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AC vs. DC Coupling: Which is Best for Your Application

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​Energy storage has grown increasingly popular in recent years, and with good reason. Batteries represent the next step toward grid independence, effectively expanding the capabilities of your solar panels around the clock by allowing you to store and use your excess solar energy, both day and night.

A hotly debated topic among solar installers today is whether AC or DC coupling is the best approach for solar+storage installations and retrofits. The truth is there really is no right or wrong answer. Both approaches have their merits, and the optimal approach depends entirely upon the application.

 

AC-coupled vs. DC-coupled – What’s the Difference?

AC or DC coupling refers to the way in which solar panels are coupled with and interact with a battery system.

AC coupled systems require two inverters: a common grid-tied solar inverter and a battery-based inverter. This means that the energy used by the batteries may be inverted as many as three times before being used in the home — i.e., from DC (PV array) to AC (load center) through the solar inverter, then back to DC (batteries) through the battery-based inverter, and then back to AC again (home loads).

DC coupled systems use a charge controller to directly charge batteries with solar generation and a battery-based inverter to power home loads (AC).

As a result, DC coupled systems are slightly more efficient than AC coupled systems because the power is not inverted multiple times.

 

AC Coupled: Best for Those Who Already Have Solar

AC coupled systems can be much more convenient for retrofits in which customers want to add batteries to existing residential grid-tied solar systems. One only needs to purchase an additional battery-based inverter to connect the batteries.

Because of the ease of installation, AC coupling can be ideal for grid-tied residential battery backup systems as well as large commercial systems, especially for retrofits where solar panels have already been installed.

While AC coupled systems may be easier to install, using battery storage to cover AC loads is likely to result in a marginal decrease in efficiency.

 

DC Coupled: Best for Those Installing Solar and Storage Together

DC coupling is ideal for new on- and off-grid solar+storage system installations in residential and small commercial applications, but not retrofits with existing solar panels, because the existing grid-tied solar inverter must be removed entirely and replaced with a battery-based inverter. In most cases, the existing PV array wiring must be reconfigured.

The ZRGP PowerBase Mate (minimum capacity 10.24 kWh, expandable to 40.96 kWh) is a great choice for DC-coupled systems. It is a low-voltage battery system with an acquired flexible modular design with no extra cables, which provides optimized safety, life span, and performance. They are perfect batteries for all applications.

The PowerBase Mate has the flexibility to be combined with any type of energy generator, including photovoltaic, bioenergy, wind, and diesel generators. This makes it a more viable option for achieving energy independence.

Will solar energy stop working if the sun is still shining?

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A common misconception about solar system is that during a power outage or grid failure, the solar system will continue to provide power to loads. After all, if the sun is shining, shouldn’t the system still work?

In fact, due to the nature of grid-tie solar systems and how they are designed, all power output to the grid must cease during an outage. There are, however, two exceptions to this: your system is equipped with energy storage, or you forgo the benefits of grid-tied solar and opt for an off-grid system.

 

Grid-Tied Solar System without Energy Storage
Residential solar without storage is designed to shut down during a power outage as most customers have grid-tied systems in their homes.In most of the world, all inverters that back-feed the grid must conform to “anti-islanding” requirements. Anti-islanding simply means that the inverter stops grid-feed-in when the grid experiences abnormal conditions (frequency/voltage) and/or in the event there is a complete power outage. The purpose of this is to protect line workers or electricians who may be trying to make repairs to the grid. This is mandated for all grid-tie systems. 

 

Grid-Tied Solar System with Energy Storage

If you want to guarantee that your solar system will continue to operate during a blackout, adding a battery storage system is the way to go. These storage units save energy produced from solar panels for later use. When there is a power outage, the combined solar plus storage unit isolates itself from the grid and immediately continues power supply to the home—providing the uninterrupted electricity service you need during times of crisis.

The battery-based system can fool the grid-tied system into thinking the grid is still functional, while also disconnecting from the grid to comply with anti-islanding. This still allows for solar productivity to feed loads and charge batteries during a grid-down situation.

 

Energy storage System
ZRGP PowerBase Mate Battery System plus solar system is unique.(1) Three-layer BMS, based on ZRGP APP to intelligently monitor and manage the battery and home energy usage.(2) Passing the UL 9540A test at the cell, module, and system level means that Mate has reached the highest international standard level in terms of safety and reliability.(3) Modular design (minimum capacity 10.24 kWh, expandable to 40.96 kWh).(4) The PowerBase Mate has the flexibility to be combined with any type of energy generator, including photovoltaic, bioenergy, wind, and diesel generators. This makes it a more viable option for achieving energy independence. 

If you are enjoying the benefits of a residential solar system, but want to take it a step further with off-grid capabilities and uninterrupted power during power outages, then solar plus storage is the way forward.