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Off-Grid, Battery-Backup, and Hybrid Solar Inverters
With the continual decrease in the cost of conventional PV systems, we believe the same will happen for off-grid and battery-backup solar systems due to their growing popularity.
The needfor battery-backup systems has grown due to changes in charged rates from utility companies, the need to install in remote locations, weather conditions, and a growing preference to be independent.
Thus, we believe that understanding the components of an off-grid and battery-backup system is a necessary and crucial first step for design or moving towards retrofitting to a battery-backup solution
A grid-tied battery-backup system is typically used to circumnavigate Time of Use (TOU) charges, create a safety net for power outages, or to simply offset electrical loads in the nighttime or when the sun is not out. These battery-backup systems can be DC- or AC-coupled.
The main components of a DC-coupledgrid-tied battery-backup system usually consist of the following:
Fuses for DC connections
Please refer to the diagram below for a depiction of the general setup. Note that the home appliances and battery inverter will be tied into the utility.
Another alternative for DC-coupledgrid-tied applications would be as shown in the diagram below. The main difference with this application is that the Solar Controller (a.k.a. Charge Controller) is integrated with the battery inverter which is called a Hybrid Inverter.
The main components of an AC-coupledgrid-tied battery-backup system usually consist of the following:
Inverter (String or Micro)
Fuses for DC connections
Please refer to the diagram below for a depiction of the general setup. Again, the home appliances will be tied to the utility.
Note that hybrid solar inverters, like the Sol-Ark 8K and 12K, can doBOTHAC and DC coupling. They’re growing in popularity because they can reduce equipment costs or be a relatively convenient solution for retrofitting conventional systems into battery systems.
Hybrid inverters in AC-coupled applications usually have the switchboard, inverter, and charger integrated into one unit.
An off-grid system is typically used to avoid costs from utility companies, eliminate dependence on the utility-grid, or energy is needed in a remote location where tying to the grid isn’t readily and/or easily accessible.
The general setup follows the same layouts for a battery-backup system, except for tying to the grid, are as follows:
|• Solar Panels||• Solar Panels|
|• Charge Controller||• Inverter (String or Micro)|
|• Fuses for DC Connections||• Hybrid Inverter|
|• Batteries||• Fuses for DC Connections|
|• Battery Inverter||• Batteries|
|• AC Disconnect||• AC Disconnect|
For residential and commercial applications... A grid-tied battery-backup system is typically going tocost significantlyless than an off-grid setup.
With a battery-backed system… Power can be drawn from the utility to supply larger loads and reduce the cost of the battery bank, which accounts for a large portion of the system’s costs.
In an off-grid application... A considerably larger power supply will likely be necessary for residential and commercial applications to create a safety net in case there is insufficient solar power and the batteries need to be able to supply all of the electrical loads for an extended period of time. This extended period of time is typically referred to as the time or days ofautonomy.
For retrofitting a conventional grid-tied system... Using a hybrid inverter that can be AC-coupled is typically a less expensive solution than converting to a DC-coupled system in order to have battery-backup.
In contrast, a completely new system with a hybrid inverter is typically more expensive than using a charge controller and battery solar inverter. Hybrid inverters essentially function as a charge controller and battery inverter.
Ease of installation
Since both off-grid and grid-tied battery-backup systems have extremely similar setups, the ease of installation is similar to one another, if not, the same.
Using a hybrid inverter reduces the amount of equipment needed. Thus, it will increase the ease of installation since many of the conventional battery-backup/off-grid components are already integrated.
Generally, off-grid and grid-tied battery-backup systems have the same setups.
Hybrid inverters are a great solution for retrofitting existing grid-tied systems but can be a more costly option when installing a new system. Also, they can be used in off-grid applications. When considering this type of solution, it is important to note that the battery bank will likely be considerably larger than a grid-tied solution. This is due to an inability to draw from the utility-grid when the demand surpasses what the battery bank can supply.
When considering the cost/benefit of either solution, the consumer should first evaluate which setup works best for their application.