Page 74 - North American Clean Energy March April 2015

energy storage

Powering Microgrid Applications

With renewable energy & battery storage
By Craig Wilkins

Image 1.
Homer model showing the near, top of charge state, where the battery Image 2. Homer model showing the balanced, charge state of the battery, greatly increasing the useable energy
commonly resides

Model
kWh/year
Battery
Renewable THERE ARE PROLIFERATIONS OF TECHNOLOGY contributing to the evolution of microgrids. Diesel
generation
However, most microgrids rely heavily on expensive diesel generators. According to IHS research,
A
10,219,967
None
70 Wind turbines
gen-sets using diesel fuel accounted for the vast majority of total sales in the market in 2013, 1,600 kW
B
*
Plus 50 Wind turbines
with $12.1 billion, or approximately 75.6% of revenues (as well as 81.6% of units shipped).
Reduces use of
*conventional peak diesel
battery
C
*
Plus Flow 40 Wind turbines
When it comes to a more sustainable energy sources, technology has also come a long way. generation Further
Battery And, there is good news: diesel consumption in the form of microgrids can be reduced by as reduces the
Zinc/Iron
much as 75% or more with the incorporation of a well-designed hybrid, renewable generation use of diesel
and energy storage platform.
generation
Table 1.
he combination of low-cost power conversion systems, based on newer insulated-gate bipolar Table 1.
transistor (IGBT) inverter technology—combined with the rapidly falling prices of renewable en-
ergy generation, such as wind and solar power or even biomass—are greatly contributing to the he following provides a breakdown, as demonstrated in Table 1.
viability of energy storage as a cost-efective solution for microgrid applications.
• Model A: Model of a microgrid with 28 megawatt-hours per day (MWh/day) of AC load, and
Battery Capacity/Production Energy Input Energy Output Levelized Cost
his, in turn, is making renewable energy microgrids an attractive alternative to fossil fuel- generation of a 3-MW nameplate of wind energy. his project includes one 4,200 kW diesel gen-
of Energy
based ones. However, to be successful in the ield and on a project site, a stable microgrid that erator and one 1,600 kW diesel generator, yielding a system cost of anywhere from $18 million
(LCOE)
relies on renewables must also meet the heavy-duty cycle demands with an efective battery.
Flow 2-MW/2-MWh 1,750,713 1,263,826 $0.327/kWh
to $23 million.
kWh/year kWh/year
Battery
• Model B: Installing a battery that has an adequate, fast-response capability, but limited energy
energy in energy out
The battery
storage to 70% SOC, reduces the numbers of wind turbines generation to 2.5 MW. It also re-
Lithium-ion 2-MW/2-MWh 649,386 506,898 $0.391/kWh
Grid-level storage, when used in microgrid applications with a high level of renewable genera- duces the use of peak diesel generation by 11%, and can decrease a system cost by 4% to 6%.
Battery
kWh/year kWh/year
tion, requires batteries with a variety of important features.
• Model C: Incorporating a low battery with a zinc/iron system that has full capabilities, as well
Table 2
as access to the entire SOC, increases the amount of usable energy. his also decreases the

hese primarily include:
number of wind turbines needed to 2.1 MW, cutting the use of diesel generation by 18%. By
• High power;
using renewable generation and a low battery storage system, a microgrid can be optimized to
• High capacity;
Renewable Diesel
Model kWh/year Battery
achieve 75% savings, or greater.
• Rapid cycling between charge and discharge;
generation
A 10,219,967 None
70 Wind turbines 1,600 kW
• An ability to be fully discharged multiple times per day; and B
It’s worth noting that a microgrid can be further optimized by using a 2-MW/2-MWh alternative
* Plus 50 Wind turbines Reduces use of
• A cost-efective price point.
*conventional peak diesel
technology battery. But, the delivered energy cost would be higher because the battery is inher-
battery generation
ently limited in providing adequate load-shifting requirements, which are needed to support
C
* Plus Flow 40 Wind turbines Further
he duty cycles must be designed to minimize diesel fuel consumption by moving the diesel gen- of-peak demands. A 2-MBWat/te2r-yMWh low battery, for exraemdupcelse,thies projected to provide 1,750,713
erator role of back-up power to the renewable/battery energy generators. Unfortunately, these Zinc/Iron use of diesel
kWh/year energy input and 1,263,826 kWh/year energy output, for a levelized cost of energy
generation
duty cycles are hard on battery life, particularly with conventional batteries—which can experi- Table 1.
(LCOE) of $0.327/kWh. In contrast, an equivalent lithium-ion battery produces 649,386 kWh/
ence a decreased lifespan anywhere between one-half to one-quarter of normal use.
year energy input and 506,898 kWh/year energy output, with a LCOE of $0.391/kWh—a 20%

Research has demonstrated that there are batteries with the right mix of power, capacity, rapid increase over low batteries (see Table 2).
switching time, along with the ability to be deeply discharged without shortening life: namely,
Battery
Capacity/Production
Energy Input
Energy Output
Levelized Cost low batteries. In particular, low battery technology that incorporates a zinc-iron chemistry has
of Energy (LCOE)
been shown to eliminate the environmental and safety risks associated with using large batteries

Flow 2-MW/2-MWh
1,750,713 1,263,826 $0.327/kWh
in remote, environmentally sensitive areas.
Battery
kWh/year energy in
kWh/year energy out
The research
Lithium-ion 2-MW/2-MWh
649,386 506,898 $0.391/kWh
he coniguration of energy storage systems and performance requirements in renewable micro-
Battery
kWh/year
kWh/year
grid applications must, simultaneously, be able to support the high variability and intermittency Table 2
of the energy source, assist with ramp loads, and/morning and/or evening peak demand. In Table 2
terms of economics, these technologies must have the capability of peak shaving for the morning
and evening ramps, as well as fast-response applications, which require rapid cycling at all states Conclusion

of charge.
Renewable energy generation ofers sustained cost savings over traditional generation methods,
Ideally, the storage medium should be fully functional across the entire state of charge (SOC), such as with diesel generation. he addition of a storage device greatly enhances the stability of
with the ability to provide power equivalent to several full charges and discharges per day. And, the energy generated, while greatly decreasing the cost of energy. Using advanced low batteries
as it turns out, these requirements it quite nicely with modern low batteries.
provides an even greater mix of capacity, power, and long life to maximize such savings.

As one study demonstrates, mapping a two-megawatt (MW) energy storage system into a
he long-life beneit of low batteries, along with their ability to support deep discharges mul-
grid with wind energy, and 10,219,967 kilowatt-hours per year (kWh/year) of AC load, showed tiple times per day, provides evidence of their signiicance when used in energy storage applica-
consistent utilization of the battery at the bottom of the charge, as well at the top, providing for tions. Simultaneously seeing 100’s or 1,000’s of rapid, short-duration charge/discharge cycles at
available services across the entire SOC. A low battery in this environment, therefore, provides a partial states of charge increases their value.

consistent capacity balance.
And, this is especially true when it equates to a substantial return on investment (ROI) for a
In contrast, other types of batteries, which don’t have full access to the SOC (and, therefore, renewable energy project developer.
that must be mitigated with control software) tend to showcase a “weighting away” from the
lower state of charges, so as to protect their own material structures. he storage medium, in Craig Wilkins is the chairman of ViZn Energy Systems, Inc.

this case, results in an imbalanced use of renewable generation into the grid. Either the battery
is used minimally at the top of charge, or remains unavailable due to the bottom of charge (see ViZn Energy Systems, Inc. | www.viznenergy.com
Image 1).

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