Peak Shaving vs Battery Backup
Many residents want the peace of mind of a solar and battery system but do not fully understand what they are getting.
Why is that battery so expensive?
What do you mean the battery won’t work if the grid goes down? That is the whole point, right?
These are common questions homeowners will have regarding battery systems.
There are two main types of operating configurations when combining Solar with a battery: Peak Shaving or Battery Backup.
Adding a smaller battery to your PV system will not be able to support your critical loads for very long. Maybe 1-3 hours, depending on the size of the loads. So why would someone want a small battery that can only last for a few hours? The answer is peak shaving.
A peak shaving configuration is set up to allow the battery to discharge every day during a set period. Typically during high electricity usage times (on-peak hours). Peak shaving works by programming the battery to discharge if consumption exceeds a certain threshold, say 4kW, and will cover any “peaks” over that 4kW threshold (to a limit).
Here is an example: A house has a peak shaving battery system with an inverter output of 5kW and a battery bank of 10kWh. The inverter is programmed to charge the battery bank during morning sun hours when house loads are minimal and solar resource is abundant.
During the day, the house runs off of solar power. When the sun goes down, most energy rates increase (on-peak hours). For this example, 3 pm-8 pm will be on peak. This is due to the high demand of electricity for everyone cooking dinner or turning on lights for the evening. At 3 pm, the battery system would start monitoring the power consumed by the house.
If the power value ever increases over that certain threshold set (4kW), the battery will discharge. If the house’s total energy is 6kW, 4kW will be covered by the grid and will supply 2kW from the battery. If this 6kW power demand were to continue for 5 hours, it would completely drain the 10kWh battery.
Since the battery inverter can only supply 5kW at a time, if the power demand were 15kW, the grid would cover 10kW, and the battery could supply 5kW. If this 15kW power demand were to continue for 2 hours, it would completely drain the battery.
Peak shaving is for energy management and can be utilized every day. Some hybrid inverters do not have the capability to throttle PV production and need a grid connection to back feed at all times. This is the main reason why certain peak shaving systems cannot operate when the grid is down.
Off-gird systems tend to be very expensive. Most people looking for power security during a blackout will turn to a solar and battery system.
What makes this any different from a peak shaving system? It does not operate every day. This battery bank will sit dormant until the grid is disconnected. The only use for this battery is during a grid outage. The battery bank is still charged by solar power and tends to be significantly larger.
This is because homes with a battery backup system are dependent on the battery during a grid outage. Most battery backup systems are sized to provide enough energy for one night (one day of autonomy). Come morning; the solar power will charge the battery and provide power to the home.
The main difference between a peak shaving and battery backup system is when the battery is used. A peak shaving system utilizes battery power every day during peak hours while a battery backup system waits for the grid to go down. There are advantages to both, and the systems can be combined if desired.