That is not the same. Then you need nutrients for cell replication as well (amino acids/protein, minerals, vitamins). But if you just collect secreted hydrocarbons from algae you in theory only need sunlight and water, and a little nutrients to maintain the cells. Maybe one issue is that most algae replicate very often, maybe once a day. I used to do bioengineering of an algee (Chlamydomonas) in my Masters