Understanding how solar panels work is essential for anyone looking to build a career in the solar industry. Whether you’re crafting digital marketing strategies for a solar firm, working as a sales representative, or involved in breakthrough manufacturing as a Mechanical Engineer, a solid grasp of solar technology is crucial. In this post, we’ll dive into a straightforward, yet comprehensive overview of solar energy, the photovoltaic (PV) effect, and how solar cells function..
How much Solar Energy is there?
The sun produces an astonishing amount of energy through the process of nuclear fusion. It released 385 septillion watts - that is 385,000,000,000,000,000,000,000,000 watts. As a reminder from high school physics class, a watt is a measure of power, or energy per time measured in Joules per second. To help contextualize this mind-boggling number, it is estimated that the entire world used 25,000 terawatt hours of electricity in 2022, or 25,000,000,000,000,000 watt hours. On average, this means the earth is consuming 2.9 terawatts of power.
So, if we could theoretically hook up a power line directly from the sun to the world’s electricity grid, the sun could power over 130 trillion Earths at the same time! The U.S. consumes about 4,000 terawatt hours per year, so we could power over 800 trillion countries like the United States at the same time.
Obviously, the vast, vast majority of the sun’s energy does not hit the earth as it’s busy illuminating the rest of the universe. NASA estimates that, on average, every square meter of the Earth receives 342 watts of solar energy. Multiplied by the number of square meters on Earth, we receive 174,000 terawatts of solar energy on the Earth’s surface.
It’s challenging to grok the magnitude of these huge numbers, but more simply, if we could harness all of this energy that hits the Earth’s surface continuously, we could power about 60,000 Earths with the energy we are receiving from the sun!
The Photovoltaic Effect - Harnessing the Sun’s Power
It’s been almost 200 years since Edmond Becquerel discovered the photovoltaic effect and we began to understand how we could harness the power of sunlight. In 1839, at only 19 years old, Becquerel discovered that when shining a light on electrodes, a voltage and current were generated. As scientists developed new technologies and theories in physics since then, we have come to a detailed and subatomic understanding of how the voltage and current are generated in the photovoltaic effect.
Light itself is composed of photons, which are little energy packets with no charge or mass. When photons strike an object with sufficient energy (intensity of light as determined by its frequency and wavelength; light travels at a fixed speed), it can cause an electron in material to be excited and eject into a different state. The flow of electrons through a conducting material is what creates an electric current, which powers everything from your dishwasher to your cell phone. So, if we can harness and guide the flow of the excited electrons, we can create electricity from sunlight.
How Solar (Photovoltaic) Cells Work
Solar, or photovoltaic (PV), cells are the building blocks of solar panels that leverage the photovoltaic effect to create an electron flow. There have been and will continue to be many advances in how solar cells are manufactured and installed. Below is a simple diagram showing a side view of what a solar cell hookup can look like:
There have been and will undoubtedly continue to be advances to improve the efficiency of solar cells. We’ll give a detailed overview of the basic solar cell here, but know that there continues to be significant experimentation and breakthroughs to improve the existing technology. Below is a diagram of the side-view of a solar cell and the electricity flow:
Solar cells are most commonly manufactured from silicon, which is the second most abundant element on Earth after Oxygen. Because of its natural abundance on Earth, it is a cheaper material to manufacture the panels. Silicon is also a fantastic semiconductor, which makes it a more efficient material to use. This is because silicon has a smaller “band gap,” which is the energy required for an electron to jump out of its current band to reach the next conduction band, which is how we can generate a flow of electrons. In silicon, the energy needed to jolt it from its location is only 1.1 electron volts.
Sunlight is composed of a spectrum of light at different wavelengths and the shorter a wavelength, the more energy a photon will have. So, at only 1.1 electron volts, most of the sun’s light has enough energy to displace an electron in silicon materials. This means that silicon today is one of the most efficient and cost-effective materials we have to generate electron movement.
Solar cells are not pure silicon and are generally composed of two different types of semiconductors to facilitate this flow of electrons. N-type semiconductors are generally “doped” (mixed) with phosphorus to leave additional electrons free in the material. P-type semiconductors are doped with boron, which creates a lack of an electron, or an electron “hole,” and therefore a positive charge. You may have been wondering what the “n” and “p” stand for - it’s “negative” and “positive” making it easy to remember.
The depletion zone between the semiconductors is where the excess electrons from the n-type layer rush to find electron holes from the p-type layer. As a result, they create a small electric field because there’s a positive charge where the electrons left and a negative charge where they filled the holes. This field creates a repelling force, preventing more electrons crossing over the border in a stable state.
However, when sunlight hits the cells with sufficient energy, it causes movement in the electrons and they can jump across the barrier.
In order to capture and direct the flow of electrons, solar cells have electric strips or conducting wires that form the grid layered on top of the semiconductor material. These are often made of silver, but can also use aluminum which is another highly conductive metal. Having more conductive strips will allow the solar cells to capture more of the “free” electrons, but there is a trade-off with less surface area to capture the sunlight itself. The metal conductors will allow the electrons to flow into the energy system. In the simple diagram above, a lightbulb is directly connected to the solar cell.
Solar cells are far from perfectly efficient. The free electrons can fall back into their “holes'' before finding their way to the conductive wires. The angle of the sunlight affects the intensity of the light. As noted above, cells can’t absorb the full spectrum of sunlight. The energy conversion process is not 100% efficient with wiring and inverters losing some energy throughout the process.
While scientists have achieved over 40% efficiency, most commercially available solar cells today hover around ~20% efficiency. There are various research and manufacturing efforts to further improve efficiency and reduce costs, but even today at only ~20% efficiency, solar is already the cheapest form of electricity for most of the United States.
Why understanding solar cells is important for your career
As a solar professional, regardless of which job you go into, you’ll very likely need to explain to customers and stakeholders (plus your family members!) how solar cells work in simple terms. Staying on top of industry advances will be much easier with a thorough understanding of the basic building blocks. We’ll certainly continue to see improvements in underlying materials over the coming years which will come from different experiments trying to improve the efficiency of solar panels in a cost efficient way. Your level of knowledge will vary by role:
PV Installer - Knowing the details of solar cells will ensure you’re mindful of the optimal placement and wiring of panels to understand energy production. Plus, your customers are gong to undoubtedly ask about the material and all the gridlines they see on the solar panels!
Technicians - Solar energy systems can fault in multiple locations. Having a good grapes of how the cell works can help you troubleshoot drops in efficiency or power output.
Sales and Marketing - Effective communication is critical to your success. Knowing the operational components of the system will demonstrate confidence and value to your customers
Manufacturing and Solar Designers - You’ll undoubtedly know the nitty gritty of how panels work and your challenge will be to help communicate and educate the details to other stakeholders you are partnering with.
Stay tuned for more information on how the full solar energy system works in upcoming posts. Subscribe below!
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