IEEE Electrification Magazine - September 2015 - 26

Currently, most
household storage
is operated within
a simple schedule
designed to charge
the BESS from the
grid during off-peak
hours and to provide
the load with either
PV generation or
combined PV
generation and
storage during
the day.

current-generation Tesla Model S has
a storage capacity of 85 kWh, and
there is the potential for some of this
capacity to be used to power households (Figure 5).
The maximum range of next-generation EVs is more than adequate
for average commuting distances in
urban areas, meaning only a fraction
of the total storage capacity is likely
to be used on a typical day. This
means that drivers may elect to use
some of their EV's storage capacity
to power their homes during evening peak times, which is typically
just after they arrive home from
work. The EV could then either
charge overnight from the grid during the nonpeak period, or drivers
may seek to charge their vehicles
from PVs while they are at work during the day.
While such charging infrastructure
is not yet available, it is highly likely
that, as the level of EV ownership
increases to a critical mass, associated infrastructure and
services such as fast-charging stations and the charging of
EVs in secure car parking (possibly utilizing renewable
generation) will follow the growing EV market.
As with traditional fixed household storage systems,
there is a need to accurately predict likely PV output and
EV usage for the following day to ensure the optimal SoC
for the EV battery based on its expected future use. This
becomes less critical, however, if there are two or more
EVs in the household, bearing in mind that many households currently have a second internal combustion engine
(ICE) car. The ability to draw power from two or more EVs

makes the system more complicated
but correspondingly allows greater
scope for optimization.
Finally, there are possible life-cycle
benefits to EVs, which could further
impact the distributed storage potential of the technology. As car owners
upgrade their vehicles periodically,
there may be an economic incentive
to extract the storage from older EVs
to install as fixed household storage,
as the capacity gained may be worth
more than the resale value of a used
EV. Bearing in mind that the depreciation in value of ICE cars can amount to
the majority of the original purchase
price in just a few years, this effect is
likely to be magnified in the context of
EVs, as the technology in and specifications of these vehicles is developing
at an even faster rate than other automotive products, meaning previous
models become obsolete faster. It may
be that the value to a household of a
used EV on the second-hand car market-even if a guaranteed buyback value is offered by the
manufacturer-would be less than the value of utilizing
the embedded storage capacity in the context of a gridindependent PV/storage system.

Large-Scale Storage Options
for High-Voltage Networks

There is a clear role for energy storage in the electricity
transmission network, although the types of storage technologies and their operation are very different at the grid
level compared to the household level. Putting aside the use
of storage for power-quality issues (that is, at the second
and subsecond time scales), storage needs to be at
the hundreds of MWh scale if it is going to have an
impact on typical high-voltage loads. Conventionally, this level of storage has been provided by hydropower. However, the effectiveness of this technology is highly dependent on location and subject to
the availability of water and suitable topography.
Other forms of large-scale storage have been
demonstrated overseas, such as underground compressed-air energy storage (CAES), with two wellknown plants in use in the United States and
Germany. However, this technology has not been
trialed commercially in Australia. Like hydropower,
CAES is somewhat dependent on topography, as
large, airtight, underground tanks or naturally
occurring caverns are required to supply significant
storage capacity.
The use of a large, single BESS for utility-scale
Figure 5. The Tesla S EV has a storage capacity of 85 kWh. (Photo courtesy of T. Dixon.)
applications is technically feasible, but the

26

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



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

IEEE Electrification Magazine - September 2015 - Cover1
IEEE Electrification Magazine - September 2015 - Cover2
IEEE Electrification Magazine - September 2015 - 1
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