A solar panel inverter (also known as a converter or PV inverter) is a device that converts the direct current (DC) output of a solar panel into alternating current (AC), making it usable in your home. Apart from the panels themselves, inverters are arguably the most important element in your solar power system. Understandinwg the solar inverter will help you develop a system that best meets your energy needs.
What else do inverters do?
Inverters do more than just convert DC to AC. Modern inverters serve a variety of useful and important functions in your solar power system, including:
Power optimization: Inverters can maximize the energy harvest from your solar panels. This is useful in cases where one panel is slightly shaded by trees or debris, or variations caused by the manufacturing process make one panel slightly more or less efficient than its counterparts. By optimizing the power production of individual panels, the inverter improves overall system performance.
System monitoring and protection: Inverters track the energy yields of the solar system and its electrical activity and signal when there is a problem. For instance, if the maximum power of the inverter is close to being exceeded, the inverter will automatically decrease the amount of power being produced. Inverters that are tied to the grid will automatically shut off when the utility power goes out, preventing power from feeding back into the power lines.
What sort of power rating does my inverter need?
Inverters are capable of producing two types of wattage: continuous (or “steady state”) wattage and surge (“peak” power). Surge wattage refers to the energy needed for appliances that require additional energy when they are turned on. Continuous wattage refers to the power usage of devices when they they’re operational.
For instance, a 60-watt light bulb requires 60 watts when it is turned on and when it is operational, so its surge wattage and continuous wattage ratings are the same. A microwave, on the other hand, requires 750 watts just to turn on (its surge wattage), and then uses 1,000 watts while it’s in use (its continuous wattage).
Your inverter needs to be able to match or slightly exceed the total power needs of both types of wattage for all your appliances. If your home needs a total of 2,000 watts of continuous energy and 4,000 watts of surge energy, for instance, your inverter should be rated for at least that much wattage. (Check the backs of your appliances for information about their continuous and surge wattage requirements.)
Additionally, your inverter will be most efficient if its wattage is about 30 percent smaller than the maximum wattage produced by the solar panels the inverter is connected to. However, if you’re considering expanding the size of your solar array in the future, you might want to get an inverter with a maximum wattage larger than that of your current solar array.
Where should my inverter be located?
Most inverters can be placed either indoors or outdoors, but keeping your inverter inside is probably the best option since hot weather can reduce its efficiency. If you place your inverter outdoors, it should be in the shade and away from direct sunlight to prevent overheating. Microinverters, notably, must always be placed outside beneath the solar panel they’re connected to.
Does my inverter need maintenance?
Inverters often have heat fins to help cool the device. These heat fins should be maintained according to manufacturer directions. Your inverter’s manufacturer might also recommend that you re-torque current-carrying conductor fasteners and clean or replace the air filter.
Inverters typically need to be replaced after 10 to 15 years; 10-year warranties are standard, but 20-year warranties and/or service plans are becoming more common.
What are the different types of solar inverters?
There are three main types of inverters: string inverters, central inverters, and microinverters. According to a 2017 report from the Fraunhofer Institute for Solar Energy, string and central inverters comprise 96 percent of all solar inverters in use today. All three types of inverters convert direct current to alternating current, but each has its own advantages and disadvantages.
Also known as standard inverters, string inverters are the second-most common type of inverter. They are mostly used in residential solar systems and in some small-scale commercial solar installations. Their name comes from the way solar panels are arranged in rows, or “strings.” Each string of solar panels requires its own string inverter. String inverters are best for solar arrays in which all the panels face the same direction and are not covered by shade.
String inverters have low power consumption, low impact of failure, and are convenient to replace and maintain. Since they’ve been around for decades, string inverters are well understood by electricians. String inverters are also cheaper than microinverters. When coupled with DC power optimizers (DCPM), they can boost the energy production of individual panels. You only need one string inverter per installation, while for microinverters you’ll need one inverter per panel.
On the downside, if the inverter breaks down, the whole solar system will be disabled. And if you want to expand the number of solar panels in your array, you would need to buy an additional inverter.
When tied to the grid, string converters are often referred to as “grid-tie converters.” This distinguishes them from “battery inverters” or “stand-alone inverters” that are not connected to the grid.
Central inverters are the most common type of inverter. They’re basically the same as string inverters, except that they can support more strings of solar panels than a regular string inverter. This type of inverter is typically used for larger commercial solar arrays and utility-scale systems.
The main advantage central inverters have over string inverters is that they save space, since you can link more panels per inverter. But that space-saving convenience will cost you, since they are somewhat more expensive than string inverters.
While string and central inverters link multiple solar panels in sequence, microinverters are installed underneath each individual panel on your roof. This allows for individual panel monitoring and means that problems or failures in a single panel won’t affect the rest of your solar system.
Microinverters are also safer than string inverters since they include a built-in rapid shutdown protection. This means that when utility workers or electricians on the DC side of the system are working, they won’t be at risk for electrocution. String and central inverters, by contrast, require additional systems to provide rapid shutdown protection.
A 2011 study conducted by Appalachian State University found that in unshaded conditions, microinverters outperformed central inverters by about 20 percent. During conditions of partial shading, the microinverter did even better, outperforming the central inverter by 27 percent.
Finally, making upgrades to a system that uses microinverters is easy. If you want to add additional solar panels, for instance, you can do so without being burdened by the string requirements of a string inverter. And since microinverters are battery-compatible, adding a residential energy storage unit at a later date is also simplified.
Microinverters do, however, have a few disadvantages. Since you’ll require one micro-inverter for each solar panel, the total cost of using microinverters is more expensive than using a string or central inverter. They’re also more difficult to maintain and replace, since each microinverter needs to be placed just below the solar panel it’s linked to. Finally, the more complex design of microinverters also makes them less reliable than their counterparts.