14-07-2014, 11:46 AM
For more than one hundred years, utilities have supplied reliable power
Design Considerations for Distributed.PDF (Size: 369.7 KB / Downloads: 13)
Abstract
This paper presents some design considerations for
distributed micro-storage systems in residential applications. In
this paper, the term “micro-storage” refers to small residential
energy storage units with a capacity of few kilowatt-hours.
Generally, energy storage systems enhance the performance of
distributed renewable generation systems and increase the
efficiency of the entire power system. Energy storage allows for
leveling the load, shaving peak demands, and furthermore,
transacting power with the utility grid. Different micro-storage
system architectures as well as analysis of system sizing are
discussed in the paper. In addition, different energy storage
technologies, inverter design considerations, and smart grid
integration issues will be also presented
INTRODUCTION
For more than one hundred years, utilities have supplied
reliable power to the globe with relatively high quality of
service. Today, as electricity demand and customers’
expectations escalate, utilities are struggling to fulfill those
needs. According to the Energy Information Administration
(EIA) in the U.S., the world electricity consumption will
increase from 18.0 trillion kilowatt-hours in 2006 to 31.8
trillion kilowatt-hours in 2030 at an average annual rate of
2.4% [1]. In addition to the rapidly increasing electricity
demand and customer expectations, the dramatically
skyrocketing oil prices, the aging of the grid infrastructure,
and the need to reduce CO2 emissions, are factors that add
more burdens on utilities to fulfill future demand.
Distributed renewable sources which can be derived from
renewable energy sources such as solar PV generators, wind,
hydro, and ocean waves, are rapidly becoming an integral part
of utility grids throughout the world [2]. However, the
integration of distributed renewable energy into the utility grid
is performed in a so called “feed and forget” fashion [3]. Yet,
large scale integration of renewable sources into the grid can
be problematic due to the intermittency of these sources which
can impact the quality and security of energy supply. Thus,
energy storage can be used to mitigate the intermittency of
supply and inject power to the grid to alleviate peak demands
SYSTEM CONFIGURATION
The power system architecture for the proposed MSS can
be inline, dc coupled or ac coupled. The inline configuration
is also known as series configuration since all the blocks are
connected in series, where the parallel connection is referred
to the method in which the blocks are connected to a common
SYSTEM SIZING
The MSS can be sized based on the average power
consumption of a typical house. Although each house has a
unique load profile that is dependent on the residents’
behavior and the number and nature of the appliances
connected to the grid, studying the load nature of a typical
house can be somehow useful in properly sizing the micro
storage system.
In a comprehensive study conducted by the Florida Solar
Energy Center (FSEC), the load profile of ten houses was
monitored for an entire year and the energy consumption was
continuously recorded [4]. The total average energy
consumption for these houses was 42.8 kWh/day, which is
close to the average energy consumption of the residential
sector in Florida namely 38.2 kWh/day in 2007 according to
the EIA [5]. In this study, the maximum and minimum energy
consumption curves for the monitored houses were
approximated and drawn as shown in Figures 5 and 6,
respectively
Power Conversion Architecture [/b]
There are two possible ways to achieve the two-way power
conversion for charging or discharging the energy storage
units. The power conversion stage can have a bidirectional
single path inverter/charger, or two unidirectional separate
paths for the inverter and the charger. Although the
bidirectional inverter/charger offers low component count,
most likely it will have a complex and a high-cost controller.
Also, it requires bidirectional switches, which is a challenge
for bidirectional power converters [22]. These switches are
implemented by using two MOSFETs or IGBTs in series,
which leads to higher losses and lower overall efficiency.
Also, the bidirectional inverter/charger must be sized to the
highest peak power in charging and disc
COMMUNICATION AND SMART GRID INTEGRATION
Establishing an external communication channel between
the utility and end users allows both utilities and end users to
monitor and control power demand resulting in an increased
security and quality of service. A residential MSS must
incorporate advanced communications and controls
functionality to allow for seamless integration with future
smart grids while allowing utilities to easily dispatch stored
energy. In fact, the MSS should be controlled remotely by the
utility or locally by the end user. To perform data gathering
and control, the MSS must incorporate internal
communication links with other devices, such as power
meters, to monitor the power consumed by the house or the
power generated by the renewable sources (solar panels or
wind turbines). Once the critical power system data is
gathered and manipulated, the MSS can be properly
controlled. Depending on the desired data communication
rate and the amount of data, the communication medium can
be selected.
CONCLUSION
Modularity, low cost and high quality power are key issues
in the design of a residential micro storage system (MSS). As
discussed in this paper, an AC coupled MSS is beneficial as it
offers a robust design and allows for a modular and flexible
storage system. Since the cost of energy storage devices are
expected to continuously decrease, and due to the
continuously increasing demand and prices of electric power,
distributed residential micro storage is expected to gain more
attention in the next few years. Other important aspects in the
design of a residential micro storage system discussed in the