High Density Photobioreactor is a custom built product. The standard size is 1000 mm (long) x 500 mm (width) x 1000 mm (height). The total volume is 0.5 cuber meter, of which eighty-eight percent are available for the microalgae cultivation. It contains internal structures and internal LED light sources to supply sufficient light and nutrients to algal cells in the culture in support of high growth rates of algal cells. When fully loaded, the unit is designed to produce 29.16 kilograms of algal biomass in a 12 hour period while absorbing 85.56 kilograms of carbon dioxide.The cost of electricity to fix the carbon and produce algal biomass is expected to be $7.91 per ton of carbon dioxide or $23.32 per ton of algal biomass. HDP presents a solution to the problem of scale versus efficiency in microalgae. HDP arrays are tools to grow microalgae in large scales and with high efficiency.