Solar Battery has been one of the fastest-growing pieces of renewable energy technology in the industry. By coupling solar with storage, the consumers are able to rely on renewable energy at all times. When it comes to the way your solar panels, batteries and inverters are all wired together on your property, There are two main approaches when it comes to wiring the solar panels, batteries and inverters all together: alternating current (AC) Coupling and direct current (DC) Coupling. Both AC and DC coupling have advantages and drawbacks that are dependent on the specifics of your solar plus storage installation.
What is AC or DC coupling?
AC is when the current flows rapidly forward and backwards (which is what the electricity grid uses to operate) and DC is where the current flows in one direction. The key distinction between an AC-couples and DC-couples system lies in the path electricity takes once it is produced by solar panels. Most electronic circuits use DC, while solar panels produce DC, and batteries store DC energy. However, most electrical appliances operate on AC circuits, which is why the DC electricity generated must be transformed into AC electricity.
What are AC Coupled Batteries?
AC coupled batteries are a relatively new evolution in battery storage for grid connected homes and allow batteries to be easily AC coupled to a new or existing solar installation. These systems are generally only designed for grid-connected homes, not off-grid homes, as the (transformerless) inverters are typically not powerful enough to run a home completely off-grid and cannot handle the surge loads of many appliances.
Generally speaking, an AC-coupled battery system uses two inverters. The first inverter is the standard solar inverter which is installed alongside every solar PV system to convert DC to AC, and the second is a portable storage inverter used to convert the current with a built-in rectifier from AC back to DC in order to charge the battery. When discharging the battery, the battery uses the inbuilt inverter to convert the battery’s DC energy back to AC so that it can be used again by the home appliances. Therefore, any electricity that is stored in the battery system that is stored in the battery system needs to be inverted three separate times before use.
The examples of AC batteries include: Duracell Energy Bank 2 and Solax Fit.
AC-coupled battery systems are both easier to design and easier to implement with, which often means a lower upfront cost. AC coupled batteries can be easily added to homes with an existing solar installation or flexible to allow expansion. Therefore, AC-coupled systems are usually an economical option if you already have solar panels installed and wish to add a battery storage system. AC coupled systems allow batteries to charge from both solar panels and the grid. This means if your solar panel system isn’t generating enough electricity to fully charge your battery, you can still rely on the grid to fuel your battery for resiliency or electricity rate arbitrage benefits.
As mentioned above, solar electricity will need to be inverted three separate times before being used by home appliances. The process of inverting will result in small efficiency losses. Therefore, AC coupled systems will experience lower power output efficiency (approximate 90%) than the DC coupled systems due to conversion.
What are DC Coupled Hybrid Batteries?
The main distinction of DC coupling solar battery systems is they only required power conversion once rather than three times. It uses DC power from the panels to charge the battery. It then converts the DC power from the battery back to AC power to be used by the home. This process is generally conducted by a hybrid inverter. A hybrid inverter is simply combining both a battery charger and a solar inverter in a box. It incorporates high voltage MPPT controller/s and battery inverter/chargers inside a common unit.
A DC-coupled battery system requires the use of only one inverter. This is a more specialized piece of equipment than the inverters used for AC-coupling, as it is a hybrid inverter used for both the battery and the solar panels.
The examples of DC coupling hybrid batteries are AlphaESS and Sofar Solar GTX5000.
DC-coupled systems are more efficient (approximately 96%) than AC-coupled systems in terms of power output, as the solar electricity only converts once. DC coupled systems will be comparatively ideal for new solar installations.
As noted above, the inverters used for DC-coupling are more specialised pieces of equipment and, as a result, are more expensive than a typical solar inverter. Additionally, because of the more complicated installation process, it will likely take longer to install than an AC-coupled system, which will also increase upfront costs and installation time.
If you are interested in placing order of battery storage systems or want to learn more about the difference between the AC-Coupling and DC-Coupling Battery systems, feel free to reach out to our friendly sales team. Raystech Group has team of professional sales account managers across QLD, NSW, VIC and WA. Send us an email or call us at 1300 799 999 to know more.