IEEE Electrification Magazine - March 2018 - 25
converter efficiency, as well as the converter type by the
precise measurement system, as displayed in Figure 4(b).
the converter efficiency is calculated by the theoretical
discrepancy current obtained from the PV and ec I-V relationship and from the real current measured by the experiment. the experiment found that duty ratio, which is
closed to the certain ratio as 1, can decrease the converting efficiency of buck-type converters. If the duty ratio
applied on converter decreases to less than 0.9, the efficiency of a converter increases to ~95% at 50-150 mW of
PV-generated electrical power range. According to this
study, the buck-type converter can guarantee a higher
converting efficiency compared to the boost-type converter. therefore, this study gives important guidelines
to design the PV-ec system with an appropriate converter
type, as well as the underlying science beneath this
whole system.
STH Efficiency
Based on Sth efficiency and the electrical energy conversion efficiency, we can plot the Sth efficiency, as shown in
Figure 5. As the years go by, the reported Sth efficiency
generally increases. moreover, the efficiency of monolithic
solar cell-based system, as well as the tandem solar cellbased system, upsurges. the monolithic solar cell-based
system record high in Figure 5(a) is the research assisted
by dc-dc converter (20.6% Sth efficiency). When it comes
to the electricity conversion ratio to H 2, presented in Figure 5(b), it indicates that the converter usage is beneficial.
even if the high A EC /A PV usually helps achieve high solardriven electricity-to-H 2 generation ratio, a high ec surface
area compared to a PV generally requires a high amount
of ec materials and, consequently, costs a lot. therefore, a
modest A EC /A PV design that still produces high amounts
of H 2 compared to the solar-driven electrical power
should be targeted.
Conclusion
the converter-assisted PV utilization, in addition to the H 2
generated by solar light for an energy system, can be generalized. For instance, solar-driven CO 2 reduction to useful
organic molecules, i.e., ethanol, methanol, acetaldehyde,
or even propanol, can be achieved with converter-assisted
PV-ec with appropriate catalyst materials designed for
CO 2 reduction. Indeed, the potential range is much narrower for CO 2 reduction, so the role of the converter with
a designated duty ratio can reap benefits for this system.
the combination of converter technology with energy
conversion catalysts and solar cells are effective ways to
reach a sustainable future in H 2 production.
For Further Reading
O. Khaselev and J. A. turner, "A monolithic photovoltaic-photoelectrochemical device for hydrogen production via water
splitting," Sci., vol. 280, no. 5362, pp. 425-427, 1998.
J. Jia, L. c. Seitz, J. D. Benck, Y. huo, Y. chen, J. W. D. ng,
t. Bilir, J. S. harris, and t. F. Jaramillo, "Solar water splitting by
photovoltaic-electrolysis with a solar-to-hydrogen efficiency
over 30%," Nature Commun., vol. 7, no. 13237, 2016.
t. J. Jacobsson, V. Fjällström, m. Sahlberg, m. edoff, and t.
edvinsson, "A monolithic device for solar water splitting
based on series interconnected thin film absorbers reaching
over 10% solar-to-hydrogen efficiency," Energy Environ. Sci., vol.
6, no. 12, pp. 3676-3683, 2013.
S. A. Bonke, m. Wiechen, D. r. macFarlane, and L. Spiccia,
"renewable fuels from concentrated solar power: towards
practical artificial photosynthesis," Energy Environ. Sci., vol. 8,
no. 9, pp. 2791-2796, 2015.
e. Verlage, S. hu, r. Liu, r. J. Jones, K. Sun, c. Xiang, n. S.
Lewis, and h. A. Atwater, "A monolithically integrated, intrinsically safe, 10% efficient, solar-driven water-splitting system
based on active, stable earth-abundant electrocatalysts in
conjunction with tandem III-V light absorbers protected by
amorphous tiO 2 films," Energy Environ. Sci., vol. 8, no. 11,
pp. 3166-3172, 2015.
m. A. modestino, K. A. Walczak, A. Berger, c. m. evans, S.
haussener, c. Koval, J. S. newman, J. W. Ager, and r. A. Segalman, "robust production of purified h2 in a stable, self-regulating, and continuously operating solar fuel generator,"
Energy Environmental Sci., vol. 7, no. 1, pp. 297-301, 2014.
W. J. chang, K.-h. Lee, h. ha, K. Jin, g. Kim, S.-t. hwang, et
al., "Design principle and loss engineering for photovoltaic-
electrolysis cell system," ACS Omega, vol. 2, pp. 1009-1018,
2017.
J. L. Young, m. A. Steiner, h. Döscher, r. m. France, J. A. turner, and t. g. Deutsch, "Direct solar-to-hydrogen conversion via
inverted metamorphic multi-junction semiconductor architectures," Nature Energy, vol. 2, p. 201728, 2017.
c. r. cox, J. Z. Lee, D. g. nocera, and t. Buonassisi, "ten-percent solar-to-fuel conversion with nonprecious materials,"
Nat. Academy Sci., vol. 111, pp. 14057-14061, 2014.
r. V. noorden, "Secrets of artificial leaf revealed," Nature
news, vol. 10, 2011.
J. Luo, J.-h. Im, m. t. mayer, m. Schreier, m. K. nazeeruddin,
n.-g. Park, et al., "Water photolysis at 12.3% efficiency via
perovskite photovoltaics and earth-abundant catalysts," Science, vol. 345, pp. 1593-1596, 2014.
A. nakamura, Y. Ota, K. Koike, Y. hidaka, K. nishioka, m.
Sugiyama, et al., "A 24.4% solar to hydrogen energy conversion efficiency by combining concentrator photovoltaic modules and electrochemical cells," Appl. Physics Express, vol. 8,
p. 107101, 2015.
A. garrigós, J. Lizán, J. Blanes, and r. gutierrez, "combined
maximum power point tracking and output current control
for a photovoltaic-electrolyser dc/dc converter," Int. J. Hydrogen
Energy, vol. 39, pp. 20907-20919, 2014.
Biographies
Woo Je Chang (woochang2021@u.northwestern.edu) is
pursuing a Ph.D. degree in materials science and engineering, northwestern University, evanston, Illinois.
Kyung-Hwan Lee (kyungahsal@snu.ac.kr) is pursuing a
Ph.D. degree in electrical and computer engineering, Seoul
national University, South Korea.
Jung-Ik Ha (jungikha@snu.ac.kr) is an associate professor of electrical and computer engineering, Seoul national
University, South Korea.
Ki Tae Nam (nkitae@snu.ac.kr) is an associate professor
of materials science and engineering, Seoul national University, South Korea.
IEEE Electrific ation Magazine / ma r c h 201 8
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