An Introduction to My Research

This blog is an introduction to my research: biological engineering for energy that is guided by physical principles. This post starts with an introduction to how I see the problem that my research aims to solve.

In the coming century, the world faces a crisis of energy, sustainability and climate. In the next 25 years, world energy use is projected to increase from 17 terawatts (TW) to 26 TW [1], [2]. If this energy is supplied by fossil sources it will pollute the atmosphere with carbon dioxide with consequences for climate [3], ecology and society [4], [5] for centuries to come [6]. Even if this carbon is sequestered, we are still faced with the peak in production of coal, the most abundant fossil fuel [7], before 2050 [8]-[11]. To get an idea of just how high world power usage might rise in the coming century, let’s apply the current power usage of the average American today of 10 kilowatts (kW) to the 10 billion people likely to be alive in 2100, and we get a total power usage of 100 TW.

Biology already gives a first draft solution to the problems of non-polluting energy capture and storage at the scale needed by civilization [12], channeling ≈ 100 TW [13] by photosynthesis into biomass. Biology is self-replicating and constructs itself from abundant elements, lowering deployment costs. However, the scale of biological energy capture belies the inefficiency of photosynthesis. The 100 TW of energy channeled by photosynthesis is small compared with the solar flux at the Earth’s surface of ≈ 80,000 TW [14]. The average energy conversion efficiency of sunlight to biomass by photosynthesis rarely exceeds 1% [15] in the field.

Figure 1 - Photosynthetic Vs Photovoltaic Efficiency Comparison

Fig 1: Comparison of estimated energy losses in photosynthesis (upper green boxes) and photovoltaics (lower blue boxes) based on published data [12, 15, 21]. The efficiency of each individual step is shown in each box. The cumulative efficiency of the entire process is shown in the box below each process. Biological primary photon capture has an upper efficiency bound of 26% [21] but in practice rarely exceeds 11% [12].

By contrast, the efficiency of hydrogen production by photovoltaic driven electrolysis is ≈ 14% [15]. A breakdown of the losses in these processes are shown in figure 1. It is estimated that for many plants, light harvesting saturates at only ≈ 13% of the incoming solar flux [12]. Moreover, biological CO2 fixation is limited by the low catalytic rate of RuBisCO. This carboxylating enzyme appears to be already naturally optimized, with little room for improvement [16]-[18].

The inefficiency of photosynthesis sets the stage for competition between land for agriculture and wilderness and land for energy crops [19]. In order to capture just 1 TW of solar energy (< 1/3rd of US energy use [20]) at an efficiency of 1%, an area equal to 0.28 times the US cropland would need to be covered with energy crops [12].
Is there a better way to harness solar energy?

Notes and References

[1] J. Conti and P. Holtberg,
“International Energy Outlook 2011,” U.S. Energy Information Administration, Washington, DC, Sep. 2011.

[2] BP,
“BP Energy Outlook 2035,” pp. 1–96, Jan. 2014.

[3] J. Rogelj, J. Nabel, C. Chen, W. Hare, K. Markmann, M. Meinshausen, M. Schaeffer, K. Macey, and N. Höhne,
“Copenhagen Accord pledges are paltry.,” Nature, vol. 464, no. 7292, pp. 1126–1128, Apr. 2010.

[4] M. D. Mastrandrea and S. H. Schneider,
“Probabilistic integrated assessment of ‘dangerous’ climate change,” Science, vol. 304, no. 5670, pp. 571–575, Apr. 2004.

[5] S. H. Schneider and M. D. Mastrandrea,
“Probabilistic assessment of ‘dangerous’ climate change and emissions pathways,” Proc Natl Acad Sci USA, vol. 102, no. 44, pp. 15728–15735, Nov. 2005.

[6] D. Archer, M. Eby, V. Brovkin, A. Ridgwell, L. Cao, U. Mikolajewicz, K. Caldeira, K. Matsumoto, G. Munhoven, and A. Montenegro,
“Atmospheric lifetime of fossil fuel carbon dioxide,” Annual Review of Earth and Planetary Sciences, vol. 37, pp. 117–134, 2009.

[7] BP,
“BP Statistical Review of World Energy,” 2010.

[8] S. H. Mohr and G. M. Evans,
“Forecasting coal production until 2100,” Fuel, vol. 88, no. 11, pp. 2059–2067, Nov. 2009.

[9] R. Heinberg and D. Fridley,
“The end of cheap coal,” Nature, vol. 468, no. 7322, pp. 367–369, Nov. 2010.

[10] T. W. Patzek and G. D. Croft,
“A global coal production forecast with multi-Hubbert cycle analysis,” Energy, vol. 35, no. 8, pp. 3109–3122, 2010.

[11] M. Höök, W. Zittel, J. Schindler, and K. Aleklett,
“Global coal production outlooks based on a logistic model,” Fuel, vol. 89, no. 11, pp. 3546–3558, Nov. 2010.

[12] Brenner MP, L. Bildsten, F. Dyson, N. Fortson, R. Garwin, R. Grober, R. Hemley, G. Joyce, and J. Katz,
“Engineering Microorganisms for Energy Production,” The MITRE Corporation, Washington, DC, JSR-05-300, Jun. 2006.

[13] R. H. Whittaker and G. E. Likens, “The Biosphere and Man,” in Primary Productivity of the Biosphere, H. Lieth and R. H. Whittaker, Eds. Berlin: Springer-Verlag, 1975, pp. 305–328.

[14] V. Ramanathan,
“The Role of Earth Radiation Budget Studies in Climate and General Circulation Research,” Journal of Geophysical Research, vol. 92, no. 4, pp. 4075–4095, 1987.

[15] R. E. Blankenship, D. M. Tiede, J. Barber, G. W. Brudvig, G. Fleming, M. Ghirardi, M. R. Gunner, W. Junge, D. M. Kramer, A. Melis, T. A. Moore, C. C. Moser, D. G. Nocera, A. J. Nozik, D. R. Ort, W. W. Parson, R. C. Prince, and R. T. Sayre,
“Comparing Photosynthetic and Photovoltaic Efficiencies and Recognizing the Potential for Improvement,” Science, vol. 332, no. 6031, pp. 805–809, May 2011.

[16] G. G. B. Tcherkez, G. D. Farquhar, and T. J. Andrews,
“Despite slow catalysis and confused substrate specificity, all ribulose bisphosphate carboxylases may be nearly perfectly optimized,” Proc Natl Acad Sci USA, vol. 103, no. 19, pp. 7246–7251, 2006.

[17] M. V. Kapralov and D. A. Filatov,
“Widespread positive selection in the photosynthetic Rubisco enzyme,” BMC Evol. Biol., vol. 7, p. 73, 2007.

[18] Y. Savir, E. Noor, R. Milo, and T. Tlusty,
“Cross-species analysis traces adaptation of Rubisco toward optimality in a low-dimensional landscape,” Proc Natl Acad Sci USA, vol. 107, no. 8, pp. 3475–3480, Feb. 2010.

[19] D. A. Walker,
“Biofuels, facts, fantasy, and feasibility,” Journal of Applied Phycology, vol. 21, no. 5, pp. 509–517, 2009.

[20] B. T. Fichman,
“Annual Energy Review 2010,” Washington, DC, Oct. 2011.

[21] X.-G. Zhu, S. P. Long, and D. R. Ort,
“Improving Photosynthetic Efficiency for Greater Yield,” Annual review of plant biology, vol. 61, no. 1, pp. 235–261, Apr. 2010.

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