Green Energy

The newest solar generation source for Entergy Arkansas is online and pumping power onto the electric grid, officials recently announced. The Searcy Solar Energy Center is among the first in the state to include battery storage and can store 30 megawatts to provide power rain or shine, according to a press release.

Searcy Solar is one of three plants producing solar power for Entergy Arkansas customers, adding 100 MW to the previous 181 MW already online. It joins Stuttgart Solar, an 81 MW facility, and Chicot Solar at Lake Village, a 100 MW facility, both of which are under long term contracts between Entergy Arkansas and subsidiaries of NextEra Energy Resources.

These solar energy resources are projected to save customers more than $190 million and will help protect the environment for many years to come, according to Entergy

“Solar energy is clean, renewable, abundant and cost-effective,” said Entergy Arkansas President and CEO Laura Landreaux. “It is a smart way to increase our electricity supply, and the battery storage at this facility will keep power flowing even when the sun isn’t shining.”

Solar generation provides a large amount of power over the course of the year with no added fuel costs, helping to provide lower cost energy – especially during peak, summer afternoon hours when there is a large demand for power.

As part of its ongoing dedication to economic development and renewable resources, Entergy Arkansas has another 280 MW under development and recently issued a request for proposals for up to 500 MW of solar and wind capacity to add to its electricity generating portfolio by 2026.

The three solar plants in the state will comprise 5% of Entergy Arkansas’ available generating capacity by 2023.

As the world’s energy demands increase, so does our consumption of fossil fuels. The result is a massive rise in greenhouse gases emissions with severely adverse environmental effects. To address this, scientists have been searching for alternative, renewable sources of energy.

A main candidate is hydrogen produced from organic waste, or biomass, of plants and animals. Biomass also absorbs, removes and stores CO₂ from the atmosphere, while biomass decomposition can lead to negative emissions or greenhouse gas removal. But even though biomass heralds a way forward, there is still the question of the best way to maximize its conversion into energy.

Biomass gasification

There are currently two main methods for converting biomass into energy: gasification and pyrolysis. Gasification puts solid or liquid biomass at temperatures around 1,000 degrees Celsius, converting it into gas and solid compounds; the gas is called syngas while the solid is biochar.

Syngas is a mix of hydrogen, methane, carbon monoxide and other hydrocarbons, and those are what are used as biofuel to generate power. On the other hand, biochar is often regarded as a solid carbon waste, although it can be used in agriculture applications.

Biomass pyrolysis

The other method, biomass pyrolysis, is similar to gasification except that biomass is heated at lower temperatures, between 400 and 800 degrees Celsius and at pressures up to 5 bar in an inert atmosphere. There are three types of pyrolysis: conventional, fast and flash pyrolysis. Out of all three, the first two take the longest time, and have the most char production.

Flash pyrolysis takes place at 600 degrees Celsius and produces the most syngas and has the lowest residence time. Unfortunately, it also needs specialized reactors that can handle high temperatures and pressures.

Banana split for hydrogen production

Now, scientists led by Professor Hubert Girault at EPFL’s School of Basic Sciences have developed a new method for biomass photo-pyrolysis that produces not only valuable syngas, but also a biochar of solid carbon that can be repurposed in other applications. The work is published in Chemical Science.

The method performs flash light pyrolysis using a xenon lamp, commonly used for curing metallic inks for printed electronics. Girault’s group has also used the system in the last few years for other purposes, like synthesizing nanoparticles.

The lamp’s white flash light provides a high-power energy source as well as short pulses that promote photo-thermal chemical reactions. The idea is to generate a powerful flash light shot, which the biomass absorbs and which instantaneously triggers a photothermal biomass conversion into syngas and biochar.

This flashing technique was used on different sources of biomass: banana peels, corn cobs, orange peels, coffee beans and coconut shells, all of which were initially dried at 105 degrees Celsius for 24 hours and then ground and sieved to a thin powder. The powder was then placed in a stainless-steel reactor with a standard glass window at ambient pressure and under an inert atmosphere. The xenon lamp flashes, and the whole conversion process is over in few milliseconds.

“Each kg of dried biomass can generate around 100 liters of hydrogen and 330g of biochar, which is up to 33wt.% of the original dried banana peel mass,” says Bhawna Nagar, who worked on the study. The method also had a positive calculated energy outcome of 4.09 MJ per kg of dried biomass.

What stands out in this method is that both its end products, hydrogen and solid-carbon biochar, are valuable. The hydrogen can be used as green fuel, while the carbon biochar, can either be buried and used as a fertilizer or it can be used to manufacture conductive electrodes.

“The relevance of our work is further heightened by the fact that we are indirectly capturing CO₂stores from the atmosphere for years,” says Nagar. “We have converted that into useful end products in no time using a xenon flash lamp.”

A novel plan that offers partnership in keeping the United States electric grid stable and reliable could be a win-win for consumers and utility operators.

The largest ever simulation of its kind, modeled on the Texas power grid, concluded that consumers stand to save about 15 percent on their annual electric bill by partnering with utilities. In this system, consumers would coordinate with their electric utility operator to dynamically control big energy users, like heat pumps, water heaters and electric vehicle charging stations.

This kind of flexible control over energy supply and use patterns is called “transactive” because it relies on an agreement between consumers and utilities. But a transactive energy system has never been deployed on a large scale, and there are a lot of unknowns. That’s why the Department of Energy’s Office of Electricity called upon the transactive energy experts at Pacific Northwest National Laboratory to study how such a system might work in practice. The final multi-volume report was released today.

Hayden Reeve, a PNNL transactive energy expert and technical advisor, led a team of engineers, economists and programmers who designed and executed the study.

“Because Texas’s grid is quite representative of the nation’s energy system, it not only enabled the modeling and simulation of transactive concepts but provided a reliable extrapolation of the results and potential economic impacts to the broader United States grid and customers,” he said.

The simulation showed that if a transactive energy system were deployed on the Electric Reliability Council of Texas (ERCOT) grid, peak loads would be reduced by 9 to 15 percent. That savings could translate to economic benefits of up to $5 billion annually in Texas alone, or up to $50 billion annually if deployed across the entire continental United States. The savings would equal the annual output of 180 coal-fired power plants nationally.

Cutting the brown out

By now, most people have experienced or witnessed how weather extremes or natural disasters can wreak havoc on our current power distribution systems. That vulnerability is magnified by our reliance on a few centralized power sources and a grid system that sometimes struggles to match supply with demand. Further, decarbonization of the electric grid will mean that more and more power will come from different kinds of renewable energy sources, like wind and solar. So, avoiding sudden spikes or dips—power brown or black outs—becomes paramount.

The study findings indicate that a transactive energy system would reduce daily load swings by 20 to 44 percent. And as more electric vehicles come into use, the study, perhaps counterintuitively, showed that smart vehicle charging stations provide even larger electric peak load reductions because they offer additional flexibility in scheduled charging times and power consumption.

“A smart grid can act as a shock absorber, balancing out mismatches between supply and demand,” Reeve said. “Through our study, we sought to understand just how valuable effective coordination of the electric grid could be to the nation, utilities and customers. Working with commercial building owners and consumers to automatically adjust energy usage represents a practical, win-win step towards the decarbonization of the electrical, building and transportation sectors without compromising the comfort and safety of participating homes and businesses.”

One key component to this strategy is adoption of smart appliances and load controls. These dynamic resources can learn how to consume energy more efficiently, adjusting their use for brief periods to free up electricity for other needs. For example, instead of charging an electric vehicle in the early evening when energy demand and price is high, transactive energy participants would rely on a smart load control to delay charging their vehicle until demand is low and electricity cheaper. This approach not only reduces stress on the existing grid infrastructure, it allows utilities more time to plan for next-generation energy storage and distribution infrastructure that is currently in development.

Transactive Energy: A central component

In a transactive energy system, the power grid, homes, commercial buildings, electric appliances and charging stations are in constant contact. Smart devices receive a forecast of energy prices at various times of day and develop a strategy to meet consumer preferences while reducing cost and overall electricity demand. A local retail market in turn coordinates overall demand with the larger wholesale market. All parties negotiate energy procurement and consumption levels, cost, timing and delivery in a dynamic pricing scheme.

While this concept may seem futuristic, it is quite possible to accomplish and is already being deployed in a demonstration project in the city of Spokane’s Eco-District. Here, the research team is developing and testing a transactive energy coordination scheme and retail marketplace. The approach also includes the use of PNNL-devised transactive software agents .

An undertaking the size of Texas

Texas’s primary power grid (ERCOT) provided the basis for PNNL’s analysis. Researchers created highly detailed models that represented the ERCOT power network, including more than 100 power generation sources and 40 different utilities operating on the transmission system. The analysis also included detailed representations of 60,000 homes and businesses, as well as their energy-consuming appliances. Researchers used the models to conduct multiple simulations under various renewable energy generation scenarios. Each simulation demonstrated how the energy system would react to the addition of differing amounts of intermittent power sources, such as wind and solar. The research team also developed a detailed economic model to understand the yearly cost impacts for operators and customers. Finally, they looked at upfront costs associated with labor and software expenses, as well as the costs for buying and installing smart devices in homes and businesses.

Another important goal of the study included evaluating the impact of a new kind of mediator in the grid economy. This entity, called a distribution system operator, would be required to manage a grid that has multiple energy sources owned and operated by distinct entities, all contributing energy to the grid at different times and amounts. In addition, this distribution system operator would negotiate the transactions with customers that allow flexible load control. The goal would be to support efficient and reliable grid operation. The study confirmed the value of establishing entities, such as a distribution system operator, to manage transactive energy.

Overall, the PNNL research showed clear benefits of reimagining how the electric grid could accommodate a future where clean renewable energy is a much bigger contributor and more of our transportation needs depend on ready access to electricity.

“These findings make a strong case for investment in scaled deployments of transactive energy systems,” said Christopher Irwin, a program manager for the Office of Electricity, Department of Energy, in its Smart Grid standards and interoperability efforts. “As the nation moves towards a zero-carbon future, a more adaptable energy system could help accelerate the broader deployment of electric vehicles, solar energy and the conversion of homes and buildings to clean electricity sources.”

In addition to Reeve, PNNL researchers Steve Widergren, Rob Pratt, Bishnu Bhattarai, Sarmad Hanif, Sadie Bender, Trevor Hardy, Mitch Pelton, Ankit Singhal, Fernando Bereta dos Reis, Ahmad Tbaileh, Matt Oster, Tianzhixi Yin, Laurentiu Marinovici and Sarah Barrows all contributed to the research and writing the final reports. The study was supported by the Department of Energy’s Office of Electricity.

Converting truck fleets to renewable energy is a goal of many fleet operators worldwide. This has also been recognized by HERE, a global navigation software company; the company is a joint subsidiary of German automakers Audi, BMW and Daimler. Intel, Bosch, Continental and the Chinese Tencent Group are also shareholders. HERE supplies cartographic material to logistics groups worldwide, including for route planning for the approximately 800 trucks of the Migros cooperative.

The software tool now acquired by HERE is based on a collaboration between Migros and Empa. As part of its decarbonization strategy, Migros sought scientific support to convert its truck fleet to renewable energy. Migros and Empa then jointly developed software to support the transformation of Migros’ truck fleet to low-CO₂ powertrains. With the help of the software, the use of trucks with alternative and renewable fuels such as hydrogen, electric, biogas and biodiesel can be analyzed in terms of performance, range, payload and costs for individual routes, while at the same time calculating the CO₂ savings to be expected in real terms compared to diesel trucks. Thanks to a link to life cycle assessment databases, synthetic fuels can also be integrated.

Test phase until March 31, 2022

The ISO- and DIN-certified software has already been in use at Migros for several months running under the name “M Opex Tower.” As the HERE Group announced at the CES in Las Vegas at the beginning of January, it will be included in HERE’s software program from now on under the name “CO₂ Insights.” In this way, Migros and Empa know-how will become available to logistics service providers from all over the world. Until March 31, 2022, the software can be used and evaluated free of charge by all HERE customers.

But the story actually began ten years ago. At a scientific conference of the Society of Automotive Engineers (SAE), Christian Bach, head of the Vehicle Propulsion Systems department, presented an Empa study on the efficiency of vehicles. He showed that the energy consumption of vehicles for any given journey can be calculated using a simple mathematical function. The underlying mathematical approach is known as the Willans approximation and is still used worldwide in many studies in the field of energy converters. It is named after its inventor Peter Willans from England, who presented his observations on steam engines in this form in the late 19th century. Researchers at Empa had used the approach to evaluate vehicle consumption data, demonstrating that it could be applied not only to internal combustion engines or electric motors, but also to complete vehicles.

From the steam engine to the electric car

Since then, Empa has used this approach more and more frequently, for example in the EU’s “eLCAr” project to study the life cycle assessments of electric vehicles, in a doctoral thesis at ETH Zurich for analyses of Switzerland’s entire vehicle fleet, and in a book project with the German Coburg University of Applied Sciences and the car manufacturer Audi in the area of evaluating the real climate impact and total costs of vehicles with different drive systems. As part of the strategic collaboration between Migros and Empa in the area of decarbonization, the idea then arose to use this approach for a software-based fleet transformation of Migros trucks to low-CO₂ powertrains.

“Transforming entire fleets is much more complex than testing individual trucks with alternative powertrains or fuels,” says Bach. The heterogeneity of transportation tasks is high and cannot be mapped with sufficient accuracy using median value models, he says, so each individual trip must be considered individually.

Certified environmental impact

Bach expressly praises the good cooperation with the project partner: “Migros invited the Empa team to internal meetings with the fleet managers, which was enormously important for finding a solution and ultimately led to the joint development of the software tool.”For several months, the software was tested on the Migros truck fleet and validation measurements were carried out on diesel, biogas, electric and hydrogen trucks. Finally, the tool was certified according to the DIN EN 16258 and ISO 14040 standards, as well as by the CO₂ offsetting consultant myclimate.

Migros’ CO₂ reduction targets are very ambitious. Currently, Migros operates eleven hydrogen trucks, 78 biodiesel and biogas trucks and 13 electric trucks. Soon, there are to be even more.

Two teams of researchers from Pacific Northwest National Laboratory (PNNL) have shown that wind energy offers logistical, economic, and environmental value to consumers and utilities from the coast of Oregon to remote villages in Alaska.

In the first study of the grid impacts of offshore wind energy in Oregon, a PNNL team paired offshore wind resource potential from the Oregon coastline with other variable renewable energy sources, including land-based wind and solar. The study helped the team understand how offshore wind could serve electricity demand within Oregon’s transmission network and across the Pacific Northwest.

In the second study, a PNNL team analyzed the value of distributed wind—wind turbines installed near where their energy is consumed, such as for homes, businesses, and communities—for the small, remote community of St. Mary’s, Alaska. The study’s results could help inform utilities of the economic feasibility for installing wind in similar isolated microgrid systems in other remote villages. Additionally, the study revealed potential economic and environmental benefits for the village’s electricity consumers.

Both studies, which were published in the journal Energies, illustrate PNNL’s growing expertise in assessing the value that renewable energy brings for bolstering the grid.

Wind energy off the Oregon Coast

The rugged winds off Oregon’s coastline are some of the strongest in the nation, holding the potential for producing over 84 megawatts of power—enough to supply a significant portion of that state’s power.

In 2021, the Biden Administration announced a national goal for deploying 30 gigawatts of offshore wind by 2030.

The state of Oregon has also instituted new clean energy policies, including the governor-issued Executive Order 20-04 to reduce and regulate greenhouse gas emissions; HB2021, which also requires electricity providers to reduce emissions 100 percent by 2040; and HB3375, which initiates planning for up to 3 gigawatts of floating offshore wind energy in Oregon’s federal waters by 2030.

Adding to the mix is the anticipated retirement of coal plants across the Western Interconnection—which includes Oregon, Washington, California, and more—over the next 20 years. Increases in vehicle and building electrification, as well as climate change—which impacts the seasonality of hydropower, a prevalent power source in the Pacific Northwest—round out the opportunities for offshore wind.

In this study, the team used a PNNL-developed valuation framework—a method for assessing the value of offshore wind. The framework was made up of a combination of historical wind attributes, a compatibility comparison of other variable renewable resources in the region, and electricity production cost models to create simulations for dispatching electricity generation resources across the region.

“Our study of coastal and regional electricity transmission flows showed that not only could offshore wind increase the reliability of electricity delivery to Oregon’s coastal communities, but deploying offshore wind opens up transmission capacity that could serve load centers throughout the Willamette Valley in western Oregon,” said Travis Douville, the PNNL renewable energy researcher who led the study.

This strategy could allow the existing electricity transmission corridor to provide additional generation from areas equipped with strong renewable energy resources, such as wind energy in the Columbia Gorge and southeastern Washington, Wyoming, Montana, or southeastern Oregon.

The team also discovered that offshore wind naturally matches hourly electricity load trends in Oregon better than land-based wind across each of the four seasons independently. It also complements land-based wind generated in the Columbia Gorge and southeastern Washington, primarily in the summer and also in the spring.

“We found that the Gorge wind could rely in part on offshore wind and less on hydropower for helping balance the electricity load on the grid,” said Douville. “This may be especially beneficial in the late summer months when river flows are at their lowest.”

Offshore wind was also shown to complement Oregon solar resources in the winter months, when electricity loads rise due to heating.

However, “Of all the variable energy resources and across all seasons, we found that the strongest complementary relationship among variable renewable energy resources is in the summer months between offshore wind and land-based wind,” said Douville.

The study was funded by the Bureau of Ocean Energy Management.

A new study, funded by the National Offshore Wind Research and Development Consortium and the Bureau of Ocean Energy Management, is focusing on understanding the clean energy, capacity, and resilience value of offshore wind in southern Oregon and northern California, as well as assessing operational impacts to system reliability and resilience.

Distributed wind in microgrids for resilient power

The remote village of St. Mary’s, Alaska, houses a population of nearly 700 people. The village is located in western Alaska along the Andreafsky River near the junction of the Yukon River.

One source of electricity to this tiny community is diesel, which is costly to deliver to remote villages like St. Mary’s. Additionally, delivery schedules can often be impacted by weather or other hazards.

The diesel power plant serves not only St. Mary’s, but two other remote communities—Pitka’s Point and Mountain Village. The three remote village microgrids, while jointly connected, are isolated from any outside transmission system. In nearby Pitka’s Point, a 900-kilowatt standalone wind energy turbine is connected to the St. Mary’s microgrid and bolsters electricity to all three villages. This type of wind power is a source of distributed wind.

The diesel power plant and wind turbine are owned and operated by Alaska Village Electric Cooperative (AVEC).

The team’s non-proprietary distributed wind valuation framework used for the analysis includes multiple stakeholder perspectives to evaluate the benefits and costs of the distributed wind to AVEC and village residents. The methodology also includes qualitative assessments of difficult-to-quantify benefits and costs, such as resilience and viewshed impacts.

“We found that the largest benefit to AVEC is the avoided cost of diesel, which translates to $5.3 million in savings over the lifetime of the turbine,” said Sarah Barrows, the PNNL economist who led the study.

The team also found that the overall largest value stream is the economic benefits to the state of Alaska, from construction and operations and maintenance of the turbines over the lifetime of the distributed wind project—at an estimated $8 million.

Another significant benefit is the avoidance of carbon dioxide emissions, which are a “side effect” of diesel generator use, at a value of $2 million.

“We didn’t include the value of other avoided pollutants in this study,” said Barrows. “So, there is likely additional value that is unaccounted for.”

However, Barrows pointed out, “We found that incentives, awards, and subsidies can help reduce high upfront costs that electric cooperatives like AVEC may not be able to overcome. Public funding appears to help the benefits outweigh the costs, with societal benefits totaling $9.8 million compared to the $5.4 million in federal and state awards that helped fund the St. Mary’s project.”

Future distributed wind valuation work could expand on other aspects, such as resilience; environmental justice impacts of distributed wind systems; and economics of potential hybrid systems using wind, solar, and energy storage.

Perovskite semiconductor solar cells are a very exciting photovoltaic technology possessing similar efficiencies to silicon but cast or printed in thin films via liquid inks. A new method that uses a simple sheet of paper to deposit the perovskite films without any expensive equipment has been developed by a team from Tor Vergata University and University of Zanjan. The trick to achieve high performance with this remarkably cheap method is to soak the paper applicator in anti-solvent which almost doubles efficiencies compared to when using it dry, reaching 11% on flexible plastic substrates. Paper, compared to other soft applicators, possesses the right porosity and smoothness for deposition of high quality perovskite films.

Perovskite semiconductor solar cells are a very exciting photovoltaic technology because they possess similar power conversion efficiencies to those based on conventional silicon but can be cast in thin films via precursor inks providing benefits in manufacturing. Most perovskite films in laboratories around the world are deposited through spin coating which guarantees high control of film thickness as well as morphology. However, most of the ink is expelled during deposition and is wasted. There have been efforts to develop coating techniques for deposition over large areas. The most efficient solar cells fabricated via spin coating involve adding drops of anti-solvent (i.e., a liquid with differing properties to those used in the perovskite precursor inks) during spinning which improves the morphological quality of the perovskite semiconductor films. This method is very difficult to implement when employing large area coating techniques, however, where the careful engineering of the drying processes involve heaters or gas flows to control the morphology of the perovskite film.

An international team of researchers from Italy and Iran has published a completely new method that uses a simple sheet of paper to deposit the perovskite films without a spin coater or other large area techniques such as slot-die coating or blade coating. Results of their project have been published in iScience, the open access interdisciplinary journal from Cell Press, highlighting the recipes that are required to achieve efficient solar cells with this method.

“When I joined CHOSE labs in Rome for my internship, I serendipitously noticed that leaving a piece of cleaning paper soaked in solvent over a wet perovskite precursor film, it turned brown turning into what looked like a rather promising perovskite semiconductor film. My supervisor in Rome, Prof. Brown, suggested I developed a coating method based on this discovery during my time there” described Nazila Zarabinia, first author of the work. “We worked on trying different soft applicators: the one that work best was paper possessing the most beneficial properties of porosity and smoothness” she added. The highest efficiency of a flexible cell fabricated with this Deposition via Anti-Solvent-Soaked Applicator method (termed DASSA) was 11%. The researchers believe this is a satisfying efficiency, particularly for flexible solar cells on plastic PET substrates, and utilizing a completely manual procedure. The corresponding efficiency achieved with spin coating devices with the anti-solvent method was 14.9 % so there is scope for further improvement. In the manuscript, the authors propose an automated procedure for further future optimization.

“We think this simple method will appeal to all those labs setting up a line in perovskite research who have not been able (for money or time) to buy expensive deposition equipment (a bit like manual blade coating of titania films which was widely used to enter the field in the days of dye sensitized solar cells) since it enables the deposition of the perovskite film incredibly cheaply. It can also be of particular interest to groups developing automated printing techniques by applying the anti-solvent, not on the perovskite film as usual, but on the applicator instead. Furthermore, it will be interesting to endeavor to extend this method also to the transport layers for full cell manufacturing,” commented Thomas M. Brown, corresponding author of the work.

The researchers show that soaking the paper used as an applicator in an anti-solvent increases the power conversion efficiency of solar cells by 82% compared to the solar cells where the application of the perovskite film was carried out with a sheet of dry paper.