In the field of green architecture, waste recycling is an important solution for its great benefits to the environment. This paper is concerned with studying algae as a source of cheap, promising and renewable energy, instead of fossil energy that is approximately in its way to depletion. Algae can be put on the roofs or facades of various buildings, by creating places for the growth of them after supplying them with sunlight and treated sewage water. Algae are the fastest-organisms growing on the surfaces and ground. They can be collected after the growth and transferred to the factories for processing and extraction of bio-fuel, which is used in aeroplanes and vehicles. Also this process results in making animal feeds rich with protein. In addition to that, Algae have a positive impact on the environment, through their role in reducing temperature and treating global warming