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  • Sarah Lozanova

Explaining The Difference Between Solar Inverters And Converters



When designing a solar system, you will need to select solar equipment that will best serve your customers’ needs. Many prospective customers may have questions about alternating current (AC) and direct current (DC), power inverters and converters. These are critical topics for installers to understand and explain to help the client make an informed purchasing decision.


AC Vs. DC Power

Electricity comes in two forms: AC and DC power. The terms describe the direction of the electrical current’s flow in a circuit. In DC voltage, the current flows in a single direction. For AC, electrons switch directions, going both forward and backward.


AC voltage is what the majority of homes, appliances, and electronic devices consume because it is better at transmitting electricity over a longer distance. If you plug into an outlet, AC power will flow from it. Most televisions, computers, routers, cell phones, refrigerators, stoves, dishwashers and water heaters use AC electricity.


But, solar batteries and solar systems use DC electricity. Thus, an inverter is needed for the battery or the solar array to power AC appliances. Occasionally, off-grid solar system owners will use DC appliances to bypass the need for an inverter, but they are limited to a small selection of appliances.


Helpful Electrical Terms

There is a lot of terminology specific to electricity. Often, your customers will be unfamiliar with the exact meaning of these terms, which makes it difficult for them to gain a basic understanding of how the solar system works. Here are some helpful terms to explain to them on a site survey or on your company website.


  • Voltage: It is the potential of power to move, and it is measured in volts. If the analogy is water, it would refer to the water pressure.

  • Ampere: The strength of the electrical current is expressed in amperes. If it were water, it would refer to the flow rate.

  • Watts:The measurement of power is expressed in watts, kilowatts, and megawatts. A kilowatt is equal to 1,000 watts, and a megawatt is equal to 1,000,000 watts.

  • Kilowatt hours: This is a measurement of electricity use over time. Most electrical bills are measured in kilowatt hours, which are equal to 1,000 watts for 1 hour. A megawatt hour is equal to 1,000 kilowatt hours for 1 hour.


Inverter Vs. Converter

Inverters convert voltage from DC to AC. Solar panels generate DC, whereas households primarily consume AC. Thus, inverters convert solar energy into a form that is usable in your customer’s homes.


There are two main types of inverters: string inverters (also called central inverters) and microinverters. The former inverts electricity from multiple solar panels, while the latter is used on each solar module.


Sometimes, inverters are mistakenly referred to as converters or power converters. It’s helpful to be aware of this in case it happens with your potential customers.


In solar applications, a charge controller, which is a DC-to-DC converter, is used to regulate the power running through the system and maximize output. The charge controller helps the battery bank and inverter to receive a more consistent current.


Off-grid solar systems can have voltage converters, which allow them to obtain 24 or 48 volts from a 12-volt battery. These are used with DC appliances, which are relatively rare.


Often, RVs have converters to enable these units to convert 120v AC power to 12v DC electricity. Therefore, the converters help RV owners to charge their batteries when plugging into a power supply. These units are now standard in new RVs and basically perform the opposite task as an inverter.


Do You Need Both In A Solar Array?

Solar systems need inverters to convert the voltage from DC to AC. By contrast, charge controllers are only needed on solar systems with batteries, in both grid-tied and off-grid applications. Thus, your projects will include either a string inverter or microinverters, but only projects with a solar battery bank will need a charge controller. In rare cases, in off-grid applications with DC appliances, a voltage converter might be helpful.


Types Of Solar Charge Controllers

The two most common types of charge controllers are Pulse Width Modulation (PWM) Controller and a Maximum Power Point Tracking (MPPT) Controller. The two names refer to how the charge controllers modify the voltage, and an MPPT Controller is more sophisticated in how it operates.


Pulse Width Modulation (PWM)

This technology is basically a switch that connects a solar system to the battery. Unfortunately, they cannot adjust for greater efficiency depending on the output of the solar power system.


Maximum Power Point Tracking (MPPT)

This DC-to-DC converter is more sophisticated in how it operates and can adjust its power intake. It typically allows for a more flexible configuration and has greater efficiency.


Types Of Inverters

All inverters complete the same basic task: converting DC to AC power. As a solar installer, you have three primary options to consider.


String Inverters

When wiring the solar system with a string inverter, each panel is wired together into a string. Then, multiple strings can be wired together to the same inverter. This means that multiple solar panels are connected to a central inverter, which is often located on the outside of the home or business, in a basement, or inside a garage. For some projects, multiple string inverters are used.


Because these are centralized units, if it fails, it can cause the solar system to completely stop producing electricity. But, since they are not located on rooftops, they are easier to access for maintenance and repairs. String inverters without power optimizers are primarily recommended when shading is not an issue and with simple rooflines, especially when keeping equipment costs down is a priority.


String Inverters With Power Optimizers

Installers can use power optimizers on each solar panel to boost overall output and help condition the power before sending it to the inverter. Optimizers are recommended when shading or complicated roof lines are an issue. Power optimizers can also assist you in meeting NEC 2017 rapid shutdown requirements.


Keep in mind that they do increase the equipment costs for the project. Unfortunately, they are located on each panel, making maintenance more difficult when they fail.


Microinverters

These inverters convert DC to AC current right on the solar panel itself. Therefore, if you install an array with 20 solar panels, it will have 20 microinverters. Using microinverters helps minimize the impacts of shading because it allows each panel to operate independently.


Microinverters tend to have a higher cost than string inverters (without power optimizers). Like power optimizers, they are located on the back of each solar panel, making maintenance more challenging than with a string inverter. Like power optimizers, microinverters can also assist you in meeting NEC 2017 rapid shutdown requirements.


Which Is Better For Your Client?

Ultimately, the equipment you select for your solar clients depends largely on their energy needs, property, and whether they charge batteries. It is critical to begin each project by understanding the project goals and budget constraints to design the optimum photovoltaic solar system. Likewise, it is critical to be able to explain the function of various pieces of equipment to your customers.


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