Top 10 “AC Coupled” energy storage models which can connect to an existing grid tied inverter
The name “AC Coupled” is confusing to any layman. They are also called “Retrofit” or “Storage” only. Still confusing? These types of solar inverters cannot connect to solar panels.
If you want to know more what are AC coupled inverters read here in our blog
AC Coupled inverter models are popular in countries where the home owner requires only an intelligent energy storage system capable of self consumption ( solar only), time of day operation ( escape evening and morning peak tariffs) and peak shaving ( high household load invites penalty).
Here is a list of highly recommended AC Coupled (also known as AC Retrofit or Storage Tower) series, based on thousands of reviews, evaluation of Bill of Material and PathToGreenHomes expert opinion.
AC Coupled inverters cannot connect to solar panels directly but may work in parallel with an existing grid tied inverter. Usually they can work with a max of 1 grid tied inverter like below.
Recommending specific brands to customers for purchase, like Top 10 Brands of inverter manufacturers is over-simplistic. Each inverter manufacturer makes 5-10 series, widely varying, based on functionality and quality. Path To Green Homes, recommends specific “Series” and “Models” based on exhaustive research over 1000s of points.
Micro Grid Function : Avoid fire.
Micro Grid function is the critical tango between battery storage (1pc) and an independently functioning grid inverter (1pc) to work together in a household, without catching a fire.
Energy storage battery is connected to the AC Coupled solar inverter for charging and discharging. An existing grid tied inverter ( connected to solar panels ) wants to keep on charging the battery even when battery charge ( SOC) is high. This can lead to a fire unless the grid tied inverter is asked to slow down.
The Grid tied and AC Coupled inverter are from different planets, have no common communication , so its easier said than done. By frequency modulation , micro grid function , this feature can be made safe. Not all inverters can achieve such safety but the above recommended AC Coupled / Retrofit / Storage only inverters have micro grid function.
High and Low Voltage battery of AC Coupled inverter
Storage only inverters come in both low voltage (48V) and high voltage systems (200-400V+) depending on battery configuration. A low voltage (48V)system is suitable when the backup needs to be 1-2 hours (<5kWhr battery capacity). The advantage of a high voltage battery system is low power loss and relative ease of adding more battery modules , in series.
Plan now : You may need additional battery later
When household load increases, like with the addition of an EV you may need to add more storage. Its possible to later add more low voltage battery modules (e.g. +2,54kwhr), by paralleling of battery. But the inverter , you choose today , must be capable of adding more batteries in parallel in the future without purchasing a 3rd party paralleling device . Such paralleling feature is supported by a very few models.
A high voltage inverter system is preferred due to ease of future battery capacity additions.
Storage only inverter common Safety issue
Is highly recommended to have fuse at battery terminals (not just slow acting MCB) for higher safety. As per PathtoGreenHomes NOT many storage only manufacturers are providing this in built fuse so we suggest use an internal / external fuse.
Integrated battery and inverter
The battery can be supplied by the manufacturer along with storage only inverter, in a nice integrated tower (IP55 rated indoor unit). Alternately, the home owner can purchase the storage inverter and a 3rd party compatible Lithium Ion battery separately. If Battery is not compatible with inverter, it may lead to fire. The advantage of an integrated solution are higher especially when combined with a wireless solution to manage loads.
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