As the name implies, a whole-home backup is a battery backup system that backs up everything in the home. On the other hand, a partial-home backup only backs up a portion of the home, typically the most critical circuits (such as the fridge, internet, lights, etc.).
As discussed in the article about how a battery backup works, we must install a switch to disconnect the home's backed up circuits and battery from the grid so the system can create a micro-grid at the home. The location of that switch determines whether the system backs up the entire home, or just the portion of the home.
By placing the switch ahead of ALL circuits, the entire home is backed up. When the system detects a grid outage, the switch disconnects from the grid and all of the home's circuits are energized by a micro-grid created by the battery system. This allows all circuits to be energized during the outage and gives the customer a seamless transition from grid to battery power (you probably won't even know the grid went down!).
On the other hand, if the switch is placed behind some of the circuits, then those circuits are not backed up. When the switch detects a grid outage and disconnects from the grid, those circuits that are behind the switch remain connected to the grid and, since the grid is down, they have no power. The circuits that are behind the switch (the backed up circuits) are disconnected from the grid and are energized by the micro-grid created by the battery system.
In the image on the left, the switch (Gateway) is placed ahead of ALL the home's circuits creating a whole-home backup. In the image on the right, the switch (Gateway) is placed behind some of the home's circuits creating a partial-home backup.
Image credit: Tesla System Design
There are many factors that go into determining if the design will be a whole or partial home backup. These include:
- The number of batteries being installed
- The size of the largest circuits in the home
- The number of circuits in the home
- The amount of time the customer wants to be able to run off-grid
When designing the system, we must ensure that the batteries have sufficient power to power the largest loads and sufficient energy to sustain the home for a reasonable amount of time during an outage. A whole-home backup doesn't do any good if it only backs up the whole home for 5 minutes! We take all of these factors into consideration when designing a battery backup system to ensure the best overall experience for the customer.
Typically, a single battery is only sufficient for a partial-home backup. Two or more batteries are almost always needed to backup an entire home. The graphic below helps to illustrate how many batteries are needed for typical home circuits.
Image Credit: Tesla Standard Backup Menu