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Design parameters of solar concentrating systems for CO2-mitigating algal photobioreactors
Energy 29 (2004) 1651–1657 www.elsevier.com/locate/energy
Design parameters of solar concentrating systems for CO2-mitigating algal photobioreactors Eiichi Ono, Joel L. Cuello Department of Agricultural and Biosystems Engineering, 507 Shantz Building, The University of Arizona, Tucson, AZ 85745, USA
Abstract The strategy of exploiting photosynthesizing microalgal cultures to remove carbon dioxide (CO2) from flue gases through fixation has potential in effectively diminishing the release of CO2 to the atmosphere, helping alleviate the trend toward global warming. The use of fiberoptic-based solar concentrating systems for microalgal photobiorectors has the potential to meet the two essential criteria in the design of a lighting system for algal photobioreactors: (1) electrical energy efficiency; and (2) lighting distribution efficiency. The overall efficiencies of solar concentrating systems have significantly improved in recent years, exceeding 45%. Meanwhile, achieving uniform lighting distribution within photobioreactors constitutes probably the greatest challenge in using fiberoptic-based solar concentrators as a lighting system for photobioreactors. The light-emitting fibers appeared to be a most promising candidate in achieving such uniform light distribution in photobioreactors. Also, when a hybrid-solar-and-electric-lighting scheme is adopted to augment solar lighting whenever needed, the hybrid lighting distribution needs to be designed accordingly. # 2004 Elsevier Ltd. All rights reserved.
1. Introduction In addition to the several commercial applications of microalgal cultures, including health foods, aquaculture feeds, animal feeds and specialty chemicals [1,2], their photoautotrophic or photomixotrophic capacity has also recently been exploited to remove carbon dioxide (CO2) from flue gases through fixation [3–7]. The strategy has potential in effectively diminishing the release of CO2 to the atmosphere, helping alleviate the trend toward global warming [4,8]. The large-scale intensive cultivation of microalgal cultures that this strategy demands, however, calls
Corresponding author. Tel.: +1-520-621-7757; fax: +1-520-621-3963. E-mail address: [email protected] (J.L. Cuello).
0360-5442/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2004.03.067
1652
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for the design of appropriate photobioreactors. The conventional method for the mass cultivation of microalgae makes use of open ponds with standard raceway design, utilizing sunlight as the light source. Such an approach, however, suffers from the following disadvantages: (1) requirement for large land areas; (2) difficulty in controlling culture conditions; (3) evaporation of the medium; and (4) reduction in light intensity with medium depth since sunlight shines only on the surface. Other methods include growing the microalgae in translucent fiberglass cylinders, polyethylene bags, carboys and tanks under electric or solar illumination in greenhouses [1]. The algal production in these systems, however, were far lower than the theoretical algal productivity of 60 g/m2-d owing primarily to light limitation [1]. For instance, at an algal density of 0.45 g/L, light penetrated the suspension only at a depth of 5 cm, leaving over 60% of the cultures in complete darkness [9]. The design of an appropriate photobioreactor will significantly reduce the requirement for large land areas since cylindrical or flat-plate photobioreactors employ vertical distribution of the algal cultures as opposed to the horizontal surface distribution employed by the open pond design. Further, closed cylindrical and flat-plate photobioreactors will obviate the difficulty in controlling culture conditions as well as the evaporation of the culture medium. In terms of the reduction in light intensity with medium depth encountered in open-pond systems, the use of fiberoptic-based solar concentrating systems for microalgal photobiorectors has the potential to meet the two essential criteria in the design of a lighting system for algal photobioreactors: (1) electrical energy efficiency; and (2) lighting distribution efficiency. This paper presents the recent efforts in the United States in designing fiberoptic-based solar concentrating systems that are compatible with algal photobioreactors, focusing on the two parameters of (1) solar concentration and (2) lighting distribution.
2. Solar concentration 2.1. National Aeronautics and Space Administration (NASA) A series of NASA-funded studies on the use of solar concentrating systems to harness solar irradiance for use in a plant growth chamber located in a subterranean facility were conducted at The University of Arizona. Two fiberoptic-based solar concentrating systems were used. First was the fresnel-lens-based Mini 7-Lens Himawari Solar Concentrating and Transmitting System (La Foret Engineering Co., Ltd., Tokyo, Japan). The fresnel-lens-based Mini 7-Lens Himawari (Fig. 1), which was developed in the early 1980’s by Kei Mori of Keio University in Tokyo, Japan [10], collected light through a protective acrylic resin capsule. Inside the capsule, hexagon-shaped, honey-combed patterned fresnel lenses captured incoming parallel light rays that were then focused onto the highly polished input ends of fiberoptic cables. The Mini 7-Lens Himawari had a capsule diameter of 0.94 m, stood 1.3 m, had a base frame of 0:9 0:9 m and had an aggregate lens surface area of 0.22 m2. Each of its seven 10-m fused-silica fiberoptic cables contained 20 optical fibers, each with a diameter of 0.51 mm. The second fiberoptic-based solar concentrating system that was used was the mirror-based Optical Waveguide (OW) Solar Lighting System [11], consisting of two solar tracking units, each equipped with two 50-cm parabolic primary mirror concentrators (Fig. 2). At the focal
E. Ono, J.L. Cuello / Energy 29 (2004) 1651–1657
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Fig. 1. The Mini 7-Lens Himawari solar concentrating and transmitting system.
Fig. 2. The optical waveguide (OW) solar lighting system.
point of each primary concentrator was a fused quartz secondary concentrator, which further concentrated the high-intensity solar flux from the primary concentrator and injected it into a fiberoptic cable. Each fiberoptic cable was 10 m long, consisting of 37 optical fibers, each with a diameter of 1 mm. The overall efficiencies of solar concentrating systems have significantly improved in recent years. Such improvement is attributable mainly to the enhancement in the light transmission efficiencies of commercially available optical cables. Table 1 shows how the overall efficiency of the OW Solar Lighting System compared with that of the fresnel-lens-based Mini 7-Lens Himawari Solar Concentrating and Transmitting System. In Table 1 the Himawari, whose fused-silica
1654
E. Ono, J.L. Cuello / Energy 29 (2004) 1651–1657
Table 1 Solar collector’s overall efficiencies System
Efficiencies
Fresnel based solar collector (Himawari) Mirror based, double mirror (PSI-Silica Cables) Mirror based, single mirror (PSI-Liquid-Based Cables)
23.2% 40.5% 46.1%
cables had a transmission efficiency of 32.4%/10 m, had an overall system efficiency of 23.2%. The OW SICTDS that was used in this study was equipped with fused-silica cables having a transmission efficiency of 64.1%/10 m, resulting in a higher overall system efficiency of 40.5%. And when proprietary liquid-based cables with a transmission efficiency of 72%/10 m was used for OW SICTDS, its overall system efficiency improved further to 46.1%. The projected average instantaneous photosynthetic photon flux (PPF) within the plant growth chamber in the subterranean plant growth facility per hour and per day throughout the year were calculated using the databases for hourly solar irradiance incident upon Tucson, AZ compiled over a 12-year period from 1987 through 1998. The results [8] showed that replacing the available solar irradiance within the growth chamber as delivered by the Himawari for the month of June, wherein the daily average instantaneous photosynthetic photon flux (PPF) delivered was 171.0 lmol m 2 s 1, would require either 97.7 W m 2 of HPS lighting or 185.9 W m 2 of CWF lighting supplied continuously for 450 h. In energy terms, these would be equivalent to 44.0 kW-h m 2 for the HPS lamp and 83.7 kW-h m 2 for the CWF lamp. For a whole year, the equivalent energy expenditures would be 0.4 MW-h m 2 for the HPS lamp and 0.7 MW-h m 2 for the CWF lamp. By contrast, replacing the available solar irradiance within the growth chamber as delivered by the OW Solar Lighting System for the month of June, wherein the daily average instantaneous PPF delivered was 402.4 lmol m 2 s 1, would require either 229.9 W m 2 of HPS lighting or 437.4 W m 2 of CWF lighting supplied continuously for 450 h [8]. In energy terms, these would be equivalent to 103.5 kW-h m 2 for the HPS lamp and 196.8 kW-h m 2 for the CWF lamp. For a whole year, the equivalent energy expenditures would be 0.9 MW-h m 2 for the HPS lamp and 1.7 MW-h m 2 for the CWF lamp [12].
2.2. Department of Energy The Department of Energy’s Oak Ridge National Laboratory has also designed solar concentrators with the solar lighting of commercial buildings as the original motivation, but now is also being adapted for use in microalgal photobioreactors. The design, shown in Fig. 3, used segmented secondary ultraviolet (UV) cold mirror to reflect and focus the visible portion of sunlight onto several 12-mm large-core optical fibers that transport visible light into buildings while transmitting the UV and infrared (IR) wavelengths to IR-thermal photovoltaics [13]. The design was selected to accommodate the use of two different commercially-available primary mirrors: (1) a polished 1.2 m diameter glass mirror with an enhanced aluminum 92% reflective coating; and (2) a steel 1.5 m diameter mirror with an 85% adhesive-backed first-surface aluminum
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Fig. 3. DOE solar concentrator design.
reflective coating [13]. The secondary mirror consists of eight segmented mirror surfaces each focusing light onto separate optical fibers [13].
3. Lighting distribution Achieving uniform lighting distribution within photobioreactors constitutes probably the greatest challenge in using fiberoptic-based solar concentrators as a lighting system for photobioreactors. Light distribution patterns from various optical devices, including silica and polymer optical cables, light pipes, woven optical pads, and light-emitting fibers, were investigated by Cuello et al. [14]. The light-emitting fibers appeared to be a most promising candidate. These light-emitting fibers were used by Cuello et al. [15] in delivering irradiance into a growth chamber from remotely-located xenon-metal halide illuminators. Also, a version of these light-emitting fibers, configured for use in a flat-plate algal photobioreactor as designed by Oak Ridge National Laboratory, is currently being tested at Ohio University (Fig. 4) [13]. There is a need for light-emitting optical cables that can emit light more uniformly at longer lengths and with numerous turns and bends. Since solar irradiance is not always available, it is only logical to consider a hybrid solar and electric lighting strategy for large-scale intensive algal photobioreactors to augment the solar lighting whenever needed. When hybrid lighting is adopted, the hybrid lighting distribution needs to be designed accordingly. An example of a hybrid lighting distribution scheme was developed by Cuello et al. [16], wherein the fiberoptic tips from the solar-concentrators formed a rectangular array with strips of light-emitting diodes (LEDs) (Fig. 5). Cuello et al. [15] also used light-emitting fibers connected to xenon-metal halide illuminators running alternately with the fiberoptic tips from the solar concentrators.
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Fig. 4. Light-emitting cables for use in a flat-plate photobioreactor.
Fig. 5. Rows of solar fiber tips running in parallel and alternately with LED strips.
4. Conclusions The overall efficiencies of solar concentrating systems have significantly improved in recent years, exceeding 45%. Meanwhile, achieving uniform lighting distribution within photobioreactors constitutes probably the greatest challenge in using fiberoptic-based solar concentrators as a lighting system for photobioreactors. The light-emitting fibers appeared to be a most promising candidate in achieving such uniform light distribution in photobioreactors. Also, when a hybrid-solar-and-electric-lighting scheme is adopted to augment solar lighting whenever needed, the hybrid lighting distribution needs to be designed accordingly.
References [1] Spektorova L, Creswell RL, Vaughan D. Closed tubular cultivators: an innovative system for commercial culture of microalgae. World Aquaculture 1997;June:39–43. [2] Benneman JR. Microalgae products and production, and overview. J Indust Microbiol 1990;5(Suppl):247–56. [3] Miyamoto K, Benneman JR. Bioreactors for fixation and utilization of carbon dioxide. Chem Eng 1991;26: 490–4.
E. Ono, J.L. Cuello / Energy 29 (2004) 1651–1657
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[4] Hirata S, Taya M, Tone S. Characterization of Chlorella cell cultures in batch and continuos operations under a photoautotrophic condition. Journal of chemical engineering of Japan 1996;29(6):953–9. [5] Negoro M, Shioji N, Miyamoto K, Miura Y. Growth of microalgae in high CO2 gas and effects of SOx and NOx. Appl Biochem Biotechnol 1991;28:877–86. [6] Laws EA, Berning JL. Photosynthetic efficiency optimization studies with the macroalga Gracilaria tikvihae: implications for CO2 emission control from power plants. Bioresource Technol 1991;37:25–33. [7] Akimoto M, Ohara T, Ohtaguchi K, Koide K. Carbon dioxide fixation and a-linolenic acid production by the hot-spring alga Cyanidium caldarium. J Chem Eng Jpn 1994;27:329–33. [8] Benemann JR. Utilization of carbon dioxide from fossil fuel—burning power plants with biological system. Energy Convers Mgmt 1993;34:999–1004. [9] Richmond A, Vonshak A, Arad SM. In: Shelef G, Soeder CJ, editors. Algae biomass. New York: Elsevier; 1980, p. 65–73. [10] Mori K. Photoautotrophic bioreactor using visible solar rays condensed by fresnel lenses and transmitted through optical fibers. Biotechnol Bioeng Symp 1985;15:331–44. [11] Nakamura T, Case JA, Jack DA, Cuello JL. Optical waveguide solar plant lighting system for life support in space. In: Proceedings of the 29th International Conference on Environmental Systems. Warrendale, PA: ICES/ SAE; 1999. [12] Cuello JL, Jack DA, Ono E, Nakamura T. Supplemental terrestrial solar lighting for an experimental subterranean biomass production chamber. In: Proceedings of the 30th International Conference on Environmental Systems. Warrendale, PA: ICES/SAE; 2000. [13] Muhs J, Earl DD. Full-spectrum solar energy systems for use in commercial building. In: Proceedings of the 36th Intersociety Energy Conversion Engineering Conference. New York, NY: ASME; 2001. [14] Cuello JL, Sadler P, Jack D, Ono E, Jordan KA. Evaluation of light transmission and distribution materials for Lunar and Martian bioregenerative life support. International Journal of Life Support and Bioshere Science 1998;5:389–402. [15] Cuello JL, Yang Y, Ono E, Jordan KA, Nakamura T. Hybrid solar and xenon-metal halide lighting for Lunar and Martian bioregenerative life support. In: Proceedings of the 30th International Conference on Environmental Systems. Warrendale, PA: ICES/SAE; 2000. [16] Cuello JL, Yang Y, Kuwahara S, Ono E, Jordan KA, Nakamura T, Watanabe H. Plant hardware equipped with hybrid lighting: combining solar irradiance with xenon-metal halide lamps or light-emitting diodes for life support in space. In: Proceedings of the 31th International Conference on Environmental Systems. Warrendale, PA: ICES/SAE; 2001.
Design parameters of solar concentrating systems for CO2-mitigating algal photobioreactors Eiichi Ono, Joel L. Cuello Department of Agricultural and Biosystems Engineering, 507 Shantz Building, The University of Arizona, Tucson, AZ 85745, USA
Abstract The strategy of exploiting photosynthesizing microalgal cultures to remove carbon dioxide (CO2) from flue gases through fixation has potential in effectively diminishing the release of CO2 to the atmosphere, helping alleviate the trend toward global warming. The use of fiberoptic-based solar concentrating systems for microalgal photobiorectors has the potential to meet the two essential criteria in the design of a lighting system for algal photobioreactors: (1) electrical energy efficiency; and (2) lighting distribution efficiency. The overall efficiencies of solar concentrating systems have significantly improved in recent years, exceeding 45%. Meanwhile, achieving uniform lighting distribution within photobioreactors constitutes probably the greatest challenge in using fiberoptic-based solar concentrators as a lighting system for photobioreactors. The light-emitting fibers appeared to be a most promising candidate in achieving such uniform light distribution in photobioreactors. Also, when a hybrid-solar-and-electric-lighting scheme is adopted to augment solar lighting whenever needed, the hybrid lighting distribution needs to be designed accordingly. # 2004 Elsevier Ltd. All rights reserved.
1. Introduction In addition to the several commercial applications of microalgal cultures, including health foods, aquaculture feeds, animal feeds and specialty chemicals [1,2], their photoautotrophic or photomixotrophic capacity has also recently been exploited to remove carbon dioxide (CO2) from flue gases through fixation [3–7]. The strategy has potential in effectively diminishing the release of CO2 to the atmosphere, helping alleviate the trend toward global warming [4,8]. The large-scale intensive cultivation of microalgal cultures that this strategy demands, however, calls
Corresponding author. Tel.: +1-520-621-7757; fax: +1-520-621-3963. E-mail address: [email protected] (J.L. Cuello).
0360-5442/$ - see front matter # 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2004.03.067
1652
E. Ono, J.L. Cuello / Energy 29 (2004) 1651–1657
for the design of appropriate photobioreactors. The conventional method for the mass cultivation of microalgae makes use of open ponds with standard raceway design, utilizing sunlight as the light source. Such an approach, however, suffers from the following disadvantages: (1) requirement for large land areas; (2) difficulty in controlling culture conditions; (3) evaporation of the medium; and (4) reduction in light intensity with medium depth since sunlight shines only on the surface. Other methods include growing the microalgae in translucent fiberglass cylinders, polyethylene bags, carboys and tanks under electric or solar illumination in greenhouses [1]. The algal production in these systems, however, were far lower than the theoretical algal productivity of 60 g/m2-d owing primarily to light limitation [1]. For instance, at an algal density of 0.45 g/L, light penetrated the suspension only at a depth of 5 cm, leaving over 60% of the cultures in complete darkness [9]. The design of an appropriate photobioreactor will significantly reduce the requirement for large land areas since cylindrical or flat-plate photobioreactors employ vertical distribution of the algal cultures as opposed to the horizontal surface distribution employed by the open pond design. Further, closed cylindrical and flat-plate photobioreactors will obviate the difficulty in controlling culture conditions as well as the evaporation of the culture medium. In terms of the reduction in light intensity with medium depth encountered in open-pond systems, the use of fiberoptic-based solar concentrating systems for microalgal photobiorectors has the potential to meet the two essential criteria in the design of a lighting system for algal photobioreactors: (1) electrical energy efficiency; and (2) lighting distribution efficiency. This paper presents the recent efforts in the United States in designing fiberoptic-based solar concentrating systems that are compatible with algal photobioreactors, focusing on the two parameters of (1) solar concentration and (2) lighting distribution.
2. Solar concentration 2.1. National Aeronautics and Space Administration (NASA) A series of NASA-funded studies on the use of solar concentrating systems to harness solar irradiance for use in a plant growth chamber located in a subterranean facility were conducted at The University of Arizona. Two fiberoptic-based solar concentrating systems were used. First was the fresnel-lens-based Mini 7-Lens Himawari Solar Concentrating and Transmitting System (La Foret Engineering Co., Ltd., Tokyo, Japan). The fresnel-lens-based Mini 7-Lens Himawari (Fig. 1), which was developed in the early 1980’s by Kei Mori of Keio University in Tokyo, Japan [10], collected light through a protective acrylic resin capsule. Inside the capsule, hexagon-shaped, honey-combed patterned fresnel lenses captured incoming parallel light rays that were then focused onto the highly polished input ends of fiberoptic cables. The Mini 7-Lens Himawari had a capsule diameter of 0.94 m, stood 1.3 m, had a base frame of 0:9 0:9 m and had an aggregate lens surface area of 0.22 m2. Each of its seven 10-m fused-silica fiberoptic cables contained 20 optical fibers, each with a diameter of 0.51 mm. The second fiberoptic-based solar concentrating system that was used was the mirror-based Optical Waveguide (OW) Solar Lighting System [11], consisting of two solar tracking units, each equipped with two 50-cm parabolic primary mirror concentrators (Fig. 2). At the focal
E. Ono, J.L. Cuello / Energy 29 (2004) 1651–1657
1653
Fig. 1. The Mini 7-Lens Himawari solar concentrating and transmitting system.
Fig. 2. The optical waveguide (OW) solar lighting system.
point of each primary concentrator was a fused quartz secondary concentrator, which further concentrated the high-intensity solar flux from the primary concentrator and injected it into a fiberoptic cable. Each fiberoptic cable was 10 m long, consisting of 37 optical fibers, each with a diameter of 1 mm. The overall efficiencies of solar concentrating systems have significantly improved in recent years. Such improvement is attributable mainly to the enhancement in the light transmission efficiencies of commercially available optical cables. Table 1 shows how the overall efficiency of the OW Solar Lighting System compared with that of the fresnel-lens-based Mini 7-Lens Himawari Solar Concentrating and Transmitting System. In Table 1 the Himawari, whose fused-silica
1654
E. Ono, J.L. Cuello / Energy 29 (2004) 1651–1657
Table 1 Solar collector’s overall efficiencies System
Efficiencies
Fresnel based solar collector (Himawari) Mirror based, double mirror (PSI-Silica Cables) Mirror based, single mirror (PSI-Liquid-Based Cables)
23.2% 40.5% 46.1%
cables had a transmission efficiency of 32.4%/10 m, had an overall system efficiency of 23.2%. The OW SICTDS that was used in this study was equipped with fused-silica cables having a transmission efficiency of 64.1%/10 m, resulting in a higher overall system efficiency of 40.5%. And when proprietary liquid-based cables with a transmission efficiency of 72%/10 m was used for OW SICTDS, its overall system efficiency improved further to 46.1%. The projected average instantaneous photosynthetic photon flux (PPF) within the plant growth chamber in the subterranean plant growth facility per hour and per day throughout the year were calculated using the databases for hourly solar irradiance incident upon Tucson, AZ compiled over a 12-year period from 1987 through 1998. The results [8] showed that replacing the available solar irradiance within the growth chamber as delivered by the Himawari for the month of June, wherein the daily average instantaneous photosynthetic photon flux (PPF) delivered was 171.0 lmol m 2 s 1, would require either 97.7 W m 2 of HPS lighting or 185.9 W m 2 of CWF lighting supplied continuously for 450 h. In energy terms, these would be equivalent to 44.0 kW-h m 2 for the HPS lamp and 83.7 kW-h m 2 for the CWF lamp. For a whole year, the equivalent energy expenditures would be 0.4 MW-h m 2 for the HPS lamp and 0.7 MW-h m 2 for the CWF lamp. By contrast, replacing the available solar irradiance within the growth chamber as delivered by the OW Solar Lighting System for the month of June, wherein the daily average instantaneous PPF delivered was 402.4 lmol m 2 s 1, would require either 229.9 W m 2 of HPS lighting or 437.4 W m 2 of CWF lighting supplied continuously for 450 h [8]. In energy terms, these would be equivalent to 103.5 kW-h m 2 for the HPS lamp and 196.8 kW-h m 2 for the CWF lamp. For a whole year, the equivalent energy expenditures would be 0.9 MW-h m 2 for the HPS lamp and 1.7 MW-h m 2 for the CWF lamp [12].
2.2. Department of Energy The Department of Energy’s Oak Ridge National Laboratory has also designed solar concentrators with the solar lighting of commercial buildings as the original motivation, but now is also being adapted for use in microalgal photobioreactors. The design, shown in Fig. 3, used segmented secondary ultraviolet (UV) cold mirror to reflect and focus the visible portion of sunlight onto several 12-mm large-core optical fibers that transport visible light into buildings while transmitting the UV and infrared (IR) wavelengths to IR-thermal photovoltaics [13]. The design was selected to accommodate the use of two different commercially-available primary mirrors: (1) a polished 1.2 m diameter glass mirror with an enhanced aluminum 92% reflective coating; and (2) a steel 1.5 m diameter mirror with an 85% adhesive-backed first-surface aluminum
E. Ono, J.L. Cuello / Energy 29 (2004) 1651–1657
1655
Fig. 3. DOE solar concentrator design.
reflective coating [13]. The secondary mirror consists of eight segmented mirror surfaces each focusing light onto separate optical fibers [13].
3. Lighting distribution Achieving uniform lighting distribution within photobioreactors constitutes probably the greatest challenge in using fiberoptic-based solar concentrators as a lighting system for photobioreactors. Light distribution patterns from various optical devices, including silica and polymer optical cables, light pipes, woven optical pads, and light-emitting fibers, were investigated by Cuello et al. [14]. The light-emitting fibers appeared to be a most promising candidate. These light-emitting fibers were used by Cuello et al. [15] in delivering irradiance into a growth chamber from remotely-located xenon-metal halide illuminators. Also, a version of these light-emitting fibers, configured for use in a flat-plate algal photobioreactor as designed by Oak Ridge National Laboratory, is currently being tested at Ohio University (Fig. 4) [13]. There is a need for light-emitting optical cables that can emit light more uniformly at longer lengths and with numerous turns and bends. Since solar irradiance is not always available, it is only logical to consider a hybrid solar and electric lighting strategy for large-scale intensive algal photobioreactors to augment the solar lighting whenever needed. When hybrid lighting is adopted, the hybrid lighting distribution needs to be designed accordingly. An example of a hybrid lighting distribution scheme was developed by Cuello et al. [16], wherein the fiberoptic tips from the solar-concentrators formed a rectangular array with strips of light-emitting diodes (LEDs) (Fig. 5). Cuello et al. [15] also used light-emitting fibers connected to xenon-metal halide illuminators running alternately with the fiberoptic tips from the solar concentrators.
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Fig. 4. Light-emitting cables for use in a flat-plate photobioreactor.
Fig. 5. Rows of solar fiber tips running in parallel and alternately with LED strips.
4. Conclusions The overall efficiencies of solar concentrating systems have significantly improved in recent years, exceeding 45%. Meanwhile, achieving uniform lighting distribution within photobioreactors constitutes probably the greatest challenge in using fiberoptic-based solar concentrators as a lighting system for photobioreactors. The light-emitting fibers appeared to be a most promising candidate in achieving such uniform light distribution in photobioreactors. Also, when a hybrid-solar-and-electric-lighting scheme is adopted to augment solar lighting whenever needed, the hybrid lighting distribution needs to be designed accordingly.
References [1] Spektorova L, Creswell RL, Vaughan D. Closed tubular cultivators: an innovative system for commercial culture of microalgae. World Aquaculture 1997;June:39–43. [2] Benneman JR. Microalgae products and production, and overview. J Indust Microbiol 1990;5(Suppl):247–56. [3] Miyamoto K, Benneman JR. Bioreactors for fixation and utilization of carbon dioxide. Chem Eng 1991;26: 490–4.
E. Ono, J.L. Cuello / Energy 29 (2004) 1651–1657
1657
[4] Hirata S, Taya M, Tone S. Characterization of Chlorella cell cultures in batch and continuos operations under a photoautotrophic condition. Journal of chemical engineering of Japan 1996;29(6):953–9. [5] Negoro M, Shioji N, Miyamoto K, Miura Y. Growth of microalgae in high CO2 gas and effects of SOx and NOx. Appl Biochem Biotechnol 1991;28:877–86. [6] Laws EA, Berning JL. Photosynthetic efficiency optimization studies with the macroalga Gracilaria tikvihae: implications for CO2 emission control from power plants. Bioresource Technol 1991;37:25–33. [7] Akimoto M, Ohara T, Ohtaguchi K, Koide K. Carbon dioxide fixation and a-linolenic acid production by the hot-spring alga Cyanidium caldarium. J Chem Eng Jpn 1994;27:329–33. [8] Benemann JR. Utilization of carbon dioxide from fossil fuel—burning power plants with biological system. Energy Convers Mgmt 1993;34:999–1004. [9] Richmond A, Vonshak A, Arad SM. In: Shelef G, Soeder CJ, editors. Algae biomass. New York: Elsevier; 1980, p. 65–73. [10] Mori K. Photoautotrophic bioreactor using visible solar rays condensed by fresnel lenses and transmitted through optical fibers. Biotechnol Bioeng Symp 1985;15:331–44. [11] Nakamura T, Case JA, Jack DA, Cuello JL. Optical waveguide solar plant lighting system for life support in space. In: Proceedings of the 29th International Conference on Environmental Systems. Warrendale, PA: ICES/ SAE; 1999. [12] Cuello JL, Jack DA, Ono E, Nakamura T. Supplemental terrestrial solar lighting for an experimental subterranean biomass production chamber. In: Proceedings of the 30th International Conference on Environmental Systems. Warrendale, PA: ICES/SAE; 2000. [13] Muhs J, Earl DD. Full-spectrum solar energy systems for use in commercial building. In: Proceedings of the 36th Intersociety Energy Conversion Engineering Conference. New York, NY: ASME; 2001. [14] Cuello JL, Sadler P, Jack D, Ono E, Jordan KA. Evaluation of light transmission and distribution materials for Lunar and Martian bioregenerative life support. International Journal of Life Support and Bioshere Science 1998;5:389–402. [15] Cuello JL, Yang Y, Ono E, Jordan KA, Nakamura T. Hybrid solar and xenon-metal halide lighting for Lunar and Martian bioregenerative life support. In: Proceedings of the 30th International Conference on Environmental Systems. Warrendale, PA: ICES/SAE; 2000. [16] Cuello JL, Yang Y, Kuwahara S, Ono E, Jordan KA, Nakamura T, Watanabe H. Plant hardware equipped with hybrid lighting: combining solar irradiance with xenon-metal halide lamps or light-emitting diodes for life support in space. In: Proceedings of the 31th International Conference on Environmental Systems. Warrendale, PA: ICES/SAE; 2001.