I've heard a number of people assert that sweet potatoes are more energy dense per acre, but it looks like that may only be true if you consider complex carbs, and even then there are contenders. They may also be talking about one particular strain whereas calorie per acre lists like to say "sweet potato".
Sugar beets appear to be higher than sugarcane, but they're under substantial threat and they don't like the tropics. Then there's palm oil, which is such an environmental disaster that it practically ranks as a humanitarian disaster. Then something called chufa (a nutsedge), something called sacha inchi (Inca nut, a kind of spurge), and cassava/manioch bringing up the rear barely ahead of corn.
But some of these have a lot of calories in the form of oil, which means two paths are required to convert it to fuel. From a health standpoint, flooding the market with a cheap 'waste' product from a particular food process has kind of been our downfall.
I used calories because it’s comparatively easy to find lists of staple crops ranked by calories per hectare, and it gets discussed among homesteaders, smallholders and permaculture people at regular intervals.
Conversion efficiency is going to give you proportional results. If you’re trying to determine how many miles your car or jet can go it’s not accurate enough. But if you’re comparing crops to each other it should be fine.
Doesn’t change the fact that you are either double processing or separating and processing. That lowers the efficiency and means you have two production lines you’re managing, with separate processes on each one. More kinds of inventory, more experts on staff.
> The transformity (TR) was equal to 1.78E+11 seJ kg-1,
> eMergy inputs are expressed
in units of eNergy (usually in solar eMergy joules, seJ) [I capitalizad some letters.]
So, ignoring the "se" it's like 2*10^11J/Kg. Each Kg of sugar has like 1.5*10^7 J, so the "efficiency" is like 10^-4 that makes more sense than 10^-11
Photosynthesis has an efficiency of 1%-2%, but they are counting more things.
For example the eMergy of planting and harvesting that makes sense, but also the eMegy of rain that makes no sense at all. So I'm not sure how relevant are the numbers they are calculating.
Oh, thanks. I missed that TR was measured by seJ/kg, mostly because its defined earlier as seJ/J.
10^-4 is way more realistic than 10^-11. Anyway the "se" is supposed to mean "solar energy", but yeah, they add quite a lot of nonsense. On a second reading, I'm not sure they added solar energy at all into it so the number may be completely meaningless for that usage. (But no crop gets anything near the photosynthesis efficiency, because most of the plant's energy goes into surviving, not growth.)
> Per hectare per year, the biomass produced corresponds to 0.27 TJ. This is equivalent to 0.86 W per square meter. Assuming an average insolation of 225 W per square meter, the photosynthetic efficiency of sugar cane is 0.38%.
> One hectare of sugar cane yields 4,000 litres of ethanol per year (without any additional energy input, because the bagasse produced exceeds the amount needed to distill the final product). This, however, does not include the energy used in tilling, transportation, and so on. Thus, the solar energy-to-ethanol conversion efficiency is 0.13%.
https://www.scielo.br/j/rca/a/GD3CT889nbKP8MZybWbTYfy/?forma...
And it's the most efficient crop we produce in a large scale.
But anyway, the efficiency is not very important. What is important is capital cost.