I thiiiiink this book makes some important mistakes, judging from a quick glance.
So, for instance—he asks how much power the regular car-user consumes. He says that energy use per day per person is distance travelled per day, over distance per unit of fuel, times energy per unit of fuel. He plugs in numbers, gets 40 kWh / day / person. Significantly, he says that a liter of petrol (dude seems British) has about 10 kWh in it (which Google seems to confirm) and that a typical car gets 12 km / liter (ok, seems fair, haven’t double-checked, whatever). So his figure of 40 kWh / day / person, implicitly involves a car gets 12 km / 10 kWh, or 1.2 km/kWh.
And later he uses these numbers, together with numbers that purport to show that if we covered all English roofs with solar panels you only get 5 kWh / day / person, leaving us with a significant shortfall of the 40 kWh / day / person. (http://www.withouthotair.com/c6/page_39.shtml)
But, um, here’s the problem. Electric motors are waaaay more efficient than internal combustion. Wikipedia informs me that a Model S gets about 3 miles per kWh, according to the EPA, which converts to about 4.8 km / kWh. (This isn’t a floor by any means. Model 3 looks like it is better, although not by a ground-breaking amount. And this is why electric cars have stupid-sounding [to me] numbers applied to them like “100 miles per gallon of gas equivalent”.) So, anyhow, approximately 4x more efficient, which leaves us with notably smaller shortfall, although one that still means that solar panels are insufficient for our total energy needs for driving. Ah well, haven’t looked into the numbers of how hard it is to get sufficient solar power. 4x off isn’t thaaaaat bad for a Fermi estimate, I guess.
Anyhow, I might have made elementary mistakes in the above. The only reason I bothered with this comment was that I saw his figures that seemed to assume we’d require the same total energy for our electric cars as for our petrol ones, and I was like “That seems wwaaaaaaay” off. And even if I hadn’t done the math I’d still have that overall impression.
I think the question of how efficient electric motors are is largely irrelevant to the purposes of the book. The whole point is to explore what our current requirements actually are, and whether renewable energy can meet them. Until and unless the majority of British drivers are in electric cars, it doesn’t seem to have a bearing on that question.
The ‘without the hot air’ angle is to eliminate this problem that environmental proposals often have where totally changing one aspect of society is totally feasible given that another aspect totally changes at the same time. You will also notice that his numbers for solar power aren’t based on theoretical, or even estimated future, conversion efficiency; they are based on the efficiency available in the market at the time he was writing (he uses 10% efficiency for the kind of panel you could feasibly install everywhere, and put 20% for the top-of-the-line models, in 2008).
That being said, you have effectively skipped to the conclusion of the book: the answer is no, at current consumption levels sustainable energy isn’t feasible; the solution we have to pursue is reducing our energy consumption. He addresses the benefits of more efficient forms of getting around (including electric cars and trains and such) in the Transport chapter.
I thiiiiink this book makes some important mistakes, judging from a quick glance.
So, for instance—he asks how much power the regular car-user consumes. He says that energy use per day per person is distance travelled per day, over distance per unit of fuel, times energy per unit of fuel. He plugs in numbers, gets 40 kWh / day / person. Significantly, he says that a liter of petrol (dude seems British) has about 10 kWh in it (which Google seems to confirm) and that a typical car gets 12 km / liter (ok, seems fair, haven’t double-checked, whatever). So his figure of 40 kWh / day / person, implicitly involves a car gets 12 km / 10 kWh, or 1.2 km/kWh.
And later he uses these numbers, together with numbers that purport to show that if we covered all English roofs with solar panels you only get 5 kWh / day / person, leaving us with a significant shortfall of the 40 kWh / day / person. (http://www.withouthotair.com/c6/page_39.shtml)
But, um, here’s the problem. Electric motors are waaaay more efficient than internal combustion. Wikipedia informs me that a Model S gets about 3 miles per kWh, according to the EPA, which converts to about 4.8 km / kWh. (This isn’t a floor by any means. Model 3 looks like it is better, although not by a ground-breaking amount. And this is why electric cars have stupid-sounding [to me] numbers applied to them like “100 miles per gallon of gas equivalent”.) So, anyhow, approximately 4x more efficient, which leaves us with notably smaller shortfall, although one that still means that solar panels are insufficient for our total energy needs for driving. Ah well, haven’t looked into the numbers of how hard it is to get sufficient solar power. 4x off isn’t thaaaaat bad for a Fermi estimate, I guess.
Anyhow, I might have made elementary mistakes in the above. The only reason I bothered with this comment was that I saw his figures that seemed to assume we’d require the same total energy for our electric cars as for our petrol ones, and I was like “That seems wwaaaaaaay” off. And even if I hadn’t done the math I’d still have that overall impression.
I think the question of how efficient electric motors are is largely irrelevant to the purposes of the book. The whole point is to explore what our current requirements actually are, and whether renewable energy can meet them. Until and unless the majority of British drivers are in electric cars, it doesn’t seem to have a bearing on that question.
The ‘without the hot air’ angle is to eliminate this problem that environmental proposals often have where totally changing one aspect of society is totally feasible given that another aspect totally changes at the same time. You will also notice that his numbers for solar power aren’t based on theoretical, or even estimated future, conversion efficiency; they are based on the efficiency available in the market at the time he was writing (he uses 10% efficiency for the kind of panel you could feasibly install everywhere, and put 20% for the top-of-the-line models, in 2008).
That being said, you have effectively skipped to the conclusion of the book: the answer is no, at current consumption levels sustainable energy isn’t feasible; the solution we have to pursue is reducing our energy consumption. He addresses the benefits of more efficient forms of getting around (including electric cars and trains and such) in the Transport chapter.