Application Note
©2014 OutBack Power Technologies, Arlington, WA 98223 Revision 2/FINAL Page 2 of 14
For these and other reasons, the benefits of storing up renewably-generated electricity for use when it is more
advantageous are obvious. Energy storage can offset electricity use during peak times, provide off-grid
independence during outages and emergencies, and contribute to greater grid stability to ensure that renewably-
generated electricity can remain a vital and proactive partner in the energy mix. This is why energy storage-based
systems represent the fastest growth area in solar installation today, and why industry surveys show battery-
charging capable inverters to eclipse grid-tied “string” inverters in the next two years (Photon International 2012).
The basics: As mentioned previously, by far the most common configuration of a PV generation system is an array
of PV modules feeding a grid-tied (GT) inverter that converts the DC power to AC power, then fed through the
building’s service panel and on out to the electrical grid (see Figure 1). The grid acts like a battery and the
renewable energy is placed on the grid for collective consumption, which, in turn, reduces generation other
sources. The grid-as-a-battery is a great concept, until it’s no longer there – the grid-tied inverter requires the grid
to stay powered per the UL1741 requirement for safety reasons. Without grid power to keep the GT inverter
operating, the available PV power just sits on the roof unused. And during an outage, a home or business with PV
electricity potentially available is in the dark just like everyone else.
A battery-based (BB) inverter system does not require the electrical grid to stay active, and is the mainstay of off-
grid homes, businesses, and industrial installations such as cell phone broadcast towers. Using battery-based off-
grid technology, a smarter type of “grid/hybrid” inverter technology is able to use PV, wind, hydro-electric and
other renewable DC energy sources to keep the batteries charged and sell the excess to the grid, just like the grid-
tied unit using the grid as its battery (see Figure 2).
For those that have not yet invested into a solar energy system and would like to have backup power, a grid/
hybrid inverter/charger with battery back-up is the best choice. Solar energy can still be sold back to the grid,
while having the security of knowing your PV based renewable energy system will still provide power during an
outage until the electrical grid is back up and running.
Why not purchase a grid/hybrid inverter from the start? For those staring at their roof full of PV modules when
the grid goes down, fully inoperable while the hours without power turn into days, and sometimes even weeks,
that very same question is probably being asked many times over. Some may not have realized they would be
without the PV power on their roofs when they bought their grid-tied system. Maybe they thought it would never
happen to them. Finally, the relatively modest extra cost of a smarter grid-interactive inverter/charger and
batteries may have initially discouraged them.
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