It is easy to assert that solar
driven renewable sources of energy, such as solar photovoltaic (PV) and wind
energy, can solve many of the problems that plague modern electricity
production. From providing environmental benefits to removing the impetus
behind marred, sometimes violent, US foreign relations, the many benefits of
wide spread renewable adoption are well known. In spite of the great promise of
solar driven renewables, in 2011, only .2% and 1.5% of US primary energy
production came from solar PV and wind energy, respectively. In total less than
12% of US primary energy came from any form of energy that is considered
renewable; including hydropower and biomass combustion (U.S. EIA, 2012) .
There are clearly significant and
powerful factors, beyond simple inertia, that explain the difference between an
idealized vision of renewable adoption and the slow, albeit accelerating,
current realized rate of adoption. Two of these factors are that solar PV and
wind energy are not currently considered reliable or viable alternatives to
conventional energy production. One way in which these renewables are not viable
is that they have not yet fully reached grid parity, i.e. the point where the
cost of electricity generated using solar PV or wind is on par with
conventional sources of energy (Lorenz, Pinner, & Seitz, 2008) . In most
areas, as a burgeoning technology, solar PV has a higher average cost/kWh than
conventional sources of energy. Considering grid parity, wind energy is further
developed with many existing, well sited, wind energy projects achieving parity
and a consensus that even “average” wind farms will achieve parity by 2016 (Bloomberg LP,
2011) .
This lack of across-the-board parity can be attributed to the current low adoption
rate of solar PV and wind energy. This low adoption has not yet pushed industry
to fully seek the economies of scale that can be realized through mass
production and deployment. It is also important to note that, in the US,
conventional energy sources enjoy substantial direct and indirect subsidies and
relief from the true cost accounting of their many externalities.
The current electric grid is the
largest industrial investment in world history (Schewe, 2006) . It is even thought by some to
represent the greatest engineering achievement of the 20th century (Wulf, 2000) . With its high
volume of delivery, the electric grid can be compared to a large retail
operation with the exception that historically the electric grid has had no
warehousing capability (Huskinson, 2013) . For the most part, electricity added
to the grid by utility generators must be consumed the instant it is delivered.
An excess of supply or demand on the grid can cause serious instability. The
responsibilities of utilities that manage the electric grid are predominantly
defined by this instantaneous delivery and consumption characteristic of
electricity on the grid.
Even with occasional outages, the
modern electrical grid is designed to provide a reliable, continuous and
seemingly inexhaustible supply of electricity at a moment’s notice. This demand
for near 100% reliability brings to light perhaps the most dominant challenge
to solar PV and wind energy adoption: the lack of reliability because of
intermittency. Solar PV’s intermittency results from its dependency on highly
variable solar access (i.e. the sun does not always shine) while wind energy’s
intermittency results from its dependency on highly variable wind resources
(i.e. the wind doesn’t always blow). This intermittency has put an upper bound
of 20% to the amount of a grid's energy that can be currently supplied by solar
PV, wind energy and other intermittent sources (APS Panel on Public Affairs, 2010) .
This 20% upper bound directly corresponds to the upper limits of the variable,
rapid response generation capacity of most conventional electric grids.
The
current electric grid, sourced by conventional means of electricity generation,
has been designed to provide grid services such as peak demand, base load demand
and power quality management. Significant and costly (therefore undesirable)
changes to the current grid architecture must be made to directly accommodate
intermittent solar PV and wind energy. This need for change to accommodate
intermittent renewables also compromises their perceived reliability and
viability.
In spite of this, early adopters of
renewable generation present a model for leading the market. Some early
adopters have implemented large scale, grid-integrated, solar PV arrays and
wind farms. Another group of early adopters can be characterized by the
implementation of small scale, distributed, grid tied solar PV and wind
installations. Some of these distributed installations are off-grid, but most
small, distributed installations remain grid tied, when possible, to improve
overall reliability. Current electric grids can tolerate only a predefined and
relatively small, number of these installations before the intermittency of
solar PV and wind generated electricity compromises grid integrity. To
compensate for intermittency, conventional generators are often left idling or
spinning. For this reason, small scale, distributed, grid tied solar PV and
wind energy systems currently, do little to viably reduce the overall amount of
required capacity and fuel consumption for conventional electricity generation (Denholm P. , Ela, Kirby, & Milligan, 2010) .
In recent years, energy storage has
garnered a significant amount of interest as a means of improving conventional
grid reliability and for mitigating renewable intermittency. Traditionally,
improving the reliability of off-grid solar PV or wind installations involved the
storage of electricity through costly lead-acid battery arrays. However the
market for both large scale centralized and small distributed energy storage is
rapidly expanding and developing. Energy storage encompasses a wide array of
technologies promising to benefit all areas of the energy market. Energy
storage is seen as the answer to the question of how to bring more and more
renewable sources of energy on line while maintaining or improving current
standards of electricity reliability. In both the large scale centralized
generation model and the small scale distributed (grid-tied or island)
generation model energy storage will play a central role in future
developments.
Works Cited
APS Panel on Public Affairs. (2010). Integrating
Renewable Electricity on the Grid. Retrieved May 22, 2012, from American
Physical Society:
http://www.aps.org/policy/reports/popa-reports/upload/integratingelec.pdf
Bloomberg LP. (2011, November 10). Onshore wind
energy to reach parity with fossil-fuel electricity by 2016. Retrieved
March 9, 2013, from Bloomberg New Energy Finance:
http://bnef.com/PressReleases/view/172
Denholm, P., Ela, E., Kirby, B., & Milligan, M.
(2010). The Role of energy storage with renewable electricity generation.
Las Vegas: NREL.
Gallagher, B. (2010). Peak Oil analyzed with a
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Huskinson, B. (2013, January 11). PhD candidate,
Applied Physics; Harvard School of Engineering and Applied Sciences. (M.
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Lorenz, P., Pinner, D., & Seitz, T. (2008). The
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Schewe, P. F. (2006). The Grid: A Journey Through
the Heart of Our Electrified World. Washington D.C.: Joseph Henry Press.
Timmer, J. (2009, January 19). DOE report paints
bleak picture of our electric future. Retrieved from ARS Technica:
http://arstechnica.com/tech-policy/2009/01/doe-report-paints-bleak-picture-of-our-electric-future/
U.S. EIA. (2012). Monthly Energy Review.
Washington DC: U.S. Department of Energy.
Wulf, W. A. (2000). Great Achievements and Grand
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