Comparing Micro inverters with Central inverters

Introduction

The basic function of an inverter is to convert the direct current generated by solar panels into alternating current.

It performs operational functions more than any other PV system component. It is the most complicated component of a home's solar system and it's also the first to fail because inverters include so many electronic elements and perform so many functions.

Inverters must shut down if an electrical arc occurs, which can be caused by system aging and material degradation. So, the selection of inverter to convert solar power into usable electricity for our daily use is very vital.

Micro Inverters

A solar micro-inverter is a type of inverter that is designed to work with just one PV module. Each panel's direct current output is converted to alternating current by the micro-inverter.

Micro-inverters are ideal for shaded roofs since the shadow that affects one panel has no effect on the other panels that are not shaded. The output of each panel is aggregated and routed to the grid or battery bank, and each micro-inverter turns DC into AC current.

Solar micro-inverter has the following advantages:

• Independent functioning of each panel
• Single-panel power optimization,
• Plug-and-play installation
• Reduced costs with system design
• Enhanced installation and fire safety

Central Inverter

A central inverter is a high-capacity inverter built for big commercial or utility-scale solar installations. They can be constructed for indoor or outdoor use and range in power from roughly 50kW to over 1MW. They are typically floor or ground-mounted.

Solar panels are connected in large arrays to a single combiner box, from which all DC power is sent to the central inverter.

The solar central inverter has the following advantages:

• Ability to produce much higher power
• Lower costs
• They are placed in protective environments, so they have a high level of reliability.

Micro Inverters Vs Central Inverter

As we have studied the inverter is the brain of the solar system and plays an instrumental role to convert the direct current (DC) to alternating current (AC) for usage in our home.

We can do a comparison between the microinverter and central inverter as follow.

• Working Principle

In micro-inverters, each solar panel has a micro-inverter attached to the back and panels work as independent units means if we have 10 solar panels, we also have 10 micro-inverters while central inverters work with the entire solar system to convert DC electricity to AC power for all of the panels at the same time means that complete solar system is powered by a single central inverter.

• Location

The inverter in a microsystem is close to the solar panels and any power loss between the panels and the inverter is small while central inverters are placed distant from your solar panels, there is a lower danger of power loss.

• Shading

In a central inverter system, performance is hampered by shade or fallen leaves on one panel and every other panel will operate at a reduced capacity while the ability of each panel to work independently using microinverters, on the other hand, allows for greater energy production and efficiency, especially when only a few panels are in the shade or covered by snow.

• Durability

Micro-inverters are placed directly on panels and they have to endure the same weather conditions that your solar system does while central inverters may operate in a temperature-controlled environment and are less susceptible to weather-related failure. So, central inverters have more durability than micro-inverters.

• Efficiency

Microinverter gives 5-15% more production over central inverters since each panel can work independently. This is frequently due to their supremacy in the aforementioned shading scenarios.

• Life Span 

Microinverters have more than 25-year life while central inverters have a lifespan of about 10-15 years.

• Suitability

Microinverters are more suitable for use in homes while central inverters are more suitable for commercial uses. Although the cost of the microinverters is high they require fewer maintenance issues as compared to the central inverters. 

• Maintenance

Microinverters have less maintenance as compared to central inverters. It is a lot easier to detect problems in microinverters while maintenance on a central inverter, solar energy technicians have to diagnose and repair a panel resulting increase in maintenance costs.

• Safety

The conversion from DC to AC occurs at the solar panel level with individual micro-inverters.

This ensures that the roof's energy remains low-voltage. Central inverters, on the other hand, combine high-voltage DC current and transport it across the roof, increasing the risk of an electrical fire.

• Future Upgrade  

If you want to add more panels to an existing array, it's considerably easier to expand a microinverter system. One by one, solar panels and micro-inverters can be added.

However, adding to a system with central inverters is more expensive and complicated because all extra panels must be linked to a separate inverter.

• System uptime

If one inverter on a central inverter fails, the entire system fails. This is not the case with microinverter systems.

One panel can be turned off while the rest of your array continues to produce energy. Overall, this results in significantly increased system uptime for micro inverter-powered solar arrays.

• Cost

A micro inverter costs about $0.34 per watt, but a central inverter costs about $0.13 per watt. So, Microinverters have a slightly greater up-front cost than central inverters.

So, the selection of inverter to converts solar power into usable electricity for our daily use is very important. We can summarize the above discussion as follow.

Comparison of parameters 

We can compare microinverter and central inverter for the important parameter as follow.

Selection of Suitable Inverter

As we know that The function of a solar inverter is to convert the fluctuating direct current (DC) output generated by PV solar panels into alternating current (AC), which can either be sent into a commercial electrical grid or used by a local, off-grid electrical network.

So, the selection of a suitable inverter for the right purpose is very important.

The following points must be kept in mind while selecting the solar inverter.

• Stability of output voltage

The steady-state output voltage variation should not exceed 5% of the rated value.

• Rated output frequency

Under typical working conditions, the output frequency of solar inverters should be a relatively constant value, which is generally 50Hz, with a fluctuation of less than 1%.

• Load power factor

Sine wave inverters' load power factor varies between 0.7 and 0.9, with a rated value of 0.9.

• Solar inverter efficiency

The nominal efficiency of conventional inverters ranges from 80% to 95%.

• Rated output current or rated output capacity

When the output power factor is 1, the inverter's rated output capacity is the product of the rated output voltage and the rated output current.

• Waveform distortion of output voltage

The output voltage should have a total waveform distortion of no more than 5%.

• Protection measures

In order to deal with numerous abnormal conditions in actual use, a good solar inverter should also have complete protective functions or measures.

• Noise

Solar inverters should not produce more than 80 decibels of noise in normal operation.

Size of the Inverter

The most significant element in selecting the optimum size for the solar inverter is the size of the solar array. Because solar inverter transforms DC electricity from the array, it must be able to manage the entire amount of power generated by the array.

As a general guideline, the size of the inverter should be comparable to the DC rating of the solar panel system; for example, if we are building a 5 kW system, the proposed inverter should be around 5000 W, plus or minus a little percentage.

Conclusion

Microinverter and central inverter both are used extensively to convert the direct current (DC) into alternating current (AC). Both inverters have their own merit and demerit according to the size and capacity of the solar system.

Microgrid inverters are used mostly for domestic purposes with having less maintenance cost, greater efficiency and safety, and future upgrades while central inverters are used mostly for domestic purposes having less cost, greater durability, and reliability.