This morning I overheard a few people fuming about the price of gasoline. I wonder if they have considered how inefficient their cars really are?
The chemical bonds in hydrocarbons are a great way to store energy. Millions of years ago green plants used the energy in sunlight to split water into hydrogen and oxygen. The hydrogen was then combined with carbon dioxide from the air forming glucose molecules and giving off a byproduct called oxygen that we've managed to use in other ways.1 The neat thing is when you burn the glucose, energy stored in its chemical bonds is released along with water and carbon dioxide. Glucose is essentially a energy storage battery. Plants turn it into other hydrocarbon-based substances largely leaving intact the chemical bonds that contain the stored solar energy. They tap some of the energy for their own purposes and animals eat the plants harvesting the stored solar energy through metabolism - another form of oxidation - releasing the same energy and byproducts as burning.
It is wonderful to realize you are really solar powered.
Most of the solar energy that powers our bodies fell on the Earth recently - usually within the past year. It turns out plants aren't terribly efficient - usually less than one percent for those directly in our food chain - but a lot of land is devoted to the cultivation of suitable plants.2
We can have some fun with some numbers. An average person requires about 2,000 Calories a day. Calories are a unit of energy so you can divide by time to find the average power requirement. Doing this and converting to watts, it turns out we need about 100 watts on average. Lower at night when we're sleeping and much higher when we're doing something athletic, but 100 watts a person is a nice number to remember for quick mental calculations.
The sun delivers an average of a bit more than 1,360 watts per meter2 to the Earth.3 Absorption in the atmosphere, the Earth's roughy spherical shape, inclination, day and night and cloud cover reduces this to something usually between 50 and 200 watts/m2 - let's pick 100 for a quick back of the envelope. Average food crops stores solar energy into those chemical bonds with at about a half percent efficiency so their power rating is about 0.5 watts/m2. If we could harvest and process these crops with perfect efficiency it would take about 200 square meters of land to supply one of us with food. Given seasonal growing issues and various inefficiencies in the chain, a more reasonable number is closer to 1,000 square meters of farmland under cultuivation for every person on the planet.4
So what does this have to do with the beauty of triangles?
Hang on - we're getting there. This is taking a bit more time to flesh out than I thought so I'm breaking my one hour rule.
The Industrial Revolution came in several phases, but at its core it allowed us to effectivvely tap the relatively vast amounts of energy stored in hydrocarbons like coal, petroleum and natural gas. Up until that time most of what we could do was limited to muscle power - from us or domestic animals. A good rule of thumb is an adult male in good physical shape can produce about a kilowatt-hour of mechanical work a day .. 100 watts of additional power in a ten hour shift.5 A horse may provide about four or five times as much. This proved to be a very low and limiting barrier to growing the civilizations - many people spend all of their time dealing only with food production and available energy for other activities was very limited.
Coal, petroleum, and natural gas formed over many tens of thousands of years millions of years ago. The efficiency of their formation was not great and local geologic conditions dictated where they are and how much exists. But many tens of thousands of years often dominates the low efficiencies and large amounts of energy were stored. We are mining sunlight from our distant past.
Most of the gasoline in our cars comes from petroleum which, in turn comes from dead algae and zooplankton that became trapped under sedimentary rock and "cooked" under great pressure and heat for ages. At about 36 kilowatt-hours per gallon it is almost an ideal fuel for transportation, it can be stored at room temperature, is relatively safe and easy to handle and transport, and we have had engines that burn it directly since the late 19th century.6
The ease and low cost of mining, transporting, processing and using this very old reservoir of stored solar energy has produced an extremely inefficient transportation infrastructure - the automobile. But early on there was so much oil that inefficiency didn't matter very much.
Cars are great for moving us long distances at speeds that give us practical commuting ranges on the order of fifty miles or thereabouts and one day trips ten times that distance. But internal combustion engines are heat engines and, despite more than one and a half centuries of refinement, only about a quarter of the gasoline you buy is used to turn the wheels of your car. The majority of it escapes out the tail pipe or heats the engine block. Improvements have been made and will continue, but they are increasingly expensive and we aren't that far from the limits for a flexible use vehicle.
There are other issues like cost and pollution, but let's focus on efficiency and ask a fundamental question.
What are we really moving?
Usually just a person or two and perhaps a few bags of groceries - a few hundred pounds at most. The average car weighs nearly 4,000 pounds. It takes a lot of energy to accelerate its mass to speed, so a good metric to consider is payload divided by vehicle weight plus payload. Let's say you and your groceries weigh 200 pounds and your car weighs 3,800 pounds. Only five percent of what is moving around really needs to be moved around.
For short trips bicycles make sense. I've done some calculations based on Colleen and her bike. She weighs about 170 pounds and her bike weighs 30 pounds. Fully 85% of what is moving around is useful payload and that number can increase a bit as she carries groceries on the bike. She gets the equivalent of 1,000 miles per gallon of gasoline. Her bike is great for speeds up to about 15 mph and trips generally under a five or six miles each way - basically almost any commute in a town or city. Much longer trips and/or higher speeds or heavy payloads require something like a car - but for short and slow trips Colleen "wins" using a bike largely by not having to carry around all of that extra weight. We can and should reduce the weight of cars as it is the next area for large (factor of two) improvements in fuel use efficiency, but bicycles are extremely low hanging fruit where practical.
In the late eighteen hundreds the biycle, like the automobile, was undergoing change. The safety bike was developed revolutionizing bike design and safety and giving us a very simple and extremely strong lightweight structure. It roughly onsists of two triangles fused together. Bicycle design has progressed, but this basic geometry hasn't changed very much since then.
A person on a bike is very efficient - about three or four times as efficient as a walker and more efficient than mamalian locomotion. Bikes are optimized for urban scale trips and payloads associated with perhaps 80%+ of human trips less than five miles.
I sometimes characterize a bicycle as "a human sweat amplifier fashioned of a diamond shaped geometry fashioned from a pair of fused triangles"... But there is something deeper to it. Building one can be straightforward - if you like you can even make one using bamboo as a primary frame material.7
Refinements, on the other hand, can be technically demanding and leading edge bike design is a convenient laboratory to material development and fabrication research and development. The aerospace industryhas been an early driver of carbon fiber use, but bicycle frames have been proven an important vehicle for perfecting less expensive fabrication technologies that are now being applied in a variety of industries.
China has used bicycle manufacture as a mechanism for learning and scaling manufacturing technologies. Beginning with aluminum bike frames in the late 1980sthey have managed to drop the price of an aluminum bike frame by nearly a factor of fifteen. For about a decade they have been working with carbon filber nad mahve made prie reductions on the order of five with eight or ten looking likely soon. The resulting techniques have driven wind turbine carbon fiber fabrication along with parts of their aerospace industry. If they can achieve success in automotive carbon fiber on the order of what they've done with bicycles, the carbon fiber automobile becomes practical and we have a fundamental revolution in the industry. It would be possible to make a 2,000 pound safe four passenger car and that would translate into much greater fuel efficiency.
But bikes may be another subtle, but potentially powerful driver of change.
It turns out there are a lot of electric bikes in China - currently 150 million with an annual production that should reach about 70 million around 2015. Most of these are very unsophisticated - a heavy bike with a small fairly inefficient electric motor and heavy lead acid battery.
Bike batteries don't have to be large and expensive. We found that Colleen required about 31 Calories to travel a mile making her about 34 times as energy efficient as a 30 mpg car. 31 nutritional Calories is about 36 watt-hours, so a 10 mile roundtrip commute requires about 360 watt-hours. But Colleen happens to be human and her efficiency at turning food energy into mechanical work at the pedal is about 20% while the battery, controller and motor in state of the art ebike exceeds 80%. So she could get a comfortable 40 mile range with a 500 watt-hour battery and pedal along a bit to increase the range even more as well as getting some exercise while she's at it.
A 500 watt-hour battery pack is about ten times the capacity of the average laptop computer battery. Currently most lithum-ion ebikes use several laptop batteries, but newer designs use repurposed automotive batteries. China appears to be encouraging ebike makers to move to lithium-ion designs. Seventy million lithium-ion ebikes would require 35 million kilowatt-hours worth of batteries. Smaller electric vehicles use batteries in the 25 to 35 kilowatt-hour range. eBike production would be equivalent to about a million new electric cars a year and may be an important bridge towards the massive production scales required.
There is also an indication that city planners are beginning to rethink the design of new megacities moving more towards a mixture of small cars (mostly electric), ebikes, bicycles, pedestrian traffic and mass transit - much like parts of Northern Europe. This type of design is much more efficient in energy use and may be less expensive in the long run.
Just two triangles joined into a diamond, but they may be giving us a hint of a possible future.
1 Atmospheric oxygen tends to react with a lot of things and doesn't stay around very long on its own - a few thousand years at most. Its presence indicates something has produced it recently and, at least on Earth, it is an indicator that photosynthesis is working away.
2 Sadly there is starvation, but this is a distribution problem. Green plants provide enough energy for the world's population - but we appear to be within about a factor of two of a fairly harsh limit.
3 1,366 watts/m2 is an accepted number that averages over our orbit and solar cycles, but the last cycle has been very quiet and the recent number is somewhat lower - perhaps about 1,361.
4 This is for diets where we consume plants. It turns out we eat meat too and making meat is inefficient. Usually under ten percent, although some meats like industrial poultry can be as high as twenty percent.
5 I use a rowing machine to exercise and measure my output directly. My normal sessions are at an average power level of 150 watts and run 60 to 80 minutes. A one hour session would represent 150 watt-hours of work. Since I'm about 20% efficient, that means I need about 600 watt-hours of food above and beyond my normal metabolic needs to support the exercise. That's about 516 Calories (nutritional - there are several types of calories). People can work at much more intense levels for short periods and expert athletes can work at about three times my level for similar periods. I note some of that in another post.
6 Unfortunately there are some nasty byproducts and side effects. Incomplete combustion produces numerous toxic chemicals and an enormous amount of carbon dioxide is released as a direct combustion byproduct even if we had complete combustion - approximately 20 pounds of carbon dioxide for every gallon of gasoline burned. This is from carbon that had been captured for thousands of years and sequestered for millions of years. This rapid desequestration is a root cause of the human caused global warming.
7 Bicycle frames are usually fabricated from aluminum, but steel is also frequently used along with the emergence of carbon fiber and, more rarely, titanium. I'm a big fan of steel as newer alloys are fairly lightweight while offering an outstanding "road feel" Steel can also be easily adapted to bespoke designs where a frame is custom tailored to the rider. My old Raleigh Pro was built in the mid 1970s using Reynolds 531 - a then exotic alloy that only one company in the world could make. One of the most exotic steels is a maraging stainless steel called Reynolds 953. The tube wall thicknesses are so thin - down to about 0.3 mm - that frames approach the weight of carbon fiber bikes. Colleen is over 6'6" tall and that dictated an unusal frame geometry that required Reynolds 953 and some careful selection of tube diameters, wall thicknesses and buttings to get it "right" ... a fair amount of numerical simulation.
Recipe Not re-frieds
I tend to approach cooking on hunches and have my share of failures. This is a nice success. I like re-fries, but rather than sautèing the aromatics with the cooked beans I wanted to sautè them first and then cook them with the beans in a pressure cooker to infuse the flavor. I used a mixture of pinto and cranberry beans because that's all I had at the time. I assume you could use any similar bean and get great results. A huge key to success with dried beans is to never use anything more than about six months old.
The quantities are approximate as I didn't carefully measure. I'll use mostly volume measurements even though that is bad form.
° 1 tbl vegetable oil
° 1 medium onion chopped
° 1 bunch cilantro stems and leaves separated and chopped
° 1/2 tsp chipotle powder - use more or less for to vary the flavor
° 1/2 tsp cumin
° 2 cups dried beans. I used a mixture of pinto and cranberry beans soaked overnight in water - borlotti would be great too
° 2 cups water
° 1 tsp kosher salt
° Heat your pressure cooker with the top off over medium heat and add the oil. Sautè the onion, cilantro stems and spices (not the salt yet) until the onion starts to soften. Don't let it brown. Add the beans and water.
° Close the lid, crank heat to high and lower heat once you reach full pressure (15 psi setting). Cook about 10 minutes and move to a cold burner allowing the pressure to drop on its own before opening.
° Reserve a few of the beans for a garnish, add salt to the rest and mash.
° Serve garnished with the whole beans, sour cream and the cilantro leaves.
I prefer whole milk greek yogurt (Fage Total) to sour cream, but your mileage may vary. Sour cream is the classic. Also I imagine parsley would be a great substitute for cilantro, but I really like cilantro.