String Inverters vs. Microinverters vs. Power Optimizers
If you are considering a solar panel system for your home, one of the key decisions you may make is selecting what type of inverter to install. Let’s examine the types of inverter options that are currently available to you for your solar energy system.
THE INVERTER IS A KEY PART OF YOUR SOLAR SYSTEM
As we’ve explained elsewhere, solar panel installations typically consist of 4 key components: solar panels, inverters, racking/mounting systems and performance monitoring systems. The solar panels generate direct current (DC) electricity, which is converted into alternating current (AC) electricity by the inverter. AC electricity is what your appliances and the utility grid use. After the panels themselves, inverters are arguably the most important equipment in your solar power system.
YOUR INVERTER OPTIONS
When shopping around for a solar system, there are essentially three different inverter technology options for you to choose from:
- Centralized inverters (also known as string inverters),
- Microinverters, and
- Power optimizers.
(Microinverters and power optimizers are collectively referred to as “Module-Level Power Electronics” or MLPE.)
Of the three, string inverters (or central inverters) are by far the most commonly deployed option globally, comprising the vast majority of the world’s inverter market. However, MLPE technologies are rapidly gaining popularity and market share as their costs have come down. Because of the changes they are bringing to the inverter industry, Navigant Research has described them as ‘disruptive’ to the status quo.
Interestingly, research by GTM Research found that over half of all residential solar systems installed in the U.S. in early 2014 used MLPE technologies – despite the clear dominance of string inverters internationally.
These technologies are explained in the sections below.
KEY TAKEAWAYS: STRING INVERTERS, MICROINVERTERS & POWER OPTIMIZERS
- Inverters are a crucial part of any solar panel system; they convert the DC electricity that your solar panels produce into appliance-friendly AC electricity.
- The three main inverter options available for homes residential and commercial solar installations are string inverters, microinverters and power optimizers.
- String inverters cost the least of the three options. They are suitable for installations where panels are installed perfectly – on a single plane and not shaded during any part of the day.
- Microinverters and power optimizers are more expensive, but are suitable for installations where one or more panels may be shaded, or where panels are installed on multiple planes and/or facing different directions.
- Microinverters and power optimizers allow you to monitor the power production of each individual panel.
- Because MLPE technologies are more efficient than string inverters, a system that uses microinverters or power optimizers will produce slightly more power than a similar system with a string inverter. This is especially true for shaded or difficult roofs, but even on the ‘perfect’ roof, a system that uses MLPE equipment will usually produce slightly more power than one with a string inverter. You should carefully consider whether the increase in electricity production is worth the additional cost.
CENTRALIZED STRING INVERTERS
String inverters are currently the most cost-effective inverter option available in the US. Internationally, there are a larger number of companies that manufacture string inverters. Solar installation companies will generally offer you a system that uses a string inverter if your roof is not shaded at any point during the day and does not face in multiple directions (like a gabled roof).
How do string inverters work?
Your solar panels are arranged into ‘strings’, which feed the power they produce into a single inverter. The inverter then transforms the power produced by the panels into appliance-friendly AC electricity.
WHAT IS A “STRING”?
For example, if you install 20 solar panels, the panels may be installed into 4 groups of 5 panels each. The group of 5 panels is called a “string”. Panels in a string are connected in parallel to each other and then connected directly to the Inverter.
String inverter technology has been used for decades. It is a tried-and-true technology, but are not suitable for certain types of installations. If even one or more of your solar panels are likely to be shaded during any part of the day, the power output from that entire string would be reduced to its level. (Imagine a hose with a kink in it – the flow of water is slowed). Similarly, if your solar panels are installed on a roof with multiple planes and/or facing different directions, a string inverter may not be a good choice.
One of the most common reasons for a panel to produce less power or stop producing power altogether is shading from nearby objects. If your roof is prone to shading anytime during the day or in certain seasons, you could either seek to remove the source of the shade (e.g. cutting down a tree) or installing the panels where they will not be prone to shading.
Who manufactures string inverters?
There are a number of companies that manufacture string inverters. Some of the biggest names are SMA, ABB / Power-One and Fronius. You learn more about inverter manufacturers in our Supplier Search.
WHAT’S A SMART MODULE?
Increasingly, microinverter and power optimizer manufacturers are partnering with solar panel manufacturers to create ‘Smart Modules’. Simply put, a Smart Module is a solar panel with a piece of MLPE equipment integrated into it. This simplifies installation and cuts down on labor costs for installers – and should ultimately deliver more value to you as the system owner. Many of the world’s biggest panel manufacturers now have Smart Module options available, including Trina Solar, ET Solar, ReneSola and SunPower.
MICROINVERTERS
Microinverters are rapidly gaining popularity, particularly for residential solar systems. At the moment microinverters tend to be the most expensive inverter option, but as they become more commonplace it is anticipated that their cost will come down.
How do microinverters work?
Microinverters convert the DC electricity from your solar panels into AC at the panel level (i.e. on your roof), with no need for a separate central inverter. If your system uses microinverters, you will have one microinverter installed at each panel. In many cases the microinverters are integrated into the solar panel itself, but they may also be mounted next to the panel on the system’s mounting system.
One of the major advantages of microinverters is that they mitigate the negative impacts of partial or complete shading. Because the DC-AC electricity conversion takes place at each panel, there is no ‘bottleneck’ when one panel produces less or no electricity.
Microinverters also allow you to monitor the performance of individual solar panels.
Who manufactures microinverters?
The dominant player in the microinverter industry at the time of writing this article is Enphase. A number of other companies also manufacture microinverters, including SolarBridge (recently acquired by panel manufacturer SunPower), Enecsys and APS. String inverter manufacturer SMA also has its own line of microinverters. (You can see a more complete list in our article about microinverter and power optimizer options.)
POWER OPTIMIZERS
The popularity of power optimizers has also grown rapidly in recent years. Power optimizers offer many of the same benefits as microinverters, but tend to be slightly less expensive. For this reason, a solar system using power optimizers can be seen as a compromise between one using microinverters and one using a string inverter.
How do power optimizers work?
Like microinverters, power optimizers are located at each panel, usually integrated into the panels themselves. However, instead of converting the DC electricity to AC electricity then and there, they instead ‘condition’ the DC electricity before sending it to a central inverter. This approach results in higher overall efficiency levels than with a conventional string inverter.
Similar to microinverters, the main advantages of power optimizers are mitigation of partial panel shading impacts and panel-level monitoring. However, solar systems that use optimizers are on the whole more affordable than those that use microinverters.
Who manufactures power optimizers?
There are currently two major players in the power optimizer market: SolarEdge and Tigo Energy. SolarEdge’s technology is packaged as a system with a SolarEdge brand central inverter, while Tigo optimizers are compatible with third party inverters like SMA and Fronius.
SOLAR FUN FACT
The sun is our most dependable source of energy! Scientists predict its energy output will remain fairly consistent for the next 50,000 years.
(source: NREL)
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