The Knowledge: How to Rebuild Our World From Scratch (20 page)

Electricity, or, to be more precise, the whole set of phenomena bundled within electromagnetism, is such an important gateway technology that you would really want to beeline for it during a reboot. The discovery of electromagnetism provides a great historical example of stumbling upon a completely new field of science, offering a whole assortment of related phenomena and therefore exploitable possibilities. These novel phenomena were then mined for technological applications, which themselves in turn opened up new avenues of fundamental scientific research.

Electricity in a steady, sustained flow, suitable for exploiting for practical purposes, was first produced by the battery. A battery is actually startlingly simple to construct. All you need to create a constant electric current is two different kinds of metal, both immersed in a conducting fluid or paste called the electrolyte.
*
All metals have a particular affinity for the particles called electrons, and when two dissimilar metals are brought together, one of the pair will give them up to the more electron-hungry metal, causing a current along the wire connecting them. All batteries, whether in a mobile phone, a flashlight, or a pacemaker, encapsulate a chemical reaction that has been subjugated to run only when the connection is completed, and the flow of electrons is then channeled along a convoluted pathway of wire to do work for us. The difference in reactivity between the two metals
involved determines the electrical potential, or voltage, that a battery produces.

A reasonable voltage is produced by coupling silver or copper with higher-reactivity metals such as iron or zinc. The first battery, the
voltaic pile, was constructed in 1800 by stacking alternating disks of silver and zinc, separated by cardboard pads soaked with salty water. Silver, copper, and iron were all known millennia before the invention of the voltaic pile, and although zinc is harder to isolate, it is present in ancient bronze alloy and was available in pure form from the mid-1700s. Wires can be made simply by rolling or pulling soft copper. So there would seem to have been no insurmountable hurdles to electricity being discovered in classical times.

In fact, perhaps it was.

In the 1930s several curious artifacts were unearthed at an archeological dig near Baghdad in Iraq. Each is a clay jar, about 12 centimeters tall, and dated to the Parthian era (200 BC–200 AD). But it’s the contents of the pottery that are so remarkable. Inside each jar is an iron bar surrounded by a sheet of copper rolled into a cylinder, and the jar shows signs of having contained an acidic fluid like vinegar. The two metal pieces are kept from touching each other, and the jar mouth is sealed with insulating natural bitumen. One hypothesis is that this ancient relic constitutes an electrochemical cell, perhaps employed for electroplating gold onto jewelry, or maybe the tingling current was believed to have medicinal properties. Replicas made of the “
Baghdad battery” do indeed successfully produce around half a volt, but it’s fair to say that the evidence for any electroplated items is weak, and the interpretation of these mysterious pots remains controversial. However, if it was built for the purpose of providing electricity, as is certainly possible, it would predate the voltaic pile by well over a millennium.

If the chemical reaction of stripping electrons off the negative terminal and passing them onto the positive electrode is reversible, then you have the makings of something particularly useful: a rechargeable
battery. The easiest rechargeable battery to build from scratch is the lead-acid battery, common today in cars. A sheet of lead is used for each electrode, and bathed in sulfuric acid electrolyte. Both electrodes will react with the acid to make lead sulfate, but during charging you will convert the positive one to lead oxide (lead rust) and the negative one to lead metal, which is neatly reversible again as the battery discharges. Each of these cells will produce just over 2 volts, and so six of them wired together in a series gives you the 12 volts of a car battery.
*

The problem with batteries, though, is that although they offer a fantastically portable power supply that our laptops, smartphones, and other modern gadgets rely upon, you’re merely tapping the chemical energy already held in the dissimilar metals (in the same way burning a log of wood only liberates the chemical energy of carbon reacting with oxygen). You’ll need to put a lot of energy into refining the reactive metals in the first place, or topping up the rechargeable battery from another electrical outlet. Batteries are a store, not a source.

The features of electricity that we rely upon so much in modern life are a related cluster of phenomena that were stumbled upon beginning in the 1820s. Place a compass next to a wire carrying a current from a battery and you’ll notice that the needle is deflected. The wire is puffing out a magnetic field that locally overwhelms that of the Earth’s global field, and so the compass needle reorients. You can maximize this effect by wrapping the wire into a tight coil around an iron rod core; the small fields from the wire all combine to create a powerful electromagnet that you can command on and off with the flick of a switch, and use to permanently magnetize other pieces of iron.

So if electricity can create magnetism, is the reverse also true—can a magnet conjure up a current within a wire? Indeed it can. A magnet pulled back and forth, or spun, or even an electromagnet flicked on
and off, will all induce a current in a nearby coil of wire. And the faster the magnetic field moves across the wire, the greater the current induced. So electricity and magnetism are symmetrical powers inseparably intertwined with each other: two sides of the same electromagnetic coin.

And it is this simple observation of magnetism inducing current that unlocks an enormous wealth of modern technology: using a magnet, motion itself can be converted into electrical energy. You’re not limited to batteries that require expensive metals and run down: you can generate as much electricity as you like from spinning a magnet inside a wire coil, or vice versa. And the converse is also true: electromagnetism can cause motion. If you place a strong magnet alongside a wire you’ll notice the wire twitches as the current through it is turned on. This is the motor effect, and with a little experimentation you’ll work out how to arrange the current-carrying wires and magnets (or even electromagnets) to drive a rapidly spinning shaft. Today, the electric motor drives industrial machinery, saws timber, and grinds flour, and you’ll be able to count dozens of them in your home: running the vacuum cleaner, turning the exhaust fan in the bathroom, or spinning the DVD in the player. Our lives today are eased by this miniaturization of labor, with the electric motor now ubiquitous and practically invisible.

Using this principle of electromagnetism causing motion, you’ll also be able to construct instruments for accurately measuring the fundamental attributes of electricity: how much current is flowing and what voltage it is at. (The earliest electricians attempted to measure it by rating the pain of the shock delivered to their tongue!) As we’ll see in Chapter 13, being able to reliably quantify a new phenomenon is the critical first stage in coming to understand it and so being able to technologically harness it for your uses.

Electric light, too, has a powerful role in our modern lives, providing illumination on demand that has fundamentally changed our
sleep patterns and working lives; our buildings and streets now blaze with a billion tiny suns. The simplest form of electric illumination is the arc lamp. This was invented in the early 1800s, supplied from voltaic piles, and is essentially just a continuous spark—an artificial bolt of lightning—held between two carbon electrodes. The trouble with arc light is that it is unbearably intense and thus isn’t suitable for interior lighting. So while using electricity to generate light is simple, using electricity to create a practical glow is fiendishly tricky.

The physical phenomena that the light bulb is designed to exploit are simple enough. You can use the material property of electrical resistance to heat up a thin filament by pushing a current through it. As materials get hotter they begin glowing with their own light—incandescence—like an iron bar shoved into a fire, becoming cherry red, then orange, yellow, and finally a brilliant white. But the devil is in the details. If a filament of carbonized thread or metal glows white-hot in air, it rapidly reacts with oxygen and burns up. You could envelop the filament in a sealed glass orb and suck out all the air with a vacuum pump, but hot materials readily evaporate in a vacuum. Filling the bulb with an inert gas like nitrogen or argon at low pressure works well, but you will still need some R&D, trial, and error with strands of different carbonized materials or thin metal wires to find what works as a reliable filament.

We’ve seen how a generator works to convert movement into electricity, but how do you create that rotation in the first place? The immediate solution is that you simply install the generator in a rudimentary windmill or waterwheel you’ve constructed. Generators work best spun at many hundreds of revolutions per minute, so you’ll need a system of gears, or pulleys and belts, to multiply up the slow but high-torque
rotation of the drive shaft. A rebooting civilization might therefore conceivably resemble a steampunk mishmash of incongruous technologies, with traditional-looking four-sail windmills or waterwheels harnessing the natural forces not to grind grain into flour or drive trip-hammers, but to generate electricity to feed into local power grids.

CHARLES BRUSH’S 17-METER-DIAMETER, ELECTRICITY-GENERATING WINDMILL, BUILT 1887.

A feasibility study in 2005 calculated that retrofitting a single traditional four-sail windmill with a gearbox and generator to replace the millstones could produce more than 50,000 kWh of electricity a year—enough to supply my apartment four times over.
But perhaps the most inspiring example of what might be achievable with rudimentary means during a post-apocalyptic reboot is offered by the American inventor Charles Francis Brush. In 1887 he built a tower on his property holding a fan 17 meters across, composed of 144 rotor blades of thin,
twisted cedar wood. This could generate more than a kilowatt of electricity, which he used to power the hundred or so incandescent light bulbs—themselves cutting-edge technology at the time—throughout his mansion, with any surplus stored in more than 400 rechargeable batteries in his basement.

The problem with such designs is that the extensive system of gears needed to multiply up the slow turning wastes a lot of the energy. The solution for windmills is to fundamentally change the design. Instead of deploying broad sails that catch large amounts of the wind as it passes, but also generate lots of turbulence and drag and can therefore never spin very fast, modern wind turbines sport a triplet of long, slender blades. These are based on the lessons of aerodynamics learned from developing the propellers on aircraft, and although their much smaller surface area means they struggle to get going at slow wind speeds, they can spin incredibly rapidly in a stiffer breeze and convert far more of the rushing energy into electricity.

The power output of a waterwheel is also fundamentally limited. The amount of energy available in a stream of water is determined by the discharge and the head. Discharge is the flow rate, whereas the head of water is the total height that it drops—between the delivery chute and the race in the case of an overshot wheel. Waterwheels are severely restricted by the maximum head they can utilize, constrained by the diameter of the wheel: you can’t construct a wheel much more than 20 meters across before it becomes too heavy and inefficient as it turns.

Water turbines, however, do not have the same limitation. China’s Three Gorges dam, the most powerful hydroelectric plant in the world, provides a head of 80 meters between the top of the reservoir and the turbines at the base, and so can deliver prodigious energy.

A simple turbine you can build that is best at exploiting a large head and a small discharge flow (i.e., a narrow pipe producing a jet of
high-pressure water) is the Pelton turbine, which consists of a ring of cups fixed around the rim of a hub (it looks a bit like a circular splay of spoons). The key is for the jet of water not to stop in each cup, but to be smartly turned around and splash out the front again. Each cup is designed like a smoothly curved bucket with two halves and a cusp-like ridge running through the middle, so that the jet of water striking the cup head-on is neatly parted by the central ridge, swirls around the curve of both halves, and streams out the front again. It is this reversal of direction that exerts a strong force on the cup and spins the turbine, the jet striking each of the cups in turn as the hub spins around.

PELTON TURBINE.

For the opposite situation, when the available flow you have is low head but high discharge, the cross-flow turbine is better suited. Here the water is guided in through the top of a wheel with short curved vanes arranged radially, which get thrust to the side by the flow, and then again as the water exits out the bottom. The cross-flow turbine
superficially resembles a traditional waterwheel, but, most important, is not turned by the weight of falling water caught in buckets but by the action of the flow of water against the backs of its curved blades.

Both the Pelton and cross-flow types of turbine are easy to construct with rudimentary metalworking tools, and today are recommended as appropriate technologies for local manufacture in the developing world. They are exactly the sort of technology that could help a rebooting post-apocalyptic society.

Despite the efficiency of wind or water turbines and their harnessing of renewable energy, most of our electricity today is not generated in this way. In fact, the age of steam never really ended. Though we don’t use steam engines as prime movers for machinery or vehicles anymore, more than four-fifths of the electricity used around the world is generated using steam: firing a boiler with the heat released by combusting coal or gas, or by the disintegration of unstable heavy atoms in a nuclear fission reactor.

As we’ve explored, producing heat is straightforward, but transforming thermal energy into movement is a trickier step. A steam engine will do that for you, but the slow thrusting of the piston cannot efficiently be converted into the rapid rotation suitable for an electrical generator.

The solution is the steam turbine, based on successful designs for water turbines but optimized for high-pressure steam. Power can be extracted from the rush of steam either by catching the flow on the back face of the blades so that they are pushed by the impulse (like a Pelton or cross-flow water turbine), or by deflecting the water over a curved surface so that it is pulled forward by the reaction force, like an aircraft wing. The key difference from water is that steam expands, to rush faster but at lower pressure, so most steam turbines combine a reaction stage for the high-pressure steam with impulse rotors farther down the shaft when the steam has expanded. It is this multistage steam turbine that has enabled the generation of prodigious quantities
of electricity with very high efficiency, and thus ushered in the modern electrical age.

For the generated electricity to be useful, though, you’ve got to be able to distribute it to where it’s needed.

Although you can rig up a generator to provide a steady direct current (DC, same as a battery), it’s easier to build one that produces a rapidly cycling alternating current (AC) as the rotor spins. The generated voltage in the coil swings from positive to negative and back again, and so the current it drives also repeatedly reverses direction, sloshing back and forth within the wire like a rapid tide. AC offers one huge advantage over DC: it presents an elegant solution to the problem of transporting electricity from where it’s generated in the power station to where it’s needed in industrial complexes or towns.

As soon as you start trying to shunt electrons around a distribution network of metal cables, you hit a fundamental problem. The amount of power delivered by electricity is the product of the current multiplied by the voltage. If you use a large current, the unavoidable electrical resistance of the wires will cause them to warm up and waste the vast majority of the precious energy you’ve generated. (On the flip side, electrical resistance is the principle that you are deliberately maximizing in the heating element of a coffee maker, toaster, or hair dryer, and if you can get a thin filament hot enough to begin glowing without burning up, then you’ve cracked the basics of the light bulb, as we’ve seen.) The only alternative for supplying high power levels is to keep the current low and ramp up the voltage. The problem with this, though, is that high voltages are exceedingly dangerous: acceptable for wires strung high between pylons striding across the countryside, but you certainly wouldn’t want them connected to your home. The beauty of AC is that it allows you to easily bump the voltage up and down, using transformers.

A transformer is essentially nothing more than two large coils of wire positioned alongside each other on the same buckle-shaped iron
core, so that the magnetic field thrown up by the first coil washes through, the second. Employing the principles of induction discussed earlier, the alternating current flowing through the primary coil creates a rapidly fluctuating electromagnetic field—expanding and collapsing more than a hundred times every second—that in turn induces an alternating current in the secondary coil. Now here’s the clever bit. If you wind the secondary coil with more turns than the first, the voltage is stepped up and the current decreases—a transformer is like an electrical currency exchange, interconverting between current and voltage. So you can use transformers to change the voltage in different stages of your distribution network to minimize both the inefficient resistance of high currents and the safety hazards of high voltage.

The beauty of electricity is that you no longer have to build all of your industry on top of windy hills, near fast-flowing rivers, or within easy transport distance of forests or coalfields, as our ancestors had to before the nineteenth century. You only need to place your power generators in these sites, and then zip the electrical energy down wires to wherever it’s needed. This is something we’ve come to take for granted. Just a century ago, all the energy for a household would have to be physically delivered: oil for lamps, charcoal or coal for cooking and heating; Victorian houses needed an outside coal bunker the size of a small room to hold enough fuel to keep warm over the winter. Today, electricity is piped directly throughout the home, supplying energy right to where it’s needed—cleanly, silently, and without requiring any storage.

Getting society back on its feet in the immediate aftermath of a cataclysm, DC offers an adequate option for pumping electricity over short distances or storing it in banks of batteries, such as a small-scale local grid of windmills and homes. But if you want to benefit from economies of scale and large centralized power stations as your post-apocalyptic civilization recovers, you’ll need to develop an AC distribution network. And in a post-apocalyptic world, where the rebooting
society is likely to feel the pinch of much lower energy availability, you will need to make as much use of the heat from fuel as possible. Combined heat and power (CHP) plants address the absurdity of power stations simply discarding vast amounts of heat though their cooling towers, when all the buildings in surrounding towns burn yet more fuel to heat themselves. Sweden and Denmark are leading the world in their use of CHP, first driving turbines to generate electricity but then using the hot steam for other purposes, such as heating buildings in the local area. They are fired by burning natural gas as well as biofuels like wood waste, timber from sustainable forests, or agricultural waste, and can approach 90 percent efficiency for electricity generation and heat production together.

So a familiar sight during the reboot may be animal-drawn carts, or even gasifier-adapted trucks, hauling loads of coppiced lumber and agricultural waste from the surrounding countryside to CHP stations, generating both power and heat for the nearby community and industries to make use of every scrap of the gathered energy. Let’s take a look in the next chapter at these transport technologies.