3.3.2. Energy Analysis
Energy analysis of bio‐based systems refers to the quantification of the balance between energy supply and energy use in three phases of energy cycle, as described in section 3.3.1. Energy analysis in agricultural production has become important because of the increase in the amount of inputs. For example, an increase in nitrogen fertilizer used in corn production has driven an increase in corn yield (Kraatz et al., 2009), but it has given rise to other issues such as eutrophication in nearby water bodies, increasing dependency of soil fertility on fertilizers, and negative impacts on human health. Similarly, energy analysis in a bio‐based industry can help quantify energy use in each processing step, so that the processes can be optimized to improve the energy efficiency. In energy analysis of bio‐based systems, all materials involved in the processing path are back‐tracked to their initial fossil energy input.
Energy inputs and outputs in agricultural fields, fuel, equipment, and consumables are quantified based on a functional unit within the defined system boundary. The functional unit for energy analysis in bio‐based systems can be expressed in terms of mass (e.g. J/ton), area (e.g. J/hectare), or economic value of the products (e.g. J/$1000) (Mousavi‐avval et al., 2018). This allows quantification of the energy used for production, harvest and post‐harvest logistics.
Direct energy use during the agricultural crop production phase includes energy content of diesel fuel used in agricultural operations, from field preparation to harvest, as well as electrical energy used in irrigation systems. Energy used in background processes is accounted for as indirect energy. Indirect energy associated with physical inputs, e.g. fertilizers, pesticides, seeds, machineries, is defined as the sum of energy consumed during the production of the input and the energy used for transportation of the input from the plant to the end user or local market. For example, indirect energy associated with agricultural machineries is estimated based on energy used during the manufacture of machineries in the factory as well as energy use for transportation of agricultural machinery from the factory to the local market. To estimate indirect energy associated with the depreciation of an agricultural machinery during specific field operation, it is assumed that total energy consumption during the manufacturing and transportation of the machine is depreciated during its economic lifetime. Lack of data availability makes the energy use estimation in the background processes more complicated. However, there are databases, e.g. Greenhouse, Regulated Emissions, and Energy Use in Transportation (GREET) model and Ecoinvent database, that provide an estimation of energy use for these background processes.
In the industrial phase, liquid fuel (mainly diesel) is used for long‐distance transportation, heating, drying, and other purposes. Direct energy of fuels and electricity is quantified based on their energy content. In addition, embodied energy of the equipment and chemicals used for processing and conversion is quantified based on depreciation of energy use for the manufacture of equipment during the economic lifetime.
3.3.3. Example: Energy Analysis in Biodiesel Production from Oilseeds
Different oilseeds can be used for energy production in the form of biodiesel. Energy use efficiency in biobased systems is defined as the ratio of energy output to energy input. Energy use efficiency of oilseeds production varies based on the type of oilseed and location. Some oilseeds such as canola and carinata have relatively low energy use, while the production of sesame requires a higher energy use (Table 3.3). Energy use efficiency of oilseeds production ranges from ~1.5 for sesame to 4.28 for canola.
Experimental studies have been conducted to analyze energy use in biofuels from bio‐based systems. Energy inputs during crop production, transportation, and conversion processes for canola and carinata were estimated based on experimental studies in Spain (Cardone et al. 2003). It was found that energy was mainly used in the oilseed production and transportation steps (Figure 3.3). There are several transportation steps, including transportation of oilseeds from fields to the elevator (local storage), which is mainly done by trucks, transportation from storage facilities to the oil extraction facilities, and delivery of oil to the biorefineries using rail transportation facilities. Energy use for extraction of oil from oilseeds and conversion to biodiesel is low because of the high capacity of industrial facilities at the biorefineries.
3.3.4. Energy Supply from Bio‐Based Systems
Biomass has been identified as the most reliable potential source of energy and feedstock for the industrial sector until 2050 (United Nations Industrial Development Organization, 2019). Currently, biomass supplies 10% of the total energy demand, and 68% of this is in the form of fuelwood (World Energy Council, 2016). One third of energy use in pulp and paper industries is supplied by biomass and waste (United Nations Industrial Development Organization, 2019). Utilization of biomass as a feedstock is being expanded to the fuels and chemicals industries that used to be conventionally supplied by petroleum‐based sources. Based on the estimation by United Nations Industrial Development Organization (2019), by 2050, biomass can supply 37%, 25%, 18% and 10% of the total process heat in chemical and petrochemical, non‐metallic minerals, paper and pulp, and wood and woody products industries, respectively. In 2016, biomass was the only renewable source of liquid fuel in the transportation sector with 103 billion L of ethanol, 31 billion L of biodiesel and 5.9 billion L of hydrotreated vegetable oil produced globally, which contributed to only 0.3% of the total energy demand (REN21, 2018). However, an increase in bio‐based products from $203 billion worth in 2015 to $487 billion worth in 2024 was forecasted (Biotechnology Innovation Organization, 2017). Biofuels and biochemicals offer several advantages such as lower environmental impacts and product security when compared to depleting petroleum‐based fuels and chemicals, which drives the expansion of the bio‐based economy and incentivizes the development of bio‐based systems.
Table 3.3 Total energy use and energy use efficiency of oilseeds production.
Sources: Adapted from Ruiz‐Mercado, G. J., Smith, R. L., and Gonzalez, M. A. (2012). Khan, S., Khan, M. A., Hanjra, M. A., and Mu, J. (2009).
| Oilseed | Total energy use (MJ/t)* | Energy use efficiency (decimal)* | ||
|---|---|---|---|---|
| Average | SD** | Average | SD** | |
| Soybean | 9360 | 3248 | 2.43 | 0.79 |
| Canola | 5565 | 1124 | 4.24 | 1.40 |
| Carinata | 4340 | 1732 | 3.14 | 1.09 |
| Sunflower | 8532 | 2580 | 3.25 | 1.09 |
| Sesame | 1 5930 | 1793 | 1.57 | 0.19 |
* Data were collected from Canakci et al.,
