The Complete Guide to Solar Inverters

It doesn’t matter whether you install an on-grid, off-grid, or hybrid residential solar power system. 

You need at least one solar inverter.

Depending on the size and type of solar panel array you choose, you may need more than one.

Inverters convert the solar power harvested by photovoltaic modules like solar panels into usable household electricity.

Some system topologies utilise storage inverters in addition to solar inverters.

But what exactly does a solar inverter do — and how does it work?

Read on to find out. 

What Is a Solar Inverter?

Solar inverters are an essential component in every residential photovoltaic system. 

PV modules — like solar panels— produce direct current DC electricity using the photovoltaic effect.  

However, virtually all home appliances and consumer electronic devices require alternating current (AC) electricity to start and run.

Similarly, utility grids worldwide primarily transmit and deliver AC electricity to homes and businesses. That’s why alternating current is commonly known as household electricity.

A solar inverter is built-in to compact off-grid electricity solutions like EcoFlow’s portable power stations. In larger residential and commercial solar balance of systems, the inverter may be a standalone component.

For example, EcoFlow DELTA Pro can provide up to 7.2 kilowatts (kW) of AC output (14.4kW surge power) and up to 3.2kW of solar charge input (12 x Ecoflow 400W rigid solar panels)

Photovoltaic modules capture photons from sunlight, convert them into DC electricity, and transmit them to a solar inverter through electrical cables. The inverter converts DC into AC electricity for use in your home or transmission back to the grid.

In off-grid or hybrid solar power systems, an additional component — the solar charge controller — directs DC current to a solar battery for storage or to the solar inverter for immediate use.

How Does a Solar Inverter Work?

A solar inverter uses solid-state components to convert DC to AC electricity.

Unlike older technologies like mechanical inverters, solar inverters have no moving parts. Instead, they utilise power semiconductors, like transistors and diodes, to switch direct current on and off at a very high frequency. 

(Source: Electronics Tutorials)

Rapid binary switching produces alternating current — ideally with a pure sine waveform. Pure sine electricity is considered the gold standard of AC waveforms because it is “clean” and free of the distortion and noise that can harm sensitive electronics when inferior inverters are used.   

Types of Solar Inverters

There are numerous types of solar inverters available today. 

Which option is best for you depends on your installation type and electricity production needs.

Here’s a brief overview of the different types of solar inverters.

(Source: Penn State)

String Inverters

String inverters are the oldest and most common type of solar inverters for small systems in the 500-watt to 3kW range. They are often used in portable and residential applications.

The principle behind string inverters for photovoltaic arrays is the same regardless of the installation’s scale. 

In grid-tied systems, solar panels connect directly to each other and transmit their combined DC electricity to the string inverter. 

The string inverter converts DC to AC electricity, transmits it to your home for immediate consumption, or, through a bidirectional or smart meter, sends the electricity to the grid. 

Net metering and Feed-in tariff schemes in South Africa are not currently viable (or available) for most consumers. 

However, President Cyril Ramaphosa has promised that will change.

In the meantime, a hybrid or off-grid solar power system is the better choice.

In off-grid or hybrid solar systems, PV modules may send DC electricity to a solar charge controller first. However, the solar inverter is still an integral part of the balance of the system.  

Benefits of String Inverters

• Easy to set up
• Low-cost
• Up to 98% efficiency
• Low maintenance
• Easy to monitor

(Source: Penn State)

Microinverters

Microinverters — also known as module inverters — are generally built into photovoltaic modules. 

In a solar panel array that utilises microinverters, each individual panel has a small dedicated inverter located on an underside made of non-photovoltaic material. 

Benefits of Microinverters

• If one solar panel is shaded for part of the day, it will not affect the performance of the entire array, as it can with a string inverter
• Individual multi-point power tracking (MPPT) capability 
• Scalability
• Minimal wiring costs
• Performance monitoring of individual panels 

(Source: Penn State)

Central Inverters

A central inverter utilises multiple strings of solar panels that connect to a power conditioning combiner box before delivering DC electricity to the inverter.

Rather than using a separate inverter for each string or panel, one DC output from the combiner connects to the central inverter, which converts DC to AC and delivers to your home and the utility grid from a single output. 

Central inverters are typically deployed in large solar power systems in the 5kW – 100MW range.

Benefits of Central Inverters

• Easy to design and implement
• Cost-effective
• Simplified maintenance and troubleshooting

(Source: Penn State)

Off-Grid Inverters

Off-grid solar power systems operate independently of the utility grid and rely on battery storage to function during hours when there’s little to no sunlight.

Solar energy is intermittent by nature. Electricity production diminishes on cloudy days, and solar panels don’t work at night.  

Grid-tied systems don’t require storage because they toggle between utility and solar electricity automatically. However, on-grid systems without solar batteries don’t work during a blackout.

Off-grid systems of sufficient size offer complete energy security, and solar batteries are an essential component.

Unlike grid-tied systems without storage, the first stop for electricity after it’s produced by solar panels isn’t an inverter. Instead, a solar charge controller is first in the chain.

There are two types of solar charge controllers: Maximum Power Point Tracking (MPPT) and Pulse Width Modulation (PWM).  Both alternate between supplying DC electricity to a solar battery for storage or to an inverter for conversion to AC.

Benefits of Off-Grid Inverters

• Battery storage can provide energy independence and security
• Electricity bill savings
• Better return on investment over time
• Can shorten the solar payback period 

(Source: Penn State)

Hybrid Inverters

The term “hybrid” can refer to several different types of residential solar power systems, including installations that utilise wind power in addition to PV-generated electricity.

Here, we’ll focus on hybrid systems that offer solar power + storage.  

A grid-tied solar power system without storage offers benefits like lower electricity bills and a reduced carbon footprint. However, on-grid PV systems that don’t have a solar battery will not provide electricity during a power outage.

Because a grid-tied system both transmits and consumes electricity from the power grid, it must shut down automatically during a blackout. Otherwise, electricity sent from a PV system could injure or kill workers trying to restore power or cause further damage to electricity infrastructure.

A correctly configured hybrid solar panel system will work during load-shedding and unscheduled blackouts.

Benefits of Hybrid Inverters

• Electricity bill savings
• Provides energy security by remaining operational during a power outage
• Reduces (or eliminates) dependence on ageing electrical infrastructure
• Can provide whole home backup with enough solar battery storage

Power Optimisers

A power optimiser is a DC-to-DC converter that maximises electricity production from photovoltaic modules and wind turbines.

In residential solar panel systems, power optimisers utilise maximum power point tracking (MPPT) to condition the electricity of an entire array and optimise inverter performance. 

A power optimiser isn’t a solar inverter per se. Instead, it converts the DC electricity produced by solar panels to an optimal voltage for maximising solar inverter performance.

Benefits of Power Optimisers

• Increased electricity production from photovoltaic modules
• Optimises inverter performance

Solar Inverters: Grid-Tied, Off-Grid, & Hybrid

One way to classify solar inverters by type is to divide them into grid-tied, off-grid, and hybrid systems. 

The solar inverter types outlined above, such as string, central, and microinverter, can be utilised in different ways by all three systems.

Here are brief definitions of each.

(Source: longmontcolorado. gov)

Grid-Tied Solar Inverters

In a grid-tied system, DC electricity from photovoltaic modules like solar panels is transmitted through cables directly to a solar inverter. The solar inverter converts DC to AC electricity for consumption in your home and transmission to the utility grid.

(Source: ResearchGate)

Off-Grid Solar Inverters

Off-grid solar power systems use solar batteries to store electricity to solve the problem of intermittency. Because off-grid systems operate independently of the utility grid, electricity must be stored for consumption during the night or at other times when your household consumes more power than your solar panels produce.

In an off-grid system, solar panels transmit DC electricity to a solar charge controller, which distributes power to a solar battery or a solar inverter, depending on whether the priority is consumption or storage.

Hybrid Solar Inverters

In some ways, a hybrid system offers the best of both worlds. It allows you to toggle between utility grid and solar battery storage automatically, depending on the parameters you set.

Most crucially, a hybrid solar + storage system provides electricity during a blackout. Depending on your solar battery capacity and electricity production potential, you can have power during even extended outages — or indefinitely.

What To Consider Before Choosing a Solar Inverter

When choosing a solar inverter, there are several essential factors to consider. 

Don’t make a purchase decision without taking the following into account.

On-Grid, Off-Grid, or Hybrid

The type of inverter you need is dependent on whether you purchase a grid-tied system, go off-grid, or combine the two by opting for a hybrid.

In an on-grid system, solar panels transmit DC electricity directly to a solar inverter that converts the current into AC power for immediate consumption or transmission back to the grid.

In off-grid and hybrid systems, DC from photovoltaic modules is sent to a solar charge controller, which routes the power to a solar battery or to a solar inverter, depending on the parameters you specify.  

Depending on your specific setup, multiple solar inverters and storage inverters may be required.

Electricity Consumption

The type of solar inverter that’s best suited to your application is partially contingent on how much electricity the system will generate.

String inverters are suitable for relatively small systems, while central and microinverters are better equipped to handle high-wattage applications.

Number and Type of Photovoltaic Modules

Inverters can be standalone components or built into devices like EcoFlow solar generators. 

No matter which setup you choose, it’s essential to ensure compatibility between your photovoltaic modules and the solar inverter and to ensure its rated power input is higher than the maximum electricity production potential of your solar panel array.

Also, confirm that your solar inverter is compatible with other balance of system components and your utility provider (for grid-tied and hybrid systems).  

Reliability

If you use a string or central inverter, your entire system will cease operating if your solar inverter fails. 

One advantage of some microinverters is that by dedicating an inverter to each individual PV panel, the balance of the array should continue to work when the inverter on one or more panels fails.

Warranty

Evaluating the warranty is one way of determining how confident a manufacturer is in the durability and longevity of its products.

Remember, if your inverter fails, your entire system will be offline. Insist on a 5-year warranty at minimum.  

Environmental Factors

The electricity production of string and central inverters can be impacted more negatively by factors like shade and debris obscuring individual panels in an array than alternatives like microinverters.

Carefully evaluate the environmental factors that exist in your installation area and do your best to position your photovoltaic panels to receive the maximum amount of peak sunlight. 

Budget

Last, but not least, the type of residential solar power system you purchase must conform to your budget.

But that doesn’t mean you should go for the cheapest option.

Thanks to government incentives and low-to-no-interest financing options direct from manufacturers, you have more freedom to make the wisest long-term investment.

(Source: Electrical Technology)

Connecting Solar Panels to an Inverter

There are three different methods of stringing solar panels together and connecting them to the solar inverter or charge controller (for off-grid and hybrid systems.)

(Source: Alternative Energy  Tutorials)

Connecting Solar Panels of the Same Model and Rated Power in Series

To connect your solar panels in series, wire the positive terminal to the negative terminal of each panel in the array. At the end, you’ll have a single positive/negative connection that will plug into your balance of system.

By wiring your solar panels in series, the output voltage of the array accumulates. In the diagram above, the output voltage of each panel is 6 volts. At the end of the series, the cumulative output is 18V (3 panels x 6V = 18V).

What’s crucial to note is that while the voltage output increases with each panel added to the series, the amperage remains the same.

Series connections are typically used for grid-tied systems that require a voltage of 24V or more.  

Advantages

Voltage Accumulation: If your installation requires high voltage to operate — standard with on-grid systems — series or hybrid series/parallel wiring is probably essential. Even if it’s not, if your application is best served by higher voltage rather than amperage, a series connection is your best choice.  

Efficiency and Performance: Without considering other factors, series connections will output slightly more electricity from the PV panel array than other wiring methods. There is less power lost delivering electricity over distance to your balance system in a series connection.

Thinner Cables: A relatively minor consideration, but parallel connections require higher gauge wiring due to how the electricity is transmitted. Series connections may cost slightly less to wire the same number of panels.

Better for Distance: Depending on the total surface area of your installation and how long the cables must be to connect to your balance of system, series connections may deliver an additional benefit. Voltage travels more efficiently than amperage over long distances.

Disadvantages

Obstruction and Shading: The most significant disadvantage of wiring solar panels in series is that the output of the entire array is dependent on the individual production of each module. 

If you have 20 solar panels with a rated voltage of 6V each, the maximum potential output during peak sun hours is 120V. However, if just one module is in the shade (or damaged) and only produces 4V, the array’s output will be reduced to 4V per panel. Instead of 120V of production, your panels will output 80V. If part of your installation area suffers from significant shade during peak sun hours, you should consider parallel or hybrid connections instead.    

Danger: High Voltage: There are many benefits to increasing the voltage output of your solar panel array. However, high voltage can be dangerous or deadly if improperly used. Working with high voltage also dramatically increases the risk for the person doing the installation. If you decide to proceed with a series connection, it’s best to hire a 

professional installer.

(Source: Alternative Energy  Tutorials)

Connecting Solar Panels of the Same Model and Rated Power in Parallel

To wire solar panels in parallel, connect each panel’s positive terminals together. You also connect all the negative terminals to one another. Parallel wiring results in amperage accumulating and voltage remaining the same. The exact opposite effect of series wiring. 

Again, using the same panels in the series example above, if the amperage per panel is 3V and you have 3 identical panels, your total output will be 9 amps (9A) and 6 volts (6V). The formula looks like this:

3A x 3 PV panels = 9A total output

Voltage doesn’t increase — the output remains 6V no matter how many solar panels you connect. If you have a 20-panel array connected in parallel with 6V/3A of rated power output, your maximum electricity production capacity is 6V/60A.

Advantages

Cumulative Increase in Current: Each PV panel you add to an array connected in parallel adds its direct current output to the system’s total output.

Less Overall Vulnerability to Shade: Unlike the voltage produced by series connections, the increased amperage (current) produced by parallel connections is not dependent on the performance of individual panels. If one PV panel is covered in shade for part of the day, the performance of the entire array is not affected. Shaded panels will contribute less current to the total output, but the maximum output of the panels receiving direct sunlight remains the same. 

For example, if you have 20 panels that output 3A of current in peak sunlight, but two are covered in shade, reducing their output to 2A, the cumulative output of your array will be reduced by 2A. The total (theoretical) output is 58A instead of 60A because each shaded panel produces 1A less.

For many rooftop installations, the advantage of parallel wiring is obvious. Depending on your location and roof structure, substantial portions of your solar panel array may be regularly shaded by obstructions like trees and neighbouring buildings for part of the day. 

But they may produce their full rated power at regular intervals, depending on the earth’s rotation around the sun. 

If the panel’s positioning means it never or rarely gets direct sunlight, you should move it. 

Solar panels still produce electricity from ambient sunlight on overcast days. But PV panels do not always produce their full-rated power.

Why?

PV panel performance depends entirely on the amount of solar irradiance (sunlight) it receives. 

That’s why solar panels don’t “work” at night. 

Investing in a mounted solar panel you know will consistently be in the shade makes little sense.    

Constant Voltage: Unlike series connections, you can add additional PV panels without increasing the voltage. This makes parallel connections invaluable in applications that require 12V power input, like many recreational vehicle systems.

Similarly, solar inverters have a maximum voltage capacity. You can add more PV panels to your array and continue using the same inverter. If you wired the same array in series and exceed the voltage capacity of your inverter, it will either shut down or permanently damage the component.   

Disadvantages

Less Efficient: The larger your solar panel array, the more power you will lose to inefficiency. Parallel wiring leaks more energy over long distances than series connections.

Less Resistant to Heat: Believe it or not, solar panels suffer in the heat. Direct sun exposure is optimal for electricity production, but solar panel efficiency declines rapidly as the temperature rises above 25°C. 

That’s because the photovoltaic effect used by solar cells captures energy from sunLIGHT, not from heat. 

All solar inverters and balance of system components like PWM or MPPT charge controllers have minimum voltage requirements. If heat (or other factors) hinder solar panel efficiency to the degree that voltage output decreases below the minimum requirement, adding more PV panels wired in parallel will not solve the problem.   

Thicker, More Expensive Cables: Amperage (current) flows through wires in a similar way to how water flows through a hose. The more current (water) you want to output, the bigger the cable (hose) has to be. Larger gauge wires are also less efficient at moving current over long distances. Parallel connections are typically better suited to smaller installations. 

Series-Parallel Connections (Hybrid)

Connecting solar panels in series or parallel each has its pros and cons. 

Can you have the best of both worlds?

Yes, many professional sizeable solar panel installations combine series and parallel wiring in one array to maximise the product of each group of panels. 

It’s possible to strike the optimal balance between series and parallel wiring by carefully planning the wiring based on the location of the panels on the roof relative to the sun and obstacles that obstruct sunlight at certain times of day. 

Typically, the goal is to achieve the right balance of producing volts and producing amps by wiring panels together in series and in parallel — not either/or.

If your residential solar installation will have more than 3 or 4 PV panels, it’s best to work with a professional installer. It will cost you more upfront but should substantially increase your return on investment and shorten your solar payback period.

For safety and performance reasons, we highly recommend that you DO NOT attempt hybrid series-parallel wiring of your solar panels on your own. Work with a reputable installer to achieve optimal results.

Some of the factors a solar power professional will consider when developing a wiring plan include.

• Desired electricity output
• Number and type of panels
• Peak sun hours at your location (how many and when)
• Direction, position, and angle of PV panels
• Any permanent obstacles to sunlight (trees and neighbouring buildings are common examples of fixed obstructions to direct sunlight)
• Average and extreme temperatures at your location

Involving an experienced installer in the process before buying your PV panels and balance of system can be an even better idea than just having them connect everything together. 

The right installer can help you make an informed purchase decision and avoid common mistakes like buying too many solar panels or incompatible components.   

EcoFlow Power Kits and Power Hub

Trying to choose an inverter and other components can become confusing. You can never be quite sure about compatibility between solar panels, batteries, inverters, and charge controllers. That’s why some companies have put together convenient all-in-one off-grid power solutions. 

The EcoFlow Power Kits are an excellent example of a plug-and-play off-grid solar power system. They are perfect for cabins, tiny homes, and RVs.

The Power Hub includes all of the essential converters, outlets, and chargers for an off-grid system, including: 

• DC-DC Step-Down Converter
• DC-DC Battery Charger with MPPT
• MPPT Solar Charge Controller
• Solar Inverter Charger

With an all-in-one system, you don’t need to worry about compatibility and whether the inverter is the right type for your solar power system. The Power Kits also work with all models of EcoFlow solar panels (rigid, portable, and flexible) and panels from other manufacturers.

EcoFlow’s Power Hub: What’s in the Box?

DC-DC Step-Down Converter 

A DC-DC step-down converter takes the high voltage of PV panels (often 50+ volts) and steps it down to the 48V that the EcoFlow Power Kit batteries expect. 

DC-DC Battery Charger with MPPT

The DC-DC battery charger with MPPT (multi-power point tracking) allows the battery bank to be charged directly by other DC power sources, such as a car alternator or a service battery. 

An MPPT is especially useful in RV and other mobile applications. The technology allows for high-efficiency charging and is superior to similar chargers that use PWM (pulse width modulation) chargers. 

MPPT Solar Charge Controller 

The integrated MPPT charge controller allows for safe, efficient charging of your battery bank using the power generated by your solar array. 

Solar Inverter Charger

The inverter charger allows your system to charge and function using AC power. For example, with an RV installation, you can connect directly to shore power at campgrounds. 

Frequently Asked Questions

Final Thoughts

In short, you can’t have a residential or portable solar power system without at least one solar inverter.

The DC electricity produced by photovoltaic modules like solar panels won’t operate your home’s appliances and systems without the conversion to AC electricity a solar inverter performs.

If you’re looking for a whole home solar power system with no compatibility headaches that’s fully functional during load-shedding, check out the EcoFlow DELTA Pro and solar panels today.

Whether you’re shopping for portable power to-go or complete energy independence, EcoFlow has a solar power solution for you.