User Manual

35
GRID-CONNECTED BACKUP
There are two distinct uses for a grid-connected battery bank. The first, and the
most common is a power backup system. The purpose is to provide temporary
power in the instance of grid loss. This is simular to a UPS system, but is typically
on a much larger scale with higher storage capacity.
The second is a grid-tied system with battery backup. This system setup is used
to generate and sell excess power produced by a renewable source to your utility
provider when you are connected to the grid. In the event of a grid failure, the
battery bank then provides storage power for the critical loads during the outage.
Systems are configured according to how much power is to be sold to the utility
vs. how much will be stored. If a higher percentage of the power generated is
pushed to the utility, this will decrease the remaining amount available for backup
and vice versa. This may be determined by personal preference or may be limited
or regulated by the utility.
For grid-tied battery backup systems, the battery bank should only be sized to
handle the loads supported for the duration of a temporary outage. These systems
are commonly used to run household necessities such as limited lighting and
refrigeration, etc. It is ideal to limit the size of the supported load to essential
services only as higher capacity battery banks require more maintenance as well
as power usage to hold at full charge, reducing the amount of generated power
which can be sold to the utility.
Typically, because outages are infrequent and occur only a few times per year
in most regions, these systems are designed for greater depth of discharge than
off-grid applications. In some cases they may be designed to discharge as far
as 80% DOD over a relatively short period of time.
In regions where the grid may not be reliable and extended or intermittent outages
occur frequently, it is necessary to size the battery bank and charging source(s)
to support a larger load over a longer period of time. This prevents the battery
bank from overdischarging and/or deficit cycling.