Energy Currencies

By Charlotte Helston

I. Introduction

To properly understand our energy system, the concept of energy carriers, or energy currencies, is essential. It is important to differentiate between energy currencies, like gasoline or electricity, and energy sources, like crude oil or uranium to interpret how the energy we use arrives at our disposal. David Scott, author of Smelling Land: The Hydrogen Defense Against Climate Catastrophe says, "One difference is that currencies are harvested from sources: Gasoline is harvested from crude oil and electricity can be harvested from uranium."

From cash dollars to telecurrencies; crude oil to gasoline — The monetary currency analogy:

Scott draws an analogy with monetary currencies to illustrate the concept: Gold is to cash, cheques and telecurrencies, as crude is to gasoline, butane, diesel, etc. Types of monetary currencies can include pesos, yen, dollars, and baht. Each monetary currency is appropriate only in certain transactions. You wouldn't use telecurrencies to buy a chocolate bar, or a fleet of moving vans full of pennies to purchase a house. Likewise, you wouldn't use electricity to fly an airplane, or Jet-A to run a computer. Thus, transactions of currencies for both monetary and energy currencies are limited.

Contents of a barrel of crude oil
Petroleum is a hugely useful energy currency for our modern transport economy, but must still be refined from the primary energy source crude oil before it can be used.

The monetary currencies analogy can also help to explain the concept of energy conversions. Some currencies are easily converted, others are not. For example, it is easy to convert paper bills into bits of plastic called credit cards, but not so convenient to convert that money into, say, gold bricks. Similarly, we can easily convert gasoline into electricity using generators, but the reverse, changing electricity into gasoline is not possible. These one-way currencies, Scott says, "severely restrict our ability to design efficient and, most importantly, robust energy systems."

As we funnel energy currencies down the conversion chain, energy is wasted. But we put up with it because the energy system demands it: We can't "jam nuclear reactors into TV sets," says Scott, we have to convert nuclear energy into electricity. And each step of the way — from converting the heat from nuclear fission to steam energy, to steam driven turbines, to rotating shaft driven generators which creates medium voltage electricity, and so on until the current has passed through several transformers and is ready to power your television — loses energy.

Energy currencies: The gateway to solving our energy crisis?

Scott goes on to say that the world's obsession with discovering new energy sources is the wrong way to address our energy problem. We have plentiful sources — solar, wind, geothermal, just to name a few — it's currencies that will ultimately determine the success of a given energy source. The bottom line: It's important to distinguish between the different parts of our energy system, and analyze how they are working both independently and as part of the whole. Looking at our energy system in this way will help to improve the entire energy pathway, from cradle to grave.

Below is a long list of energy currencies used today, from fossil fuels to biofuels, fuel cells to batteries. Remember, every currency has a source that possesses its own set of impacts, as well as a pathway and series of transformations that also generate impacts. Consider the concept known as "cradle to grave" or the vehicle-specific "wells to wheels" when reading over the following currencies. How, and from what, are they derived? How are they converted from source into currency, and currency to currency?


Electricity is a secondary energy source, or in other words, an energy currency. This means that electricity is created from the conversion of other sources of energy, like coal and nuclear power plants or wind turbines (primary energy sources). The energy sources used to generate electricity may be renewable (hydroelectric) or non-renewable (natural gas), but electricity itself is neither renewable nor non-renewable.

Electricity is used to power lights, heating and cooling systems, and electronics like televisions and computers. Because you can't see it, it's hard to visualize the resources it consumes. For example, it takes 0.014 lbs of coal to light one fluorescent tube for one hour. If that bulb was left on for a year, a lump of coal the size of large dog (122.64 pounds) would be consumed. It is important to understand that electricity doesn't come from your wall: it comes from a variety of energy sources that can either have a greater or lesser impact on the environment.

Liquid Fuels

Fossil Fuels

Fossil fuels are forms of compacted carbon that are dug out of the ground and used to power our civilization. They provide over 80% of all the primary energy used in the world. Coal and natural gas are primarily used to provide electricity and heating, while oil runs the world's transportation economy.

Fossil fuels form over the course of millions of years. It is commonly thought that fossil fuels were formed from the decayed remains of dinosaurs. But the reality is that ancient forests, algae blooms and plankton provided the vast majority of the carbon for making fossil fuels. Though, undeniably, there were some dinosaurs mixed in too. Depending on what kind of life and the geological conditions, one of the three fossil fuels might form (coal from forests, oil and gas from plankton and algae).

Oil and Gas Formation

Over millions of years these decayed remains were covered over by thousands more layers of other decomposing remains, and then rock and sand which pressed down on them. Pressure from the rocks above, and the heat from the Earth's core below, cooked the once-living carbon, breaking the bonds that held the molecules together. This led to the formation of huge reserves of oil, coal or gas. This process is extremely slow and incremental, and, like biological evolution, can only be understood when viewed on the timescale of hundreds of millions of years. Most of the carbon we burn in our tailpipes comes from creatures that lived around 360 million years ago, an inconceivably long time scale when compared to a human lifespan, or even the existence of the human species.

Humans have known since the Roman Empire and Han China that coal, oil and gas can be burned to create heat, and mines were dug and fossil fuels extracted on a small scale even at these early dates. But what was not understood until the 18th and 19th Centuries was that the heat from those other fossil fuels could be used for things other than heating, lighting or cooking. They could be used to move machines. The steam engine developed in England around this time was the first to burn coal, which heated water, creating steam which spun a turbine.

A more comprehensive history of the fossil fuel economy can be found here.

1. Coal

Coal is still hugely important today for generating electricity, though it is not used for transportation anymore. Coal is an inexpensive and technically simple, if dirty and damaging, way to create the usable energy currency, electricity.

2. Oil

Contents of a barrel of crude oil
Refining the primary energy source crude oil creates a number of useful energy currencies. Here is what the average barrel of crude oil is converted into in the U.S.

Oil was the second fossil fuel to become widely utilized in the modern age. Oil is extracted from the ground in a form known as crude oil. Crude oil has many impurities making it useless for most of the energy applications we use today.

It must therefore be refined after it is extracted from the ground. This refining usually means heating the oil. At each temperature a different carbon molecule is separated out from the rest of the oil, each of which have their own specific uses. These range from extremely high-quality aviation gas, to heavy bunker oil used in ships and oil heating tanks, with petroleum and diesel for automobiles in the middle. Therefore these refined forms of oil are each an energy currency, while crude oil is the primary energy source from which it is all derived. Most oil is used in efficient internal combustion engines.

Oil is so popular as a transportation fuel because it has such a high energy density. You can learn compare the energy densities of various forms of energy at our energy converter here.

Natural Gas Pipeline Odorant
A sign at a natural gas pipeline warning about pipeline odorant.

3. Natural Gas

Natural gas became popularized during the course of the 20th Century as the technology to harness the fossil fuel in a gaseous state came into its own. Like oil, natural gas must be refined to remove impurities in order to be usable. It is also injected with an odorant that makes it smell like rotten eggs, to tip off people about a gas leak. Natural gas is today used primarily for electricity generation and heating. Older natural gas plants (such as British Columbia's Burrard Thermal) run on the same steam principle that powers coal plants, but newer plants use turbines that burn gas directly, and even use a combination of steam and turbine technology. As oil prices rise vehicles that run on compressed natural gas (CNG) are also becoming more attractive (which run on the same internal combustion engine as oil).


Where fossil fuels are formed by millions of years-old, decomposed organisms, biofuels are derived from recently living organisms (biomass). Material from plants, animals and organic wastes (the metabolic by-products of animals) is broken down and processed using a variety of technologies, discussed here. The principle biofuels in use today are:

1. Solid Biomass

Hundreds of millions of people worldwide continue to rely upon solid biomass for all their fuel needs.

Solid biomass includes materials like wood, sawdust, charcoal, agricultural waste, dried manure, and plants from dedicated fuel-crops. Raw biomass such as wood can be burned in a stove or furnace to generate heat for warmth and cooking. Wood and manure fuels remain a principle source of heating in the developing world.

Materials such as sawdust, wood chips and agricultural waste are typically put through a densification process before use. The result is what is commonly referred to as "hogfuel" — compact biomass in the form of pellets, cubes or pucks.

2. First Generation (First-Gen) Biofuels

First-generation, or conventional biofuels, are derived from plant starches, sugars and oils, as well as animal fats. Commonly, they use materials already in demand as food sources, like corn and soybeans. There are several types of first-gen fuels. Below, they are listed in order of prominence on the global energy scene.

Bioalcohols: Produced from fermented sugars and starches (and from cellulose as a second generation biofuel) biologically manufactured alcohols offer the same functions of fossil fuels like gasoline. The difference is we can easily grow first-gen fuels in crops like corn and sugarcane. The most common product is ethanol, and to a lesser extent propanol and butanol. Ethanol can be produced using the sugars contained in wheat, corn, sugarcane, molasses, potatoes — basically anything you could make an alcoholic beverage from. Ethanol is used in a range of concentrations, from E100 (100% ethanol) to E5 (5% ethanol). Blends of E15, E20, and so on are all possible. Ethanol possesses a smaller energy density than gasoline, meaning vehicles require more fuel to deliver the same power. Read more about ethanol in the Biofuels Energy Profile.

Yellow corn, one of the most important sources of biofuels today.

Biodiesel: Derived from oils or fats by means of transesterification, biodiesel can be blended with petroleum diesel in any percentage, or used in its pure form (B100 for 100% diesel). B20 (20% biodiesel) is the most common blend and can be used in nearly all diesel equipment. When blends increase above 20%, certain drawbacks tend to occur, such as lower energy content per gallon (8% less energy per gallon than petro-diesel), low-temperature gelling where the fuel's viscosity is too high for use, and microbial contamination. Read more about biodiesel in the biofuels energy profile.

Vegetable oil is an oft-used feedstock for biodiesel, but it can also be used simply as is, in the form known as straight vegetable oil (SVO). Using SVO can have unfavourable long-term effects on engines, and is thus not a choice fuel at this point in time. Some individuals concoct their own SVO by heating up waste oils. There are numerous "how to's" on the web.

Bioethers: Bioethers are primarily used as blending components for gasoline. Combined with any fuel, bioethers improve performance and emissions levels due to their high octane and oxygen content. Bioethers are produced by the dehydration of organic substances. The feedstocks for bioethers include ethanol (derived from fermented sugars and starches) and methanol (derived from biomass).

Biogas: Biogas is produced when methane rich substances (sewage sludge gas, corn silage, liquid manure, etc...) undergo a process called anaerobic digestion. This process involves microorganisms that break down biodegradable matter into usable methane. Biogas supports a range of applications including: in CHP gas engines (combined heat and power), for use in cooking, space heating, water heating, and as a replacement for compressed natural gas in vehicles. Biologically produced methane also has potential as a sustainable source of hydrogen for use in fuel cell technologies.

Syngas: Syngas, the short form for Synthesis gas, is a gas mixture made up of carbon monoxide, carbon dioxide and hydrogen. The name emerges from syngas' use as an intermediate in creating synthetic natural gas. It is produced through the gasification of a carbon-containing fuel to a gaseous product. Syngas can be derived from coal, wherein the coal is first converted to coke, then combusted under high temperatures.

3. Next generation (next-gen) fuels

Miscanthus sinensis has potential as a dedicated fuel crop, on top of being a lovely ornamental grass.

Next generation biofuels offer the possibility of using non-food sources as feedstocks for fuels like ethanol and biodiesel. Such materials include: waste biomass, the stalks of wheat, corn stover, wood, and special energy crops like miscanthus and algae. The technology involved in this branch of biofuels is called BtL (Biomass to Liquid). Products under development include: biohydrogen, biomethanol, DMF, Bio-DME, Fischer- Tropsch diesel, biohydrogen diesel, and mixed alcohols. This technology is not yet cost comparative to first generation biofuels.


How do we obtain pure hydrogen?

The Hydrogen Life Cycle
The Hydrogen Life Cycle

Hydrogen, comprised of only one proton and one electron, is rarely found in a natural state. Commonly, it is bonded to other elements, like oxygen, which gives us H2O, or water. It is also found in the hydrocarbons that make up fuels like gasoline, natural gas, methanol and propane. There are a range of methods in use today to produce hydrogen. The predominant technologies are electrolysis, a process that splits hydrogen from water, and extraction from fossil fuels in a heating process called reforming.

Extracting hydrogen from other materials uses energy. If both the source of material and the energy used to split hydrogen from it are clean, hydrogen fuel could indeed make a significant contribution to the greenhouse gas problem. Unfortunately, it is primarily dirty sources of energy that are used to create hydrogen, rendering the clean end product far from environmentally benign.

Presently, the majority of hydrogen is produced by steam reforming natural gas. Though the resulting fuel is clean, the process of obtaining it is not without problems. Natural gas is already a usable fuel, one that is becoming scarcer. Additionally, the reformation process emits carbon dioxide, contributing to the greenhouse effect. Efforts to produce hydrogen from renewable energies (like solar and hydroelectric) are currently underway.

Hydrogen Fuel Cell Diagram
An array of different types of small portable batteries.

Hydrogen Fuel Cells

Fuel cells are what make hydrogen appealing as a fuel for transportation, as well as stored energy for homes and other applications. Fuel cells produce direct-current electricity (and the by-products of heat and water) by combining pure hydrogen with oxygen. Certain properties of fuel cells are similar to batteries, though the technologies are quite different. Fuel cells use external fuel while batteries are charged with already stored electricity. Both use a chemical reaction, rather than combustion, to create power. A key difference is that fuel cells will continue to produce electricity as long as hydrogen is supplied, never losing their charge. Batteries eventually "die" and need to be thrown out or recharged.

Fuel cells use various catalysts (chemicals that trigger chemical reactions without themselves being consumed in the reaction), like platinum, to convert the stored energy to electricity. Catalysts in fuel cells are, at the moment, predominantly expensive metals — a certain barrier to their expanded use. When the reaction is triggered in, for example a Polymer Electrolyte Membrane (PEM) fuel cell, the hydrogen molecules split into protons and electrons. Protons are filtered through a membrane, while the electrons flow through an electrical conductor, creating electricity. This process also generates heat, which can be of use in co-generation plants.

The term "fuel cell" may refer to a single unit, or a stack of cells. Depending on the application, fuel cells can be built of anywhere between one and dozens of individual cells, lending to their diverse uses. Fuel cells can thus be used in an array of applications, including: laptop computers, homes, vehicles, and central power generation systems.

Hydrogen Myths

Hydrogen is not a source of energy, rather it is an energy carrier. It cannot be mined or harvested as it rarely occurs naturally by itself. Other energy sources are used to make hydrogen, which can then be transported or stored for use when and where it is needed.

How Can We Use Hydrogen?

The dominant application for hydrogen, at present, is for industrial processes, such as refining, treating metals, and food processing. Hydrogen is either delivered to factories through pipelines in the form of compressed or liquid hydrogen, or is generated on-site by electrolysis or reforming.

As a transport fuel, hydrogen is most notably used in the sky, rather than on the ground. The National Aeronautics and Space Administration (NASA) has been using hydrogen in its space program since the 1970s due to hydrogen's high energy-to-weight ratio. Liquid hydrogen fuel is used to lift space shuttles into the air, while hydrogen fuel cells power the shuttle's electrical systems. The by-product, water, is used for drinking by the crew.

Hydrogen fuel cells create electricity, something humans use a lot of. In theory, anything that uses electricity — refrigerators, lights, heating systems — could be supported by a hydrogen fuel cell. Due to the high cost of manufacturing fuel cells, this wont be a reality for some time, if ever. The same goes for large hydrogen power plants which are possible, but out of the budget for now. In some niche cases, like emergency power systems in hospitals and wilderness locations, fuel cells are currently demonstrating their potential.

And of course, hydrogen fueled vehicles: cars, buses, motorcycles, airplanes — if you can drive it, fly it, ride it, you can probably fuel it with hydrogen.

Hydrogen powered light plane and scooter
On the left is Boeing's Fuel Cell Demonstrator, powered by a hydrogen fuel cell. On the right is a Yamaha scooter powered by a fuel cell.

Though hydrogen can be used in internal combustion engines, most applications use fuel cells to convert the energy into electricity to power electric motors. If hydrogen was to be used in an internal combustion engine , a massive fuel tank would need to be installed, because though hydrogen supplies more energy per pound than gasoline, it possesses a much lower density in both liquid and compressed gas form. The costs of opting for an electric, hydrogen powered vehicle remain much higher than for a conventional, fossil fueled vehicle. Additionally, what some call the "chicken and egg" dilemma of the hydrogen economy highlights the challenge in selling hydrogen cars before refueling stations become abundant, and the flip side, building refueling stations when there are no hydrogen cars or customers. Integrating the hydrogen fueled vehicle into our present system of energy sources, currencies and infrastructure will prove difficult without government support for the transition.

Why Use Hydrogen Fuel?

The two main barriers to the commercialization of hydrogen fuel cells are high production costs and poor durability.

The use of fossil fuels in vehicles produces carbon dioxide and water. Blending hydrogen into fossil fuels results in fewer CO2 emissions, and greater quantities of water. The higher the hydrogen content, the cleaner the fuel. Not only are hydrogen fuels cleaner than fossil fuels, they can also have double to triple the efficiency of traditional combustion technologies. The US Department of Energy notes the efficiency of a combustion-based power plant at 33-35%, compared to fuel cell systems that can generate electricity of 60% (more when the heat generated from the reaction is used in cogeneration). It was further noted that gasoline engines in conventional cars are less than 20% efficient at converting the energy in gasoline into power that propels the vehicle. Hydrogen fuel cell vehicles, which use electric motors, use 40-60% of the fuel's energy. Simple math shows that this corresponds to a reduction in fuel consumption of over 50%.

Challenges Ahead

The two main barriers to the commercialization of hydrogen fuel cells are high production costs and poor durability. Many of the component pieces of the fuel cell are expensive, and until alternative materials are discovered the monetary cost of the cells will bar expansion in the field.

The hydrogen powered Hindenburg
The disaster that befell the German airship Hindenburg in 1937 has helped shape public perceptions of hydrogen power.

The membrane component of the fuel cell, the part that protons filter through but electrons do not, remains problematic for its lack of durability. The challenges of developing a membrane that functions in both hot and cool temperatures, and can remain stable under cycling conditions are a main focus for researchers.

As well when talking about the use of hydrogen people often think back to the Hindenburg disaster where an airship went up in flames as the hydrogen gas inside it burned. While the technology exists to make the process safer there is still a social stigma which challenges the implementation of technologies with dangerous properties.


Batteries allow us to store energy in a portable format. Without them, everything that uses electricity would have to be plugged in at all times. No cell phones, no portable laptops, no flashlights, no car motors as we know them.

Batteries are comprised of three main parts: an anode (the negative end), a cathode (the positive end) and an electrolyte which facilitates the flow of energy. Batteries are either primary (non-rechargeable) or secondary (rechargeable).

An array of different types of small portable batteries.

Primary and Secondary Batteries

The electrochemical reaction that causes batteries to release energy can be reversed in rechargeable (secondary) batteries. Running current into the cell replenishes its stored energy by running the chemical reaction in reverse. This makes rechargeables suitable for use in automobile starters, portable electronics, electric cars — anything that would be costly to have to replace each time the battery died.

In primary batteries or "disposable batteries", the electrochemical reaction is not reversible, which prevents the cell from recharging. All batteries exhibit a phenomenon called "self-discharge" where internal chemical reactions inside the battery reduce the stored charge and shorten shelf-life. When you use a battery that has been stuck in a drawer for several months, it will likely have less charge than you expect. Primary batteries have significantly lower self-discharge rates, making them useful in applications that require long periods of storage. This good charge retention makes primary batteries appropriate for use in such items as flashlights, smoke detectors, and remote controls.

This is not an exhaustive list of primary battery types, rather a review of some of the most common ones.

Primary Batteries and their Uses

This is not an exhaustive list of secondary battery types, rather a review of some of the most common ones.

Secondary Battery Materials and their Uses

Chemical Fuel Cells

Fuel cells convert chemical energy into electric energy. Unlike batteries, fuel cells rely on the addition of an external fuel to function. A reaction between the fuel supply (typically hydrogen, but can be hydrocarbons and alcohols) and an oxidizing agent (usually oxygen, and sometimes chlorine and chlorine dioxide) triggers a reaction that ultimately creates electric current.

Three parts — the anode, the electrolyte and the cathode — are common to all types of fuel cells. The reaction begins at the anode where a catalyst oxidizes the fuel, splitting it into positively charged ions and negatively charged electrons. The electrolyte, also referred to as a membrane, draws the hydrogen ions through it, but not the electrons. The electrons are forced through an external circuit, giving way to electric current that can be used to power an array of applications requiring electricity. Fuel Cell Diagram


To ensure continuity of material, all of the external web pages linked and presented on our site were cached in May 2012. Readers are recommended to explore the current links for any changes.

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