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.