By Eva Kurilova
Solar energy is an abundant source of renewable power that is easily harnessed all around the world. The sun’s rays deliver about 1,000 watts of energy per every square meter of the earth’s surface,1 and solar technologies are becoming ever more efficient at capturing and using this energy. But before it’s ready for home use, solar energy must first be converted from direct current (DC) to alternating current (AC) by way of an inverter.
Solar panel systems may seem complicated, but the process of generating solar electric current and converting it into usable electricity is actually fairly straightforward. Understanding how solar systems and electric currents interact can help homeowners decide whether solar generated electricity could be a viable option for meeting their energy needs.
Solar panels use semiconductive materials to capture energy from the sun.
Most solar panels are made of silicon because of the unique semiconductive properties of silicon crystals. When impacted by the photons that make up sunlight, the electrons in most matter will simply vibrate in place—this reaction creates heat instead of an electrical charge, and is why we feel the sun’s warmth on a bright summer day. When silicon crystals absorb photons, however, a different reaction takes place. When exposed to the sun’s rays, the atomic structure of crystalline silicon changes: the silicon atom’s electrons become so high-energy that they are knocked loose from the atom and flow to other parts of the crystal structure.2
Some newer types of solar panels, namely thin film solar panels, use semiconducting materials other than silicon, such as copper indium gallium selenide or cadmium telluride. These materials generate solar electric current in the same way as silicon panels, just not quite as efficiently. Nevertheless, thin film panels are continually becoming more efficient and have a variety of useful applications.
No matter what semiconductive material it is made of, each solar panel contains an electric field which guides the flow of loose electrons in a desired direction, creating an electrical current. Before it can be used to power a home, this direct current of electrons must first make its way to a solar panel inverter.
Solar panel inverters convert DC power into usable AC power.
When most people think of solar energy systems they assume that the solar panels are the most important component. However, if the power generated by solar panels was not converted into standard AC power by an inverter, then it couldn’t be used to power televisions, computers, or any wired appliances. The inverter is, in a sense, the “brains” of the whole system.
Inside of a solar panel inverter are a set of solid state switches.3 By flipping on and off in very rapid succession, these switches halt the direct current generated by the panels, and reverse the flow of electrons in that current between 50 and 60 times a second.4 This alternating current is then funnelled out of the inverter and into the home’s wiring, where it can be used to power appliances and devices.
While all inverters change DC to AC, string inverters and microinverters connect to solar panels in different ways.5
- String inverters receive power from groups of solar panels wired together within an array. String inverters are commonly used in residential applications for their reliability and affordability. However, shade and accumulated debris can pose a significant problem for string inverters. If even one panel on a string is shaded or covered, the performance of the rest of the panels on the same string will suffer.
- Microinverters work on a module level. They are attached to each individual panel and so convert DC to AC at the panel itself. Microinverters systems are more expensive than string inverters but can also be more efficient, as shading issues with one panel won’t affect others.
The efficiency of the inverter impacts the actual output of a solar array.
Solar panels deal in direct current, and inverters convert it to alternating current for residential usage. But most solar panels are rated by their DC wattage—in other words, the direct-current power a panel is capable of generating. Is the final output the same amount of power, once it’s been converted to alternating current watts? The answer is not quite, but it depends on the inverter. Most inverters operate at around 95% efficiency.6 This means that, when converting electrical current from DC to AC, the inverter loses about 5% of the total energy generated. A panel rated for 300 DC watts will only product 285 AC watts under ideal conditions. An inverter with a higher efficiency will convert DC to AC without losing much power in the process.
As with all things solar power, technology is constantly improving. Manufacturers are coming out with more efficient string inverters and microinverters every year. Some string inverters available today can reach DC to AC conversion efficiency rates of up to 99%.7 Though these more efficient inverters are more expensive than the average 95% efficiency inverter, they can represent a good investment if installed from the outset. Getting even just 3% to 4% more efficiency out of your system over the course of an inverter’s operating life can represent significant savings.
Microinverters are catching up in efficiency as well, with the leading types seeing conversion rates as high as 95%8 and 96.5%.9 Many homeowners assume that a string inverter, because of its higher efficiency, is always the best choice for a home solar power system. While this is likely to hold true for an average-sized solar array with no shading and plenty of direct sunlight, there are many situations where microinverters can be the better option. In systems that experience some shading, debris, or snow cover, microinverters can actually contribute to a greater overall efficiency of the entire system. Microinverters are also a good choice for homeowners who want to start with a smaller array, but who want the option of expanding it in the future.
The different types of inverters contribute to flexibility in home solar system design, allowing homeowners to optimize their arrays.
The truth about home solar is that there are more possible customizations to a home solar system than ever before. The many different types of panels, array designs, and inverters means that it’s possible to design a well-functioning system for just about any home. With the right combination of these factors, solar generated electricity can lead to major savings on energy bills and can possibly even supply enough power to provide for all of a home’s energy needs.
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- Rinkesh. “How Do Solar Power Panels Work.” Conserve Energy Future. Conserve Energy Future, n.d. Web. 08 Feb. 2017.
- Locke, Susannah. “How Does Solar Power Work?” Scientific American. Scientific American, 17 Oct. 2008. Web. 08 Feb. 2017.
- Worden, James, and Michael Zuercher-Martinson. “How Inverters Work.” SolarPro. Home Power Inc., Apr.-May 09. Web. 08 Feb. 2017.
- Woodford, Chris. “How do inverters convert DC electricity to AC?” Explain that Stuff. Explain that Stuff, 2009. Web. 15 Feb. 2017.
- Zipp, Kathie. “What are the different types of solar inverters?” Solar Power World. WTWH Media, LLC., 25 May 2016. Web. 08 Feb. 2017.
- Lalonde, Louis. “Don’t Judge A Solar PV System’s Efficacy By Inverter Efficiency Alone.” Electronic Design. Penton Media, 25 Oct. 2011. Web. 13 Feb. 2017
- Zipp, Kathie. “The new age in solar inverter conversion efficiency: 99%” Solar Power World. WTWH Media, LLC., 5 Feb. 2015. Web. 13 Feb. 2017.
- “Micro Inverters.” Solar Panels Plus. Web. 13 Feb. 2017.
- “Micro Inverters.” Rk Solar & Consulting Services. Web. 13 Feb. 2017
Editor: Kelsey Tollefson
Executive Editor: John Lenker