Connecting your solar installation to the utility grid is the simplest way to ensure you have 24/7 access to power – both day and night:

• When the sun is shining, you get the electricity you need from your solar panels.
• When the sun goes down, you buy the electricity you need from the utility grid.

But thanks to falling storage prices, a growing number of homeowners are now turning to solar batteries. Doing so makes it possible to store the clean electricity from your panels for night-time use or backup –  a strategy that can dramatically cut down on utility spending across the board.

If you’re also thinking about installing solar batteries, it’s important you understand the advantages and disadvantages of the 2 most popular competing options:

• DC-coupled Batteries for Solar. This approach stores the direct current (DC) electricity from your solar panels and AC to DC converted from the grid.
• AC-coupled Batteries for Solar. This approach stores both solar and grid power as alternating current (AC), which is the type of electricity most home appliances use.

The Pros and Cons of DC-Coupled Solar Batteries

The main advantage of DC-coupled batteries is that this type of solar storage is slightly more efficient. Because your batteries and panels share the same inverter, the DC to AC conversion only happens once. However, there are significant downsides as well. For example, DC solar storage solutions are harder to install since you might need both:

• A charge controller to top up your solar batteries directly with DC power.
• A battery-based inverter to convert the DC electricity from your solar panels into AC power for your home’s appliances.

These extra components increase the total installation cost, which can delay the payback period of your solar investment substantially. DC-coupled battery solutions are also harder to retrofit with existing solar installations. This is because the existing grid-tied inverter must be removed and replaced with a battery-based inverter.

The Pros and Cons of AC-Coupled Solar Storage

Although AC-coupled batteries are relative newcomers to the solar storage industry, the technology continues picking up steam due to the unique benefits that it offers.

The primary drawback is that the solar power from your panels must be converted up to 3 different times:

This multi-step conversion creates efficiency losses. However, the decrease is most noticeable in large-scale installations. Moreover, the type of AC storage technology used makes a difference. The Encharge™ storage system, for example, boasts efficiency rates comparable to many leading DC alternatives due to its unique chemistry and design. For most residential solar applications, however, the upsides of AC storage far outweigh the downsides.

AC-coupled battery systems are much easier to install – particularly for retrofits. These solar storage solutions automatically work with your current grid-tied inverter. You just need to add a battery inverter. The end result is faster installation times, lower upfront costs, and shorter payback periods – for your batteries and your panels.

Better still, AC solar storage solutions allow you to charge your batteries using both your panels and the utility grid – whichever energy source is cheaper or more available at that moment in time. This dual-charging capability allows AC batteries to deliver higher overall savings – especially when using smart technology like Envoy that can intelligently manage your home’s energy.

Which Solar Storage Solution Is Right for You?

There is no universal “best” approach for all solar applications. But given their affordability, set-up ease, and dual-charging capabilities, AC-coupled solar batteries are ideally suited for residential installations. This is particularly true when adding storage capacity to an existing system. If you’re concerned about efficiency losses, the Encharge storage system is a leading AC solar battery technology whose performance rivals many of the leading DC alternatives on the market.

What is an AC coupled PV system?

In an AC-coupled system, a grid-tied PV inverter is connected to the output of a Multi, Inverter or Quattro. PV power is first used to power the loads, then to charge the battery, and any excess PV power can be fed back to the grid.

Do solar panels use DC or AC?

Direct current (DC) electricity is what solar panels produce and what batteries hold in storage, while alternating current (AC) electricity is the type used on the grid and in most household devices. A device called an inverter is required to convert the DC electricity from solar panels into appliance-friendly AC

What is AC coupled battery storage?

What is AC-Coupled Storage? AC coupled storage is the connection of a battery energy storage system to a solar system via AC (alternating current) electricity. Energy from a solar system is generated in the form of DC (direct current) electricity which is then turned into AC by the solar inverter.

How does a solar panel convert DC to AC?

A solar inverter converts the DC (Direct Current) output of a PV solar panel into a utility frequency AC (alternating current) that can be fed into a commercial electrical grid (or) used by a local, off-line electrical n/w. In this proposed system, the solar energy is stored in the battery from PV cells

Can I use AC with solar power?

ACs can easily run on on-grid solar systems with capacities ranging between 3 kW to 10kW. An on-grid solar system can support the running of ACs in the large commercial office spaces (with electricity bills as high as Rs. 1 lakh) to residences (with bills of Rs. 5-10k per month).

 What is AC or DC coupling?

AC or DC coupling refers to the way solar panels are coupled or linked to an energy storage or battery system.

The type of electrical connection between a solar array and a battery can be either Alternating Current (AC) or Direct Current (DC). AC is when the current flows rapidly forward and backwards (this is what the electricity grid uses to operate) and DC is where the current flows in one direction. Most electronic circuits use DC, while solar panels produce DC, and batteries store DC energy. However, most electrical appliances operate on AC. This is why all homes and businesses have AC circuits. DC can be converted to AC using an inverter but, as explained below some energy is always lost in the conversion

More details here

https://www.cleanenergyreviews.info/blog/ac-coupling-vs-dc-coupling-solar-battery-storage

The 4 main solar battery System types

Note: Generally only DC or AC coupled systems are used for off-grid solar installations.

Recommended DC Coupled Systems

• Victron Energy Multiplus inverter/chargers and solar charge controllers,
• Selectrconic SP PRO multi-mode inverter/chargers DC coupled with the AERL Coolmax MPPT solar charge controllers.
• Outback Power Radian, FXR Inverters & FLEXmax MPPT solar controllers
• Schneider Conext XW+ with Conext MPPT controllers

Details on the attached video

https://www.youtube.com/watch?time_continue=29&v=l0LWhKto188&feature=emb_logo

Hybrid Inverter systems

Hybrid systems can be described as a grid-connected DC coupled solar battery systems. They come in many different configurations and typically use a hybrid or multi-mode inverter. Modern hybrid inverters incorporate high voltage MPPT controller/s and battery inverter/chargers inside a common unit. The first generation hybrid inverters were compatible with 48V lead-acid or lithium battery systems, however over recent years higher voltage (400V+) hybrid systems have become increasingly popular

The new generation higher voltage (400V) batteries and compatible hybrid inverters use lithium battery systems operating between 120-500V DC, rather than 48V. Higher voltage batteries can be configured in two different ways:

Since most solar arrays operate at high voltages around 300-600V, high voltage batteries use efficient DC-DC converters with very low losses. The first generation Tesla Powerwall was the first 400V battery available and was mated to the popular SolarEdge Storedge hybrid inverter.

AC vs DC coupled for off-grid systems

Why would you use an AC coupled off-grid system rather than DC coupled?

Advanced AC coupled off-grid systems use modern solar inverters to convert solar DC power directly to AC which can then be used immediately by most appliances during the day. This is very efficient, especially when powering high loads such as air-conditioning systems, modern kitchen appliances and water/pool pumps. Additionally, the installation cost of AC coupled string solar inverters is lower for larger systems above 5kW, due to the multiple MPP trackers, higher string voltage up to 1000V, and higher capacities up to 10kWp single phase.

Note: If an AC coupled system is used for off-grid installation the solar inverter/s must be compatible with the main (multi-mode) battery inverter/charger to enable charge control. This is required so the solar generation can be 'managed' or ramped up and down to ensure safe and accurate battery charging. There are several management systems used by different manufacturers such as frequency ramping (used by SMA and Victron) or direct communication - refer to manufacturers specifications.

As explained previously DC coupled systems are extremely cost effective for small to medium size systems. Another advantage of DC coupled systems is solar controllers are very flexible and scalable meaning additional panels can be easily added if required using relatively low cost DC solar controllers.

AC and DC coupling Combined

Most modern interactive inverter/chargers and such as Selectronic's SP PRO, SMA sunny island and Victron multiplus can function in both AC and DC coupled configurations. This offers the best of both worlds and provides back-up DC battery charging in the event of an AC shutdown.

If there is a shutdown in a remote location due to low battery voltage or low SOC the DC coupled solar charge controllers will continue to function (without AC operation) and charge the battery system which preserves the battery life and can restart the system if configured correctly. This creates a more fail-safe setup unlike a pure AC coupled system which are unable to be automatically or remotely restarted unless a back-up generator/source is functioning.

details here:

https://www.cleanenergyreviews.info/blog/ac-coupling-vs-dc-coupling-solar-battery-storage

Learn What AC & DC Coupling Mean for Your Solar Battery Storage System

When you decide to add battery storage to your solar system, there are two main ways to connect or couple these two sources — known as AC or DC coupling. AC & DC are the two types of voltage used to transmit and conduct the electrical energy you use at home every day.

What is AC Power?

“AC” stands for Alternating Current, which is the electricity flowing first in one direction and then the other.1 This is the type of electrical current used on the grid and in most of your household devices and appliances.

What is DC Power?

“DC” stands for Direct Current, and it flows in one direction only.2 This is the type of electrical current generated by the solar panels on your roof and stored by your home solar battery.

Since your solar system produces direct current (DC) energy, but almost all homes run on alternating current (AC), a solar inverter is required to convert the DC electricity into appliance-friendly AC electricity to power your home.3

Solar inverters are included with every solar system, and there are three different kinds:4

1. Traditional Inverters

Also called central inverters, draw power through all your panels. Usually, this kind of inverter is a single box installed right next to your home breaker box. The inverter combines the DC energy of all of the solar panels and converts it to AC energy.

2. Micro Inverters

These small inverters are placed on the backside of each solar panel. Installing individual inverters allows each solar panel to perform independently by converting the DC energy of each panel into AC energy.

3. DC-Optimizers

Similar to micro inverters, these devices go on the back of each panel. However, instead of converting the DC energy to AC, optimizers “condition” the DC energy and send the power to a central inverter. This creates a hybrid system combining the best of both traditional inverters and micro inverters.

Contact your solar installer to help determine the ideal choice for your unique home energy needs.

Is a Battery DC or AC?

Similar to solar panels, which produce DC power, batteries store and produce DC power, as well. Because the electricity in your house is AC, this means the batteries inside devices like your smartphone and your laptop need to use a converter to turn the AC power coming out of the outlet into DC power so it can be stored in their respective batteries.

Home batteries also store and produce DC power. The main difference here is a DC battery will use the same solar inverter to convert its stored DC power into AC power, whereas an AC battery has its own built-in inverter allowing the battery to directly convert its stored DC power into AC power to electrify your home devices and appliances.

DC- vs. AC-Storage Architecture

Strengths and Weaknesses of DC- & AC-Coupled Battery Power Storage Systems

1. DC-Coupled Systems

A DC-coupled system connects to the grid main supply in the same place as your solar panels, the reason why a hybrid inverter is required. As its name implies, this inverter is shared by your panels and your solar battery.

Strengths:

• Since your power is only converted from AC to DC once vs. in an AC-coupled system, there is less energy loss5
• If your DC-coupled system is below 10kW and directly connected to the renewable generator, it will be eligible for Net Energy Metering (NEM) to get credits for the excess energy it produces (if available in your state)6
• Simplicity — requiring only one inverter means fewer components (which usually translates as lower costs)
• Advanced functions are easier to coordinate with one inverter vs. synchronizing with two different inverters
• A smart option if you are yet to start your solar journey

Weaknesses:

• It is a higher-cost and more complex option if you already have a PV system at home and want to retrofit a DC solar battery

2. AC-Coupled Systems

An AC-coupled system uses a conventional solar inverter in addition to a second inverter, known as a “storage inverter,” to charge your solar battery. Although simple to setup, it offers slightly less battery power storage efficiency when charging than a DC-coupled system.7

Strengths:

• More flexibility — since AC-coupled systems require two or more inverters, you can adjust the location of your batteries and other equipment
• Works with all kinds of solar inverters, even micro inverters
• It is a more cost-effective option if you already have a PV system at home and want to add an AC solar battery

Weaknesses:

• Slightly lower efficiency to charge your solar battery vs. a DC-coupled system — due to AC (grid) - DC (battery) - AC (home) conversion6
• Having more than one inverter and equipment in different locations may increase your system points of failure, which could equal a need to purchase more replacements

AC vs. DC coupling: Which is best for your application and why?

There are many factors that determine whether AC or DC coupling is best suited to a given application, so it’s important to understand the particular conditions and constraints of each project. Be sure consult with the battery manufacturer and/or the inverter manufacturer(s) to help you design the best energy system that optimizes the cost and performance of all the equipment for your particular project.

However, 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.

Details here:

https://solarbuildermag.com/batteries/ac-vs-dc-coupling-solar-systems-with-storage/

Go big, go DC: an in-depth look at DC-coupled solar-plus-storage

DC-coupled system requires only one inverter, which means simpler installation and reduced costs. Additionally, one inverter to manage the system means functionality benefits, such as simpler synchronisation and coordination of advanced features

DC-coupled solar and battery installation allows the system owner to use PV power above the inverter rating and the inverter does not limit power, in other words act as a bottleneck for the power flow due to energy conversion.

Compared with alternating current (AC) coupling, DC coupling the PV array and the battery storage system in front-of-meter installations, such as utility-scale plants, is a much newer, less standardised approach. This had led some US utilities to begin piloting these configurations to see how the technology performs. On the supply chain side, balance of plant (BoP) equipment manufacturers are delivering more standardised and simpler to use power electronics equipment for enabling DC-coupled plants.

Details here

https://www.energy-storage.news/blogs/go-big-go-dc-an-in-depth-look-at-dc-coupled-solar-plus-storage

AC-coupled high-voltage battery over alternative solutions

https://zerohomebills.com/ac-coupled-high-voltage-battery-over-alternative-solutions/

Sizing of Residential PV Battery Systems

Article Sizing of Residential PV Battery Systems

Solar Energy

AC vs DC battery storage explained

https://www.solarchoice.net.au/blog/ac-vs-dc-solar-battery-storage-explained

Which one is right for you?

Whether an AC-coupled or DC-coupled battery solution is right for your home depends on a number of factors, including whether you have a pre-existing solar system or are starting from scratch with a brand new system

The type of electrical connection between a solar array and a battery can be either Alternating Current (AC) or Direct Current (DC). AC is when the current flows rapidly forward and backwards (this is what the electricity grid uses to operate) and DC is where the current flows in one direction. Most electronic circuits use DC, while solar panels produce DC, and batteries store DC energy. However, most electrical appliances operate on AC. This is why all homes and businesses have AC circuits. DC can be converted to AC using an inverter but, as explained below some energy is always lost in the conversion.

You can read this article at URL:

https://www.hindawi.com/journals/ijp/2017/6736928/

I agree Slah Farhani

DC coupled system is better as comparatively design is easy

The PV panels cannot be connected directly to the grid. They should be connected to a Battery Management System, then connected to the grid through converters. This is the most convenient approach.

For smaller systems (less than 5KW) it is economically to use Dc coupled configuration due to its simplicity and high performance which is around 99% efficiency for battery charging (MPPT).