Biological Photovoltaics: Testing Algae for the Optimal Battery

YU HAN (Veronica) GUO

she/her | age 16 | Vancouver, BC

Gold Medal, Intermediate Energy Challange Award, and Intermediate Youth Can Innovate Award, Canada Wide Science Fair 2023

Edited by Angela Xu

INTRODUCTION

This project aims to further explore biological photovoltaics (BPVs)–a sustainable alternative to conventional batteries. Global battery demand is predicted to increase significantly from 555GWh in 2023 to 2035GWh in 2030, and global energy generation is predicted to increase from ~700TWh in 2023 to ~900 TWh in 2027.[1][2] Currently, the energy sector contributes to 73.2% of global emissions, while 15 billion batteries are thrown away each year.[3][4] Lithium-ion or other traditional batteries use non-renewable materials and are toxic to the environment if leaked.[5] Today, batteries require many resources to be made, do not always have a long life cycle (lithium-ion batteries can last for 3-5 years on average), and are inefficiently recycled.[6] Since current battery production methods are not sustainable, it is important to find renewable alternatives. Algae is scalable and being explored for mass production, which could allow for further production of BPVs. BPVs can last for an extended period, as demonstrated by a six-month durability in one experiment; this lifespan mitigates the need for frequent disposal.[9] Even once disposed, BPVs are more sustainable than conventional batteries because they use abundant and renewable materials that do not harm the environment. By comparing the performance between BPVs and control batteries in this experiment, this will allow one to discover BPVs' relative efficiency, as the light-dependent reactions of photosynthesis could help to increase its power output. This study thus chose to use Spirulina algae for its higher efficiency compared to Nannochloropsis as found in the paper “Bioelectric Batteries: Using Algae to Make the Battery Renewable” and Spirulina’s adaptability to alkaline solutions, which would be the pH of the electrolyte.[4] Chlorella vulgaris algae was chosen because it multiplies rapidly and does requires a minute amount of nutrients along with water, carbon dioxide, and sunlight to reproduce.[12] BG (Blue-green) 11 medium, the electrolyte used in this project, is a media that is used to grow and maintain cyanobacteria (blue-green algae).

The purpose of this project is to determine the ideal type of algae, algae concentration, and wavelengths of light that can produce the greatest power output. Finding the optimal factors of BPVs could serve as a low-cost, non-toxic solution to support the growing demand for batteries.[7]

The hypothesis is that Spirulina algae will produce more power than Chlorella vulgaris algae because Spirulina algae are more adaptable, so they may be better accustomed to the pH level of adapted BG (Blue-Green) 11 medium.[2] The second part of the hypothesis is that 15 mL of each type of algae will produce more power than 10 mL and 5 mL because more algae will increase the rate of photosynthesis. Finally, it is thought that violet light (380 nm) will be more effective for Chlorella vulgaris, and blue light (445 nm) will be more effective for Spirulina algae because each type of algae absorbs most of that specific wavelength. The null hypothesis is that the mean of the power output of the concentrations of the algae, types of algae, and wavelengths would be equal.

MATERIALS & METHODS

To make the electrolyte, 1.5 g of NaNO3, 0.04 g of K2HPO4, 0.075 g of MgSO2·7H20, 0.036 g of CaCl2·2H20, 0.006 g of Citric Acid·H20, and 0.02 g of Na2CO3 is measured. All are added into a volumetric flask, then dissolved in 1 L of distilled water. After swirling the chemicals until the solutes are dissolved, autoclave the liquid medium to prevent contamination. This makes adapted BG11 medium.[6] I tested 21 BPVs with two types of algae and three concentrations, and each set of 7 BPVs (each concentration from each type of algae and the control BPV) cycled under three different wavelengths of light for over 2 weeks. To assemble the BPVs, add 100 ml of adapted BG11 medium into each glass jar (the BPV housing) and add the electrodes, an aluminum sheet and carbon rod, into 21 BPVs. Measure out three different concentrations of liquidized algae using a pipette to put into each BPV (5mL, 10mL, 15mL). Create another battery but with no algae and 15 ml of water, which will be the control battery. Repeat these steps two more times. The experimental design is made by placing 7 BPVs made from Assembling BPV equidistant from the lamp. For the first light cycle, turn on the lamp with a blue light lamp bulb. Measure the pH, temperature, current, and voltage using a pH meter, thermometer, and ammeter, and voltmeter with a Labquest to collect the data. Repeat the previous two steps with different light bulbs in a sequence of blue light, violet light, no light, then violet light, blue light, no light. I collected around 47 million datasets by measuring each one-hundredth of an hour. 630 trials were collected.

RESULTS

Legend: (P > 0.05 = ns, P ≤ 0.05 = *, P ≤ 0.01 = **, P ≤ 0.001 = ***, P ≤ 0.0001 = ****)

In the first study, the average power output of the Spirulina algae BPV was greater than that of the Chlorella BPV, specifically, 0.015 Watts more. The batteries that contained algae performed better than the control group, which can be seen in Figure 1. 

Figure 1. Average power output in each BPV by each type of algae. The results of a one-way ANOVA test showed p < 0.0001. A Tukey HSD test revealed significant pairwise differences between control and Chlorella p < .0001, control and Spirulina p < .0001, and Chlorella and Spirulina p < .0001. Therefore, we can reject the first null hypothesis. 

In the second study, the BPVs produced the greatest power at the highest concentration. From low to high concentration, the Spirulina BPVs produced 0.020 Watts, 0.033 Watts, 0.069 Watts, and the Chlorella BPVs produced 0.021 Watts, 0.027 Watts, 0.029 Watts, as seen in Figure 2. 

Figure 2. Average power output of different concentrations of Chlorella Vulgaris and Spirulina algae. The results of a one-way ANOVA indicate statistical significance in average power output between the three concentrations of Spirulina algae showed p < 0.001. A Tukey HSD test revealed significant pairwise differences between 3x and 2x: p < .0001, 3x and 1x: p < .0001, and 2x and 1x: p < .0001. A one-way ANOVA test revealed significance in average power output between the concentrations of Chlorella algae: p < 0.001). A Tukey HSD test revealed significant pairwise differences between 3x and 2x: p < .0001, 3x and 1x: p < .0001, and 2x and 1xL: p < .0001. Therefore, we can reject the second null hypothesis.

In the third study, both BPVs performed better when the light was turned on rather than off for all concentrations. Spirulina BPVs performed better under blue light. Chlorella BPVs performed better under violet light, as seen in Figure 3. 

Figure 3. Average power output of each type of algae in different wavelengths of light. A one-way ANOVA test concluded no significant average power output between the effects of no, blue, and violet light on Chlorella algae: p < 0.001. A Tukey HSD test revealed significant pairwise differences between no light and violet light: p = .039, but not for no and blue light: p = .41, and violet and blue light: p = .41. Another one-way ANOVA test revealed significance for Spirulina algae: p < 0.001. A Tukey HSD test revealed significant pairwise differences between no light and blue light p < .001, and violet and blue light: p < .001, but not for no and violet light: p = .96. So we fail to reject the null hypothesis for Chlorella algae, but are able to reject the null hypothesis for Spirulina algae.

The BPV was able to perform for two weeks with no significant drop in power output.

These results highlight the long-lasting nature and the realities of the light reactions of photosynthesis in BPVs. By testing multiple factors of BPVs, it is seen that the greater the concentration of algae, the greater the power output. Additionally, the pigments within each algae influence its absorbance of light, which, depending on what wavelength it shone on the BPV, would affect the rates of photosynthesis. With non-toxic BPVs providing high power outputs and lasting for longer times compared to conventional batteries as shown in the results, they should be explored to be further improved.

DISCUSSION

The optimal factors of the BPV were determined to be Spirulina algae at 15 mL under blue light, therefore accordingly, one could engineer high concentrations of Spirulina in batteries shone under blue light. For those results, p < 0.05, suggesting that it was a statistically significant experiment. Although this experiment was executed carefully, the Labquests emitted light from the screens, and the Spirulina algae were more concentrated than Chlorella which was determined by the microscopic viewings. The results display the ideal factors of BPVs, which could help reduce battery waste and power the growing Internet of Things, which are devices that exchange data with other another through different Internet networks.[5] This project’s BPVs produced strikingly more power (0.08 Watts) than earlier work (0.01 Watts).[4] The results reinforce the idea that BPVs can produce more power than conventional batteries through the light-dependent reactions of photosynthesis. Since algae can be grown in large quantities to be used in bigger BPVs, the feasibility of their scalability should be evaluated. BPVs could be deployed in more remote locations to provide long-lasting energy from mass amounts of algae. They could also be tested on other devices, such as electric cars and sensors. Further research could be conducted to discover the inherent biological natures of various algal species by analyzing datasets to identify the most efficient genes for energy conversion. The BPVs producing more power than the control batteries highlight their energy efficiency, tackling the increasing energy demand.[3] Since the low-cost BPVs lasted for long periods while using abundant and renewable materials that reduce battery waste, it makes them a sustainable energy storage.

CONCLUSION

Further research has shown that algae continuously growing on the anode will cause excess buildup.[5] An article by Yildiz, H. et al. about developing thylakoid membranes capable of imitating photosynthesis helps to prevent such buildup while ensuring a higher power output than control batteries, which could be applied when creating BPVs to improve them further.[9] To tackle the severe issue of growing battery waste, energy demand, and depleting non-renewable resources, BPVs should be further explored as they are long-lasting and produce high power outputs. These are some potential experiments that can be conducted to further explore BPVs' power output capabilities and applications: combine results from previous experiment to create the optimal BPV, utilize algae’s scalability to deploy long-lasting BPVs in remote locations, analyze datasets to identify algae’s most efficient genes for energy conversion and their optimal environments, and use impedance and cyclic voltammetry to better understand the behaviour of algae in the BPV. In the future, an Aluminum-air (aluminum as the anode, air as the cathode) BPV’s high energy density, long-lasting nature, and use of sustainable materials could help pave the way to be used in water management, a growing issue as nitrogen and phosphorus levels rise, and perhaps even electric cars, diminishing the waste of lithium-ion batteries.

REFERENCES

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  2. Environmental Protection Agency. (2023). Global Greenhouse Gas Emissions Data. EPA. Retrieved 2023, from https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data

  3. Bowman, M. (2019). World net electricity generation, IEO2019 Reference Case (1990-2050). U.S Energy Information Administration. Retrieved 2023, from https://www.eia.gov/todayinenergy/detail.php?id=41533.

  4. Guo, Y.H (2022). Bioelectric Batteries: Using Algae to Make the Battery Renewable. Canada-Wide Science Fair 5-page Report.

  5. Bombelli, P., Savanth, A., Scarampi, A., et al. (2022). Powering a microprocessor by photosynthesis. Energy & Environmental Science. Retrieved 2022, from https://pubs.rsc.org/en/content/articlelanding/2022/ee/d2ee00233g

  6. YouTube. (2013). An introduction to biological photovoltaics. YouTube. Retrieved 2022, from https://www.youtube.com/watch?v=uPNDOw041Q8

  7. O'Dea, S. (2023). Size of the global battery market from 2018 to 2021, with a forecast through 2030, by technology. Statistica. Retrieved 2023, from https://www.statista.com/statistics/1339880/global-battery-market-size-by-technology/.

  8. UTEX. (n/d). BG-11 Medium Formulation. Retrieved 2023, from https://dpl6hyzg28thp.cloudfront.net/media/bg-11-medium.pdf

  9. Yildiz, H. B., Cevik, E., & Bezgin Carbas, B. (2019). Nanotechnology for biological photovoltaics; industrial applications of nanomaterials. Industrial Applications of Nanomaterials, 65-89. https://doi.org/10.1016/B978-0-12-815749-7.00003-7

  10. Ira Toyota of Danvers. (n.d.). How long do car batteries last? Toyota of Danvers. Retrieved 2023, from https://www.toyotaofdanvers.com/how-long-do-car-batteries-last-danvers-ma/  

  11. Environmental impacts of lithium-ion batteries. UL Research Institutes. (2022, March 16). Retrieved 2023, from https://ul.org/research/electrochemical-safety/getting-started-electrochemical-safety/environmental-impacts

  12. Algae Research Supply. (n.d.). ALGAE RESEARCH SUPPLY: ALGAE CULTURE CHLORELLA VULGARIS. Retrieved 2023, from https://algaeresearchsupply.com/products/algae-culture-chlorella-vulgaris 

ABOUT THE AUTHOR

Yu Han Guo

​​Yu Han Guo is a Grade 11 student who is passionate about biochemistry and electrical engineering. She is intrigued by the ways those two fields can be used to tackle environmental issues, specifically the energy crisis by creating more sustainable batteries . Since participating in CWSF for the past three years, she has also founded the Science Fair Club at her school where she encourages other students to pursue STEM interests. Outside of science projects, she plays competitive chess, does cross country, basketball, enjoys walking her dog, and blasting Taylor Swift’s music.