Berzin has an operational "bioreactor" running off the MIT power plant. The claimed yield is 15,000 gallons of biodiesel per acre (presumably per year) using an algae that is 50% oil by weight, and from the other numbers mentioned, that would consume the CO2 output from about 400 kW-yr of fossil fuel generation. A 1000 MW fossil fuel plant with attached algae ponds could therefore yield 40 million gallons per year, using close to 3000 acres of algae.
It's not clear how that averages over the summer and winter months - the sample algae shown are not in open ponds, but enclosed in tubes through which the output gases of the generator are bubbled. The greenhouse-like nature of the enclosures may mean the temperature stays relatively constant; probably one of the production variables that needs to be well controlled, in any case.
It's also not clear what the energy return on energy input is here - how much energy does it take to create these large enclosed algae ponds, and to convert their output to fuel, compared to the yield? Nevertheless, this may well be a better biofuel than those usually considered.
For one thing, this algae solution requires much less land than other bio-fuels - but still a lot. At 15,000 gallons (or 357 barrels) per acre per year, meeting US petroleum needs (roughly half total US energy needs of 20 million barrels/day would take some 20 million acres. That's 31,000 square miles, or some four times the land area of the state of New Jersey.
That may seem like a lot, but ethanol from corn or biodiesel from soy beans would take at least 10 times as much land area - just to meet petroleum (half US energy) needs. And that's if they actually have any positive energy return.
Solar cells could produce an equivalent electric energy supply (about 500 GW) by covering somewhat over 10,000 square miles.
One question beyond net energy return is going to be capital cost; Greenfuel is rolling out prototypes so we'll probably see soon whether companies can actually make money from it. More than that though, this biodiesel solution can only really be a stopgap, as it's dependent on high CO2 levels directly from fossil-fueled power plants, rather than just capture of CO2 at atmospheric concentrations. Presumably algae farms using ambient CO2 levels would require much larger land areas for equivalent yields.
But, if it's cost effective, it's not a bad thing to do in the interim, and could significantly augment biodiesel supply during the transition to real alternatives. Worth some investment in the near term.