Microalgae Spirulina platensis were attached to the anode of a membrane-free and mediator-free microbial fuel cell (MFC) to produce electricity through the consumption of biochemical compounds inside the microalgae. An increase in open circuit voltage (OCV) was observed with decreasing light intensity and optimal biomass area density. The highest OCV observation for the MFC was 0.39 V in the dark with a biomass area density on the anode surface of 1.2 g cm(-2). Additionally, it was observed that the MFC with 0.75 g cm(-2) of biomass area density produced 1.64 mW m(-2) of electrical power in the dark, which is superior to the 0.132 mW m(-2) produced in the light. Which also means the MFC can be applied to generate electrical power under both day and night conditions.