Special Session: Net Energy Analysis / Insights for Early Technology Assessment

Net energy analysis (NEA) analyzes energy technologies by quantifying the energy cost of providing an energy service, typically expressed by an energy return ratio such as the energy return on investment EROI). In contrast to standard LCA practice, NEA distinguishes between the (extracted) feedstock energy provided to a process and the (external) embodied energy invested in building and operating the process infrastructure. NEA’s unique insight is therefore the energy intensity with which a process utilizes the feedstock energy provided to it.

Discussion of NEA has grown recently, both for application as a technology assessment tool and for methodology development. NEA has recently been applied to photovoltaic electricity generation [1,2], grid storage [3, 4, 5] and biofuels [6, 7, 8]. Recent work on NEA methodology has introduced a matrix-based approach to NEA [9, 10] and developed systematic definitions of energy return ratios [11].

The objective of the session is to share insights from recent applications of net energy analysis to specific energy technologies. The session will begin with a brief overview of net energy analysis in the context of LCA, then proceed to standard oral presentations. The talks will be followed by a 10-20 minute moderated discussion to address methodological topics such as consistent system boundaries.

08:30 Charles BarnhartMatthew Pellow and Adam Brandt

Ideal limits to energy storage energy cost minimization.

ABSTRACT. Special Section: Net Energy Analysis

Energy storage technologies have two energetic costs: life-cycle embodied energy costs and energy losses due to inefficient operation. From this perspective, net energy cost minimization theoretically occurs when the battery is 100% efficient and has 0 embodied energy costs. These limits define two energy cost ideals: thermodynamic perfection and zero energy investment. How do current storage technologies fair in relationship to these limits and how can we use these ideal limits for early technology appraisal? To make this comparison, we define a new energy return ratio: the energy stored on energy expended (ESEE). In this work we demonstrate the superiority of this ratio over a previously defined ratio for energy storage, the energy stored on energy invested (ESOI). This presentation will report the life cycle energy costs of several energy storage technologies in reference to these ideals. Primary and electrical embodied energy requirements for storage technologies were obtained by a) conducting a meta-analysis of several published LCA studies, b) harmonizing, when possible, these data by a cradle-to-gate LCA boundary, c) converting primary energy data to electrical energy by a applying a standard conversion factor of 0.3, and d) binning results into quartiles and applying only the IQR to our calculations. Sources and energy accounting methodology is described in prior work (Barnhart, Dale, Brandt and Benson, 2013). We recognize that storage technologies are rapidly evolving and that the paltry LCA and LCI data available is likely out of date. Our theoretical framework however is grounded in first principles and can be repeatedly employed as data becomes refined. Results to date show that per cycle embodied energy costs matter, but for technologies with sought-after charge-discharge cycle life values above 3000, round-trip efficiency really dominates the energy balance sheet. Moreover, energy losses due to storage inefficiencies critically depend on the energy intensity of the resource.

08:45 Adam Brandt

Using life cycle net energy metrics to assess impacts of oil resource depletion and technological change in the oil industry

ABSTRACT. So-called “conventional” oil resources are becoming increasingly limited due to resource depletion, political limitations on development, and technological challenges associated with remote resources. At the same time, technological change has allowed unconventional reservoirs (like “tight” oil) and unconventional hydrocarbons (like the oil sands) make up an increasing fraction of our oil supply. How can net energy analysis illuminate the impacts of these important trends? And does net energy analysis point to ways to assess the impacts of oil resources?

This talk examines these questions as follows: first, we explore the use of so-called “net energy analysis” to examine oil resources, including the various metrics that have been defined in the literature and their implications. Next, we illustrate what these metrics can tell us based on two case studies: unconventional oil from oil sands operations in Alberta and hydraulically-fractured oil resources of the Bakken formation in North Dakota. We illustrate how different metrics can give different insights into these resources, despite their similar economic profiles.

The results of these analyses suggest some interesting trends. First, although both oil sands and tight oil resources are considered similar in economic profile (50-80$/bbl break even cost), their net energy results are quite different. Using the NER (net energy return) metric, oil sands mining operations have NER of about 5 MJ produced per MJ consumed. On the other hand, hydraulic fracturing operations in the Bakken have NER of about 50 MJ output per MJ consumed. In contrast, a different metric, the net external energy return (NEER), which measures output of oil product compared to inputs from the rest of society, the oil sands operations have ratios of approximately 25 MJ output per MJ consumed.

We argue that the NEER metric is a better indicator of the economic sustainability of a project, because it compares output energy to purchased external energy supplies. However, the NER metric is more inclusive and includes energy resources consumed on-site from on-site deposits. This makes NER better correlated with environmental impact analysis and traditional LCA metrics (e.g.., cumulative energy demand).

09:00 Garvin Heath

Meta-analysis for net energy analyses – preliminary thoughts from the LCA Harmonization project
SPEAKER: Garvin Heath

ABSTRACT. This presentation will review preliminary thoughts about the applicability of methods and experience with systematic review and meta-analytical harmonization of life cycle assessments to net energy analyses. Such approaches should be equally applicable to net energy analyses, yielding the potential to leverage prior work for collective insight. NREL’s LCA Harmonization study collected not only LCAs but also net energy analyses, even if less comprehensively, giving a first look at available evidence which, like for LCAs, displays considerable variability for the same technology (several orders of magnitude in many cases). NEA suffers from less conformity on metrics within its research community relative to LCA (which is not free of such suffering). Harmonization will thus be relatively more challenging for NEA. NEA estimates can be potent messaging tools in support or opposition to certain energy technologies, and like LCAs, analysts can obfuscate their methodological choices and differences from norms to make a subjective case. The International Energy Agency’s Photovoltaic Power Systems (PVPS) Task 12 on Environmental Health and Safety is attempting to address this concern by developing a guideline for NEA methodology with respect to PV electricity, analogous to our LCA guidelines. If we are successful, such a guide could help to establish a consistent standard of reporting NEA results for PV, and if successful there, could be extended to other energy technologies by other groups.

09:15 Michael Carbajales-Dale

Lifecycle assessment and net energy analysis – birds of a feather, or uneasy bedfellows?

ABSTRACT. Lifecycle assessment (LCA) and net energy analysis (NEA) are complementary approaches with a common historical basis but different underlying motivations and methodologies. As LCA practitioners move more and more beyond the bounds of attributional to consequential LCA the methodological concerns of NEA become more and more appropriate. As such, it is important to understand the large overlaps in method, but also the important distinctions between the two frameworks.

This paper will outline these differences along a number of important dimensions including:goal (motivation and aim), scope (system boundary and assumptions), methodological structure (allocation and aggregation) and interpretation.

The hope is that NEA practitioners will appreciate more of the common elements between NEA and LCA adopt more of the methodological rigor of LCA and that practitioners of LCA will understand more of the underlying differences between the two frameworks and see insights and opportunities for developing consequential LCA.