Member since: Mon Mar 6, 2006, 04:51 PM
Number of posts: 16,127
Number of posts: 16,127
Hydrogen or batteries for grid storage? A net energy analysis
Matthew A. Pellow,*a Christopher J. M. Emmott,bc Charles J. Barnhartd and Sally M. Bensonaef
Energy Environ. Sci., 2015,8, 1938-1952
Received 22 Dec 2014, Accepted 08 Apr 2015
First published online 08 Apr 2015
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
Energy storage is a promising approach to address the challenge of intermittent generation from renewables on the electric grid. In this work, we evaluate energy storage with a regenerative hydrogen fuel cell (RHFC) using net energy analysis. We examine the most widely installed RHFC configuration, containing an alkaline water electrolyzer and a PEM fuel cell. To compare RHFC's to other storage technologies, we use two energy return ratios: the electrical energy stored on invested (ESOIe) ratio (the ratio of electrical energy returned by the device over its lifetime to the electrical-equivalent energy required to build the device) and the overall energy efficiency (the ratio of electrical energy returned by the device over its lifetime to total lifetime electrical-equivalent energy input into the system). In our reference scenario, the RHFC system has an ESOIe ratio of 59, more favorable than the best battery technology available today (Li-ion, ESOIe = 35). (In the reference scenario RHFC, the alkaline electrolyzer is 70% efficient and has a stack lifetime of 100 000 h; the PEM fuel cell is 47% efficient and has a stack lifetime of 10 000 h; and the round-trip efficiency is 30%.) The ESOIe ratio of storage in hydrogen exceeds that of batteries because of the low energy cost of the materials required to store compressed hydrogen, and the high energy cost of the materials required to store electric charge in a battery. However, the low round-trip efficiency of a RHFC energy storage system results in very high energy costs during operation, and a much lower overall energy efficiency than lithium ion batteries (0.30 for RHFC, vs. 0.83 for lithium ion batteries). RHFC's represent an attractive investment of manufacturing energy to provide storage. On the other hand, their round-trip efficiency must improve dramatically before they can offer the same overall energy efficiency as batteries, which have round-trip efficiencies of 75–90%. One application of energy storage that illustrates the tradeoff between these different aspects of energy performance is capturing overgeneration (spilled power) for later use during times of peak output from renewables. We quantify the relative energetic benefit of adding different types of energy storage to a renewable generating facility using |EROI|grid. Even with 30% round-trip efficiency, RHFC storage achieves the same |EROI|grid as batteries when storing overgeneration from wind turbines, because its high ESOIe ratio and the high EROI of wind generation offset the low round-trip efficiency.
The rapid increase in electricity generation from wind and solar is a promising step toward decarbonizing the electricity sector. Because wind and solar generation are highly intermittent, energy storage will likely be key to their continued expansion. A wide variety of technology options are available for electric energy storage. One is a regenerative hydrogen fuel cell (RHFC) system that converts electricity to hydrogen by water electrolysis, stores the hydrogen, and later provides it to a fuel cell to generate electric power. RHFC systems are already operating in several dozen locations. In this net energy analysis, we compare the quantity of energy dispatched from the system over its lifetime to the energy required to build the device. We find that, for the same quantity of manufacturing energy input, hydrogen storage provides more energy dispatched from storage than does a typical lithium ion battery over the lifetime of the facility. On the other hand, energy storage in hydrogen has a much lower round-trip efficiency than batteries, resulting in significant energy losses during operation. Even at its present-day round-trip efficiency of 30%, however, it can provide the same overall energy benefit as batteries when storing overgeneration from wind farms.
Energy storage in hydrogen is a technically feasible option for grid-scale storage, and is already in pilot demonstrations. Because of its low round-trip efficiency, it may be overlooked in spite of its potential advantages, such as high energy density and low rate of self-discharge. In order to examine the potential benefits and drawbacks of hydrogen as a grid-scale energy storage technology, we apply net energy analysis to a representative hypothetical regenerative hydrogen fuel cell (RHFC) system. We introduce and apply a method to determine the energy stored on invested (ESOIe) ratio of a reference case RHFC system.
We find that the reference case RHFC system has a higher ESOIe ratio than lithium ion battery storage. This indicates that the hydrogen storage system makes more efficient use of manufacturing energy inputs to provide energy storage. One reason for this is that the steel used to fabricate a compressed hydrogen storage cylinder is less energetically costly, per unit of stored energy, than the materials that store electric charge in a battery (electrode paste, electrolyte, and separator). However, lithium ion batteries remain energetically preferable when considering the operation of the system, as well as its manufacture, due to their higher round-trip efficiency (90%). This is reflected in the overall energy efficiencies of the two storage technologies: the overall energy efficiency of a typical lithium ion battery system is 0.83, compared to 0.30 for the reference case RHFC system. This highlights that in spite of its relatively efficient use of manufacturing energy inputs, the round-trip efficiency of a RHFC system must increase before it can provide the same total energy benefit as other storage technologies. Higher RHFC round-trip efficiency relies on improved electrolyzer and fuel cell performance.
When storing overgeneration from wind turbines, energy storage in hydrogen provides an energy return similar to batteries, in spite of its lower round-trip efficiency. The aggregate EROI of wind generation augmented with RHFC storage is equal to that of the same wind facility augmented with lithium ion battery storage, when up to 25% of the electricity output passes through the storage system. For spilled power from solar photovoltaics, storage in hydrogen provides an EROI that is slightly higher than curtailment, though lower than batteries. As with other storage technologies, energy storage in hydrogen coupled to wind generation provides an overall EROI that is well above the EROI of fossil electricity generation.
Posted by OKIsItJustMe | Mon Mar 28, 2016, 11:42 AM (1 replies)
Public Release: 17-Jun-2015
Renewable energy's record year helps uncouple growth of global economy and CO2 emissions
Record installations for wind and solar PV in 2014; renewable energy targets created in 20 more countries, new total: 164
Renewable energy targets and other support policies now in place in 164 countries powered the growth of solar, wind and other green technologies to record-breaking energy generation capacity in 2014.
With 135 gigawatts added, total installed renewable energy power capacity worldwide, including large hydroelectric plants, stood at 1712 gigawatts, up 8.5% from the year before and double the 800 gigawatts of capacity reported in the first REN21 report in 2005.
In 2014, renewables made up an estimated 59% of net additions to global power capacity and represented far higher shares of capacity added in several countries around the world. By year's end, renewables comprised an estimated 27.7% of the world's power generating capacity. This was enough to supply an estimated 22.8% of global electricity demand.
The quantity of electricity available from renewables worldwide is now greater than that produced by all coal-burning plants in the USA (in 2013 coal supplied ~38% of US electricity, down from ~50% in the early 2000s).
Posted by OKIsItJustMe | Wed Jun 17, 2015, 06:27 PM (5 replies)
Livermore scientists develop CO2 sequestration technique that produces 'supergreen' hydrogen fuel, …
(Please note, Press Release from US National Laboratory — Copyright concerns are nil.)
For immediate release: 05/27/2013 | NR-13-05-07
Livermore scientists develop CO2 sequestration technique that produces 'supergreen' hydrogen fuel, offsets ocean acidification
Anne M Stark, LLNL, (925) 422-9799, firstname.lastname@example.org
LIVERMORE, Calif. -- Lawrence Livermore scientists have discovered and demonstrated a new technique to remove and store atmospheric carbon dioxide while generating carbon-negative hydrogen and producing alkalinity, which can be used to offset ocean acidification.
The team demonstrated, at a laboratory scale, a system that uses the acidity normally produced in saline water electrolysis to accelerate silicate mineral dissolution while producing hydrogen fuel and other gases. The resulting electrolyte solution was shown to be significantly elevated in hydroxide concentration that in turn proved strongly absorptive and retentive of atmospheric CO2.
Further, the researchers suggest that the carbonate and bicarbonate produced in the process could be used to mitigate ongoing ocean acidification, similar to how an Alka Seltzer neutralizes excess acid in the stomach.
"We not only found a way to remove and store carbon dioxide from the atmosphere while producing valuable H2, we also suggest that we can help save marine ecosystems with this new technique," said Greg Rau, an LLNL visiting scientist, senior scientist at UC Santa Cruz and lead author of a paper appearing this week (May 27) in the Proceedings of the National Academy of Sciences.
When carbon dioxide is released into the atmosphere, a significant fraction is passively taken up by the ocean forming carbonic acid that makes the ocean more acidic. This acidification has been shown to be harmful to many species of marine life, especially corals and shellfish. By the middle of this century, the globe will likely warm by at least 2 degrees Celsius and the oceans will experience a more than 60 percent increase in acidity relative to pre-industrial levels. The alkaline solution generated by the new process could be added to the ocean to help neutralize this acid and help offset its effects on marine biota. However, further research is needed, the authors said.
"When powered by renewable electricity and consuming globally abundant minerals and saline solutions, such systems at scale might provide a relatively efficient, high-capacity means to consume and store excess atmospheric CO2 as environmentally beneficial seawater bicarbonate or carbonate," Rau said. "But the process also would produce a carbon-negative 'super green' fuel or chemical feedstock in the form of hydrogen."
Most previously described chemical methods of atmospheric carbon dioxide capture and storage are costly, using thermal/mechanical procedures to concentrate molecular CO2 from the air while recycling reagents, a process that is cumbersome, inefficient and expensive.
"Our process avoids most of these issues by not requiring CO2 to be concentrated from air and stored in a molecular form, pointing the way to more cost-effective, environmentally beneficial, and safer air CO2 management with added benefits of renewable hydrogen fuel production and ocean alkalinity addition," Rau said.
The team concluded that further research is needed to determine optimum designs and operating procedures, cost-effectiveness, and the net environmental impact/benefit of electrochemically mediated air CO2 capture and H2 production using base minerals.
Other Livermore researchers include Susan Carroll, William Bourcier, Michael Singleton, Megan Smith and Roger Aines.
Posted by OKIsItJustMe | Tue May 28, 2013, 09:10 AM (13 replies)
The 'rebound' effect of energy-efficient cars overplayedhttp://dx.doi.org/10.1038/493475a
January 23, 2013
The argument that those who have fuel-efficient cars drive them more and hence use more energy is overplayed and inaccurate, a University of California, Davis, economist and his co-authors say in a comment article published Wednesday in the journal Nature.
Critics of energy efficiency programs in public policy debates have cited the “rebound effect” as a reason that hybrid cars and plug-in electric vehicles, for example, don’t really save energy in the long run.
The “backfire” concept, a more extreme version of “rebound,” actually stems from a 19th century analysis in a book titled “The Coal Question,” by Stanley Jevons. The book hypothesized that energy use rises as industry becomes more efficient because people produce and consume more goods, according to the Nature article. But the article’s co-authors found that in the modern economy, the effect is not supported empirically.
“If a technology is cheaper to run, people may use it more. If they don’t, they can use their savings to buy other things that required energy to make. But evidence points to these effects being small — too small to erase energy savings from energy efficiency standards, for example,” said David S. Rapson, assistant professor of economics at UC Davis.
Posted by OKIsItJustMe | Thu Jan 24, 2013, 01:17 PM (24 replies)
(Moderators, please note, NASA publication—copyright concerns are nil.)
2012: Killer Solar Flares Are a Physical Impossibility(Video at the link.)
Given a legitimate need to protect Earth from the most intense forms of space weather – great bursts of electromagnetic energy and particles that can sometimes stream from the sun – some people worry that a gigantic "killer solar flare" could hurl enough energy to destroy Earth. Citing the accurate fact that solar activity is currently ramping up in its standard 11-year cycle, there are those who believe that 2012 could be coincident with such a flare.
But this same solar cycle has occurred over millennia. Anyone over the age of 11 has already lived through such a solar maximum with no harm. In addition, the next solar maximum is predicted to occur in late 2013 or early 2014, not 2012.
Most importantly, however, even the biggest solar flares are not powerful enough to physically destroy Earth.
This is not to say that space weather can't affect our planet. The explosive heat of a solar flare can't make it all the way to our globe, but electromagnetic radiation and energetic particles certainly can. Solar flares can temporarily alter the upper atmosphere creating disruptions with signal transmission from, say, a GPS satellite to Earth causing it to be off by many yards. Another phenomenon produced by the sun could be even more disruptive. Known as a coronal mass ejection (CME), these solar explosions propel bursts of particles and electromagnetic fluctuations into Earth's atmosphere. Those fluctuations could induce electric fluctuations at ground level that could blow out transformers in power grids. The CME's particles can also collide with crucial electronics onboard a satellite and disrupt its systems.
In an increasingly technological world, where almost everyone relies on cell phones and GPS controls not just your in-car map system, but also airplane navigation and the extremely accurate clocks that govern financial transactions, space weather is a serious matter.
But it is a problem the same way hurricanes are a problem. One can protect oneself with advance information and proper precautions. During a hurricane watch, a homeowner can stay put . . . or he can seal up the house, turn off the electronics and get out of the way. Similarly, scientists at NASA and NOAA give warnings to electric companies, spacecraft operators, and airline pilots before a CME comes to Earth so that these groups can take proper precautions. Improving these predictive abilities the same way weather prediction has improved over the last few decades is one of the reasons NASA studies the sun and space weather. We can't ignore space weather, but we can take appropriate measures to protect ourselves.
And, even at their worst, the sun's flares are not physically capable of destroying Earth.
Posted by OKIsItJustMe | Wed Dec 14, 2011, 11:37 AM (2 replies)
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