IEEE Electrification Magazine - September 2015 - 18

Bidirectional
ac

ac

dc
Inverter

PV Panel

dc
Grid

Inverter

PV Panel

Bidirectional

Bidirectional

dc

ac

dc
Batteries

Grid

dc
Batteries

(a)

(b)

Figure 6. Battery storage schemes: (a) dc--dc coupling and (b) ac coupling.

With the right energy-storage system, this kind of support can be achieved for larger-scale applications. Li-ion
energy-storage systems can provide sustainable, affordable, and reliable support for residential and commercial
applications. The extended capacity of these systems can
handle more severe emergency conditions where repairs
can take longer than a few hours and houses experience
inclement weather while power is restored.
In many regions of the United States, backup is needed
for other reasons, like the lack of consistent and reliable
electrical energy services. These services can be interrupted
or degraded by the occurrence of natural events, such as
the sudden strike of a tornado or a snow storm. These can
paralyze a region and slow down the recovery process. Also,
more prevalent and equally significant are other causes
that can chip away at the stability of the grid. In fast-growing localities, inaccurate energy planning can affect how
robust the grid is and how flexible it is to withstand sudden
changes in demand. The same can occur in remote areas
where there is an existing grid that is already weak due to

the separation in distance between the generating plant
and where the demand resides. In all cases, the strategic
use of storage systems can be a major component of a stable and comprehensive grid solution. It offers an extra layer
of flexibility that will help stabilize the grid and offer better
energy management support during periods of normal and
peak demand.

Residential and Commercial
Battery Storage System
The inclusion of battery storage has two main schemes, as
shown in Figure 6 (Romero-Cadaval et al., 2015).
xx
DC-DC coupling has the potential to be the more
effective and cost-effective solution for new systems.
It requires a bidirectional inverter and dc-dc converter, which is typically in a buck-boost configuration.
xx
AC coupling requires two inverters; only one needs to
be bidirectional, increasing the initial cost but dividing
the stress between the two inverters of the system, PV
and battery. This scheme allows easy retrofitting.

German Market
Number of
Storage Systems

120,000
100,000
80,000
60,000
40,000
20,000

20
11
20
12
20
13
20
14
20
15
20
16
20
17
20
18
20
19
20
20

0
Year
New and Old PV Installations with Storage
Storage Share of New PV Installations
Storage Share When Retrofiting

Figure 7. The forecast for German market development for PV-storage battery systems.

18

I E E E E l e c t r i f i cati o n M agaz ine / SEPTEMBER 2015

Renewables now produce around 30% of the electricity consumed in Germany. It is forecast that by 2050 this quantity
will increase to 80%, according to German government plans
(GTAI, 2015).
More than 1.4 million renewable power plants have
been installed in Germany over the past 25 years, with a
total capacity of 35.7 GW peak. The majority are solar
power plants with a capacity of less than 10 kWp installed
on residential rooftops. They constitute the basis for the
market development of small energy-storage systems. As
of 2014, around 15,000 households and commercial operations in Germany had already invested in PV-battery systems, with an average of at least 60 MWh of installed
capacity (GTAI, 2015).
The forecast for the market development of PV-battery storage systems in Germany looks to be very strong, with an
increase of almost 500% over the next five years. Figure 7 depicts



Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2015

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