Using Curtailed Renewable Energy to Produce Green Hydrogen

Written by Doug Houseman

In 2020 California curtailed more than 1.3 Tera-watthours (TWH)1 up from 1 TWH in 20192. Curtailment is rising faster than installation of new renewables and will continue to grow until storage catches up with renewable production.

California is pushing for more battery storage; in Assembly Bill (AB) 2514 there is a legal requirement for 1.3 GW of storage by the end of 2020. As of May 2020, more than 500 MW were operational3. This is a small amount in comparison to the California Public Utility Commission’s (CPUC) findings of a need for 9.8 GW of additional storage by 20304, or the California Energy Storage Association’s report that shows a need for 55 GW in 20455. Long duration storage typically requires 4 or more hours of energy storage at full capacity. So, the total energy needing to be stored will be at least 220 GWH in 2045.

Batteries are not cheap and have a limited life before replacement. The media widely discusses lithium-ion batteries as the primary grid storage battery6 and indicates that the price for the battery cells (which is not the installed cost) is under $100 per kilowatt-hour (KWH)7. Using that number, the cost of 220 GWH would be $22 billion (US) for just the batteries. The installed cost is currently running more than 5 times that of the cells8. The cost of equipment is easy to reduce with economies of scale, but the costs of labor, land, interconnection, and the balance of plant (the portions of the facility that are not batteries, like foundations, or grounding) are all much harder to reduce, as the US Department of Energy (DOE) proved with their SunShot initiative9. Even with an additional 50% reduction of the battery cell costs, California may face a $900 billion cost for storage batteries over the next 25 years.

With an average life of 6-10,000 cycles10, battery cells require a replacement every 8-15 years. Because significant labor is required to change out cells, battery-based power storage systems will incur an additional cost of $150 billion for every change out.

Pumped hydro, better batteries, and newer technologies could radically reduce these costs. One of the more promising technologies is to storage electricity as hydrogen. Five years ago, hydrogen was an option that was not economic, and it is still sometimes dismissed out of hand. More than 120 million tons of hydrogen are now used annually in industrial processes11 resulting in 830 million tons of CO2 emissions12. Using renewable power to make hydrogen removes this contribution to emissions.

 

Hydrogen

Hydrogen is classified by colors today. Grey hydrogen is created using fossil fuel power; blue hydrogen is also from fossil sources, where the carbon is captured and stored. Today grey hydrogen provides more than 90 percent of the world’s consumption13. Green hydrogen is made using renewable power sources, pink hydrogen is created by electrolysis powered by nuclear energy. More than a dozen other colors have been proposed, but these four are the most common defined colors. Green and pink are the only assured carbon-free sources of hydrogen.

 

What has changed in the green hydrogen world?

Five years ago, hydrogen was a poor choice for storage, due to number of factors, such as low efficiency, short run time before cleaning as measured in hours, requirements to have very high water purity, and expensive hydrogen storage mechanisms while limited research conducted at that time. Most labs were not very interested in hydrogen research even though in 2005, the US Energy Policy Act14 and two years later the 2007 Energy Independence and Security Act of 200715 established the “H Prize” to reward hydrogen research. The work done in the US under these acts provided the research base for more efficient methods of electrolyzing water to make hydrogen.

One of those methods is Photon Exchange Membrane (PEM) production. The basic research proved that typical fuel cell technology could be “run backwards” to produce hydrogen instead of taking in hydrogen and producing water and power. This technology is now commercially available and rapidly being improved.

In 2014 the capital costs for hydrogen production were approximately $1000 per KW, in 2020 that cost for commercial scale plants had dropped to roughly $400 per KW16. Further future reductions in capital cost are expected from increased manufacturing volume, improved materials, and higher efficiencies. Renewable energy prices have also fallen since 2014 from power purchase agreements paying $120 per MWH to under $3017. Efficiency of PEM membrane electrolysis has shown gains from 60% to 80% efficiency over the last decade, most of that being realized in the last 5 years18. Finally, the efficiency of converting hydrogen back to electricity has improved by more than 25% since 201419 where 60% efficiency was considered world class.

There is significant work being done on other methods of hydrogen production, but none of them have been commercialized yet. Some would directly replace solar panels with panels that would use sunlight directly to convert water to hydrogen, instead of using curtailed renewable energy. Photo-electrochemical water splitting (PEC) uses specialized semiconductors, sunlight, and water to produce hydrogen. Research in this area is now focused on metal-organic frameworks to produce high stability, long life, and low-cost PEC units20.

 

Research Needs

Focusing on electrolyzers, there are several areas where research is both required and funds are available from government sources in North American, Europe, Australia and China. They include21:

  • Membranes with higher mechanical strength in saturated operation
  • Membranes with lower permeation
  • Membranes operating at a higher voltage that have low creep
  • Catalysts with higher activity in oxygen evolution
  • Transport layers with a better two-phase flow
  • Higher speed coating processes and equipment
  • Precision layer deposition
  • Systems integration of the whole electrolyzer
  • A reference standard for research, so that improvements are repeatable between labs

 

Semi-truck example

One kilogram of hydrogen contains 33.6 MWh of usable energy and at 100% efficiency requires 39MWH of energy to create from water22. At 100% efficiency, California’s 1.3 TWH of curtailed energy would yield more than 38,000 tons of hydrogen; at today’s efficiency it would yield 30,000 tons. Put that hydrogen into a fuel cell Class 8 (semi-truck) vehicle and it could be driven 1,000 miles per ton of hydrogen or about 30,000,000 total Class 8 vehicle miles driven.

A typical semi-truck will carry between 150 and 300 gallons of fuel. A 150-gallon tank of diesel could be replaced by a 40Kg of hydrogen stored in metal hydrides in the same space and at about 60% of the weight. Lithium-ion batteries have a density of up to 256 watt-hours per kg23. 1 KG of hydrogen stored in metal hydrides takes 0.5 cubic feet including the container. Metal Hydride materials are non-explosive and do not burn in and of themselves. Hydrogen is stored at less than 100 psig and so is not at a compression level that would burst the typical tank. Because hydrogen is much lighter than air, it will escape a rupture in the tank in an upward direction quickly rising away from the vehicle24. This may mean that the best location for these relatively lightweight tanks may be higher on the vehicle than typical diesel tanks are today.

The comparison values are summarized below.

Energy Source Quantity Weight (power source & structure) kg Useful kWH25 Range (miles)
Diesel (ICE) 150 gallons 550 2,80026 900
Lithium-Ion batteries 800 kwh 3,125 60027 300
Hydrogen (fuel cell) 40 kg 300 800 400

 

As the table shows, approximately 2,500 kg per truck can be saved by using hydrogen instead of batteries in semi-trucks for energy storage. A 5KW fuel cell for transportation has about the same mass as a diesel engine. The lithium-ion vehicle using electric motors in place of ICE saves about 650 Kg, so the total disadvantage for a battery electric semi-truck is 2,000 kg. This translates into a 2% loss in rolling efficiency28.

 

Resources:

  1. http://www.caiso.com/informed/Pages/ManagingOversupply.aspx retrieved 27 December 2020
  2. ibid
  3. https://www.cpuc.ca.gov/energystorage/ retrieved 27 December 2020
  4. https://static1.squarespace.com/static/5b96538250a54f9cd7751faa/t/5fcf9815caa95a391e73d053/1607440419530/LDES_CA_12.08.2020.pdf retrieved 27 December 2020
  5. ibid
  6. https://www.greentechmedia.com/authors/julian-spector retrieved 27 December 27, 2020
  7. https://about.bnef.com/blog/battery-pack-prices-cited-below-100-kwh-for-the-first-time-in-2020-while-market-average-sits-at-137-kwh/
  8. https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2017/Oct/IRENA_Electricity_Storage_Costs_2017_Summary.pdf?la=en&hash=2FDC44939920F8D2BA29CB762C607BC9E882D4E9 retrieved 27 December 2020
  9. https://ieeexplore.ieee.org/document/6745192
  10. https://www.eesi.org/papers/view/energy-storage-2019 retrieved 27 December 2020
  11. https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2019/Sep/IRENA_Hydrogen_2019.pdf retrieved 27 December 2020
  12. https://www.iea.org/fuels-and-technologies/hydrogen retrieved 27 December 2020
  13. https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2019/Sep/IRENA_Hydrogen_2019.pdf retrieved 27 December 2020
  14. https://www.govinfo.gov/app/details/PLAW-109publ58 retrieved 6 January 2020
  15. https://www.govinfo.gov/app/details/PLAW-110publ140  retrieved 6 January 2021
  16. http://nas-sites.org/dels/files/2018/02/1-1-AYERS-NAS-2018-Proton.pdf retrieved 6 January 2021
  17. https://pv-magazine-usa.com/2020/02/04/utility-scale-solar-ppa-pricing-down-4-7-in-2019-with-13-6-gw-of-corporate-deals-signed/ retrieved 6 January 2021
  18. https://www.sciencedirect.com/science/article/pii/S2589299119300035 retrieved 6 January 2021
  19. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7280957/ retrieved 6 January 2021
  20. https://onlinelibrary.wiley.com/doi/full/10.1002/advs.201500243 retrieved 6 January 2021
  21. http://nas-sites.org/dels/files/2018/02/1-1-AYERS-NAS-2018-Proton.pdf retrieved 6 January 2021
  22. https://rmi.org/run-on-less-with-hydrogen-fuel-cells/ retrieved 27 December 2020
  23. https://www.cei.washington.edu/education/science-of-solar/battery-technology/ retrieved 27 December 2020
  24. https://www.sciencedirect.com/science/article/pii/S0360319919302368 retrieved 16 January 2021
  25. Applied at the wheels, conversion losses are already calculated.
  26. https://www.energy.gov/sites/prod/files/2014/03/f8/deer11_edwards.pdf retrieved 27 December 2020
  27. Assumes useful state of charge from 10-85% with fast charging
  28. https://www.internationaltrucks.com/en/blog/fuel-economy-weight retrieved 27 December 2020

 

This article edited by Hossam Gabber

For a downloadable copy of the February 2021 eNewsletter which includes this article, please visit the IEEE Smart Grid Resource Center.

houseman
Doug Houseman has extensive experience in the energy and utility industry and has been involved in projects in more than 70 countries. Doug is a leader in grid modernization thinking, he was asked to author significant portions of the IEEE’s GridVision 2050, DOE’s QER and to revise CEATI’s Distribution Utility Technology Roadmap. Doug is a NIST fellow and member of the GridWise Architecture Council (GWAC) where he had a hand in both the Smart Grid Interoperability Maturity Model and Transactive Energy. He has led the IEEE Power and Energy Society’s Intelligent Grid Coordinating Committee and Emerging Technology Committee for the last five years. He has presented more than 20 tutorials and webinars for grid modernization for IEEE.

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