A Guide to Solar Inverters: How They Work & How to Choose Them

Solar panels, while important, are just one part of the solar array—the complete system that produces energy from sunlight. Another essential component is the inverter, and thanks to technological advancements, there are inverter options. Keep reading as we walk you through what an inverter is, how it works, how different types of inverters stack up, and how to choose which kind of Inverter for your solar project. 

Solar power is on the rise. According to Energy.gov, solar energy production rose from 0.34 GW in 2018 to over 97 GW in 2020. 

What is a solar power inverter? How does it work?

A solar inverter is really a converter, though the rules of physics say otherwise. A solar power inverter converts or inverts the direct current (DC) energy produced by a solar panel into Alternate Current (AC.)

Most homes use AC rather than DC energy. DC energy is not safe to use in homes. If you run Direct Current (DC) directly to the house, most gadgets plugged in would smoke and potentially catch fire. The result would be that most appliances, computers, power strips, TVs, entertainment systems, home security devices, and a whole host of other electronics would become fried. Solar arrays use inverters to change the DC to AC, which is safe for home usage. 

How do Solar Power Inverters Work? 

The solar process begins with sunshine, which causes a reaction within the solar panel. That reaction produces a DC. However, the newly created DC is not safe to use in the home until it passes through an inverter which turns it from DC to AC. 

Understanding different types of solar inverters; plus their pros and cons

There are four main types of solar power inverters:

Standard String Inverters 

Also known as a central inverter. Smaller solar arrays may use a standard string inverter. When they do, a string of solar panels forms a circuit where DC energy flows from each panel into a wiring harness that connects them all to a single inverter. The inverter changes the DC energy into AC energy. Most standard string inverters are mounted on the home, garage, or near the power meter if the house connects to the power grid. 

Pros—

• Generally the least expensive option. 
• Easy to diagnose problems as it is usually the inverter that fails. 
• Cheaper installation due to fewer parts.
• Easier to maintain as they are not mounted on the roof and have easier access.

Cons—

• Can limit power production of the array for complex roof/system designs, especially with shade situations.
• A single solar panel with a drop in energy production, such as when shading occurs, can decrease the power production for the entire string of panels. 

Optimized String Inverters

Optimized string inverters, sometimes called power optimized string inverters, are two parts. The first part is the power optimizer, which handles DC to DC and optimizes or conditions the solar panel's power. There is one power optimizer per solar panel, and they keep the flow of energy equal. For example, with a standard string inverter, if one solar panel produces less energy, all the solar panels in that string will produce less energy. With the power optimizer, each solar panel produces energy, and when that energy reaches the optimized threshold, the power optimizer sends it to the Inverter. For this setup, the string inverter only has to convert the DC energy to AC energy. 

Pros—

• Consistent energy flow to the converter without the drop in energy that can occur with a standard string inverter. 
• Helps to optimize power production on complex roof/system designs, including shading. 
• Optimized string inverters enable power production data and monitoring at the individual panel level.
• More extended warranty—most power optimizers have a 25-year warranty.

Cons— 

• Expect the price of power optimized string inverters to be more than a standard string inverter. There are more parts, and that also means more labor. Each solar panel has a power optimizer. 
• Warranty may or may not include labor.
• Some power optimizers are installed at the factory and may not be repairable. In those cases, panel replacement is necessary.

NOTE: The cost to produce a watt of solar energy has dropped from around $3.50 per watt in 2006 to $0.50 per watt in 2018

Micro Inverters

Microinverters convert DC to AC at the panel level. They differ from a power optimizer in that a power optimizer only deals with DC. The microinverter installation occurs on each panel. Some may be factory installed or physically installed on-site, and there is no central inverter on a solar array with microinverters. The energy conversion occurs at the micro-inverter—on the roof at each solar panel. 

Pros—

• Optimization of energy conversion at the panel
• Appropriate for complex roof/system designs, especially where shading may occur. 
• Helps energy production with smaller systems by maximizing energy at the panel level
• Micro-inverters enable single panel monitoring and data collection.
• They keep power production at a maximum, even with shading.
• Unlike string inverters, a poorly performing panel will not impact the energy production of other panels. 
• Micro-inverters have more extended warranties—generally 25-years. 

Cons—

• More expensive than a string inverter and generally more costly than power optimizers. 
• Harder to access for repairs as they are installed on the roof and under the panel.

NOTE: The initial cost of microinverters may be offset by the fact that their warranty matches the solar panel at 25-years. String inverters have a warranty that ranges by brand from 10-15 years. 

Hybrid Inverter Systems

A hybrid solar power inverter system, also called a multi-mode inverter, is part of a solar array system with a battery backup system. The hybrid inverter can convert energy from the array and the battery system or the grid before that energy becomes available to the home. 

Pros—

• Intelligent devices and programmable—they help manage energy availability based on programmable perimeters. For example, some can draw energy from the grid when grid energy is cheapest and use stored energy when grid energy is most expensive. They may also use power directly from the array and convert it from DC to AC when the array energy production is highest or when the storage system is full. 
• All-in-one system
• You can utilize it with or without a battery backup system.
• Ideal for array designs where expansion is likely or when a battery storage system may be added later. 
• Time-tested in off-grid systems. 

Cons—

• Can limit system design in comparison to microinverters
• Can reduce energy efficiency in contrast to inverters that are dedicated. 

NOTE: Ideal for situations where energy options come from multiple sources—array, batteries, grid. It can also be ideal in cases where you plan to add a battery backup. 

	Standard String Inverters	Optimized String Inverters	Micro Inverters	Hybrid Inverter Systems
Price	Usually cheapest	More expensive than standard string inverters and more economical than microinverters	Slightly more expensive than optimizers but not by much.	The most expensive inverter but it does more.
Warranty	10-15 years by brand—may not cover labor	25-years—may not include labor	25-years	5-12 years
Ease of Maintenance	Generally not repairable just replaceable. Easy access due to location.	Failure can mean panel replacement, or on-site repairs	Difficult due to installation under panels	Easily accessible
Shade Mitigation	The output of one panel can limit the output of the entire string.	Helps optimize power production on complex array designs, including shade.	Excellent as energy is optimized at the panel	Does not help with panel efficiency
Aesthetics	Installed near the power meter	Installed under the panel	Good, installation makes then invisible.	Good. Installed inside or near y our power meter.

Which type of solar power inverters should I choose?

When it comes to choosing a solar inverter, there is no honest blanket answer. Which one is best for your home or business? That depends on a few factors:

1. How complex is your solar array design? If your solar array has many north-facing solar panels, you will likely have some shade mitigation issues. Those north-facing panels will receive less sunlight than panels with southern exposure. That level of complexity rules out the standard string inverter as those northern panels will reduce the overall power production of the entire string of panels. A good bet for this situation would be either the optimized string inverter or, better yet are microinverters.
2. Is your system grid-tied? Depending on how the system ties to the grid, you may be better off with a hybrid inverter that can handle different types of energy input at the same time. Suppose the system has a designated switch that shuts off access to the grid while the solar array is functioning. In that case, you might be okay with micro-inverters, power optimizer string inverters, or even a standard string inverter—providing there is not a battery backup system tied to the array. 
3. Does the array include batter storage? If so, then a hybrid inverter is the best option, especially if the system is also grid-tied. The hybrid inverter is most capable of dealing with different types of energy at the same time. 
4. Warranty—How long is the Inverter's warranty. If you have to replace the inverter every five years, then the lower cost may not benefit you, and an inverter with a more expensive initial cost may be more cost-efficient. Also important is what the warranty covers. Parts, labor, travel, replacement inverter, are all factors that enter into the cost of diagnosing, repairing, or replacing an inverter. The best inverter may differentiate itself with only the components of its warranty. 
5. Wave Type—Pure sine wave inverters prepare the energy for your home that is close to what your home receives from the grid. A modified sine wave inverter can be damaging to appliances and electronics. While the modified sine wave inverter is generally cheaper, it may cost you more if you have to replace appliances sooner. 
6. Efficiency—is the amount of energy the inverter can supply. Ideally, you want an inverter that is 96% efficient or higher. 

Bonus: Solar Inverter Oversizing vs. Undersizing

Oversizing means that the inverter can handle more energy transference and conversion than the solar array can produce. The inverter capabilities are more significant than the solar array maximum energy production rating. Undersizing means that the solar array can make more energy than the inverter can handle. Extra power is lost or clipped. 

There is only one situation where you would want oversizing to occur, and that is when a pre-planned expansion of the solar array will occur. Oversizing in that situation saves the owner money by not paying extra labor and buying a bigger inverter during the expansion. 

Undersizing can be beneficial if the environmental impact of location, weather, and usage means the solar array will rarely hit its top energy production. There are only a few days when too much energy is produced for the inverter to handle, making buying a larger inverter a waste of money. 

Generally, you want the efficiency rating of the inverter to match the efficiency rating of the solar array. 

The Wrap Up

Choosing a solar power inverter is a big decision. Much of the information about selecting an inverter has to do with the challenges that a solar array on your roof would have. For example, is there shade, or is there not sufficient south-facing panels, etc. Other questions, such as how much energy you need and how much space you have for solar, also impact which inverter is best for your property. 

This article explains what solar power inverters are, how they work, and the situations where they excel, along with why one type may not be a good fit for your project. It is likely you still have questions. If so, reach out to us or leave a comment below.