This article provides information and options for customers that want to remain connected to the utility (grid-tied) while having the added benefit of being able to continue to have power in the event the electric grid is down, such as during a power outage. This is accomplished by utilizing batteries. The details below will help you to estimate the load requirements for the batteries.
First off, here's a laymen's rundown on how it technically works:
- The solar array is connected to the inverters which are tied into the breaker box. The array is additionally connected to the battery bank.
- The battery bank is connected into the inverters as well.
- You may wish to backup only part of your load in order to save cost on installing battery backup capacity. In this case, loads that are covered by the battery bank vs. loads that are NOT covered by battery backup are segregated.
- A transfer switch is installed between the utility connection and the sub-panel where the loads that are covered by the battery bank are connected.
- The battery bank is connected through the inverter into the sub-panel with the covered loads.
- In the event that the utility has an outage, covered will be automatically shifted to use the battery bank via the transfer switch.
- In the event the sun is shining, the solar array will also continue producing power and recharging the battery bank.
In order to figure out how much battery capacity is required, it is necessary to answer two questions:
- What do you want to cover and how much power is required to cover it?
- How long do you want it to run the above loads off of battery?
Example: 3 hours
Using this information an engineer can prepare an estimate showing the battery capacity necessary to meet your requirements.