EES Blog

In an exciting breakthrough in photoelectrochemical (PEC) solar generator development, a new report describes a methodology for robust H₂ production in a near neutral environment.

The development of practical, sustainable solar fuel generators comes with many challenges. Not only do the materials and components used need to be cost-effective and abundant, but the devices also need to be able to consistently produce purified fuels over long periods of time under environmentally benign conditions. A challenge to meeting all of these requirements has been in the creation of devices that are stable using either strong acid or basic electrolytes. A recent EES paper by Modestino et al. describes the development of a controlled recirculating stream across reactions sites to yield continuous solar-hydrogen generation in near neutral pH electrolytes.

In this report, researchers from the Joint Center for Artificial Photosynthesis and collaborating institutions describe alternate ion transport pathways that allow for operation under a near neutral pH. By creating a recirculation scheme to balance the concentration across the membrane in a membrane-separated photoelectrochemical (PEC) system, the authors achieved robust production of separated product streams (pure hydrogen and oxygen) via their ion-transport membrane components.

Designing a PEC device that operates using neutral pH electrolytes enables the use of catalytic and light absorbing components that would degrade in acidic or basic environments. The methodology described in this paper can provide researchers with a platform to experiment with different materials and hopefully optimize solar-to-hydrogen efficiency. It will be interesting to see the implementation of this methodology in future research, and if this approach ultimately provides a good solution to one major obstacle in the creation of scalable, sustainable, and robust solar fuel generators.

Read more in the full EES article here:

Robust production of purified H₂ in a stable, self-regulating, and continuously operating solar fuel generator
Miguel A. Modestino, Karl A. Walczak, Alan Berger, Christopher M. Evans, Sophia Haussener, Carl Koval, John S. Newman, Joel W. Ager and Rachel A. Segalman
Energy Environ. Sci., 2014,7, 297-301
DOI: 10.1039/C3EE43214A

In a new broad analysis researchers model the impact of fossil fuels for non-energy purposes vs. lower-emission alternatives, such as the use of biomass.

In research and popular media, much attention is focused on the impact of fossil fuels used for energy purposes. In a new EES paper, researchers focus instead on the non-energy uses of fossil fuels, their impact, and lower-emissions alternatives. Non-energy uses are defined as “fuels that are used as raw materials […] and are not consumed as a fuel or transformed into another fuel,” and primarily include feedstock for chemical production of ethylene, methanol, and ammonia, and oil products like waxes and lubricants. Coal, gas, and oil usage for non-energy purposes currently account for up to 7% of global CO2 emissions.

In their paper, Daioglou et al. present a global model for emissions reduction in non-energy processes, called the Non-Energy Demand and Emissions Model, or NEDE. This model projects that the global demand of non-energy processes will more than double over the next 100 years. Their analysis explores the alternative of using biomass for feedstock chemical production, promoting fuel switching in climate policy, and post-consumer waste management such as mechanical recycling and cascading processes. By comparing current usage and feedstock substitution costs, and by projecting based on economic, population, and fuel price developments, the model predicts that substituting fossils fuels, particularly coal, with biomass for non-energy purposes could significantly reduce emissions. Post-consumer waste management processes are currently too inefficient to significantly reduce emissions; however, climate policy that promotes fuel switching through carbon taxation can help to implement emissions-reducing practices.

It is interesting that Daioglou et al. point out that there are currently a lack of broad studies on the emission reduction potential of using biomass in non-energy processes, as was apparently pointed out in the recent Special Report on Renewable Energy Sources of the Intergovernmental Panel on Climate Change. Speaking as someone outside of this field of research, I would say that lowering emissions of non-energy processes certainly takes a back seat in the media to the use of fossil fuels for energy purposes. While the relative impact of non-energy processes may seem small by comparison, if the NEDE model is correct then analyses such as this one will grow increasingly important. As the authors note, there is still much research to be done to determine if biomass is optimal for reducing emissions for non-energy purposes, but his broad analysis is certainly a good start.

Read more in the full EES article here:

Energy Demand and Emissions of the Non-Energy Sector
Vassilis Daioglou, Andre Faaij, Deger Saygin, Birka Wicke, Martin Patel and Detlef Peter van Vuuren
Energy Environ. Sci., 2013, Accepted Manuscript
DOI: 10.1039/C3EE42667J

Researchers compare the energy return on energy investment (EROI) ratios of electricity storage versus curtailing electricity production for renewable, but variable, resources.

Wind and solar power are current leaders in renewable energy resources, but pose a challenge to more widespread use because of their variable, weather dependent nature. Currently, wind and solar energy harvesting is curtailed during times of oversupply, resulting in a forfeiture of energy.  A clear solution to keep from losing all of this energy would be to store it for later use; however, storage can come at its own energetic cost that is often greater than the gain of the energy stored.

In a recent EES paper, Barnhart et al. examined the EROI ratios for methods of energy storage and compared the ratios with those during curtailment of electricity production for solar and wind power generation. Specifically, they explored electrical energy storage through both battery and geologic storage technologies, and compared the electrical cost of those storage methods to curtailment energy losses.

Barnhart et al. found that, depending on the type of energy resource, usage patterns, and storage type, there are cases in which it is more energetically favorable to store excess electricity, and cases in which it is more favorable to curtail the resources. Conventional battery technologies did not perform well in terms of energy cost compared to geologic storage technologies. Based on these findings, the authors recommend focusing on ways to improve battery EROI ratios, such as improving cycle life, as the next step toward developing electricity storage in which the energy cost is less than loss incurred from curtailment of electricity generation.

This paper recognizes that wind and solar energy are becoming more widely used and are proving to be excellent resources, which is great news from the perspective of reducing carbon usage in electricity production. But it is clear from the findings, as well as from a practical standpoint, that energy storage needs to be the next step for an increase in usability of these resources. These power generation technologies continue to grow, but due to variability, production does not always match with consumer usage patterns. Wouldn’t it be great, from the perspectives of both affordability and sustainably, to be able to run your appliances with solar power at night, or with wind power on a still day? Energy storage that is cost-effective from an energy expenditure standpoint is clearly the next step in paving the way for more widespread use of these sustainable, low-carbon energy resources.

Learn more about this analysis in the full EES article here:

The energetic implications of curtailing versus storing solar- and wind-generated electricity
Charles J. Barnhart, Michael Dale, Adam R. Brandt and Sally M. Benson
Energy Environ. Sci., 2012, 5, 8430
DOI: 10.1039/c2ee21581k