Thin harvest

MAKING fuel from the solar energy stored in living organisms by photosynthesis is a tempting idea. It sounds inherently green, and so biofuel schemes--ranging from fermenting starch, to recycling cooking oil, to turning algae into jet fuel--have drawn more than $126 billion in investment since 2003, according to Bloomberg New Energy Finance (BNEF), a research outfit. The results, though, are like a Venn diagram whose sets barely overlap. Those biofuels that can best compete commercially are not,...