Heat

The U.S. consumes about 100 EJ = 100 Exajoules = 100 x 1018 Joules of energy, annually. Americans, being Americans don’t often express energy in Joules. Rather, they prefer to use British Thermal Units (BTUs), where 1 BTU = 1055 J. Another way of expressing this is to say that Americans use about 100 quads of energy, where 1 quad = 1015 BTUs. If one is willing to accept a 5.5% error, one can say that 1 EJ is about equal to 1 quad.

Only about one third of energy consumed is used for productive work. The above Sankey diagram shows energy inputs and outputs, productive work is clumped together as energy services, in a dark gray box. The other 2/3 is wasted as heat, which in the above diagram is referred to as rejected energy, which is clumped together in a light gray box.

Renewable energy comes from solar (1.04 quads), hydro (2.5 quads), winds (2.75 quads) and geothermal (0.21 quads) sources, for a total of 6.5 quads. Thermal energy systems burn fuel or split atoms, and accounted for about 93.5% of American energy inputs in 2019. Most of this fuel come from fossil sources, that is responsible for most of the carbon emissions associated with climate change. Wasted/ rejected energy is a proxy/ surrogate/ substitute for the damage being done to the planet. The exception is the energy provided by nuclear power, although it also has issues of its own. In contrast, renewable energy (wind, solar, hydro, geothermal) capture energy, without creating heat. While there are some transmission loses, most of that energy provides energy services.

A modern electric vehicle (EV) with regenerative braking is about 95% energy effective. Even the most efficient internal combustion engine (ICE) vehicles, can only achieve about 30% energy efficiency. This means that an EV only needs about 1/3 of the energy inputs that an ICE vehicle needs.

The United States transportation sector uses 28% of the total energy. Of this, cars, light trucks, and motorcycles use about 58%, while 23% is used in heavy duty trucks, 8% is for aircraft, 4% is for boats and ships, 3% is for trains and buses, while the last 4% is for pipelines (according to 2013 figures). This means that road transportation accounts for over 80% of the total. From the Sankey diagram, one can see that the transportation sector has 28.2 quads of input of (mostly) fossil-fuel energy, which means that 22.5 quads are road related. This results in 5.93 quads of transportation services, of which 4.75 quads are road related. These figures show about a 21% efficiency, because transportation related engines are considerably less efficient than other engines, including those used for electrical power generation.

If one uses renewable energy for road transportation, 4.75 quads of transportation services could be produced from about 5.0 quads of renewable (wind/ solar/ hydro/ geothermal) energy. At the same time, 22.5 quads of oil production would be eliminated, without any negative energy-related consequences. In fact, there would be benefits in terms of improved health, and less pressure on the environment.

A shift to renewable sources in other sectors would also have benefits. Natural gas and coal currently make a large contribution to inputs for electricity generation used elsewhere, 11.7 and 10.2 quads each, respectively, for a total of 21.9 quads. However, using the 1/3 service, 2/3 rejected formula, this means that these fossil-fuel inputs only produce 7.3 quads of electrical services. This contribution could be replaced by 7.5 quads of renewable energy.

Gasoline has an energy density of about 45 MJ/kg, which can provide about 15 MJ/kg of energy services, and 30 MJ/kg of rejected energy, as discussed above. A litre of gasoline has a mass of 0.76 kg and produces 2.356 kg of CO2 and 11.4 MJ of energy.

For American readers: The United States Energy Information Administration (EIA) estimates that “About 19.64 pounds of carbon dioxide (CO2) are produced from burning a gallon of gasoline that does not contain ethanol. About 22.38 pounds of CO2 are produced by burning a gallon of diesel fuel. U.S. gasoline and diesel fuel consumption for transportation in 2013 resulted in the emission of about 1 095 and 427 million metric tons of CO2 respectively, for a total of 1 522 million metric tons of CO2. This total was equivalent to 83% of total CO2 emissions by the U.S. transportation sector and 28% of total U.S. energy-related CO2 emissions.Under international agreement, CO2 from the combustion of biomass or biofuels are not included in national greenhouse gas emissions inventories.”

Since 1 MJ = 0.2778 Kilowatt hours (kWh), 11.4 MJ is the equivalent of 3.17 kWh. According to Electric Choice, the average price a residential customer in the United States pays for electricity is 13.31 cents per kWh in December 2020. This means that gasoline would have to sell for 42.19 cents per litre to be cost effective. Since there are 3.785 litres per American gallon, a gallon would have to sell for about $1.60 to provide an equivalent price. According to Global Petrol Prices, the average price of mid-grade/ 95-octane gasoline was $2.752 per gallon, the equivalent of $0.727 per litre, as of 2021-02-01.

In Norway, the price is about NOK 1 per kWh for electricity, but with wide variations. The price of 95-octane gasoline is about NOK 16.33 per litre, once again according to Global Petrol Prices. This helps explain why EVs are so popular. To be price equivalent, gasoline would have to sell for about NOK 3.17 per litre. Currently, Stortinget, the Norwegian parliament, is debating increasing the CO2 tax by NOK 5 per litre, which would bring the price to over NOK 21 per litre. Not all political parties are in agreement, with this proposal.

There is a great deal of discussion about consumption figures for electric vehicles in Norway. In part, this is because the terrain varies greatly. Some people drive in urban landscapes, others out in the country. Some people are flatlanders, while others have more mountainous environments. However many consumers have experienced real-world energy consumption levels of about 15 kWh/100 km for vehicles such as a Hyundai Kona, Kia Soul and Tesla Model 3. This gives a fuel cost of about NOK 15/ 100 km. In American terms, this would be about 24 kWh/ 100 miles, or $3.20/ 100 miles, with the electrical costs noted above.

3 Replies to “Heat”

  1. Hi Brock, thanks for yet another thought provoking blog, this one with very convincing statistics regarding huge amounts of energy waste that result from converting fossil fuels to useful energy (work). Your account also peaked my curiosity into why burning a litre of gasoline, with a mass of 0.76 kg, produces a much greater 2.356 kg mass of CO2. For a simple layman’s explanation I did find a fact sheet from Natural Resources Canada but as my attempt to hyperlink it was unsuccessful, here is the gist of it:
    Burning any hydrocarbon (CxHx) requires oxygen for combustion. This reaction produces useful heat energy but also two by products; molecules of water (H2O) and carbon dioxide (CO2). On the face of it, we may not be bothered by water being a product of fossil fuel combustion but each carbon atom, atomic weight 12, obtained from a non-renewable resource, combines with 2 oxygen atoms (each of atomic weight 16) to produce a CO2 molecule with an atomic weight of 44 (3.67 times heavier than Carbon). So, what may appear to be an increase in mass is actually not, its just that burning gasoline takes a lot of oxygen from the atmosphere, some of which bonds with hydrogen to form water while a larger proportion bonds with carbon to form CO2, a greenhouse gas.
    I didn’t intend this explanation to lead into an alarmist warning but credible scientific consensus does make it clear that burning ancient fossil fuels, created over hundreds of thousands to millions of years, to support our ever increasing energy demands, has resulted in global warming within relatively few generations of human life.
    Thanks again Brock. For all of our growing energy needs, I look forward to a rapid transition in my remaining lifetime, from fossil fuels to renewable energy sources. Thankfully Scandinavian countries are certainly moving quickly to do so and now at last, there is renewed promise for us in North America to do likewise.

  2. Dear John,
    Thanks for a most interesting comment. I am just going to repeat what you said, in slightly different terms.

    Gasoline is a mixture of many different types of hydrocarbons, typically with between 4 and 12 carbon atoms per molecule (commonly referred to as C4–C12). Here, I am going to pretend that it all consists of octane, C8H18 or CH3 (CH2)6 CH3, structurally. 1 mole of this has a mass of 8 x 12 = 96 g (for the carbon atoms) + 18 x 1 = 18 g (for the hydrogen atoms) which gives a total of 114 grams.

    When this Octane is burned it result is carbon dioxide and water: 8 x CO2 = 8 x (12 + 16 + 16) = 8 x 44 = 352 g and 9 x H2O = 9 x (1 + 1+ 16) = 9 x 18 = 162 g. Altogether, 352 g + 162 g = 514 grams. 514/114 = ca. 4.51 which means that the water and carbon dioxide produced through combustion has a mass that is 4.51 times more than the octane one started out with. The carbon dioxide alone has 352/114 = ca. 3.09 times greater mass.

    If one starts out with 1 litre of Octane = 0.76 kg x 3.09 (the increased mass after combustion) = ca. 2.347 kg, which is close to the starting value of 2.356 kg, originally stated that relied on a real-world mixture of hydrocarbons.

  3. While geothermal energy is regarded as a renewable/ non-depletable resource, there are issues with it:
    1. There is a release of over 120kg CO2/MWh of electricity produced. This contrasts with about 1 000 kg CO2/MWh for coal.
    2. Greenhouse gas emissions increase close to geothermal power plants. They are also associated with silica emissions and sulphur dioxide, and contain heavy metals such as mercury, boron and arsenic. However, it is claimed that the pollution caused by these is minimal and much below that produced by coal and other fossil fuels.
    3. Building geothermal plants often involves hydraulic fracturing. This can trigger earthquakes.
    4. Fluid has to be re-injected into geothermal reservoirs to prevent them from becoming unsustainable.
    See: https://greencoast.org/pros-and-cons-of-geothermal-energy/

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