Categorysort descending Sources Indicator Units Type
Energy security Dale et al., 2013 Energy security premium Dollars per liter of biofuel Quantitative
Energy security Dale et al., 2013 Fuel price volatility Standard deviation of monthly percent price changes over one year Quantitative
External trade Dale et al., 2013 Terms of trade Ratio (price of exports per price of imports) Quantitative
External trade Dale et al., 2013 Trade volume Trade volume Quantitative
Profitability Dale et al., 2013 Return on investment (ROI) Percent (net investment per initial investment) Quantitative
Profitability Dale et al., 2013 Net present value (NPV) Dollars (present value of benefits minus present value of costs) Quantitative
Physical capacity of an Industry Golden et al., 2018 Total ethanol production Billion gallons Quantitative
Physical capacity of an Industry Golden et al., 2018 Number of States that have an ethanol production facility Number Quantitative
Physical capacity of an Industry Golden et al., 2018 Number of new ethanol plants that went on line Number Quantitative
Physical capacity of an Industry Golden et al., 2018 Number of ethanol plants in the United States number Quantitative
Physical capacity of an Industry Golden et al., 2018 Number of existing plants that were put on standby Number Quantitative
Physical capacity of an Industry Golden et al., 2018 Number of existing plants that were closed-shut down Number Quantitative
Physical capacity of an Industry Golden et al., 2018 Number of existing plants under construction Number Quantitative
Physical capacity of an Industry Golden et al., 2018 Total ethanol volume from corn stover plants Million metric tons Quantitative
Physical capacity to meet demand Golden et al., 2018 Total volume of ethanol imported Billion gallons Quantitative
Physical capacity to meet demand Golden et al., 2018 Total volume of ethanol exported Billion gallons Quantitative
Physical capacity to meet demand Golden et al., 2018 Total ethanol production versus total ethanol consumption Billion gallons Quantitative
Resource Demand Golden et al., 2018 Total bushels of corn used for fuel ethanol Billion bushels Quantitative
Viability GBEP: © Natural Resources Defense Council 2014 Compliance with Financial Laws and Regulations Legal and regulatory compliance review process, annual corporate compliance statement, or equivalent alternative is required. Quantitative
Viability GBEP: © Natural Resources Defense Council 2014 Financial Viability Business plan is required and available for review with confidential business information (CBI) provisions. Quantitative

Categorysort descending Sources Indicator Units Type
Soil Quality McBride et al. 2011 Extractable phosphorus (P) Mg/km² Quantitative
Soil Quality McBride et al. 2011 Bulk density g/cm² Quantitative
Soil Quality McBride et al. 2011 Total nitrogen (N) Mg/km² Quantitative
Soil Quality McBride et al. 2011 Total organic carbon (TOC) Mg/km² Quantitative
Water quality and quantity McBride et al. 2011 Herbicide concentration in streams (and export) concentration: mg/L, export: kg/km²/yr Quantitative
Water quality and quantity McBride et al. 2011 Peak storm flow L/s Quantitative
Water quality and quantity McBride et al. 2011 Minimum base flow L/s Quantitative
Water quality and quantity McBride et al. 2011 Consumptive water use (incorporates base flow) feedstock production: m³/km²/day, biorefinery: m³/day Quantitative
Water quality and quantity GBEP: © Natural Resources Defense Council 2014 Water Quality Compliance with CWA and permitted discharges (TOC= Total Organic Carbon; P= Phosphorous; N= Nitrate), if applicable, is demonstrated. Water management plan is available.16 Present evidence of BMP use. Evidence of origin nation water program compliance and Quantitative
Water quality and quantity McBride et al. 2011 Nitrate concentration in streams (and export) concentration: mg/L, export: kg/km²/yr Quantitative
Water quality and quantity McBride et al. 2011 Total phosphorus (P) concentration in streams (and export) concentration: mg/L, export: kg/km²/yr Quantitative
Water quality and quantity McBride et al. 2011 Suspended sediment concentration in streams (and export) concentration: mg/L export: kg/km/yr Quantitative
GHG emissions McBride et al. 2011 CO2 equivalent emissions (CO2 and N2O) kg/GJ Quantitative
Air quality McBride et al. 2011 Carbon monoxide ppm Quantitative
Air quality McBride et al. 2011 Total particulate matter less than 10 µm diameter (PM10) µg/m³ Quantitative
Air quality McBride et al. 2011 Total particulate matter less than 2.5 µm diameter (PM2.5) µg/m³ Quantitative
Air quality McBride et al. 2011 Tropospheric ozone ppb Quantitative
Air quality GBEP: © Natural Resources Defense Council 2014 Air quality Compliance with air permitting and reporting requirements, if applicable, is demonstrated. Air emissions management plan is available. Evidence of origin nation compliance or air management plan, as applicable. Quantitative
Air quality GBEP: © Natural Resources Defense Council 2014 GHG Emissions EPA RFS2 program life cycle GHG emissions are > 50% better than 2005 petroleum baseline (g CO2-e/MJ). Producer/blender life cycle GHG emissions are > 50% better than 2005 petroleum baseline (g CO2-e/MJ). Quantitative
Biodiversity McBride et al. 2011 Presence of taxa of special concern Presence Quantitative
Biodiversity McBride et al. 2011 Habitat area of taxa of special concern km Quantitative
Productivity McBride et al. 2011 Aboveground net primary productivity (ANPP), Yield g/m²/yr Quantitative

Environmental Indicators

Source: McBride, A, VH Dale, L Baskaran, M Downing, L Eaton, RA Efroymson, C Garten, KL Kline, H Jager, P Mulholland, E Parish, P Schweizer, and J Storey. 2011. Indicators to support environmental sustainability of bioenergy systems. Ecological Indicators 11(5) 1277-1289.

Soil Quality Category

Soil quality is important because it affects the broader ecosystem, the immediate productivity of bioenergy crops, and the maintenance of productive capacity for future generations. Soil quality indicators reveal changes in soil properties as a function of bioenergy crop management, including carbon balance, nutrient availability and mineralization, cation exchange capacity (CEC), humification, microbial community dynamics, erosion, leaching potential, soil porosity, and soil water holding capacity.

1. Total organic carbon

Total organic carbon (TOC) is a measure of the total amount of carbon in organic compounds in an aqueous system. Often seen as the most important indicator of soil quality, it integrates a wide range of important soil properties and functions and is a direct cause of several positive soil responses. TOC is typically measured in Mg/ha.

2. Total nitrogen

Total nitrogen (N) and extractable phosphorus (P) measure the two most important soil nutrients in typical productive land management systems. Most nitrogen in soil is bound in organic compounds and is not available to plants. However, total nitrogen is considered a valid indicator because nitrogen mineralization is driven by the availability of organic nitrogen in the soil, so that plant-available nitrogen (ammonium and nitrate) is closely related to total nitrogen. Excessive soil nitrogen and phosphorus can result in nutrient runoff and leaching, leading to downstream eutrophication. In addition, excess soil nitrate may increase nitrogen volatilization as the potent greenhouse gas nitrous oxide. Conversely, depletion of soil nitrogen and phosphorus threatens the future productivity of soil. Total nitrogen is typically measured in Mg/ha.

3. Extractable phosphorus

Extractable phosphorus (P) and total nitrogen (N) measure the two most important soil nutrients in typical productive land management systems. Excessive soil phosphorus and nitrogen can result in nutrient runoff and leaching, leading to downstream eutrophication. Conversely, depletion of soil nitrogen and phosphorus threatens the future productivity of soil. Extractable phosphorus is typically measured in Mg/ha.

4. Bulk density

in grams per cubic centimeter (g/cm3). Soils with a bulk density higher than 1.6 g/cm3 tend to restrict root growth.

Bulk density, a physical indicator of soil quality, is defined as the weight of a given volume of soil, often measured Bulk density can be rapidly affected by human agronomic practices. Bulk density is a concern whenever machinery use or other management activities can cause soil compaction. Increases in bulk density are the most common concern, but insufficient soil bulk density exposes soils to erosion and sometimes leads to inadequate seed germination.

Water Quality and Quantity Category

The properties of water in streams draining bioenergy croplands or forest stands influence the ecosystems within and downstream from those streams. Indicators based on water properties can be used to assess whether the agricultural aspects of bioenergy production allow for the maintenance of soil quality, aquatic ecosystems, and clean and plentiful water for human use. Water indicators are affected by some of the same pressures that influence soil indicators, but they can change more rapidly and integrate changes over an entire watershed, allowing for finer temporal resolution and broader spatial integration of relevant effects. In this sense, water quality and quantity reflect the diversity of environmental conditions and land practices that occur upstream and upslope as well as in the past.

In addition to concentrations of nitrate, total phosphorus, herbicides, and sediments, export (run-off) levels per unit watershed area of these substances are also important. Whereas concentrations are indicators of the effects these substances may have on the streams in which they are measured, export levels are related to the effects of these substances on downstream bodies of water. Area-specific export levels can be calculated by multiplying stream concentrations of each substance by flow measurements and dividing by total watershed area.

5. Nitrate and total phosphorus

Concentrations of nitrate and total phosphorus (P) in streams are indicators of potential eutrophication. Whereas aquatic systems respond to nitrogen (N) in other forms, nitrate is usually the most abundant form, relatively inexpensive to measure, highly mobile, and expected to be sensitive to the management of bioenergy feedstock systems. Furthermore, nitrate in drinking water is also associated with health risks such as methemoglobinemia. In-stream concentrations of nitrogen are typically measured in mg/L, while run-off levels are measured in kg/ha/yr.

6. Total phosphorus

Concentrations of nitrate and total phosphorus (P) in streams are indicators of potential eutrophication. In streams, total phosphorus includes dissolved phosphate, organic phosphorus, and phosphate sorbed to suspended sediment. Measurement of total phosphorus instreams is especially important during storm events because phosphorus export during storm events tends to dominate watershed phosphorus export and is sensitive to crop management practices. In-stream concentrations of phosphorus are typically measured in mg/L, while run-off levels are measured in kg/ha/yr.

7. Suspended sediments

Suspended sediments are fine soil particles that remain in suspension in water for a considerable time without contact with the bottom. Suspended sediment concentration is an indicator of stream habitat quality. Siltation diminishes interstitial space in stream substrata, impairs fish spawning grounds, and reduces the ability of sessile benthic organisms to attach to streambeds. Increased turbidity reduces the ability of benthic plants and attached algae to photosynthesize. Reduced benthic productivity and biodiversity can reduce available food for grazing organisms. Suspended sediment also clogs the gills of fish and hinders nutrient uptake by filter feeders. In addition to its adverse effects on aquatic habitat, suspended sediment also serves as an indicator of soil erosion, which can be used to assess the sustainability of bioenergy systems. In-stream concentrations of suspended sediments are typically measured in mg/L, while run-off levels are measured in kg/ha/yr.

8. Herbicides

Concentration of herbicides in streams measures exposure of aquatic life to these chemicals and their potentially toxic effects. Most pesticide use in the U.S. consists of herbicides. Schäfer et al. (2007) found that various pesticides, including herbicides, were detrimental to stream macroinvertebrate community structure and ecosystem function when they occur at concentrations lower than those previously known to have such effects. Since measuring herbicide concentrations is expensive, we recommend that only herbicides known to be used or of concern in an area should be measured. In-stream concentrations of herbicides are typically measured in mg/L, while run-off levels are measured in kg/ha/yr.

9. Peak flow

Peak flow is the maximum instantaneous discharge of a stream or river at a given location, represented as volume over a given time (e.g., liters/second). It usually occurs at or near the time of maximum stage. Increased peak flow during storm events can be caused by decreased infiltration and water holding capacity in soil. High peak flows during storms can increase erosion and sediment loading. In addition, high peak flows can reduce benthic organism biomass and habitat and can contribute to potential flood damage downstream.

10. Minimum base flow

Base flow typically is defined as the groundwater contribution to streamflow and is measured as volume over a given time (e.g., liters/second). As an indicator of water quality, base flow should be considered at its minimum, often occurring in summer or early fall, because lotic habitat quality can be limited by minimum base flow (Bunn and Arthington, 2002). During periods of low base flow, dissolved oxygen levels in streams are usually at their lowest due to lower rates of oxygen diffusion into water from the atmosphere and greater depletion of available oxygen supplies in water from respiration by aquatic organisms. Very low dissolved oxygen levels can lead to stress or death of some aquatic organisms, particularly fish.

In addition to its utility as an indicator of lotic habitat quality, base flow also serves as one of two measures of consumptive water use. Consumptive water use in bioenergy systems, mostly during feedstock production and in biorefineries, may affect the amount of water available for other human uses (Berndes, 2002; de Fraiture et al., 2008; Stone et al., 2010). Changes in base flow can reflect consumptive water use in feedstock production. For this purpose, base flow should be considered throughout the growing season. It should also be measured sufficiently downstream to capture both irrigation return flow (Huffaker, 2010) and the surface discharge of groundwater sources drawn upon by deep-rooted crops.

11. Consumptive water use

Water withdrawn from public sources is recommended as an indicator reflecting consumptive water use in biorefineries (NRC, 2008). Most consumptive water use in biorefineries consists of evaporation from cooling towers and dryers/evaporators during distillation (NRC, 2008; Wu et al., 2009). Total water withdrawal is typically metered and easily reported by biorefinery managers. Not all water withdrawn represents consumptive use, but the extent to which water withdrawal overestimates consumptive use is decreasing as water recycling in biorefineries increases (NRC, 2008).

Greenhouse Gases Category

Estimated net carbon equivalent (Ceq) flux to the atmosphere is recommended to measure the effect of bioenergy systems on atmospheric concentration of greenhouse gases that contribute to climate change (IPCC, 2007). The direct and indirect environmental effects of elevated atmospheric Ceq concentrations do not depend on the locations of Ceq release or sequestration. Therefore, Ceq release and sequestration throughout the bioenergy supply chain can be summed, and the marginal environmental effects of those fluxes can be estimated using standard global climate models.

12. CO2 equivalent emissions (CO2 and N2O)

To estimate net Ceq flux associated with bioenergy, nitrous oxide (N2O) flux and carbon dioxide (CO2) flux should be considered—measured in CO2equivalent emissions. Estimated values for these various sources and sinks of N2O and CO2 can be collected and summed using the life cycle assessment (LCA) approach. Standard and useful tools for LCA are multidimensional spreadsheet models such as the GREET (Greenhouse gases, Regulated Emissions, and Energy use in Transportation) and GHGenius software models, which are designed to address full fuel cycle (or well-to-wheels) effects (Wang, 2002; Stanciulescu and Fleming, 2006). Some default values in spreadsheet models are best replaced with empirical measurements where available. Assuming soil carbon measurements are made, the accuracy of site-specific LCAs can be improved by substituting those measurements for statistically modeled estimates in spreadsheet models.

Air Quality Category

Most air pollutants resulting from bioenergy use derive directly or indirectly from combustion in feedstock production and processing as well as in final use (e.g., powering vehicles by burning liquid biofuels). Carbon monoxide, tropospheric ozone, and two fractions of suspended particulate matter (PM10 and PM2.5) are recommended as indicators to measure the effects of bioenergy on air quality.

Methods for measuring these indicators vary by location. Extensive ambient air monitoring networks have been installed in many regions of the U.S. (AIRNow, 2010) as well as in Europe. The U.S. EPA requires large emitters such as biorefineries to report emissions of some pollutants. Feedstock producers can report equipment usage, which can be combined with data sources such as the EPA’s Mobile Source Observation Database (MSOD) to calculate emissions of CO and primary PM2.5. Because tropospheric ozone and much PM2.5 are created at a regional scale from locally emitted precursor pollutants, models such as Community Multiscale Air Quality (CMAQ) (Appel et al., 2007, 2008) must be employed to connect regional PM2.5 and tropospheric ozone measurements to bioenergy-related precursor emissions.

Emissions from liquid biofuel combustion in mobile sources can be estimated from country-scale estimates of consumption by fuel type combined with estimates of emissions from those fuels (Niven, 2005; Anderson, 2009; Gaffney and Marley, 2009). Emission estimates by fuel type should also be country-specific, as emissions vary with atmospheric conditions and policy-influenced design factors.

13. Tropospheric ozone

Tropospheric, or ground-level, ozone is an important pollutant and is also associated with smog and haze. Ozone can aggravate or damage the respiratory system and can also damage vegetation, potentially reducing crop yields and biodiversity. Tropospheric ozone is formed by the reaction of nitric oxide and nitrogen dioxide (NOx) with non-methane organic gases (NMOGs) or with CO. These compounds are emitted in varying amounts from all combustion processes involved in the production and use of bioenergy. NOx is particularly associated with distillation processes for ethanol production. The reaction of these ozone precursors may occur far from emission sources. Therefore, NOx associated with bioenergy may react with NMOGs or CO from unrelated sources or vice versa. Tropospheric ozone is typically measured in parts per billion.

14. Carbon monoxide

CO is a minor contributor to climate change, but it is of environmental concern primarily for two reasons:

  1. It has severe effects on human health in high concentrations and may also be harmful at low, chronic concentrations (Townsend and Maynard, 2002; Chen et al., 2007).
  2. It is a precursor to ozone production. The emission of CO in biofuel combustion varies widely based on fuel type and combustion method.

Because present-day liquid biofuels are oxygen-containing compounds, burning biofuel either as an additive to petroleum products or as a primary fuel can result in lower CO emissions than burning pure gasoline or petroleum diesel fuel. Carbon monoxide is typically measured in parts per million.

15. Total particulate matter < 2.5 µm diameter (PM2.5)

Particulate matter is the term for a mixture of solid particles and liquid droplets found in the air. Two classes of particulate matter are typically monitored. PM2.5 measures mass per unit volume of all airborne particles less than 2.5µm in diameter, also known as the fine particle fraction. Fine particles can be emitted directly from point sources (primary sources) or formed in the atmosphere from gaseous emissions (secondary sources). Fine particles are associated with increased mortality due to lung cancer, cardiopulmonary disease, and other factors (Pope et al., 2002). Bioenergy systems can contribute to fine particulate pollution through solid biomass combustion or through the emission of various secondary particulate precursors through biofuel combustion (i.e., NMOGs leading to SOA), through burning of fossil fuels during feedstock production or processing [i.e., oxides of sulfur (SOx), NOx], or from soil biochemical processes during feedstock production (i.e., ammonia).

16. Total particulate matter < 10 µm diameter (PM10)

Particulate matter is the term for a mixture of solid particles and liquid droplets found in the air. Two classes of particulate matter are typically monitored. PM10 measures mass per unit volume of all airborne particles less than 10µ minimum diameter and thus includes those particles measured by PM2.5. In addition to fine particles, PM10 includes coarse particles, those between 2.5µm and 10µm in diameter. Agricultural systems can affect this coarse fraction through tilling and solid biomass combustion (Aneja et al., 2009). As with the fine fraction, the coarse fraction can affect human respiratory health, though health effects may be restricted to the short term (Brunekreef and Forsberg, 2005). Coarse particles also impair visibility, though also to a lesser extent than fine particles (Malm, 1999).

Biodiversity Category

Biodiversity can relate to any type of organism, including plants, animals, fungi, and microbes. Biodiversity indicators are useful in comparing different agricultural systems because, in addition to being valued for its own sake, biodiversity is affected by other environmental changes such as erosion, nutrient loss, and land-use change.

17. Presence of taxa of special concern

Here species of concern means species of importance to local stakeholders, either because of their desired presence (e.g., game birds) or because of their desired absence (e.g., noxious weeds). Actual taxa that are of special concern vary in identity and number by site and region. Examples include rare native species, biodiversity-related keystone species, and taxa that are part of bioindicators.

18. Habitat area of taxa of special concern

Various methods exist for measuring the habitat area (Turlure et al. 2010) for those species identified as being of concern to local stakeholders. Ideally, habitat area will increase for desired species and decrease for undesired species. The recommended measurement unit is hectares.

Productivity Category

The amount of biomass that can be produced and sustainably removed from an agricultural system is affected by soil, water, climate and other environmental conditions. Aboveground net primary productivity (ANPP) is the indicator recommended assess the ecosystem productivity of bioenergy associated land use. However, crop yield is more commonly measured in agricultural systems and can serve as a proxy for ANPP.

19. Aboveground net primary productivity (ANPP)

The selection of this indicator is motivated by the importance of net primary productivity (NPP), which is defined as the net flux of carbon from the atmosphere into green plants per unit time and measures the rate of production of useful net energy by all plants in an ecosystem. NPP is a measure of the condition of both the land (e.g., soil fertility, topography, vegetation type, and prevailing weather conditions) and several ecological processes (including photosynthesis and autotrophic respiration as affected by local hydrology and temperature). NPP manifests physically as total new plant biomass generated by photosynthesis per unit time (typically measured per year).

Because of the challenges involved in directly measuring NPP, ANPP is often used as a substitute for NPP. Measuring ANPP accurately is not trivial, but certain difficult-to-measure components of ANPP (e.g., biomass consumed by herbivores or that dies and decomposes during the growing season) are often assumed to be small enough to ignore.

Social and Economic Indicators

Source: Dale, V. H., R. A. Efroymson, K. L. Kline, M. H. Langholtz, P. N. Leiby, G. A. Oladosu, M. R. Davis, M.E. Downing, and M. R. Hilliard. 2013. Indicators for assessing socioeconomic sustainability of bioenergy systems: a short list of practical measures. Ecological Indicators 26:87–102.

Social Well-being Category

Well-being refers to the condition of the people and social systems with regard to prosperity, safety, and health. Other services and health issues that affect social well-being are covered by environmental indicators (e.g., potential for disease can be related to measures of air quality while the provision of food and other services is related to indicators of productivity, soil quality, and water).

1. Employment

Employment is measured as the number of full-time equivalent jobs. This includes net new jobs created, plus jobs maintained that otherwise would have been lost, as a result of the system being assessed. Employment impact analysis typically considers direct, indirect, and induced employment.

2. Household income

This indicator refers to the household income of those employed in the bioenergy industry, measured as dollars per day of household income. Methods consistent with those applied to the employment indicator should be used to identify activities that are clearly linked via the supply chain, such as biomass storage and management, trucking and transportation, and other agricultural or forestry-based employment associated with biomass production, harvesting and logistics. At a minimum, data should be collected to estimate the average income of employees in the industry.

3. Work days lost due to injury

Work days lost to injury associated with the bioenergy industry can be measured as average days lost per worker per year in a defined sector or industry. In a calculation of average days lost per worker per year, consider the employment directly and indirectly generated by bioenergy industries.

4. Food security

Food security can be measured as the percent change in price volatility of food crops attributable to biofuels. The inherent complexity of establishing and measuring an indicator of food security implies that significant time, cost, and analytical effort will be needed to reach agreement on its definition, methodology, and application. In the meantime, we propose that the previous indicators for employment and household income serve as practical proxy measures for food security.

Energy Security Category

Energy security is closely related to economic security and has important military, foreign policy, and national security dimensions. For biofuels to enhance energy security, they must lead to reduced imports of non-competitively supplied fuels and a shift in consumption toward more stably supplied fuels. Energy security for biofuels also requires reliability and security of resources and activities that support the biofuel supply chain (e.g., water, nutrients, and production operations) in spite of highly variable commodity and product prices.

5. Energy security premium

This “oil security premium” (Plummer, 1981; Bohi and Montgomery, 1982; Leiby et al., 1997; Leiby, 2008) estimates the difference between the marginal economic cost to society and the market price paid for petroleum. This approach has been extended to estimate the energy security benefits of substituting biofuels for petroleum in vehicle fuels, measured in $/gallon biofuel (Leiby, 2008; USEPA, 2010). This measure needs additional effort to develop consensus around a standard measure capable of capturing the range of energy security factors described above.

6. Fuel price volatility

Fuel price volatility is an expression of the volatility in the biofuel and feedstock prices under analysis. It can be calculated as the standard deviation of monthly percent price changes over one year.

External Trade Category

External trade refers to movement across borders. Exports represent the portion of production that is sold outside a defined boundary, while imports represent the portion of internal consumption that is purchased from the exterior.

7. Terms of trade

Terms of trade (TOT) is defined as the ratio of the price (or price index) of exports to that of imports. TOT is a measure of one jurisdiction’s gains from trade. A higher TOT means the jurisdiction can purchase more imports per unit of its exports.

8. Trade volume

The contribution of bioenergy to trade volume, measured as the amount of money expended for net exports or balance of payments. Net exports measure the surplus/deficit in goods and services trade. The balance of payments captures the surplus/deficit in both the flow of current income and payments (current account), including net exports, and that of investments (capital account) across borders.

Profitability Category

Economic viability represents one of the three pillars of sustainability, along with environmental and social requirements. Profitability is perhaps the most basic indicator of economic sustainability. It is pertinent to sustainability of the entire supply chain as well as to specific components, and it is a function of product price and costs of production, both of which are influenced by various policy and market conditions, which are subject to change.

9. Return on investment (ROI)

ROI is the ratio of money gained (or lost) on an investment relative to the amount of money invested and is often expressed as a percentage. It is calculated as follows:

ROI = (final value of investment – initial value of investment)/ initial value of investment

To account for the time value of money, final value of investment and initial value of investment should be expressed as a sum of discounted present values. In discounting, lower interest rates emphasize long-term economic viability over short-term profit. Thus, the implications of ROI as a sustainability indicator are subject to the planning horizon and discount rate used in its calculation.

10. Net present value (NPV)

NPV is the sum of discounted benefits minus the sum of discounted costs of a project, expressed in monetary terms:

where NPV is net present value; R is the net cash flow at time t; t is the time of the cash flow; i is the real interest (or discount) rate.

If the NPV is less than zero, the project is not profitable, while an NPV exceeding zero is profitable, with higher profitability indicated as NPV increases. Like ROI, NPV is sensitive to the discount rate used in calculating discounted present values, with long-term cash flows and economic sustainability more heavily weighted with lower discount rates.

Resource Conservation

Indicators for resource conservation reflect progress toward equitable distribution of resources among people on earth today and in the future—a challenging concept to define and measure.

Indicators for resource conservation are recommended in cases where the energy supply chain affects a resource that is vital for sustainability, resource stocks are being depleted, and this depletion is not otherwise captured in the suite of sustainability indicators.

Moreover, indicators of resource conservation draw attention to the renewability of bioenergy, a key element of sustainability that is not captured in other indicators.

11. Depletion of non-renewable energy resources

Depletion of non-renewable energy sources can be measured as metric tons of petroleum extracted per year. Data on petroleum removals are available from the International Energy Agency (IEA), Energy Information Agency (EIA), and US Geological Survey (USGS).

Petroleum fuels can also be monitored in terms of metric tons per unit of equivalent liquid fuel (MJ) supplied, and this information may be applicable for comparisons of pathways. For smaller scale analyses and comparisons, the total use of petroleum associated with different energy production pathways is of strategic value.

12. Fossil energy return on investment (EROI)

Fossil EROI is defined as the ratio of the amount of usable energy acquired from an energy resource to the amount of energy expended to obtain that energy resource. Typically, EROI considers all direct energy consumed to provide a useful unit of energy, as well as energy associated with significant material inputs. For the purposes of a biofuel indicator, we recommend using the protocol and definitions provided by Murphy et al. (2011) for the fossil fuel EROI or “fossil energy ratio.”

Social Acceptability Category

Social acceptability of bioenergy technologies and management systems reflects many values that are not considered in environmental and economic analyses. These include aesthetic values, recreational values, cultural values, and public perceptions that may be as important in determining sustainability as are economic and environmental factors. A production system is not sustainable if the local community does not accept it.

Social acceptability issues are pertinent to the entire supply chain but emphasized for the feedstock production stage.

13. Public opinion

Public opinion (% favorable opinion) can be determined using a standard survey instrument to gather data on public perceptions of the bioenergy project under assessment. This indicator provides a direct measure of social acceptability.

Public opinion surveys are common for energy technologies and measure the percentage of the surveyed community that rates the project as acceptable. Surveys may also include measures that categorize respondents as favorable, neutral or unfavorable. Surveys should be designed to measure the public’s reaction to high probability and low impact events in contrast to focusing on risk of catastrophe, a separate indicator which is discussed below. Standard protocols need to be validated and applied consistently over time to track changes in public opinion.

14. Transparency

The extent to which timely and accurate information is made available, and the degree to which this information addresses issues of interest to stakeholders, reflect measures of transparency supporting sustainability. The unit of measurement, the percentage of indicators for which performance is reported in a timely manner, is context-specific.

This public reporting should provide relevant baseline, target and performance data for all environmental, social and economic indicators identified. The suite of indicators may be adapted and prioritized for a given project or situation based on stakeholder participation. Furthermore, annual reporting should meet an established standard (e.g., such as that proposed by the Global Reporting Initiative.

15. Effective stakeholder participation

Effective stakeholder participation is measured as the percentage of stakeholder concerns and suggestions addressed in documented responses, reported on an annual basis. This indicator can provide a vehicle to express commitment to, and document progress toward, what are often difficult to measure sustainability values. For this indicator unit to be reliable, consistent and transparent reporting mechanisms should ensure that documented responses legitimately address the concerns and suggestions related to sustainability criteria and indicators and that the mechanisms for dialogue remain open to all without fear of reprisal.

16. Risk of catastrophe

The probability of catastrophe (annual probability of catastrophic event) is a measure of social acceptability of bioenergy that can be informed by transparent reporting and public participation and can affect public opinion. Catastrophes are adverse events that occur at such a large scale or with such extreme intensity that they are not projected within the project life cycle (except in cases where worst-case scenarios are evaluated). They are events with high-consequences and relatively low probability of occurrence.

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This research was supported by the U.S. Department of Energy (DOE) under the Bioenergy Technologies Office, award number EE0007088. Oak Ridge National Laboratory is managed by the UT-Battelle, LLC, for DOE under contract DE-AC05-00OR22725. The views and opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.