[adrianN]

ICEs running on renewables need a lot more renewables. An EV turns something like 80-90% of the power a wind turbine produces into movement. If you want to use synfuels in an ICE you lose >>50% just by turning the electricity into fuel and then the ICE only turns 30% of that into movement.

[cesarb]

Playing devil's advocate, the parent comment didn't mention "synfuels" at all, it mentioned "renewable fuel", which includes things like sugarcane alcohol, which is very common here in Brazil as a car fuel; many cars come out of the factory with flex fuel engines which can run on either gasoline or alcohol, and every fueling station I've ever seen always has at least one pump for alcohol.

[adrianN]

That is of course a good point. You can make small amounts of those from agricultural waste. If demand outstrips supply from waste though, the area you need to farm to drive a couple of miles is really large. I didn't do the math, but I wouldn't be surprised if you got more energy out of agricultural waste if you turn it into electricity+heat in a biogas setup.

[rightbyte]

How much of the power of the wind does the turbine turn into electrical power? It is not really a fair comparison.

I think BEVs are a better solution for most cases, but my feeling is that renewable ICEs and EVs with smaller batteries and "trolley bus" solutions just are way downplayed and underrated.

[adrianN]

I don't understand what you want to say. The comparison between BEVs and ICEs running on synfuels starts at the point where you want to turn electricity into motion. BEVs are more efficient by a factor of around 6. The efficiency of the wind turbine doesn't matter. You'll need six times as many of them if you want to burn synfuels instead of driving a BEV.

[rightbyte]

Is that true for e.g. ethanol too? I mean sure, it is true for H2-gas made with electricity but when making ethanol you are starting with lower grade energy.

Ethanol is made from wood or grain and any losses during the harvesting etc for the end product is comparable to the wind losses around the turbine (note that it is a bad comparison, since wasting wind is kind of no cost ...) or comparable with burning wood to power a steam machine generator to power EVs.

I.e. the degenerate case is using gasoline do power a powerplant to power a EV. You would be better off just using it in an ICE car. My point is turning wood into ethanol might be a good supplement to solar and wind EVs. E.g. for wood ethanol 1J product requires 0.6J input (except the wood of course) [1].

https://afdc.energy.gov/fuels/ethanol_fuel_basics.html https://ilsr.org/wp-content/uploads/files/ethanolnetenergy.p... (table 1)

[adrianN]

Biofuels don't scale very well. You can indeed produce some "for free" from waste, but once you start planting areas solely for producing biomass to turn into biofuels, you're environmentally much better off to leave the land to nature and put up some PV or wind turbines there.

But yes, a tiny sliver of fuel demand can be satisfied from plants. You're right about that. I'm less convinced that you're better off burning the fuel in an ICE than turning it into electricity in a large power plant and running an EV. Large generators are more efficient than small ones. If you manage to do something useful with the waste heat of your power plant (e.g. use it for district heating), there is no way a small ICE can compete, even if you take into account transmission and charging losses.

[rightbyte]

In general I agree, but lets do some napkin math:

UK 9.34 million hectares agriculture area. [1] 6,470 l/ha ethanol in Brazil [2]

60,4 billion liter ethanol for all agricultural land in the UK. (Surely a big share of the land is not good for this usage but what ever.)

About 45 billion liter of gasoline and diesel used in UK per year.[3]

I mean, it is not totally off by orders of magnitude to be practical for a significant share of driving.

[1] https://en.wikipedia.org/wiki/Agriculture_in_the_United_King... [2] http://www.globalbioenergy.org/uploads/media/0907_Goldemberg... [3] https://www.racfoundation.org/data/volume-petrol-diesel-cons...

[adrianN]

Well, most of that land is already used to produce food. I'm not so sure whether it would be a good idea to start up serious competition to food production.