May 31, 2024

String Inverter vs Microinverter: What installers need to know

image of 3 inverters with the larger central inverter attached to four wires

When you’re installing solar panels there are two types of inverters you will need to choose from. These are microinverters and string inverters.

Both have their place, but choosing which one to recommend will vary depending on your customer's particular requirements.

To help you out we’ve broken down the pros and cons of each converter, with a look at the use cases for each type.

What is a string inverter?

What is a microinverter?

Are microinverters better than string inverters?

What are the disadvantages of microinverters?

How expensive are microinverters vs string inverters?

What is the failure rate of microinverters?

What is the failure rate of string inverters?

What is the life expectancy of micro vs string inverters?

How easy are inverters to install?

What is a string inverter?

String inverters are the most basic type of inverter.

With this setup, the solar panels are connected in a series and operate as a single unit.

The combined DC current that is produced is passed through the string converter, turning it into an AC current.

An AC current is used by the mains electrical grid as it allows for more efficient energy transportation, hence why the inverter is needed to convert this current.

The string converter is situated away from the solar panels near a main service panel or electric meter. The current produced from each solar panel is combined into a single stream as it passes through the converter.

This is indicated by the name ‘String inverter’ as the device is designed to handle a series (or "string") of photovoltaic (PV) solar panels connected in a sequence.

electrical box containing many wires connected up

What is a microinverter?

Microinverters get their name due to their much smaller size.

These converters are attached directly to individual solar panels, meaning that each panel sends its own current through each converter.

Unlike string converters that receive a combined current from a cluster of panels, microinverters individually receive a separate current from each individual panel.

This means these inverters are much smaller than their string counterparts and have an increased efficiency.

Are microinverters better than string inverters?

Microinverters and string inverters serve slightly different purposes, so depending on what you’re after, one option might be the better choice.

When it comes to efficiency across a whole set of solar panels, microinverters are better than string inverters. This is because microinverters are connected to individual panels meaning they can process different currents simultaneously.

If you use a string inverter the current is taken uniformly across all the panels. This means if one panel experiences a drop in efficiency, all the panels will drop to this panel's level.

So if you get any dirt on a panel or a shadow falls across one, they are all affected. If there is a mechanical issue in one, all will fail. Microinverters don’t have this problem.

What are the disadvantages of microinverters?

Despite the benefits, there are some scenarios in which string inverters are the better choice.

When it comes to high-voltage systems, string inverters are better. This is because they are far more robust and can better handle powerful currents and transfer them at greater efficiency.

Generally speaking, microinverters need more regular maintenance.  While they are easier to maintain individually, string inverters (in ideal conditions) are less likely to require frequent repairs.

Due to the fact microinverters are situated outside (unlike string inverters that are installed in a shed, cellar or other sheltered space) they are exposed to the elements increasing the risk of damage.

animated english house with a roof with solar panels on it

Microinverters also have a much higher upfront installation cost and are more complex to install (which further adds to the cost).

One notable disadvantage is the effect of heat degradation.

As microinverters are fitted directly to each solar panel, this means they are exposed to direct sunlight and can get very hot. This can cause damage and reduce efficiency.

To combat this, many microinverters use a feature called "derating," where the inverter reduces its power output to prevent overheating. While this protects the inverter, it also means less energy is converted during peak periods.

How expensive are microinverters vs string inverters?

As a general rule, the upfront cost of microinverters is higher as individual inverters need to be added to each solar panel, while a string inverter can handle multiple solar panels at once.

This also makes installing microinverters a more time-consuming process. As an installer, you will need to charge more for the longer more technical installation process required.

However, over the duration of an inverter system's lifespan, microinverters are more cost-effective. This is because they are far easier to maintain, requiring the replacement of one inverter rather than having to troubleshoot a whole string of panels.

Diagnosing issues is also far easier with microinverters as they provide advanced monitoring capabilities and real-time data that can allow a person to isolate an issue far more quickly.

Furthermore, microinverters typically generate more power, as each panel works independently, rather than changes in conditions affecting the whole system.

To give you an idea of how to advise potential customers, here is a cost breakdown.

Feature comparison

Feature Micro Inverters String Inverters
Initial Cost per Watt $0.30 - $0.60 $0.15 - $0.25
Total Initial Cost (5 kW System) $1,500 - $3,000 $750 - $1,250
Installation Complexity Higher due to individual inverters per panel Lower, fewer inverters to install
Maintenance and Reliability Low maintenance (failure of one doesn't affect others) Moderate (failure impacts all panels on the string)
Warranty Up to 25 years 10 - 15 years
System Efficiency Higher (panel-level optimization) Lower (impacted by weakest panel)
Performance in Shaded Conditions Excellent Poor to Moderate
Panel-Level Monitoring Yes No
Potential Energy Yield Higher Lower
Best Use Case Complex installations, shading issues, varying orientations Uniform sunlight, identical orientation

Example Cost Breakdown

Component Micro Inverters String Inverters
Inverter Cost (5 kW System) $1,750 (average of range) $1,000 (average of range)
Installation Cost $1,000 (higher due to complexity) $700 (simpler installation)
Total Initial Investment $2,750 $1,700

Total Cost and Potential Savings Over 25 Years

Factor Micro Inverters String Inverters
Annual Energy Production (5 kW system) 6,000 kWh (standard) + 10% = 6,600 kWh 6,000 kWh
Annual Savings (at $0.12/kWh) $792 $720
Total Savings Over 25 Years $19,800 $18,000

Are microinverters worth the extra money?

So are microinverters worth the extra money? In most cases, yes.

Although the upfront cost of installing microinverters is higher, over their 25-year lifespan, these costs are more than made up for and can save a customer up to 2 grand compared with the string alternative.

In some instances, if the solar panels are installed in a non-shaded area, with easy access and consistent weather then string inverters might be worth considering, but in most instances, micro is the best investment.

However, do bear in mind that if you’re looking to make the switch from an existing string system to micro, then it’s likely that making the change won’t be worthwhile. Although microinverters tend to be the smarter upfront investment the cost of switching isn’t cost effective.

What is the failure rate of microinverters?

The failure rate of any given microinverter will vary from system to system and depending on the brand.

In general, the failure rate of microinverters is between 0.1% and 2% however there is evidence to support failure rates as low as 0.05%

Based on this percentage, if you consider this failure rate across the whole system of inverters rather than individually, then the failure rate equates to 1 failure per 100 systems, so there is a 1 in 100 chance of failure.

Furthermore, given the relatively straightforward nature of a micro repair, microinverters make for a reliable solution.

What is the failure rate of string inverters?

String inverters typically have a failure rate of around 0.5 to 2%, however, there is evidence that these failures can massively increase, reaching as much as 34.3% after 15 years.

That being said, when you equate failure rates to issues per system, a 0.55 failure rate (which is typical) will produce only one failure for every 200-string inverters installed.

As an installer, if you compare this with microinverters, then you can expect to have to perform much more regular maintenance jobs for the micro rather than the string inverters you install.

However, it’s important to note that replacing a single microinverter is far more straightforward than repairing a whole string inverter system.

What is the life expectancy of micro vs string inverters?

Microinverters generally have a longer life expectancy compared to string inverters, with typical ranges of 20 to 25 years for microinverters versus 10 to 15 years for string inverters.

This extended lifespan is supported by longer warranties offered by microinverter manufacturers.

However, achieving these life expectancies requires careful attention to installation environments and regular maintenance for both types of inverters.

How easy are inverters to install?

If you’re looking to get into solar installations you will probably be interested to know how difficult it is to install the two different types of inverters.

When it comes to maintenance the micro option is generally considered to be more straightforward. This is because in most cases you just need to unplug a single small inverter and replace it, rather than having to replace the whole string system.

a wavy haired young male installer fitting wires to a solar panel

The advantage string inverters have is that they are typically located on the ground, whereas the micro inverters are on the panels, usually on the roof. This means with the micro option you’re always going to have to get on the roof to perform the fix, which isn’t always the case with the string.

The same applies in the initial installation process. With the micro option, you have to install each converter to each individual solar panel which involves more wiring and more time spent on the roof. In general, micros take longer altogether.

On the other hand, string inverters require more careful planning to deliver an efficient string design whereas micro inverters are simpler and work independently.

Overall string inverters are probably the easier initial installation, taking less time and requiring less time on the roof but micro inverters are generally easier to maintain.