Figure 1 shows the current step in the evaluation methodology…
Figure 1 Showing the current step (step 7: considering the environmental impacts ) in the methodology for evaluating a facility level energy storage deployment.
It is important to consider the environmental impact associated with energy storage technologies. Ultimately one of the primary goals of implementing a renewable energy generation project, balanced by energy storage, is to achieve beneficience, or “the relationship of being a net-positive environmental influence on the planet” (Norris, 2011) .
Certainly, the overall reduction in emissions related to implementing an energy
storage project should be calculated. Because so many factors contribute to the
overall reduction in emissions beyond the simple calculation of energy offset
by the storage device (including changes in power plant operation; reduction in
idle or spinning generator time), such a calculation is rather complicated.
It is important to consider the environmental impact associated with energy storage technologies. Ultimately one of the primary goals of implementing a renewable energy generation project, balanced by energy storage, is to achieve beneficience, or “the relationship of being a net-positive environmental influence on the planet”
Another important consideration is
the Life Cycle Assessment of the energy storage equipment itself. “Life CycleAssessment (LCA) is a technique to assess the environmental aspects and
potential impacts associated with a product, process, or service” (US EPA, 2012) . An LCA is performed
by first compiling an inventory of relevant energy and material inputs and
environmental releases; this is often called the Life Cycle Inventory (LCI).
Next the environmental impacts associated with each input and release is
determined and aggregated to develop an overall understanding of the
environmental impacts of the product.
In order to facilitate the comparison
between two essentially different energy storage devices, a functional unit
must also be defined. The functional unit describes what each energy storage
device must do to be considered equivalent such that a comparison of the
environmental impacts of each device using LCA is valid (Norris, 2011) .
When comparing the LightSail RAES V1 to the VRB-ESS® the functional unit could be to
produce 1 MWh of electricity at a power rating of 250 kW every day for 20
years. This functional unit will need to be adjusted to consider other energy
storage devices. Considering a combined system of renewable generation and
energy storage would require yet another functional unit.
As such nascent technologies, I have not been able to find a full
LCA of an energy storage device and without knowledge of the major components
that comprise each device an LCA would be difficult to estimate with any
reasonable level of accuracy. However the relative environmental impact can be
estimated by looking for drivers of environmental impact that are unique in
each energy storage device. The LightSail RAES V1, the VRB-ESS® and the Ice Bear are all large pieces of industrial equipment that are each made of various
quantities of metals, plastics and other materials that required quantities of
fuel and energy for manufacture. A very detailed LCA would be required to
determine if one product resulted in reduced environmental impacts compared to
the others. There is no single factor in the construction of the power
conversion system or the balance of the plant that stands out in one device
relative to the others. For this reason, it is assumed that when considering
only these two storage device components, the three products would have the
same environmental impacts.
The remaining device
component, the storage medium, should then be compared across the three devices
to see if one stands out above the others. For the Ice Bear, distilled water is
the primary storage medium (Ice Energy, 2012). For the LightSail RAES V1,
air is the primary storage medium but it should be noted that distilled water
is also used to capture, store and release heat required for the operation of
the device (Lightsail Energy, 2012) . Though producing distilled water does require significant amounts
of energy, these devices are closed loop systems so water consumption over the
life of the device will not likely be significant. Above these two devices,
vanadium redox flow batteries, such as the VRB-ESS®, have a vanadium
electrolyte as the storage medium. In a vanadium redox flow battery, the
electrolyte solution is commonly composed of vanadium pentoxide (V2O5)
in a solution of sulfuric acid (H2SO4) (Huskinson,
2013) .
With proper handling, the electrolyte can be fully recycled with little
environmental impact but it is the acquisition of vanadium itself that is
considered to be the major driver of environmental impacts for a vanadium flow
battery (Huskinson, 2013) . In a 1998 LCA study
by Carl Johan Rydh, it was determined that to meet the functional unit of 150
kWh/day over 20 years, the vanadium electrolyte would have the following
environmental impacts:
Table 1 showing LCA results for a study of vanadium
electrolyte (Rydh, 1999) .
Environmental Impact
|
Unit
|
Amount (150 kWh/day)
|
Global Warming Impact
|
kg CO2 e
|
8929
|
Water Eutrophication
|
kg PO4 e
|
6
|
Air Acidification
|
kg SO2 e
|
59
|
Scaling
these impacts up to a 1000 kWh/day system will give an estimation of the
environmental impacts attributed to the vanadium electrolyte (the storage
medium). The vanadium electrolyte impacts are assumed to be the impacts
associated with the VRB-ESS® that are above the impacts of the other two
devices.
Recent
research out of Stanford University revealed that compared to the amount of
energy they can store, the following battery technologies require significant
amounts of energy to produce:
- lead-acid
- lithium-ion
- sodium-sulfur
- vanadium-redox
- zinc-bromine
According to
Charles Barnhart, a study researcher, “This is somewhat intuitive, because
battery technologies are made out of metals, sometimes rare metals, which take
a lot of energy to acquire and purify (Shwartz, 2013) .” The study went on
to develop a metric called the ESOI (Energy Stored on Investment) which “is the
amount of energy that can be stored by a technology, divided by the amount of
energy required to build that technology. The higher the ESOI value, the better
the storage technology is energetically (Shwartz, 2013) ." It was found
that a pumped hydro facility had an ESOI of 210: i.e. a pumped hydro facility
will store 210 more energy than is required to produce the facility. In
contrast, of the electrochemical storage devices, lithium-ion batteries had the
highest ESOI value of 10 while lead-acid batteries had an ESOI value of 2 (Shwartz, 2013) .
It is easy for someone to assume
that any technology that increases the proliferation of clean renewable energy
(as is the promise of energy storage) would inherently be beneficient. However
a product that can only store twice the energy that it takes to produce cannot
be considered beneficient from an environmental perspective, especially when
significantly more efficient alternatives exist. We must strive for the best
solution and be willing to change rapidly when better solutions exist.
It
is interesting that the same team at Stanford has continued its research into
the most appropriate application of energy storage by considering whether it is
energetically more efficient to store or curtail solar energy or wind energy.
The research found that because solar panels have a significantly less
favorable ratio of output energy to energy required for production than wind
turbines, it may be a better choice to curtail rather than store wind energy
production (and in some instances solar energy production) depending on the associated
storage device (Shwartz, 2013) . The research indicates
that electrochemical energy storage (with the lower ESOI) is more appropriate, from
a financial and energetic perspective, for storing solar energy than wind
energy across a wider range of scenarios. Charles Barnhart reasons that "You
wouldn't spend a $100 on a safe to store a $10 watch. Likewise, it's not
sensible to build energetically expensive batteries for an energetically cheap
resource like wind, but it does make sense for photovoltaic systems, which
require lots of energy to produce. (Shwartz,
2013) "
Works Cited
Huskinson, B. (2013, January 11). PhD candidate,
Applied Physics; Harvard School of Engineering and Applied Sciences. (M.
Banta, Interviewer)
Lightsail Energy. (2012). Technology.
Retrieved January 14, 2013, from Lightsail Energy: http://lightsailenergy.com/tech.html
Norris, G. (2011). Doing More Good than Harm:
Footprints, Handprints, and Beneficience. Retrieved September 8, 2011,
from
http://isites.harvard.edu/fs/docs/icb.topic979929.files/Week%201%20Docs/Basic%20Beneficience%20Primer.pdf
Rydh, C. J. (1999). Environmental assessment of
vanadium redox and lead-acid batteries for stationary energy storage. Journal
of Power Sources, 21-29.
Shwartz, M. (2013, March 5). Stanford scientists
calculate the carbon footprint of grid-scale battery technologies.
Retrieved November 28, 2013, from Stanford news:
http://news.stanford.edu/news/2013/march/store-electric-grid-030513.html
Shwartz, M. (2013, September 9). Stanford
scientists calculate the energy required to store wind and solar power on the
grid. Retrieved November 28, 2013, from Stanford News:
http://news.stanford.edu/news/2013/september/curtail-energy-storage-090913.html
US EPA. (2012, August 5). Life Cycle Assessment
(LCA). Retrieved February 15, 2013, from US EPA: http://www.epa.gov/nrmrl/std/lca/lca.html
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