About This Project

Plants absorb carbon dioxide (CO2) and sunlight to grow in a process called photosynthesis. Cacti, however, absorb CO2 at night and store it as malate, which is broken down by sunlight during the day. Cacti are opaque, so the sunny and shaded sides do this independently and a voltage difference occurs. We want to know what factors influence this voltage difference. Results could reduce the impact that renewable energy has on biodiversity via a new cactus-based electricity generation technique.

Ask the Scientists

What is the context of this research?

Plants photosynthesize to make sugars to grow. While most plants do this during the day, cacti undergo Crassulacean Acid Metabolism (CAM). They take up carbon dioxide at night, which is stored as a compound called malate. During the day, sunlight breaks down the malate to make sugars. Because cactus stems are opaque, sunlight cannot pass through the stem, meaning each side breaks down the malate at different rates. The concentration difference creates a voltage differential across the stem. Previous studies have harvested electricity from electrical potentials in living plants, such as the pH differences between tree tissue and soil, yet none have attributed the voltage potential to CAM. We will explore how much of this electricity can be harvested and the factors that influence voltage.

What is the significance of this project?

Meeting climate goals requires a shift away from fossil fuels and towards adopting more renewable energy. Unfortunately, utility-scale renewable energy systems, like wind and solar, have detrimental effects on avian populations. For instance, thousands of birds die each year in California from impact collision injuries with solar panels at utility-scale solar facilities. The results of our research will increase the understanding of how voltage develops in living CAM plants and if this electricity can be harvested. Future research can then explore the potential of plant-based electricity to supplement renewable energy demands with a lower impact to wildlife. Cactus-based electricity could help meet rising renewable energy demands while also meeting biodiversity conservation goals.

What are the goals of the project?

Our goal is to answer the questions: How much electricity can we harvest from prickly pear stems? and What factors influence the voltage difference? We have broken these overarching goals into five sub-goals:

1) measure how much electricity can be harvested from the stems;

2) understand how metal electrode composition influences the amount of electricity harvested;

3) refine the electricity harvesting device based on electrode results;

4) deploy 20 devices at a commercial cactus farm for a year to determine how seasonal environmental conditions (sunlight, temperature, soil moisture) influence electricity production; and

5) publish the results of this research and conduct future research that compares cactus-based electricity to other energy sources.