String Inverters, Micro Inverters and DC Optimizers

What's the difference between micro inverters, string inverters and DC Optimizers and which one is best for me? Its not as complicated as it may seem.  The answer to those questions depends heavily on your property's architecture, and available space.  Each inverter system has its advantages and disadvantages so lets break them down individually.  

First, what is an inverter?  An inverter is what alters the current coming out of the solar panels from DC (direct current) to AC (alternating current) so it can be used readily in residential/commercial properties. There are different types of inverters for different voltages - 240V for most residential solar applications, and 208V, 480V and 600V for commercial applications

There are 3 classes of inverters - micro inverters, string inverters, and a hybrid between the two, optimized string inverters

Micro Inverters

Micro inverters  are mounted beneath the solar panels on the roof. Typically there are one to four solar panels for every one inverter, depending on what make and model micro inverter. The solar industry is moving towards higher numbers of solar panels interconnected to each micro inverter. With micro inverters the electricity is inverted at the module-level and brought into the property as AC.

Key Advantages: 

• mounted on the roof out of sight
• no space required inside the property
• allow each module to operate independently, i.e shade on one solar panel will not hurt the entire array (or string within an array)
• solar panels can be mounted on different faces at various pitches/azimuths without production loss
• systems can be easily expanded over time
• often more cost-effective than string inverters, although this is site dependent
• Failure of one inverter will still allow partial system production

Micro inverters should be used when:

• partial shading of the property occurs regularly (i.e. from a chimney, or tree)
• system expansion is desired over time
• solar panels are to be mounted on multiple incongruent faces
• module level monitoring is desired

String Inverters

String inverters are significantly larger than their aptly named counterpart.  String inverters are roughly 3' tall x 1.5' wide x 1' deep or approximately the same size as a water cooler.  String inverters are typically mounted next to the electrical panel or can also be mounted outside.  The major downside to string inverters is that shading on one solar panel can negatively impact the entire array (or string within the array).  

Key Advantages:

• Most cost effective inverter system
• Scalability for large/commercial solar arrays

String inverters should be used when:

• solar modules are mounted at the same pitch/azimuth
• a large-scale project is desired
• an unobstructed ground-mounted solar array is desired

DC Optimizers

DC Optimizers are an additional component that work with string inverters to eliminate their key disadvantage - if shading occurs on a system with DC Optimizers, the remaining system outputs maximum power, similar to the effect of a micro inverter. Optimizers are mounted on the roof beneath each module, however, a string inverter is still required.

Key Advantages:

• Allow each module to operate independently, i.e shade on one solar panel will not hurt the entire array (or string within an array)
• Solar panels can be mounted on different faces at various angles without production loss

DC Optimizers should be used when:

• partial shading of the property occurs regularly (i.e. from a chimney, or tree)
• solar panels are to be mounted on multiple incongruent faces
• module level monitoring is desired

DC Optimizers sounds very similar to micro inverters - which is better?

The best option depends on your exact site. Different jurisdictions have different electrical code interpretations which may make one inverter system more favourable over another. The best system generally comes down to what will be the most cost-effective for your project.

The Cost

String inverters are the most cost effective, but are only applicable in select circumstances.  Because of string inverters' selectivity, micro inverters and DC optimizer systems are gaining in market share.  

Both micro inverters and DC optimizers are fairly comparable in cost.  If there is no room in your home or building for a string inverter, then micro may be more applicable.  Similarly, if you are planning a large installation, DC optimizers' scalability may give them the edge.  Deciding a clear cut winner between optimizers and micro inverts is a difficult task and one that can only be evaluated as the technology develops and inevitable corporate feuds ensue.

Additionally, the cost of various inverters' may be impacted by CE Code rule changes and international trade issues (such as tariffs on one country or technology type).

Part of what we do at Kuby Energy is regularly investigates what inverter systems are the best quality and value for the given social, political and economic conditions. It is in everyone's best interest to make sure you have the best product options at the lowest prices.