Solar panels produce vast amounts of electricity. But none of it would be very useful to the average American without an invertor on solar panels. Since solar panels are a big investment, you’ll want to make sure you have the best solar panel inverter for your home energy system.
Solar panels produce DC, or direct current power. This is good for things like LED lights, motors, and other low-power devices. However, most of the appliances and electronics used in a U.S. home run off AC electricity—or alternating current. In order for the power created by solar panels to be usable in most day-to-day activities, it has to be converted by an inverter first.
How Do Solar Panel Inverters Work?
Here are the four different jobs solar panel inverters do to create a highly functional solar power system for your home:
1. Solar Power Inversion
The very first thing you need to know if you’re wondering “what is a solar inverter?” is that they invert DC power so that it functions as AC power (the type that U.S. homes use to operate). To do this, the device sends the power stream through a set of physical switches—usually MOSFET or IGBTs—and the power takes on the same alternating frequency as AC power used around the country.
2. Tracking Maximum Solar Power
During operation, a solar inverter keeps track of the maximum power produced by the panels. This is to boost the system’s efficiency. Keep in mind that the maximum is constantly changing, thanks to varying temperature and sunlight conditions.
3. Solar Power Grid Detection
An inverter on a solar panel also has sensors to detect when the power grid is attached to a home’s power lines versus when it is not. This is a safety mechanism to help protect the power company. When the power grid isn’t connected properly, the inverter won’t feed any power to the home so that it does not throw power at transformers and cause unsafe conditions for utility workers.
4. Monitoring Solar Panel Conditions
Many inverters on a solar panel also serve as a tracker for that solar panel. They keep track of the amount of power produced by the panels throughout the day. This can help homeowners figure out when one panel is underperforming so they can make any necessary corrections. Monitoring conditions can also help homeowners understand if selling excess electricity from solar panels is a viable option.
What’s the Difference Between Types of Solar Inverters?
There are two different types of solar inverters—the string inverter and the micro-inverter. Each type has its advantages — but when you pick between one or the other, you’re really choosing between cost and efficiency. Here are the different types of solar panel inverters:
1. String Inverters
When using a string inverter to convert your solar panel power to usable power for your home, only a single inverter is needed for a cluster of panels. Many people will only get one or two string inverters for their entire home – but some may require more. There are some benefits to setting up string inverters, but there are also some downsides as well.
- Less Maintenance
- Very reliable
- Not good for shady roofs
- Not the best choice for flat roofs
- Can cause larger power outputs if one fails
Pros of Solar String Inverters
The main benefit of a string inverter setup is that it’s the most cost-effective way to convert DC energy to AC energy. For instance, if you have 20 solar panels, you’ll likely only need 4 or 5 string inverters to get the job done. Compared to the 20 micro-inverters needed, it’s much more affordable. String inverters are also known for their reliability, and will require less maintenance than micro-inverters since there are less of them to worry about.
Cons of Solar String Inverters
There are some downsides to string inverters, however. They could be a deal breaker for you. The first and most prominent downside is that the lowest producing panel in the string is equal to the maximum amount of energy every panel will supply. That means if one of the panels is under shade, all of the other panels will produce as if they, too, are in shade. That’s why many homes with shade issues do not use string inverters. Even for flat roofs without any shade, there will still be a lower efficiency level from the system than there would be with micro-inverters.
Another major downside of string inverters is that if one stops functioning properly, more power output will be lost than with micro-inverters. A single failure could stop your system from doing its job properly.
2. Solar Micro-Inverters
A solar micro-inverter is a compact inverter that is attached directly to a single solar panel. Often the inverter is built into the panel on the mounting system, or attached to the back of the panel. There is a single inverter for each solar panel used in the array. This allows AC power to be produced right at each panel, and then pooled into one power line for distribution.
- Very power-efficient
- Can quickly spot under-producing panels
- Good for shady roofs
- Significantly more expensive than string inverters
- Require more maintenance
Pros of Solar Micro-inverters
Micro-inverters have many benefits — we’ll start with the most dramatic one first. They offer improved power efficiency, and also help a solar array produce more usable power than an array connected to string inverters. This occurs regardless of the roof’s shape, design, or location.
It’s also much easier to keep an eye on specific solar panels, since each one has its own inverter. This will allow you to see which panels are under-producing at a glance. It also means that maintenance will be easier to take care of on a panel-by-panel basis.
Micro-inverters tend to be more reliable than string inverters overall. Not in the sense that they break down less often than string inverters, but instead, they affect the array of solar panels less. If one micro-inverter breaks, it only puts one panel out of commission. If a string inverter breaks, it can stop five or more panels from doing their job.
Micro-inverters are much more effective when you have a roof that is not under optimal conditions. Whether you have shade from trees, a split roof that faces off in a few different directions, or you simply don’t have much south-facing roofline available — a micro-inverter setup can help you avoid power bottlenecks and efficiency loss that you would experience with a string inverter.
Cons of Solar Micro-Inverters
Micro-inverters have a few downsides to them, as well. The biggest drawback is the price. Micro-inverters are significantly more expensive to purchase and install. They also require more maintenance in general than string inverters do since there are more of them in place.
3. Power Optimizer Inverters
Power optimizers are an improvement compared to standard string inverters. They help create a more affordable solution than micro-inverters, as well, while still being ideal for less than optimal roofs with multiple orientations and/or shade.
- Easy to track each panel's performance
- Good for battery storage
- Good for shady roofs
- More expensive than string inverters
- Few available manufacturers
Pros of Power Optimizers
Each of your solar panels will have a power optimizer affixed to the back, which will help track each panel’s performance in real time. This helps adjust the DC power from the panel without actually converting it to AC, which means your whole system works more efficiently. This is an especially great option if you are storing DC power in a battery.
A power optimizer also splits up the solar panels more so they are not all connected in a series. If one of them is affected by a shadow, all the other panels will not have reduced solar output as a result. Power optimizers help boost efficiency of a string inverter setup, while being much more affordable than micro-inverters are.
Cons of Power Optimizers
Power optimizers are relatively new technology. That means two big drawbacks: price and limited manufacturers. Though this option is still more affordable than micro-inverters, you can expect it to add at least several hundred dollars to your final installation costs. Finding an installer in your area may also be tricky. If you do not have a challenging roof with shade or orientation issues to contend with, you should carefully consider if the benefits outweigh the drawbacks for your home.
Energy Efficiency & Solar Panel Inverters
Converting from DC to AC current is always going to waste some power. Most solar panel calculations conclude you will be able to use around 85% of the power, at most. The amount of power that is wasted during the conversion process depends on the efficiency of the inverter.
While it’s important to consider the different types of solar inverters and their purposes, you also have to consider the efficiency of the unit itself. You can have different efficiencies in a range of string inverters and micro-inverters. If you want the most power production from your panels, pay attention to how efficient each of the different inverters is in particular.
What Size Solar Inverter Do I Need?
Solar inverters are rated to handle different power loads. This means you need to choose an inverter that matches your solar array.
Consider the size of the solar array you’re planning to install. Add up the total power that all the cells will produce at peak. Then, pick a solar panel inverter that can handle that power with no problem.
When choosing a solar panel inverter, consider the minimum number of watts it needs to function properly, as well as the maximum. It’s important to get something with a bit of wiggle room on either side. Choosing an inverter that can handle even more power is good if you think you might want to expand your array later on without having to invest in another inverter.