Care to explain to the ignorant (specifically, me) how you make biodiesel from a tallow tree ?

Good question since I haven't done it yet. Apparently step 1 is remove the waxy coating of the unbroken seeds using hot water. I'm not sure if the wax is a lipid however. Step 2 is mush the seeds and heat them in hot water (maceration) and squish the oil out (think coffee plunger) which should float to the top to be poured off. After filtering out the debris process into biodiesel via normal methods. Use the leftover mash on the compost heap.

That's how I think it works. The questions are whether the acreage yields are adequate and the seed gathering takes too much effort. It could be that if algae experiments fail we are already close to peak lipids based fuel ie using plant oils and chicken fat.