You do know you can burn stuff that is not dug up from the ground right? From ethanol to sun flower and coconut oil. You can pretty much just pour them in a gas tank and the engine will just work.

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floatrock 3 hours ago | parent | next [-]

Sure you can burn them, doesn't mean you're accomplishing anything from a thermodynamic point of view.

Metric to look at is EROI - Energy Return on Investment. How much energy do you put into growing these crops to get a unit of energy out?

Corn ethanol in the US is stupid because it's a 1.6:1 return at best, often a 1:1. To get a unit of energy out of corn ethanol, you need to put almost a unit in. And that's economic inputs, we know the sunshine is free. Sugarcane is a bit better, but you can only grow it in the tropics.

For reference, solar tends to be something like 4:1 - 10:1, wind is 10:1 +/- onshore or offshore, fracked oil tends to be down around 5:1-8:1, and a saudi well is (or at least used to be) 40:1.

	▲	matthewdgreen 3 hours ago \| parent \| next [-]
		Once you have a sustainable process, these last holdout areas like dredging (where you can't use batteries or wires) can have relatively terrible EROI as long as they're a small minority of the economy. All aviation and shipping combined is about 6% of final energy, and with major redesigns for shipping it could be as low as 4%. So you'd trade a much better EROI for 96% of the economy for a terrible one that only affects 4%.
	▲	throwawayffffas 3 hours ago \| parent \| prev \| next [-]
		You are looking it from the wrong angle the way I see it. First there are significant quantities of oils grown used in cooking and discarded, in an often environmentally damaging way. Reclaiming and burning these adds value to a waste product. What is the EROI on batteries surely under 1. These oils can provide energy storage and transmission in applications where electricity is ill suited, jet engines (coconut oil is especially suitable for this) and shipping come to mind.
	▲	estearum 3 hours ago \| parent \| prev \| next [-]
		EROI is also why we really need to get off of fossil fuels long before we actually literally run out (i.e. now would be great) As a resource reaches depletion, there are two forces acting on EROI: 1) the increased cost of each unit of energy input, and 2) the reduced yield from that energy input. The EROI curve bends negative faster than you think by looking at history.
	▲	fragmede an hour ago \| parent \| prev [-]
		> Sugarcane is a bit better, but you can only grow it in the tropics. Not for long! Or rather, the range of the tropics are moving, so that won't be the thing holding us back if that's the route we wanna take.

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Tagbert 5 hours ago | parent | prev | next [-]

All too often those have bad environmental impacts of their own. Coconut oil ends up being grown in plantains that require clear cutting natural forests. The agricultural process to plant, grow and harvest sunflowers produces significant CO2 just as it does for growing corn for ethanol.

	▲	smallerize 5 hours ago \| parent [-]
		I don't think anyone grows extra coconuts for fuel. It's processed from the waste after the more profitable parts are extracted.

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seiferteric 5 hours ago | parent | prev | next [-]

Good point, liquid and gas fuels will continue to be important into the future where energy density is needed, fuel cells could be a good option also.

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zahlman 5 hours ago | parent | prev [-]

Depending on the engine, perhaps. But this still releases CO2. This is not about supply limitations.

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hakimg 5 hours ago | parent [-]

These are carbon neutral as they remove atmospheric CO2 when the plant matter is grown

	▲	IrishTechie 4 hours ago \| parent [-]
		The savings in CO2 emissions for the likes of rapeseed, sunflower etc per MJ of energy is only around 50% compared to diesel. You have to release a lot of CO2 to grow these crops intensively. And that’s before you even consider where the land for these crops come from, potentially chopping down CO2 absorbing rainforests in many sorts of the world. Biofuel from Used Cooking Oil is worthy considering for sure, but the quantities possible are tiny compared to the petrol/diesel we use.