How do grid-tie inverters match the phase utility power?

By Matthew Joseph Nandirio •  Updated: 10/11/21 •  4 min read

Grid-tied inverters are increasingly becoming popular as many homeowners are adopting them for their solar systems. These systems produce a higher output voltage than the input. Consequently, they store the excess voltage for future use. Besides, these systems have a straightforward installation with fewer points of failure which explains why it is highly reliable.

Additionally, unlike the off-grid inverters, these devices do not require batteries, significantly simplifying their installation process. However, the lack of the battery brings and the fact that it communicates directly to the grid in a difference in their functionality. 

Therefore, there has been a lot of fuss on the internet on how the grid-inverters match the phase utility power. No one wants to risk purchasing an inverter that produces destructive voltages, which may damage the entire solar system. Let’s discuss that in detail.

How does the grid-tie inverter operate to match the phase utility power?

Just like other types of inverters, the grid-tie inverter should convert the direct current to alternating current. This type of inverter receives current with a square wave which has to be modified to pulse width modulated wave, which is also known as a sine wave. Its working rule is that 50% of the squared wave must be modified to 48% of the sine wave voltage.

However, unlike other types of inverters, the grid-tied inverter can communicate with the grid directly. Consequently, it can import power from the utility as well as export power to the utility. Although, the exported power must match the utility power. How does that happen?

Additionally, the grid-tie inverter has a control system that monitors the inverter frequency, voltage, and phase angle. The system continuously adjusts these parameters, ensuring that the inverter is well synchronized to the desired output. Consequently, the grid-tie inverters are not prone to destructive voltages, which is common inverters.

Apart from that, the grid-tie inverters operate within the NEC requirement. As a result, they are designed to disconnect from the grid automatically in case the grid utility goes down. In other words, grid-tie inverters shut down in a blackout event to prevent supplying bad energy or not matching the needed utility power.

Further, most of the manufacturers are embracing fixed unity power factor technology. This new construction technique ensures that the phase angle of the grid-tie inverter is approximately 1 degree of the AC power grid. Additionally, the output current and voltage are always lined up to the stated requirements with this technology.

Another thing that helps this inverter match the needed utility power is its onboard computer. This incorporated computer monitors the AC grid waveform and the output voltage and ensures that they correspond with the grid.

Besides that, the voltage impedance fluctuates and must be synchronized to match the needed impedance to drive the voltage. Correspondingly, the inverter voltage is significantly raised above the grid to sufficiently drive the current through the given source impedance at any given time to deal with the fluctuating impedance of the voltage.

How much does a grid-tied solar system cost?

Since the grid-tied solar system does not require a storage battery, its initial and installation cost is cheaper. Instead, it stores the excess electricity in a utility grid. Moreover, with its incorporated net metering, you will incur lesser monthly bills and has fewer points of failure for consistent power supply.

A typical grid-tied inverter solar system is estimated to cost between $11 200 and $14,419. However, their prices may vary significantly depending on the inverter brand, the state you live in, and the size of the system, among many other factors.

Below is a table showing the costs of the grid-tied inverters with their sizes. The average price is calculated after deducting the federal solar tax incentive in 2021.

System sizeAverage system cost*
As per 10/10/2021: price may differ

Final words

Grid-tied inverters are used in grid and local electric power generators such as wind turbines, solar panels. Moreover, most people are daily purchasing this equipment due to its affordable costs. Instead of using a battery, it stores the excess power in a grid, significantly lowering its prices.

As if that is not enough, these systems are highly reliable and have fewer points of failure, which significantly upgrades their lifespan.  However, these systems function differently from the typical inverters. For instance, they communicate directly to the grid. Moreover, an extra effort is needed to ensure that the current produced by this system matches the utility power,

One of the things that this system deploys to ensure that the grid inverter matches the utility power is monitoring all its outputs. Therefore, it ensures that the output voltages, impedance, and other things are synchronized with the system.

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Matthew Joseph Nandirio

Matthew Joseph Nandirio is the Founder of walkingsolar. After graduating from the University of Houston in 2002, matt started working as an electrical and electronic engineer for several multi-national solar energy companies. He has a wide range of experiences including solar system requirement analysis, planning, maintaining, debugging and even solar device development through research. He now shares his 20 years of expertise through his articles on the walkingsolar website. Further, he is also the author of two books on Solar Technology, “Solar Power for Villages” and “DIY Solar System for Dummies”.