The Main Kinds of Solar Power Inverters: String Inverter, Power Optimizer, and Microinverter
When you are thinking of solar energy, it is good to explore the choices. Finding an inverter can be a daunting task. There are many kinds of inverters, but what are the main differences between the most common inverters we see used in solar today? The largest key difference is how the inverters handle the power on the solar panels. The three most common configurations are:
- String Inverter
- Power Optimizer
Even though the goal is the same, each one of these inverter configurations has individual benefits and applications. The main goal of harvesting sunlight for solar is to create power. The small yellow dwarf star also called our sun creates energy in DC power (direct current), but the power we use in our homes and businesses is AC (alternating current). Since we need to make AC power, we can “invert” the power into AC. This is where the three kinds of solar power inverters come into play.
The string inverter used to be the most common method of solar power control. This technology arranges the panels in a “string” of one panel connected to the panel next to it. Because of this, there is less equipment on the roof. This means fewer materials and less complication. String inverters also cost less and this is why large-scale power companies use these kinds of inverters to power the grid. The inverter is responsible for regulating the DC on the rooftop or panel area. The DC is then brought down a pipe to a central inverter that will change the power to be usable.
Since the inverter does not know what every single panel is doing on the roof - it can only take what the “string” of solar panels will give. Since every panel cannot be regulated in a string such as this, there are inefficiencies in the panels due to factors such as snow, dirt, or shading. This creates small dead zones inside the loop of the string, that cause power loss. Since the inverter cannot compensate for any of those factors it loses potential power that would be coming from the solar panel array.
A string inverter also cannot monitor each panel on the roof, which means that if any panels are underperforming or broken, there is virtually no way to tell which panel is causing your system issues. All you see is that the overall system is less efficient, or that your utility bill increases.
Because of these various reasons we usually only see these inverters on older installations before the newer technology became available, or in large-scale commercial applications, such as a ground mount solar field with no shading at all, facing directly south, and perfect orientation. Usually, on a house, we do not have those perfect site conditions, so the ability to regulate and maximize DC on the solar panels is paramount.
Power optimizers introduce a new level of power control. Typically, each solar panel has its own optimizer. The power optimizer will regulate the DC voltage coming from the solar panels. The DC power is routed to a central inverter. The panels are still connected in a string, but there is now an added piece of hardware that can control how the panel received and distributed solar power.
This has a variety of benefits. If there are any shading effects due to clouds or trees, the optimizer can negate any harmful effects that shading has on the system’s production. It can do this by boosting the voltage of the affected solar panel, keeping the whole string producing at its peak efficiency.
There are also factors such as improper angle or orientation that the optimizers can negate to keep the system functioning at peak performance. We see this a lot when a home has multiple roof surfaces with different angles, pitches, and shading. The sun moves from east to west throughout the day, and this movement throughout the day affects where and how much sun different areas of the roof and solar system hit.
The optimizer keeps the system operating within the parameters and ensures a clean power flow from all the solar panels throughout the whole day. Typically these systems will “wake up” sooner and “sleep” later. As soon as the sun comes up the system will try to balance any light it can harvest and it will start producing as soon as it detects enough sunlight.
Another benefit of power optimizers is the ability to offer panel-level monitoring. The feature allows the owner of the system to view production and data from any panel in the system, it also allows the installer to perform accurate diagnostics of the system to ensure every panel is performing as it should. These solar optimizers are highly popular and work well for a variety of applications.
The final kind of system is the Microinverter. In many ways this functions as an optimizer system, regulating the available system power and having a corresponding piece of hardware near the panel. However, instead of regulating the DC sunlight voltage in a string and then down to a central inverter, the microinverter converts the sunlight DC to AC right there at the solar panel. This frees up any space if there are restrictions at the home, and gets rid of the central inverter.
This kind of control has positive benefits such as the ability to monitor the panels, much like the power optimizer system. Every panel will have a corresponding microinverter and will report back to the respective monitoring platform. This allows for diagnostics and ease of any potential repairs in the future. Another benefit of doing the AC conversion on the roof is that there is no varying of different power levels in the system because of shading or panel orientation. Each panel will produce the power individually and negates issues due to other neighboring panels' inefficiency if there are any. These types of systems have benefits where AC power is needed and where there are multiple areas of solar arrays.
What’s the Best Inverter?
String inverters are almost always a bad idea, but at the end of the day, microinverters or optimizers are a personal preference. They both perform. We prefer optimizers for four reasons:
- Getting the most out of each panel. The more shade, the more this matters.
- Power optimizers have historically fewer maintenance issues than microinverters.
- They are easier to service as the most sophisticated pieces of equipment are consolidated at the ground level instead of being distributed throughout the roof. With AC power on the roof, the cabling is more complicated to service in the future.
- With microinverters converting at 97% efficiency and power optimizers converting at 99% efficiency, there is a nice power gain. 2% does seem like much, but over the 25-year warranty period, it adds up.