July 27, 2017 Solar Energy Written by Sara Slavikova
How solar creates electricity
Solar energy is a renewable energy resource

that is more affordable now than ever before and is used to produce electricity for a wide variety of residential and commercial uses. Electricity produced from sunlight will be a key part of our journey toward sustainable energy in the future.

Solar power is a good way to help the environment because with it, we can reduce fossil fuel use. We also save money because the electricity generated by solar systems is considered free once the systems are in place.
 

How can solar energy be used to produce electricity?

Human ingenuity has developed two different ways how to harvest the energy of the sun and turn it into electricity:

Solar thermal systems and Solar photovoltaic systems

A solar thermal system generates electricity indirectly by capturing the heat of the sun to produce steam, which runs a turbine that produces electricity.

A solar photovoltaic system produces electricity directly from the sun’s light through a series of physical and chemical reactions known as the photovoltaic effect.

Let’s examine each of these systems in more detail.
 

How does solar thermal generate electricity?

You might be familiar with solar thermal technology from a widely publicized series of photos that debuted in the press in 2013, featuring the Ivanpah Solar Power Facility in the Mojave Desert, California. At the time, it was the largest solar power plant in the world. The array of 170,000 heliostats, which look like large mirrors are tracking the sun’s movement across the sky to power over 140,000 households [1].

Mirrors are one of the main components of the solar thermal system. They reflect sunlight onto a receiver containing a heat-transfer fluid, which is warmed up by the sun. The fluid used for this purpose is often molten salt, which is a mixture of 60 percent sodium nitrate and 40 percent potassium nitrate. Molten salt has a great capacity to store and transfer heat [2]. This allows the storage of the heat generated from the sun for periods of time with no sunlight.

For example, Gemasolar power plant in Spain can store enough heat to produce electricity for an extra 15 hours with no solar input [3].  

The rest of electricity generation process is much the same as it is at coal-fueled power plants. The heat transferred by molten salt creates steam that runs steam turbines, which power a generator that produces electricity.
 

How do solar panels generate electricity?

The energy of collected sunlight is transformed directly into electricity thanks to the photovoltaic effect. In short, this effect takes place when photons (tiny electromagnetic particles) of light are absorbed by a specific material, which in turn releases electrons from atoms. Released electrons are then available to do the electrical work, such as powering a light bulb.

Although we cannot see the photovoltaic effect with our own eyes, we can look more closely at the solar panels where this process takes place.
 

What are solar panels?

Solar panels have become a familiar sight to many of us. Other than the classic, dark blue panels, scientists have also been working in the past years on diverse alternatives such as producing more aesthetically pleasing green-colored panels or cyanobacteria-powered bio-panels. But no matter how they look, solar panels serve as devices for capturing the energy of light.

One solar panel consists of many smaller units called photovoltaic cells. Inside these cells, the photovoltaic effect takes place. On average, one cell produces around 0.5 volts. Multiple cells are wired together in series to increase their output.

For example, a solar panel consisting of 36 interconnected cells generates around 18 volts. 

Solar cells are made of a semiconducting material, such as silicon, placed between two conducting materials to establish an electric field. Commercially available cells contain phosphorus to provide negative electric charge and boron for the positive charge. The electric field pushes electrons knocked by photons out of the silicon layer to metal plates on the sides of the cells, where they are transferred in a form of direct current [4].

One of the biggest disadvantages of photovoltaic systems is the conversion rate of the sunlight into electricity, otherwise referred to as the efficiency. At most installations, this number remains between 15 and 18 percent. This means that over 80 percent of the sunlight falling on the solar panel is not transformed into power.
 

Where does the electricity go next?

When the solar energy is captured and collected by the solar cells, it is converted into direct current. The current flows into an inverter, a device that transforms the direct current into alternating current, which is used to power our electronic devices [5].

For any extra solar-generated electricity that is not used right away, there are two primary options and one hybrid option of their utilization. These are:

  • On-grid systems
    On-grid systems feed electricity back into the electrical grid. Electricity companies typically give customers credits for any extra electricity that is fed back into the grid from their solar panels. You can use these credits to draw electricity from the grid on days when your solar array doesn’t produce any. One drawback to this type of solar system is that when the grid is down, the system might not be utilized.

 

  • Off-grid systems
    Off-grid systems are standalone solar systems that rely on batteries to store solar energy for use during the night and at other times when more electricity is needed than is generated by the solar system.

 

  • On-grid solar systems with a battery backup
    On-grid solar systems with a battery backup feed solar energy-generated electricity back into the grid when the grid is operating, but in the event of a grid blackout, these systems will switch to an off-grid mode. In this off-grid mode, the backup battery is used to supply stored solar power, and the solar panels charge the battery [6].

 

Both of these concepts show us that we are capable of satisfying our demand for electricity by harvesting power from renewable resources. The only limitations arise from the technology available at the moment. This is an issue that can be tackled over the time, especially if we focus our full attention on finding solutions to current obstacles such as the low efficiency of residential photovoltaic systems. Who knows? Perhaps the twenty-first century will someday be known as the era of the “Renewable Energy Revolution.”

 


References

[1] https://goo.gl/VwjM0i
[2] https://en.wikipedia.org/wiki/Molten_salt
[3] http://torresolenergy.com/TORRESOL/gemasolar-plant/en
[4] https://www.livescience.com/41995-how-do-solar-panels-work.html
[5] http://www.originenergy.com.au/for-home/solar/about-solar.html
[6] http://www.wholesalesolar.com/grid-tie-battery-backup