Second-level power generation comes from the combustion of ancient or modern biomass. It is clear that fossil fuels are a dirty business from start to finish. On the surface and from an engineering point of view, fossil fuels are extremely efficient because they hold a great amount of energy in a concentrated substance, but let’s start at the beginning. Whether it is an off-shore oil platform, a coal strip mine, or fracking in Oklahoma, obtaining fossil fuels either destroys the local environment by design (perform a Google image-search for “mountain top removal” or “tar sands extraction site”) or by accident (see also “Deepwater Horizon,” “Oklahoma Fracking Earthquakes,” and “Fracking Methane Leaks”). In addition, we have to consider the waste products of extraction, be they the proprietary (read “toxic”) compounds used in fracking to the leachate from coal-mining backfill. Fossil fuels must be refined, which requires complicated chemical reactions to be contained in huge facilities, as anyone who has driven into or around Houston will know. To release the energy stored in fossil fuels, we must burn them, putting tons of greenhouse gasses into the atmosphere. According to the US Environmental Protection Agency (US EPA), coal puts out about 2.10 lbs of CO2 per kWh, natural gas comes in at 1.22 lbs, and oil somewhere around 1.70 lbs.i If we take an average of 1.80 lbs per kWhii for fossil fuels (which generate about 65 percent of the 3.8 trillion kWh used by the US each year), we get 4.4 trillion lbs of CO2 emissions, or about 2 billion metric tons (about a quarter of total greenhouse gas emissions globally). Each of us is responsible for about 38 lbs per day. Between each one of these steps, fossil fuels must be transported by pipelines, rail, truck, or ocean-going tanker. Each field has had its own share of accidents (see also “Kalamazoo River,” “Casselton, North Dakota,” and “Exxon Valdez,” as well as the comprehensive list compiled by Riverkeeperiii). We have repeatedly patched problems in the fossil-fuel system instead of accepting the fact that it is fundamentally broken. We can draw an analogy to an old car: at what point are the repairs costing more than the vehicle is worth? The time has come to stop repairing the fossil-fuel system and get a better model.
Modern biomass is a more likely candidate for careful use in the future. Unlike fossil fuels, which are nonrenewable, biomass is a constantly growing resource. This means it must be carefully managed, as we have seen what happens when societies overharvest forests for fuel (see also the ancient Maya and Romans). In most cases, biomass will decompose and release its stored carbon into the atmosphere when it dies, and therefore burning it does not really contribute much more. This does not mean, however, that everybody can simply use woodstoves and virgin timber to heat their houses in the winter. Burning does contribute particulate matter to the local atmosphere, so high-efficiency stoves are needed and a careful source of fuel must be chosen and managed. With careful building design, a minimal amount of heating would be necessary anyway. A superior alternative to biomass, though, is biogas, which will be discussed below.
The third level of energy generation uses the consumption of biomass to create energy. Before the industrial revolution, animals were used to pull plows and carts as well as turn treadwheels. These animals converted their biomass feed into kinetic energy. Indeed, animals combined with ingenious engineering can achieve a high output of energy per calorie: a bicyclist burns about 50 (kilo)calories per mile (ca. 3 kcal/lb/mi); comparable to a 35-mpg car, which requires 900 kilocalories (ca. 2.89 kcal/lb/mi) to do the same work.iv In addition to fueling muscle power, biomass consumption also sustains life and is later converted into nutrient-rich compost. This type of energy generation is almost certainly sustainable in the long term, as it is impractical to create an engine that runs on too many horse treadmills, for example. Furthermore, traction animals can often eat fodder not suitable for humans, which helps dissipate our ecological footprint.
The industrial world has harnessed biomass to create fossil-fuel replacements. Unfortunately, turning corn, sugarcane, or switchgrass into ethanol to dilute gasoline is not sustainable. On the surface, we can look at how many units of energy are needed to produce another unit of energy (or energy return on investment [EROI]).v Coal, for example, is a concentrated and fairly easily obtained fuel, which returns up to 80 units of energy for each unit expended in its extraction. Ethanol from sugarcane might only return 10 units of energy for the same energy expenditure. Corn is much worse, returning only 1.6 units. Raw EROI is a useful tool for analysis, but it only shows the comparison of energy. To get a more complete picture, we must strive for EROISOC, that is, Societal EROI. EROISOC is nearly impossible to measure because of the complex and myriad variables that go into it; it is found by “summing all gains from fuels and all costs of obtaining them.”vi For example, along with terrible raw EROI, biofuels might be made of food crops, which raises the price of food. Biofuel crops are often overfertilized and grown on marginal lands, which leads to nutrient-rich runoff and massive surface erosion. These indirect costs must be weighed against the minimal gains.
One sustainable way that biomass can be converted into fuel is through the capture of otherwise wasted biomass. Although switchgrass and sugarcane have higher EROI values than other vegetation, they have to be purposefully grown and harvested, meanwhile millions of tons of vegetation is dumped into the waste stream; the energy lost in decomposition might be better used by being converted into a flammable gas. Indeed, animal waste, green waste, and food waste can all be turned into a fuel equivalent to natural gas. Even though the basic EROI of biogas is modest (ca. 5–10), the EROISOC of this fuel must be judged highly, especially since it sequesters methane from manure, which has less of an impact when combusted as biogas than when it is simply released into the atmosphere. Furthermore, the use of “waste” products reduces the cost of input materials. A modest use of biogas for heating on an individual or community level might well be a viable strategy for our future.
i United States Environmental Protection Agency. 2016. How much carbon dioxide is produced per kilowatthour when generating electricity with fossil fuels?” Accessed June 1. https://www.eia.gov/tools/faqs/faq.cfm?id=74&t=11.
ii Fossil fuels account for about 65 percent of US electrical generation. This percentage is broken up at 65 percent coal, 34 percent natural gas, and 1 percent petroleum. Therefore fossil fuels average: (2.10 lbs/kWh × 0.65) + (1.22 lbs/kWh × 0.34) + (1.70 lbs/kWh × 0.01) = 1.80 lbs/kWh.
iii Riverkeeper. n.d. “Crude Oil Transportation: A Timeline of Failure.” Accessed June 1. http://www.riverkeeper.org/campaigns/river-ecology/crude-oil-transport/crude-oil-transportation-a-timeline-of-failure/.
iv That is, a 155-lb bicyclist, going 1 mile burns about 50 kcal, whereas a 2,600-lb Honda Fit burns about 900 kcal in that same mile; obviously 900 kcal of gasoline (0.0286 gal) is cheaper than 50 kcal of food.
v All data here from summary article: Hall, Charles A. S., Jessica G. Lambert, and Stephen B. Balogh. 2014. “EROI of Different Fuels and the Implications for Society.” Energy Policy 64:141–52.
vi Hall et al. 2014:142–143.