[Reeses]

a thousand square miles of land

How about a thousand square miles of open ocean? It's free, algae floats, there are fewer clouds far from land, and fish are willing to harvest it. Rather than going for optimum greenhouse conditions which is capital intensive, it makes sense to go for volume. This is really how traditional farming works. Let mother nature do most of the work. Farmers deal with weeds and disease in the open successfully. We're giving up on the open algae farm approach too quickly. Petroleum could be completely replaced using about 3% of Earth's ocean surface.

[count-your-change]

Stay off them peanut butter cups, 3% of the ocean's surface is about 4 million, (MILLION) square miles.
Once that little detail is ignored the storms, waves and weather may not seem so large. And the means to efficiently harvest the algae? Supposing the fish won't regurgitate on command?