February 17, 2020

AC-Coupled vs. DC-Coupled Batteries : Which Is Better?

 AC-Coupled vs. DC-Coupled Batteries : Which Is Better?

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.
But first, let’s explore some of the downsides of AC-coupled storage.
The primary drawback is that the solar power from your panels must be converted up to 3 different times:

  1. DC to AC through a solar inverter
  2. AC to DC via a battery inverter
  3. DC to AC again for your home

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 IQ™ 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 IQ Battery system is a leading AC solar battery technology whose performance rivals many of the leading DC alternatives on the market.

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