable to insect attack as the sugar content increases on drying, and solar drying helps get rid of insects. 

In many regions, the current practice of drying chilies by spreading them on the floor requires a lot of space and manual efforts. Moreover, it is difficult to maintain its quality and taste unless drying is done in a controlled atmosphere. Also, often, the products that are left to dry in an open space get spoiled due to sudden rains, dust storms, or by birds. As a result, the chilies become prone to fungi and bacteria attack. This is why a dryer operated with solar energy helps to overcome most of these disadvantages.

Some of the common agricultural products that are solar-dried are grains or maize and paddy, potato chips, grains of maize and paddy, peas, pepper, ginger, cashew nuts, timber and more. A couple of examples of solar-dried animal products are spray drying of milk and fish.

Solar Furnaces

In case of a solar furnace, the process of obtaining high temperature is done by concentrating the solar radiation onto a specimen using several heliostats or turn-able mirrors ar­ranged on a sloping surface. The solar furnace is used for assessing the proper­ties of ceramics at very high temperatures, above the range measurable in laboratories with electric currents and flames.

It is possible to accomplish heating without any contamination and temperature can easily be controlled by chang­ing the position of the material. This method is particularly useful for metallurgi­cal and chemical operations. In the future, an important application of solar furnaces will be the production of nitric acid and fertilizers from the air.

Solar Electricity Generation

Solar electricity or electric energy can be generated directly from solar energy through photovoltaic cells. A photovoltaic (PV) cell is a device that is used to convert photons of sunlight directly into electricity. It is made of semiconductors that absorb the photons received from the sun and create free electrons with high energies.

These high-energy electrons are induced by an electric field, to move out of the semiconductor. This electric field in PV cells is usually provided by a p-n junction of materials that various electri­cal properties. There are different fabrication techniques to enable these cells to reach maximum efficiency. Some of the key features of these modules are reliability, zero fuel expenses, the minimum cost of maintenance, long life, portability, and pollution-free working.

PV cells are generally used to operate irrigation pumps, navigational signals, railroad crossing warnings, automatic meteorological stations, highway emergency call systems, and others in areas where laying power cable is challenging.

In addition, PV cells are also used as a power source for calculators, televisions, watches, watches, computer card readers, battery charging and in satellites, and for providing electricity in rural areas.

Production of Solar Thermal Power

Producing solar thermal power is about converting solar energy into elec­tricity through thermal energy. In this method, first solar energy is used to heat up a working fluid, gas, water, or any other volatile liquid. This heat energy is then converted into mechanical energy through a turbine. Finally, a traditional generator attached to a turbine converts this mechanical energy into elec­trical energy.

Generating Electricity through Solar Ponds

A solar pond is a natural or artificial water body used for collecting and absorbing sunlight and storing it as heat. A solar pond is a shallow (5-10 cm deep) and has a bottom that absorbs radiation. It also has a curved fiberglass cover on it to let the solar radiation enter and reduces heat losses and convection (air movement). Loss of heat to the ground is minimized by providing a bed of insulating material in the pond.

Solar ponds use water for collecting and storing the solar energy that is used for many applications such as space heating, industrial process heating and to produce electricity by operating a turbine, which is by evaporating an organic fluid at a low boiling point.

Solar Green Houses

A greenhouse is a structure or a building with walls that are covered with a transparent material (glass or plastic), which collects solar energy and use that energy to grow plants. A greenhouse has heating, cooling, and ventilating devices that can control the temperature inside the greenhouse.

Solar radiation can pass through the greenhouse glazing. However, the thermal radiation emitted by the objects within the greenhouse cannot escape through the glazed surface. Due to this, the radiation gets trapped within the greenhouse and result in a spike in temperature.

As the boundary surrounding a greenhouse is closed, the air inside the green­house gets enriched with CO2 as the greenhouse air, and the ambient air does not mix. In addition, there is reduced moisture loss due to limited tran­spiration. All these features help to sustain the growth of plants the whole day, at night, and throughout the year.

Solar Energy Storage

Solar panels have become one of the major and fastest-growing sources of energy in all over the world. A report by the Solar Energy Industries Association, the solar market is expected to grow twice the size by 2023, and it will be worth $4.5 billion.

The popularity of solar electricity has made way for another renewable technology: solar energy storage. In this method, batteries are used to store extra solar power for later use. Companies like Tesla are working on developing batteries that can be installed along with solar panels to create “solar-plus-storage” systems for households. 

Thermal mass systems can store solar energy as heat at temperatures that are appropriate for domestic use for daily or in certain seasons. Thermal storage systems generally use materials that are readily available with high heat capacities such as water, earth, and stone. Efficient systems can lower peak demand, shift time-of-use to off-peak hours, and bring down overall heating and cooling requirements.

Paraffin wax and Glauber’s salt, the phase change materials are another thermal storage medium. These materials are inexpensive, easily available, and can deliver temperatures suitable for domestic use (around 64°C or 147°F). The “Dover House” in Massachusetts was the first to apply a Glauber’s salt heating system, in 1948. It is also possible to store solar energy at high temperatures using molten salts. Salts are said to be an effective medium for energy storage as they are low-cost, have a high specific heat capacity, and can deliver heat at temperatures that are compatible with traditional power systems. The Solar Two project applied this method for storing energy, and it was able to store 1.44 terajoules (400,000 kWh) in its 68 m³ storage tank. The annual storage efficiency was nearly 99%.

In the modern era, a typical solar energy system comprises solar panels, an inverter, equipment to mount the panels on the roof, and a performance monitoring system for tracking electricity production. The solar panels capture energy from the sun and convert it into electricity. Subsequently, the electricity passed through the inverter and converted it into a form that consumers can use to power their home.

Generally, most of the residential solar energy systems are connected to the electricity grid (or “grid-tied”). When solar panels produce more electricity than a household needs, the excess energy is fed back into the power grid. On the other hand, when a home needs more electricity than solar panels are generating, consumers can draw power from the electric grid.

In most cases, consumers receive a credit on their utility bill for the electricity they send back to the grid. Later, when they use more electricity than their solar panels have generated, they can use those credits instead of paying more for their utility. This process is known as “net metering.”

Net metering programs provide residential PV systems a credit for any excess electricity they deliver to the grid. This is managed by ‘rolling back’ the meter whenever a household PV system produces more electricity than it consumes. 

If the net electricity usage is below zero, the utility rolls over the kilowatt-hour credit to the next month. Other methods involve using two meters, to measure electricity consumed vs. electricity produced. This is less common due to the higher increased installation cost of the second meter. Usually, most standard meters accurately measure in both directions and make a second meter unnecessary.

Practical approaches like using a solar-plus-storage at households can store excess solar energy onsite for later use when the sun is not shining. An additional advantage is since solar batteries store energy at households; they also provide short-term backup power if there is a power outage in an area.

Solar Panel Manufacturing

Solar panels comprise a silicon semiconductor, which is surrounded by a protective material in a metal frame. The protective material has an encapsulant of transparent silicon rubber or butyryl plastic (used in automobile windshields) bonded around the cells and subsequently embedded in ethylene-vinyl acetate. A polyester film makes up the backing.

The solar panel manufacturing process:

Purification of the Silicon

Silicon is purified by placing the silicon dioxide into an electric arc furnace. Then a carbon arc is applied to release oxygen, and the outcomes are carbon dioxide and molten silicon. This simple process purifies silicon with just one percent impurity. However, it is still not useful in the solar industry. 

In the next process, the 99 percent pure silicon is further purified using the floating zone technique. A rod of impure silicon passes through a heated zone several times in the same direction. This process drags the impurities toward one end with each pass. At a certain point, the silicon becomes pure.

Creating Single Crystal Silicon

Solar cells are made from silicon boules. The most common process for creating the boule is called the “Czochralski method.” During this process, a seed crystal of silicon is dipped into melted polycrystalline silicon. As the seed crystal gets withdrawn and rotated, then a cylindrical ingot or “boule” of silicon is formed. 

Making Silicon Wafers

After the boule is formed, silicon wafers are sliced using a circular saw one at a time, or many at once with a multi-wire saw. In the process, only around one-half of the silicon is lost from the boule to the finished circular wafer. Then wafers are polished to remove saw marks. 


The conventional way of doping silicon wafers with boron and phosphorus is to add a small amount of boron during the Czochralski process. Thereafter, the wafers are sealed back to back and placed in a furnace to be heated to slightly below the melting point of silicon (2,570 degrees Fahrenheit or 1,410 degrees Celsius) in the presence of phosphorus gas. The phosphorus atoms “burrow” into the silicon. The temperature and time in the entire process are carefully controlled to ensure a uniform junction of proper depth.

Placing Electrical Contacts

Electrical contacts connect one solar cell to another and the receiver of the produced current. The contacts need to be very thin, so they do not block sunlight to the cell. Metals such as palladium/silver, nickel, or copper are vacuum-evaporated. The cells are encapsulated in ethylene-vinyl acetate and placed in a metal frame that contains a mylar backsheet and glass cover. After the contacts are in place, thin strips are placed between cells. The most commonly used strips are tin-coated copper.

The Anti-reflective Coating

Due to the shiny nature of pure silicon, it can reflect up to 35 percent of the sunlight. To reduce the loss of sunlight, an anti-reflective coating is applied on the silicon wafer. The most commonly used coatings are titanium dioxide and silicon oxide. The material that is used for coating is either heated until its molecules boil off and move to the silicon and condense or the material undergoes sputtering. 

Encapsulation of the Film

Finally, the finished solar cells are encapsulated, which are sealed into silicon rubber or ethylene-vinyl acetate. Subsequently, the encapsulated solar cells are placed into an aluminum frame that has a backsheet of mylar or tedlar and a glass or plastic cover.

Solar Manufacturing Companies

The following are the top five solar panel manufacturers in 2019. These manufacturers are ranked according to the highest efficiency solar panel they offer:

  • SunPower (22.8%)
  • LG (21.7%)
  • REC Solar (21.7%)
  • Panasonic (20.3%)
  • Silfab (20.0%)

Solar Panel Cost

Price of solar panels as the cost of installation are major determining factors for consumers to install a PV system at their household. Though there is no straightforward answer to this question as there are a lot of variances that influence the price such as country, region, industry standard, and so on. 

Residential solar systems with a typical size between 3 and 8kW may cost in the range of  $15,000 to $40,000. The cost per watt (inclusive of parts, labor, permitting fees, overhead costs, and profit) has dropped significantly over the last decade. For example, in many parts of the US, the current cost is now between 6 and 8 ($/W). Usually, the larger the solar system, the lower the cost per watt.

Top Solar Energy-producing Countries

The ranking of leading solar producing countries changes frequently. Besides the consistent leaders like China and the USA, other countries like India, Australia, Italy has climbed up the ranking in recent times. The following is the list of top 10 solar energy-producing countries in terms of installed capacity.


China has been getting the top rank for the past several years. In 2018, China installed 44.3 GW of solar capacity. By 2030, the country has a target to produce 20 percent of its electricity using renewable resources.

The United States

The United States has the technology, talent pool, and environment requirements for large-scale solar energy production. However, lack political support for renewables has made it future a little doubtful. Still, it is one of the leading countries in the world in solar energy generation. In 2018, the country added 10 GW solar capacity.


In recent times, India has made significant progress in solar energy production. By 2020, the country is expected to huge strides in solar energy production. In the financial year of 2018-19, India installed 1,836 MW of solar capacity.


Japan has a well-established technology and manufacturing sectors and was one of the early adopters of solar power generation. The country is aiming to meet 10 percent of the country’s energy requirements by 2050. Japan is expected to add 17 GW of installed capacity by 2020.

Germany (48.4GW)

Germany was one of the early leaders in solar energy generation before other countries caught up. Germany has rolled out a strategy called “Energiewende,” which aims to ensure that the country obtains a minimum of 60 percent of its energy from renewable sources. In 2018, Germany installed nearly 3,000 MW of new solar PV capacity, which was an increase of 68 percent compared to 2017.

The Future of Solar Energy

In order to create more advanced solar cells, a new design will be required that can capture more sunlight, transform light energy to electricity more efficiently, and be cost-effective. Energy producers and consumers will be more inclined to adopt solar power if the produced energy is equally or less expensive than non-renewable forms of electricity.

Currently, designing electronics that are able to accurately track the position of the sun for several decades at a reasonable cost is a major challenge. However, innovation in this area is in progress. 

Another way to improve the performance of solar cells is to improve their efficiency of converting energy from sunlight into electricity. Solar cells that have more than one layer of light-capturing material can collect more photons than solar cells that contain only a single layer. Recently, lab-tested solar cells with four layers were able to capture 46% of the incoming light energy. These cells are still too expensive and difficult to roll out for commercial use.

In the near future, silicon solar cells are expected to have lower cost and be installed in large numbers. In the US, these cost drop may increase solar power production by a minimum of  700% by 2050. Meanwhile, the ongoing research on finding alternative designs for more efficient and less expensive solar cells is expected to bring in positive results. In the coming years, there are likely to be alternatives to silicon that may be used on rooftops, solar farms that will provide clean and renewable sources of energy. The benefits of these improvements will continue with the help of increasing the production of solar cells and implementing new technologies that make the cells more affordable and efficient.

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