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.
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.
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.
What is a "significant quantity"? Significant in terms of volume relative to a single restaurateur? Or significant in terms of megajoules as a percentage of say, the shipping industry? (Or we can be generous and just narrow it down to the dredging industry).
Put another way, what is the recoverable megajoules of all of the Netherlands discarded cooking oil in a year as a percent of megajoules needed for all the dredging the Netherlands does in a year? My gut tells me it trends towards negligible.
All for recycling, but biofuel refiners already specializing in this do at most 5-20% recycled biooil : traditional oil blends. Don't know why they don't sell "pure" recycled biofuels, but it's probably a mix of availability and performance needs. Should always question yourself: "if it's so simple, why haven't the people already doing this commercially figured it out yet?" You'll truly understand the space if you can produce a good answer to that (and you'll have a business model if you can enunciate why their constraints or limits are wrong).
----
> What is the EROI on batteries surely under 1.
EROI is used for energy sources. Batteries are an energy store. You can still do a similar "how much energy can I get out of this vs. embodied energy to create it" analysis, but energy out is measured over all the cycles in the useful lifetime of the device. It's a slightly different concept, and that metric is called Energy Stored on Energy Invested (ESOI). Lithium ion are about a 10:1 - 30:1.
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.
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.
Biofuel from Used Cooking Oil is worthy considering for sure, but the quantities possible are tiny compared to the petrol/diesel we use.