Another factor in microalgae cultivation is the availability of light, which is determined by the ratio of working volume to illumination surface (V/S, L/m2). Light energy decays with water depth; hence, as the V/S ratio increases, the net available light energy decreases. The common V/S ratio for different reactors is 50–150 L/m2 for flat panel and tubular reactors, and 100–300 L/m2 for raceway reactors. Based on a land area of 1 hectare, and with the working volumes reported by Fernandez-Sevilla et al. (2010) and Jorquera et al. (2010), illumination depth for cultivation in raceway reactors is 20 cm, yielding a V/S ratio of 200 L/m2 and working volume of 2000 m3. The flat panel reactor is composed of 112 units consisting of 20 flat panels, each 10-cm thick with a liquid height of 90 cm, which is equivalent to a V/S ratio of 50 L/m2 and working volume of 910 m3. The tubular reactor consists of tubes 9 cm in diameter, according to data reported by Acien et al. (2012), with a V/S ratio of 70 L/m2 and working volume of 750 m3.