How Solar Power Works

Solar research as we know it today began in the early 1950s at Bell Laboratories (now AT&T labs) however it did not receive serious attention until the 1970s during the oil embargo which caused oil prices to peak. Today solar power is all around us, from calculators to heating nearby buildings to satellites in space. As an abundant and relatively untapped electrical resource utilizing the sun’s natural energy is an appealing concept both for the environment and financially. Although the goal of a solar cell is clear, to convert sunlight into electricity, few truly understand how solar power works. Before delving into the mechanics of solar power, it is important to understand more fully its main component: solar cells.

What are solar cells?

Solar cells or photovoltaic cells are generally made up of silicon crystals.  Silicon crystals are critical to the structure of a solar cell because of its unique anatomic construction. A silicon atom has 14 electrons on 3 different shells. The most exterior shell is incomplete, having 4 of the necessary 5 electrons. To fill the remaining 4 electron spots, a silicon atom will bond (also can be thought of as sharing) with neighboring silicon atoms until it fills its exterior shell. This bonding is how silicon crystals are formed.

Pure silicon crystals are not good conductors of electricity. Electricity is created when electrons break off from their atoms leaving behind a hole and then float around until they find a new hole to fill. As a result of silicon bonding with its neighbor, very few electrons actually break free and create energy. It is for that reason that scientists add impurities to the silicon to make it a more viable conductor. This process of purposefully adding impurities is referred to as doping.

The goal of doping is to create more free carriers or electrons that will break off and create an electrical current. Two impurities are added, boron and phosphorous and can be considered complimentary additions. Boron is added to the bottom layer to create a positive charge (called p-level or p-type) while phosphorous is added to the top layer to cause a negative charge (n-level or n-type). Boron has 3 exterior electrons rather than the 4 found in pure silicon which causes the bottom layer to have an absence of electrons or free holes. Phosphorous has an extra electron which means it has one free unbounded electron or free carrier. The space between the two layers is where the electrical movement takes place and creates an electric field that restricts the travel of electrons from the positive layer to the negative layer. The electrical field causes all the free carriers from the negative layer want to fill all the holes on the positive layer. It is precisely at that movement when energy is produced.

What happens when solar cells are struck by sunlight?

When a solar cell absorbs sunlight, it affects the electrons which bind the silicon atoms. Although there are many types of sun rays, solar panels only absorb photons.  The photons create an influx in energy that releases the electron from its original location and therein creating a current. However, the electric field between the positive and negative currents prevents this current from going from the positive layer to the negative layer. To trap this current, an external circuit of wires along the top layer (the negative layer) will connect the two layers. The electric field between the two layers is what causes the voltage. This completed circuit creates a usable power source.  

How solar energy is used:

Solar panels are many solar cells or modules combined together to form a solar panel, generally 36 cells are connected. Several solar panels are needed to convert sunshine into a direct current (DC) of electricity. This current then enters an inverter which transforms the DC current into what is used by most home or office appliances: 120-volt AC. Once converted, the AC current is then sent to the building’s utility panel which disperses the electricity throughout the building. Excess electricity can be stored in batteries which allow power to be used when there is no sunshine available. The utility grid can be accessed at times when the batteries are empty and there is no sunshine to refill them. Likewise, if properly connected to the utility grid and the batteries are full, spare electricity can be sold to the utility grid. This push-pull system with the utility grid ensures that you pay only for actual energy used. For example, if you exported a large amount of energy back to the grid and then only accessed the utility grid for a small amount of electricity, you could have a net gain. A utility meter measures how much energy is used and how much is sent back to the utility grid. This back and forth is called “net-metering”.