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Using RNG to Power EVs Reduces Total US GHG Emissions by 25%

image credit: Courtesy, https://cleanfuelsohio.org/ and www.carmagazine.co.uk/electric/cheapest-electric-car/
Alan Rozich's picture
Director BioConversion Solutions

Providing quantitative sustainability insights using sound technical analyses with a management consulting approach to craft strategies that address the mega-trends that are occurring in the...

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  • May 9, 2022
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Synopsis

Going "all in" with electric vehicles (EVs) has the potential to significantly reduce energy resource consumption and greenhouse gas (GHG) emissions in the US and other countries. A scenario where EVs are powered with energy produced using RNG (renewable natural gas) is compelling. An EV initiative by itself is an energy efficiency play with the potential to reduce annual US energy consumption by as much as 11% and provide cost-savings to consumers. That scenario is significatively improved when EVs operate using green electricity produced by utilizing RNG. It is feasible to realize disruptive reductions of 25% in US GHG emissions economically. It is notable that utilization of RNG for EV energy production avoids egregious land use challenges but other green energy sources can be substituted if appropriate.

Introduction

Sustainability engineering can be a complicated enterprise given the myriad of constraints that must be addressed in conjunction with a seemingly complex and diverse assortment of solutions that are available. A couple of considerations must be first and foremost as one approaches framing problem solutions:

Closer inspection shows that there is much more to the EV sustainability value proposition than meets the eye. This realization may not even be apparent to EV aficionados. The key takeaway for EV architecture is, first and foremost, that it is a compelling energy-efficiency play for societal functionality.

Thus, with just the basic strategy of reducing energy consumption, one realizes lower GHG emissions. However, by also simultaneously incorporating the use of a green energy source such as RNG for generating electricity to power EVs, it is feasible to achieve even much greater aggregate emissions reductions.

Assessing Potential EV/RNG Impact on US GHG Emissions Reduction

The basic strategy with EVs and RNG is to utilize RNG to make green electricity. A basic value proposition is devised by analyzing the basic metric that apply to this situation. The key assumptions are:

  • The number of automobile miles driven in the US per year the associated amount of carbon dioxide GHG generated per mile.
  • The amount US GHG carbon dioxide emissions by the US in one year which is around 4,800 million metric tons of CO2 while global emissions are 36,300 million metric tons.
  • Assume that an EV/RNG configuration can effectively eliminate automotive GHG emissions. This is stated because they EVs already are more energy efficient than gasoline autos and green electricity can be generated using a green energy source such as RNG.

The graph below shows total US CO2 GHG emissions, total US CO2 automobile GHG emissions, and US CO2 GHG emissions with elimination of automobile emissions.

The depicted results show a reduction of total US CO2 emissions of 27% (((4800-3485)/4800) x100) which is probably closer to 25% if one assumes some inefficiencies. Obviously, these projections are an ambitious stretch goal. Nevertheless, it is uncommon in the climate change/sustainability arena where one initiative can realize large impact on emissions while simultaneously bringing economic efficiencies. Consequently, even more "modest" goals in this situation suggest the possibility of double-digit reductions in emissions while preserving economic efficiency.

50:50 RNG/NG and Other RNG/NG Blend Scenarios

As an example, consider 50/50 RNG/NG (natural gas) or 25/75 mixtures. RNG can be generated at existing anaerobic digester installations where it can be blended with natural gas that is extracted from existing deposits. A simplified analysis performed with the help of the data shown in the graph above suggests that:

A 50/50 RNG/NG blend used to power EVs would result in US emissions reduction of almost 14% while a 25/75 RNG/NG blend realizes US emissions reduction of over 9%.

It is important to appreciate that the emissions reductions achieved by either one of the blended scenarios is noteworthy, if not hugely impressive. Consequently, the strategy of providing power to EVs using green energy is compelling on many levels.

Summary

Formulating groundbreaking sustainability and climate change initiatives requires perseverance, technical acuity, and a bit of luck. Achieving such goals can be as elusive and rare as witnessing a planetary alignment in the solar system. The opportunity to integrate two existing platforms, EVs and RNG/NG, that are demonstrated, have considerable existing infrastructure, and a respectable track record is even more fortuitous and attractive. In summation, analysis shows that using RNG or blends of RNG and NG to provide energy for EVs can achieve double digit reductions in US GHG emissions while providing energy efficiency. By having existing infrastructure in conjunction with experiential gravitas lowers both the costs and risks for embarking on this initiative.

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Matt Chester's picture
Matt Chester on May 9, 2022

It is important to appreciate that the emissions reductions achieved by either one of the blended scenarios is noteworthy, if not hugely impressive. Consequently, the strategy of providing power to EVs using green energy is compelling on many levels.

These are valuable gains to be making as soon as we can. Are there any concerns that doing so would perpetuate the greater use of natural gas than a fully decarbonized system? We surely want to avoid the 'bridge to nowhere' fuel mentality again, but the importance of emission reductions ASAP is so great. 

Julian Silk's picture
Julian Silk on May 9, 2022

This is a question and not a statement.  How would the renewable natural gas blends compare to using hydrogen to replace some of the natural gas?

Alan Rozich's picture
Alan Rozich on May 9, 2022

Appreciate the question. I was going to put hydrogen in the mix but was afraid of over complicating the narrative. My initial thought from your suggestion is that one would proceed by replacing NG with the hydrogen since RNG results in no GHGs and hydrogen eliminates GHG. I assume that you proceed by running the engineering and cost-effective gamut to find the sweet spot when replacing NG with hydrogen.

Thanks.

Julian Silk's picture
Julian Silk on May 11, 2022

I am going to quote

https://afdc.energy.gov/files/pdfs/hyd_economy_bossel_eliasson.pdf

This argues that per cubic foot, depending on the pressure involved, hydrogen carries less than 1/3 to 1/10th the energy content of methane and other fossil fuels.  So it is not obvious that there is a sweet spot just on cost with no adjustment for emissions.  Yes, there should be an adjustment for emissions, but then it is a question of what it should be.  Taking current natural gas price to be $7.64 per MCF (1000 cubic feet) and 1 GJ per approximately 947 cubic feet, I am estimating (and will be pleased to be corrected), a cost of about $7.24 per GJ for fossil-derived natural gas.  The source above argues for a cost of $20.10 per GJ for hydrogen derived from electrolysis of water, which is presumably what the renewable energy would do.  So, to put it mildly, there would need to be a very substantial emissions charge to make hydrogen derived from renewables comparable in cost.  Of course, these figures can change, but it is certainly reasonable to be worried about the costs involved and what the reaction will be.

Jim Stack's picture
Jim Stack on May 11, 2022

Yikes, calling unnatural gas renewable is like calling Nuclear Renewable. It is NOT RENEWABLE  never has been and never will be. The change to NG and CNG  is a big mistake. Ww hit peak NG in 2014. It is only from bad Fracking that we have any NG. 

Alan Rozich's picture
Alan Rozich on May 11, 2022

Yikes. The idea is to increase energy efficiency using blends of fossil fuels and renewables. 

Alan Rozich's picture
Alan Rozich on May 12, 2022

Jim, did you read the article and the analyses that shows that double digit reductions in GHG emissions are feasible by leveraging NG/RNG and EVs?

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