Biofuel vs. PV – stop drinkin’ the ethanol! June 13, 2015Posted by Maury Markowitz in balonium.
Tags: electric cars, solar power
David MacKay has made a name for himself as the green energy “reality man”, bringing what he suggests is a dose of reality to the new energy discussion.
For instance, in a recent TED Talk he suggested that biofuels are a hopeless alternative for transport. He uses a simple calculation to show you’d need a strip of land 8 kilometres wide beside the road to fuel the cars running on that road.
But we already knew biofuels are a bad solution. What happens when you consider a good solution?
But first, let’s just run his numbers. Here’s the relevant part of the talk:
Okay, so let’s put in some numbers. Let’s have our cars go at 60 miles per hour. Let’s say they do 30 miles per gallon. That’s the European average for new cars. Let’s say the productivity of biofuel plantations is 1,200 litres of biofuel per hectare per year. That’s true of European biofuels. And let’s imagine the cars are spaced 80 meters apart from each other, and they’re just perpetually going along this road. The length of the road doesn’t matter, because the longer the road, the more biofuel plantation we’ve got. What do we do with these numbers? Well, you take the first number, and you divide by the other three, and you get eight kilometers. And that’s the answer. That’s how wide the plantation would have to be, given these assumptions. And maybe that makes you say, “Hmm. Maybe this isn’t going to be quite so easy.”
First off there’s a statement about the speed of the cars. Notice that it is not actually used in the calculation. He could have said 6 mph, or 600, it has equally zero effect. So why did he even say it? Well I suspect because saying 60 mph, an everyday number, gives the argument a patina of reality. Had he said 6 mph your BS detector would fire. And that’s what he definitely doesn’t want, because here comes the BS…
Now the next major statement is that the cars are perpetually running down this infinite road 80 m apart. Now at this point your BS detector should be firing, but did it? 80 metres? Why not 8? Or 8000? And that’s important, because the calculation basically comes down to the spacing of the cars. As he says, “you take the first number, and you divide by the other three”. Ok, so if you select the equally correct 8000 m between cars, you only need 100 m of plantation to fuel them.
The problem here is that the setup is completely arbitrary. You can pick any numbers you want and end up with any answer you want. But we’re not interested in arbitrary roads with arbitrary traffic, we’re interested in real roads with real traffic.
There’s this thing called Google
It’s the 21st century, these numbers are at your fingertips.
To start with, let’s consider how many miles are actually driven. The talk in question used UK numbers, so I’ll do the same.
According to the UK government statistics, in 2014 cars and taxis drove 244.5 billion miles. Heavier vehicles add to that number, about 60 billion, but I’m going to keep that separate for now (you’ll see why later).
So, assuming that same 30 mpg average, and 244 billion miles driven, that’s a little over 8 billion gallons of fuel, or 36 billion litres. Now taking the 1,200 litres per hectare, we need 30 million hectares.
Ok, one last number. According to the same UK government, there are 245 thousand miles of roads in the UK, or just under 400,000 km. A hectare is 10,000 square metres, or a strip 10 metres wide and a kilometer long. So…
30 million / 400 thousand x 10 = 750 metres
Now don’t get me wrong, I don’t want to see 750 metres of biofuel plantation beside the roads of the UK any more than 8 kilometres. But come on, he’s off by an order of magnitude.
But we’re only getting started. Recall that these are numbers for European production of biofuel. Why would you do that? The UK doesn’t get its oil from the Europe, it gets it from the middle east where it’s cheaper. So an apples-to-apples comparison would be to buy the biofuel where it’s the cheapest. Where is that? Brazil. And how much do they make per hectare? 9,000 litres.
So then we don’t need 30 million hectares, we need 4 million. Which means we need 100 metres of plantation per kilometre of road. That doesn’t sound quite so bad now, does it? Still a big chunk of land, but we’re two orders of magnitude down already.
To put all of this in perspective, the UK has about 17 million hectares of agricultural land, so if we try to grow this fuel in the UK we can’t do it. But Brazil has 900 million hectares in total, of which 260 is currently used for agriculture and lots is undeveloped, so they could easily do it.
So basically he takes a craptastic fuel, sets up a strawman argument, and then concludes with a flourish “that won’t work”.
But what if your aim was to explore actual solutions to the problem? You know, like using electric cars instead of ICE?
Ok, the UK drives 244 billion miles a year in cars and taxis. Now if we replaced those with electric cars, the average efficiency would triple, to about 90 “mpg equivalent”. A more useful number is that the average for electric cars is 35 kWh per 100 miles, so those 244 billion miles would burn about 85 billion kWh a year, or 85 TWh.
85 TW is a big number. But not so big, considering the UK generated 320 TWh in 2012.
So basically reasonable additions to the existing power supply, or just running the plants more often at night, would power every car and taxi in the UK. Right now. Today.
But let’s keep going…
The answer, my friend, is shinin’ in the sun…
In a previous article I noted that the amount of wind power in the US is enough to drive all its cars. I already did that one, so this time, just for fun, let’s do the calculations to see how many solar panels you’d need to power all of the UK’s cars.
Ok, so we’ve done this before. Click on this link to PVWatts. There’s a search area at the top, type in London and hit return. You should see Gatwick selected on the next page, but feel free to pick another location. Hit the right-pointing orange Go button in the upper right. Ok, now change the DC System Size to 1 (I still don’t understand why they have 4 here, everyone uses 1 as a standard measure). Change the tilt angle to 40, which is correct for the UK (no idea where they get 20). Hit the orange Go button again.
On the new screen that appears there’s a big number at the top, which is 932 kWh per year. So to get 85 billion kWh we need 85 billion / 932 = 91 million of these 1 kW systems. Using modern panels you need about thee 350W panels to make that 1 kW, and a panel is about 1.6 square meters, so that’s a total of 436 million square metres of panels (44 thousand hectares).
So that means over the 400,000 km, or 400 million meters of road, we need a strip of panels 1 metre wide. That’s basically the width of the panel.
It’s less than the width of the shoulder.
Planes, trains and heavy trucks
Remember I said I wanted to leave out the heavier vehicles for the moment. That moment is now.
According to the same UK statistics, heavy traffic accounts for about 60 billion driven miles. Now I don’t think we can practically replace those with electrics, they simply drive too far every day for charging to be practical (with current tech at least). So lets consider what happens when we replace this part of the transit problem with biofuels.
Well if we assume the average truck gets about 10 mpg, we need 6 billion gallons of fuel, or 27 billion litres. Using the European biofuel production numbers, that means we need 27 million / 1,200 ~= 225,000 hectares.
London is 170,000 hectares. So it not a small patch of land, but it’s hardly inconceivable.
And if you consider all the biofuel land along with all the solar panels, you need about 270 thousand hectares, compared to the total agricultural land available at 17 million.
A drop in the bucket. And that will power every vehicle in the country, forever. That doesn’t sound quite so impossible now, does it?
Glory hounds and just-so stories
I’m perfectly aware that the name of the media game these days is to write just-so stories to get into the press. Just ask Malcolm “I have funny hair so people will take my picture” Gladwell. And the good Dr. MacKay is certainly making the best of this, at least he’s doing a hell of a lot better than I am.
But the question here is what are his intentions? If the intent is to consider whether or not we can run our cars on renewables, the he’s done a terrible job. He’s selected the wrong fuel in the wrong place and plugged that into the wrong calculation.
But in my opinion this is deliberate. He builds a bogus system so he can conclude that “Maybe this isn’t going to be quite so easy.” But the actual reality is that it’s not going to be quite so hard. Whenever you actually run the numbers, electric cars fix any problem you can think of. But no one will ever quote this article in the news or invite me to give a TED talk. They can’t sell good news.
But if we keep telling people it is hard, then they’ll think it’s hard, and then they won’t do anything to fix the problem. And that is a very bad thing. It’s a wonderful tiny example of the problem that plagues the entire climate change debate.
p.s. My thanks to Footprint to Wings for pointing me to this TED Talk.