Turkey Power: What does it take to cook a Christmas Turkey?

Even for the most organized of us, the holiday season is a hectic one. Your time is split between getting your shopping done, visiting all your friends and family, and upping the festive factor of your house, to the point where Clark Griswold himself would be giving you a solid high five. But even within this chaotic holiday season, there’s one thing that many people look forward to – a perfectly cooked Christmas Turkey.

So, what’s the secret to the perfect Christmas Turkey? Some would say freshness, others may argue that it's seasoning. But at Sketchy Science,  we believe the key is in perfecting the Rube Goldberg-esque process by which energy is transferred between system boundaries countless times, until it reaches your cooking device, manifests itself as kinetic energy at the molecular level, that eventually enables material phase changes and the high speed molecular dance, which breaks and re-forms chemical bonds. How else would you ensure your turkey is lip-smackingly juicy and delicious?

Of course, I’m talking about cooking the turkey, and when you think about it, the molecular dance is a result of turning on your oven to 350 degrees Fahrenheit and pumping your bird full of heat energy for three to four hours (or until golden brown). But have you ever thought about how much energy it takes, where it comes from, or what else you could be doing with that turkey-cooking energy?

Probably not, and that’s why we’ve done the thinking for you.

Let’s begin with the basics. Loosely speaking, energy is the ability to do work, and we measure it in units called Joules (J). It comes in many shapes and sizes, and can be converted from one form to another. For example, the sun emits solar energy, which plants convert into chemical energy through the process of photosynthesis. When you eat the plant, your body metabolizes the sugar to power your muscles. If you then use your muscles to lift some weights over your head, you’re converting the chemical energy into gravitational potential energy. If you happen to give up on that last rep and drop the barbell, the falling weight has kinetic energy. Even the agonizing scream you may let out when the weight falls on your foot is a form of sound energy. But what kind of energy does it take to cook a turkey? Let’s take a closer look at our friend, heat energy.

There’s a simple formula to figure out how much energy it takes to heat a material to a certain temperature:

Q = mc(T2-T1),

where Q is the amount of energy in joules, T1 is the starting temperature of the material, T2 is the final temperature of the material, m is the mass of the material, and c is something called the specific heat capacity. Specific heat capacity is a property of the material in question; it tells us the energy required to raise the temperature of one gram of material by one degree Celsius. With this handy formula, we can figure out how much energy it takes to cook a turkey from room temperature (about 23 degrees Celsius) to the safe consumption temperature of 74 degrees Celsius. In case you’re wondering, the specific heat capacity of turkey is 2.81 J/goC (and yes, someone put in the effort to figure that out empirically.

Assuming an average bird mass of 12 lbs., after crunching all the numbers, we get about 780,000 joules, or approximately 800 kilojoules (kJ). Note that we don’t take the inefficiencies of the oven into account; in reality the energy usage would be a bit more. How much is 800 kJ of energy, you ask? Let’s take a look at what we can do with it.

Since energy is such a fundamental concept, we can compare its quantities across many domains. For example, Calories are a measure of food energy, and one Calorie has energy equivalent to 4.184 kJ. So, the 800 kJ in question is about the same as 191 Calories. In other words, a handful of M&M’s has enough food energy to cook a Christmas Turkey.

Electrical engineers measure the capacity of a battery in units called watt-hours. But since all a battery really does is store energy, we can always convert it back to our old friend, the joule. Knowing this, 800 kJ is enough energy to charge the 5.45 watt-hour battery of your iPhone 540 times. On the flip side, when we apply a similar analysis to the battery of a Tesla Model S, we see that the 800 kJ is only enough energy to drive the Tesla 1.3 km. This gives you an appreciation of how much energy is consumed to move a car around.

What if we were to scale the problem up a bit? In Canada, we eat approximately 3.9 million turkeys at Christmas time each year. Multiply that by the 800 kJ of energy used to cook each turkey, and we arrive at 3.12 terajoules (TJ). To give you a sense of scale, 1TJ is 1,000,000,000 kJ. This is about the same amount of energy that is released in a 1 kiloton (kt) explosion. One kiloton, as you would expect, is the amount of explosive energy released when you detonate 1000 tonne of TNT. If we gave all of that explosive energy to Santa, he would have the equivalent of 100 Davey Crocket missiles - perfect for “tactical defence” of the North Pole.

Let’s scale it up one more time.  During Christmas every year, Canada, the USA, and the UK consume a combined 36 million turkeys. At 800 kJ per turkey, that is a whopping 28.8 TJ of energy. To put this into perspective, let’s say we wanted to launch a projectile from Earth. We can calculate how much energy we can supply to it using the expression for kinetic energy:

Ek = (½)mv2,

where Ek is the amount of energy in joules, m is the mass of the object in kg, and v is the velocity of the object in m/s. Now let’s say, hypothetically of course, that our projectile is the International Space Station (m = 419,000 kg), and we give it enough energy to achieve the escape velocity of the Earth (v = 11,200 m/s).  Plugging in all the numbers, we arrive at approximately 27 TJ, which is about the same amount of energy used to cook turkeys in just three countries every Christmas.

Though to be fair, we didn’t take into account the air resistance, which would also require additional energy to overcome.  But, why try to go through the air when you can just get rid of it all together?  If we were able to build a perfectly sealed column 100 m by 100 m wide, and tall enough to reach the edge of our atmosphere (about 100 km), we could evacuate all of the air and never have to worry about air resistance ever again!  Using a few standard 10 HP air pumps that can move 60 cubic feet of air per minute, we could get rid of the air with an energy cost of about 26 TJ, which is slightly less than the global turkey energy consumption per year.  

What does this all mean? The amount of energy we use during just two Christmases to cook festive turkeys could hypothetically remove the air from a sufficiently sized tube, and shoot the ISS from a cannon with enough speed to escape the gravitational pull of the planet.

Of course, there are other types of energy we didn’t discuss. The sun uses a process known as thermonuclear fusion to keep itself shining and shower us with energy goodness. In fact, the Earth receives about 122,000 TJ of energy from the sun every second. That’s enough energy to cook the world’s Christmas turkey dinners for 4300 years!

So, the next time you are stuffing your face with Christmas turkey, take a step back and think about all the chain of energy processes that took your bird from raw to golden brown and delicious.  Perhaps do a few of your own back-of-the-envelope calculations and ponder upon the other things on which you could be spending your energy.   

You may just be surprised.

The Heat Beneath Your Feet: The Toe-Tingling Science of Geothermal Energy

A few months ago we learned about using the sun as a source of energy and were impressed by how convenient it is to have a super massive power plant in the sky. The trouble with the sun is that unless you have homes at the north and south poles that you can travel between, it is only available for half the day. Renewable energy is fantastic and it will eventually save the world, but people are going to want to be able to recharge the batteries in their electric cars while they sleep. That being said, we have to branch out from solar power alone.

Fortunately, there is another molten ball of pure energy that is a little closer to home than the sun. While the sun steams along at an insanely blistering 15 million degrees C (27 million degrees F) in its core, the alternative, our home earth, is a relatively chilly 4,200 degrees C (7,600 F). What it lacks in heat, it makes up for in proximity. If you want to find this potential source of limitless energy, all you have to do is start digging.

It’s not something that we think about on a daily basis, but every moment of your life will be spent on a thin sheet of rock surrounding a ball of magma. At its thickest, the Earth’s crust is barely more than 50 km thick. If you take a bite out of an apple and look at how thick the peel is in relation to the size of the whole fruit, you will have a reasonably good idea of what separates you from volcano juice. Luckily, our tenuously insubstantial barrier provides a great advantage for anyone looking to escape the use of fossil fuels. It’s called geothermal energy, and it combines the Earth’s heat with the water that flows through the crust to create useful energy.

There are three main ways to use geothermal energy. The first is the easiest and involves piping water from hot springs (pools of heated water that seep to the surface) directly into homes and buildings to provide heat. If there isn't a hot spring nearby you will have to build a geothermal heat pump, which takes water from a few feet under the ground (this water has a consistent temperature of 10 to 15 degree C (50 to 60 F)) and circulates it through pipes. The relatively minor amount of heat from the water can be transferred to homes using electric compressors and heat exchangers. In the summer, the process can even be reversed to draw heat from the home and put it back into the ground to cool things off. The third option is a geothermal power plant which pipes hot water and steam from deep within the Earth through turbines, making them spin, creating electricity in the process. 

The last of these options offers significant advantages where it is practical. We humans may appreciate a warm house in the winter, but we really appreciate electricity sucking things like iPods and televisions. Sometimes we even use electricity for worth-while things. I bet you didn’t realize that up to 30% of the electricity produced by people is used to treat and distribute clean drinking water. Now imagine if we could use clean, renewable, geothermal power to do that same job.

Fortunately you don’t have to imagine too hard, because engineers in British Columbia (BC) already had that idea. BC is home to Canada’s largest water filtration facility, called the Seymour Capilano Filtration Plant (SCFP). BC is also Canada’s most geologically active province, with the Juan de Fuca tectonic plate slowly crashing into the North American plate, creating heat as it goes. The SCFP takes advantage of this happy coincidence by employing an underground geothermal exchange system that saves the facility enough energy to power 160 homes per year. And if you think that’s impressive, hop on a flight over to Reykjavik, Iceland where 95% of the buildings are heated and powered by that country's abundance of volcanic awesomeness. 

Of course, we don’t all live on a fault line or next to a volcano, so the opportunity to build a geothermal power plant isn't always available. However, we can all dig a few feet underground and install a geothermal heat pump. Domestic systems can be built for around $30,000 US and they save enough energy to pay for themselves in 5 to 10 years… Maybe it’s time we all got a little bit more Icelandic.

Solar Power: Not Just for Hippies, Anymore

Wouldn’t it be great if somebody invented a free source of power that anyone could use to power their lives? Ideally it would be an entity of pure energy positioned in the sky so we could all make use of it. If you made it big enough and powerful enough you could even put it 150,000,000 km’s away.

Fortunately for humans, the laws of physics have done the job for us and the bright, hot, skin bronzing power plant we call the Sun has been powering our planet since its fusion switch was first flipped on around 5 billion years ago. Unfortunately, we humans really suck at taking advantage of it.

Give a plant a steady stream of sunlight and it will work wonders. Plants can take the particles of light given off by the sun (photons) and directly use them as food. Photons power plant growth as well as photosynthesis, which is something all of us air-breathers should be thankful for. Since every food chain on the planet begins with plants, it is easy to see how the whole notion of “food” is based on transferring the sun’s energy from one body to another. Compared to plants, we humans are solar sissies.

The trouble with people is that having enough energy to power our bodies just doesn’t cut it anymore. We also need to power our houses, cars, computers, iPods, robot vacuums, dancing Santa’s and all the other things that modern life would be impossible without. It turns out that coaxing the sun into juicing our electronics for us is trickier than it might at first seem.

Conventional solar cells do a remarkably bad job turning photons into useful energy. Your average solar panel has an efficiency of about 20% - meaning that only 20% of the energy input (light) is converted into useful output. The way they work is complicated but basically you take some semi-conductive material (usually silicon (Si)), form it into a sheet, wire it up, and place it in the sun. Photons excite the electrons in the material, knocking them loose and sending them off to do useful things. To get electrons to do what you want, you need to create a current for them to flow along. 

Where you will run into trouble is primarily in 2 places:  the nature of light itself, and willfully moving electrons. As anyone who has ever seen a rainbow can tell, light comes in different wavelengths – each represented by a different colour. Different wavelengths have different amounts of energy. Only a small proportion of the Sun’s light has the exact amount of energy needed to excite electrons in a given material (ex. silicon). If a photon doesn’t have enough energy, it won’t knock any electrons loose. If it has too much energy, it uses just the amount is needs to nudge an electron and the rest is wasted. In the end, you lose about 70% of the possible energy in a beam of light to this problem. Even when you manage to get your electrons going and try to move them from one place to another, you lose energy if the distance is too far or if they are flowing through something that isn’t a very good conductor.

The upshot of these limitations is that you usually need a whole lot of solar panels if you want to power anything beyond a calculator with reliability. Recently, though, there has been some cause for optimism. Researchers at Caltech led by Dr. Harry A.Atwater have created a commercially viable solar panel that is up to 50% efficient. That still may not sound great, but it represents a massive leap forward in solar energy. 

Dr. Atwater and his team, working under the company name Alta Devices, have done away with silicon and instead build their cells from gallium arsenide (GaAs). The researchers argue that this material builds purer crystals than silicon (increasing efficiency), absorbs more photons, and produces more energy than conventional solar panels. On top of that, they have engineered their devices to recycle unused photons and be 1/40 the thickness of a human hair, making them doublely useful and ridiculously flexible. A few other innovations offer promise in creating more efficient solar cells including organic polymers and dye-sensitized materials that can absorb more photons.

Arun Das, PhD student at the University of Waterloo’s Autonomous Vehicles Lab, told Sketchy Science that, “low weight solar cells are very exciting. We would no longer be constrained to using [solar panels] on rooftops and solar farms. We could soon see solar cells as a viable option for charging our smartphones, extending the range of electric cars, and powering small unmanned rescue drones in disaster scenarios.”

As you can imagine, the impact all this would have on fossil fuel emissions would be immense. But that pales in comparison to the benefits of being able to watch The Biggest Loser in the middle of the woods.