Green Energy

Researchers at Oak Ridge National Laboratory recently demonstrated a new technology to better control how power flows to and from commercial buildings equipped with solar, wind or other renewable energy generation. “We are creating an electric grid of the future that allows renewable energy to be deployed in the most effective way,” said ORNL’s Madhu Chinthavali, who leads the research. “With this new grid interface architecture, operators can control energy flows much more meaningfully, even when power generation is decentralized.” Renewable energy is key to helping the U.S. electricity sector achieve national decarbonization goals. But they also add uncertainty to the electrical grid because they are unevenly available across the country and generate electricity intermittently. Developing and coordinating power electronic systems to incorporate these resources more easily is vital to creating a more resilient grid for reliable electricity. Chinthavali’s research team designed a hybrid AC/DC power electronics hub to act as a gatekeeper between the larger grid and subsystems including renewables, generators and battery storage. The technology was developed and tested in the Department of Energy’s Grid Research Integration and Deployment Center, or GRID-C, at ORNL. GRID-C offers a unique platform for building power electronics systems, starting with the smallest component, then testing and demonstrating full systems that incorporate both hardware and simulation. In the low-voltage lab, rows of metal containers house ORNL-developed power electronic converters, trailing cords thicker than a wrist and ending in plugs as wide as a plate. These converters provide different levels of power to electrical feeds based on different scenarios. They are paired with equally large power emulators that can mimic energy delivered by a solar array or a battery system. Huge touchscreens allow engineers to rearrange the system and tweak its operation. ORNL engineers designed the power electronics hub to control how the converters interact with each other and the grid. Emulators are set up to mimic the electrical draw and generation of a solar array, a storage battery, an emergency generator and a critical data center with high electrical demand. The power electronics hub was programmed to autonomously manage the power flow of all these electrical loads, helping prevent fluctuations in supply and demand on the wider electrical grid. The power electronics hub plays the role of a middle manager between the larger electric grid and the local power electronics. “Instead of the utility talking to, say, a million resources, this technology reduces that number by a factor of 10,” said ORNL’s Michael Starke, lead software architect for the project. “From a utility’s point of view, all the equipment managed by the power electronics hub functions as a single system.” This is an advantage for power companies faced with incorporating distributed and intermittent energy from solar, wind, geothermal and other renewable sources into a century-old grid that was designed to push steady flows of energy out from centralized power plants. Similar concepts have been tested by some utilities, but these approaches use a single vendor’s proprietary products in a prescribed way, Starke said. Because ORNL constructed the power electronic converters and many of the components, the resulting technology is openly available and can be customized to achieve specific goals. For example, experiments by Chinthavali’s team have shown the power electronics hub can prioritize providing the most cost savings to customer-owned systems or providing a consistent supply of power for utility systems. ORNL researchers demonstrated that these objectives can be integrated directly into the hardware and software, and they have also developed the supporting communication and control infrastructure. “It starts with pretesting and pre-automating systems that can be easily scaled up and deployed quickly,” said Chinthavali, adding that the project has led to three patent applications. “We’re trying to standardize systems so they are interoperable.” Moving beyond modeling to demonstrating the technology in wired hardware was a milestone that was only possible because of ORNL’s capabilities in GRID-C. “This is the only place where we could develop both the software and hardware to fully prepare to deploy this technology to industry,” Chinthavali said. Several industries could see significant benefits. The technology could be used by a builder or building owner to save money and energy, or it could be installed by a utility for enhanced power control and reliability. The team is moving to the next step in the research: substituting higher-power, commercial converters secured directly from industry. This will demonstrate that the power electronics hub can manage the megawatts of power handled by electric utilities using components from commercial suppliers. The ORNL team that developed the power electronics hub includes Steven Campbell, lead architect for systems integration; Ben Dean, communication interface developer; Jonathan Harter, hardware systems specialist; and Rafal Wojda, magnetic systems specialist. “We’re now working on how to extend these power electronics hubs from small scale to thousands working together, coordinating to deliver energy as needed from all sorts of different angles and different sources,” Starke said. “We’re trying to show that the power electronics hub can act like a battery almost, pushing power in and out under our control. That provides all kinds of flexibility to the grid that wasn’t there before.” The power electronics hub is an example of the type of technology developed in GRID-C that could be deployed with a potential consortium of partners. ORNL held an interest meeting today with stakeholders from industry, utilities and research institutions to discuss power electronics challenges and strategies. Participants discussed a possible framework for an organization to accelerate development and deployment of power electronics systems for managing the electric grid of the future.

The 100 MW Dalian Flow Battery Energy Storage Peak-shaving Power Station, with the largest power and capacity in the world so far, was connected to the grid in Dalian, China, on September 29, and it will be put into operation in mid-October.

This energy storage project is supported technically by Prof. Li Xianfeng’s group from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences. And the system was built and integrated by Rongke Power Co. Ltd.

The Dalian Flow Battery Energy Storage Peak-shaving Power Station was approved by the Chinese National Energy Administration in April 2016. As the first national, large-scale chemical energy storage demonstration project approved, it will eventually produce 200 megawatts (MW)/800 megawatt-hours (MWh) of electricity.

The first phase of the on-grid power station project is 100 MW/400 MWh. Based on China’s average daily life electricity consumption of 2 kWh per capita, the power station can meet the daily electricity demand of 200,000 residents, thus reducing the pressure on the power supply during peak periods and improving power supply reliability in the southern region of Dalian.

Energy storage technology can help power systems achieve the strain and response capability needed after large-scale access to the power grid. It is also particularly important in facilitating the use of renewable energy, which is key to helping China achieve its carbon peak and carbon neutrality goals but is not always accessible due to variations in wind and sunlight, etc.

The Dalian Flow Battery Energy Storage Peak-shaving Power Station, which is based on vanadium flow battery energy storage technology developed by DICP, will serve as the city’s “power bank” and play the role of “peak cutting and valley filling” across the power system, thus helping Dalian make use of renewable energy, such as wind and solar energy.

These renewable energy sources will be used to charge the station’s batteries during the grid load valley period by converting electrical energy into battery-stored chemical energy. Later, at peak grid load, the stored chemical energy will be converted back into electrical energy and transmitted to users.

The station’s energy storage technology uses vanadium ions of various valence states. Electrical energy and chemical energy are converted back and forth through redox reactions of these ions in the positive and negative electrolytes, thus realizing large-scale storage and the release of electrical energy.

This technology is promising in large-scale energy storage applications because of its excellent safety, good reliability, large output power and storage capacity, long life, good cost-performance, use of recyclable electrolytes, and environmental friendliness.

Additionally, this technology can work with conventional thermal power, nuclear power, and other power sources, providing peak regulation and frequency regulation for the power system as well as improving its flexibility.

The Dalian Flow Battery Energy Storage Peak-shaving Power Station will improve the renewable energy grid connection ratio, balance the stability of the power grid, and improve the reliability of the power grid, thus serving as a model for electricity peak-shaving and renewable energy grid management in China.

Researchers have devised a method to determine the impact of climate change on the supply and variability of local renewable energy.

An increase in unusual weather patterns related to climate change means the demand for power and the availability of solar, hydro and wind energy can all become more variable.

The method by researchers at the University of Alaska Fairbanks Geophysical Institute and in Spain will help local energy planners determine the optimal mix of renewable energy sources and energy storage needs.

The research was published in August in the journal Land. Geophysical Institute atmospheric sciences professor Uma Bhatt is the lead author.

“It is important for society to understand the impact of climate change and variability on renewable energy resources in order to design a resilient power system and prepare for the future,” Bhatt said.

The researchers studied intermittency, power production and energy storage in the context of historical climate data at two locations: the Alaska city of Cordova in Prince William Sound, which has a subpolar oceanic climate, and Palma de Mallorca, a city on a subtropical Spanish island. The researchers obtained 60 years of climate data for each location.

Wind, solar and hydropower are all susceptible to a climate that is becoming less predictable and producing more extreme weather events. Increased cloud cover could decrease the availability of solar power. Decreased precipitation could reduce the availability of hydropower. Increased winds could increase the availability of wind power.

Without proper planning, power grids risk becoming less reliable as renewables make up an increasingly larger portion of the supply.

“If you have too high a percentage of high-variability renewable power without appropriate backup power in your system, it actually degrades the system’s reliability a lot,” said David Newman, a study co-author and physics professor at the UAF Geophysical Institute.

Further complicating the situation, the demand for power changes in unpredictable ways as the weather becomes increasingly variable. Even when demand is normal, a sudden drop in the availability of a renewable source—wind ceasing to turn the turbines, for example—can cause blackouts if a backup source is not in place for immediate use.

“How do you fix it? You have to find a way to remove the variability or to have a way to quickly compensate for it,” Newman said.

The easiest and most obvious way is to have fossil fuel-based generators on standby. Of those, generators powered by natural gas can be started fairly quickly when needed. But it’s still a fossil fuel product, though cleaner than other fossil fuel sources.

Another, cleaner method is to store excess energy produced by renewable sources during times of normal demand.

Advances in technology have improved grid-scale batteries, which can store excess power that can be distributed for short-term use during a widespread blackout.

Other storage methods include pumped storage hydropower, gravity energy storage, flywheel energy storage and compressed air energy storage. All are fundamentally simple methods and explained by the National Renewable Energy Laboratory.

“This is one of the really exciting areas [of study] right now,” Newman said.

Pumped storage hydropower accounts for 95% of all utility-scale energy storage capacity in the United States. Water is pumped from one hydropower reservoir to another at a higher elevation during times of excess power, raising the level of the higher reservoir. That water is released to the generators of the lower reservoir when needed.

Gravity energy storage involves using excess energy to raise massive weights consisting of sand, gravel or rock and leaving the weights suspended. When power is needed, the weights are allowed to fall, with their attached cables turning a generator.

Flywheel energy storage is typically used in small applications and for much shorter energy needs than other storage methods. A motor powers a flywheel, a heavy wheel that spins freely when the motor loses power. The freely spinning wheel turns a generator, which produces electricity for several minutes.

Compressed air energy storage can provide power on a grid-scale for several days. Electricity is used to compress and store air underground, often in salt caverns. When needed, the air is released and heated to expansion to power a generator.

The research papers’ authors offer a notable caveat to their work: Climate change is complicated and varies by location, as do the available sources of renewable energy.

“Both climate and energy are interconnected complex systems, and it is important that we educate the next generation to think across disciplines so they are prepared to address the complex problems that are looming,” Bhatt said.

Large obstacles, like clouds and buildings, can block sunlight from reaching solar cells, but smaller sources, such as dust and leaves, can also create similar problems. Understanding how the loss of incoming radiation affects power output is essential for optimizing photovoltaic technology, which converts light into electricity and is an important contributor to the green energy transition. In the Journal of Renewable and Sustainable Energy, researchers from Shanghai Polytechnic University, Shanghai Engineering Research Center of Advanced Thermal Functional Materials, and Shanghai Solar Energy Research Center Co. Ltd explored how different shade conditions impact performance of single solar cells and two-cell systems connected in series and parallel. “In the real world, photovoltaic cells are sometimes shaded by obstacles, which significantly alters the amount of incoming light,” said author Huaqing Xie, of Shanghai Polytechnic University and Shanghai Engineering Research Center of Advanced Thermal Functional Materials. “The degradation effects make power optimization difficult and result in significant power loss.” Photovoltaics connected in series create a single path with the electrons flowing from one cell into the next. In contrast, cells in parallel provide two lanes for electrons to travel through, then recombine later. In practical applications, networks of solar cells are connected in series and parallel to expand the output current and power capability. The team found that the decrease in output current of a single cell or two cells connected in parallel was nearly identical to the ratio of shade to sunlight. However, for two cells running in series, there was excess power loss and a rise in temperature, which can cause further output degradation. For example, with 29.6% of the series photovoltaic module in the shade, the current decreased by 57.6%. “Our study indicates that many factors, including shadow area, shadows on different cells of the module, and the connection of cells and modules, may affect the performance,” said Xie. Previous studies have explored the consequences of shade on large photovoltaic modules but have largely ignored single cells and simple systems. “In these complicated systems, shadows on one single cell may play vital role on the system output and reliability,” said Xie. “Therefore, studying single cells or a simple arrangement of two connected cells is necessary for solar panel development.” In the future, the authors hope to examine the microscopic interaction behaviors and mechanisms in photovoltaic cells subjected to different shadows. The article, “Experimental study on the power losses of a single photovoltaic cells and two series and parallel connected cells with partial shadows,” is authored by Xiaoxue Guo, Jiapu Zou, Zihua Wu, Yuanyuan Wang, and Huaqing Xie. The article will appear in Journal of Renewable and Sustainable Energy on Sept. 27, 2022.

Under the unprecedented current energy crisis, wind targets have been raised by EU member states, sending a clear signal about the vital role that wind will play in achieving energy security goals.

Europe’s future as a leader in renewable energy, and its freedom to make independent energy decisions, is jeopardized by the severity of the current energy crisis. The wind industry can contribute to providing Europe with energy security and independence through domestic, clean and competitive sources, but only if the European governments act swiftly to guarantee it is treated as a strategic industry.

With this in mind, Siemens Gamesa, a pioneer and one of the global leaders in the sector, published its white paper “Europe’s energy sovereignty is in imminent danger: why we need the European wind industry – and how to safeguard it,” today. The white paper highlights how the recent exceptional pressures on the wind industry led to a challenging financial situation, and the steps that can be implemented at a Europe-wide level to mitigate these risks and realize the green energy transition.

While benefits of utility-scale wind energy are well understood, the white paper calls for the sector as a whole to be declared an industry of strategic importance, in order to be able to instigate the technology and capacity necessary to deliver the European Green Deal.

Siemens Gamesa’s CEO Jochen Eickholt comments, “This white paper clearly states the simple safeguards that the wind industry requires from regulators to deliver European energy security and timely energy transition. Without intervention and cooperation among governments, manufacturers and suppliers, the energy transition here in Europe will become unattainable and Europe will lose its position as a global leader in the wind industry. The implications for European countries, and the rest of the world, are obvious. We urge regulators to take on board the five imperatives detailed in this white paper, and to work with us to deliver them. Without these safeguards, Europe’s energy independence is impossible.”

Why Europe’s wind industry needs support and why it’s crucial to safeguard it

European wind turbine manufacturers currently create the most advanced wind turbines for use both on land and at sea. The industry also plays a leading role within the green hydrogen production value chain, which will be crucial in the future for creating both sustainable industries and energy supplies for households. The industry not only serves the domestic market, it also creates new opportunities abroad.

However, the sector’s ability to produce profitably is currently threatened by auctions solely driven by price, slow permitting and, ultimately, soaring prices for energy, commodities and transport. On top of that, the pandemic resulted in a scarcity of key components for wind turbines, and Russia’s war of aggression against Ukraine worsened supply chain issues. As a result, wind turbine manufacturers are operating at massive losses and cannot invest to satisfy growing demands for wind energy.

The white paper also highlights the exceptional pressures the wind industry has faced in recent years, and what can be implemented at a Europe-wide level to mitigate these and deliver the green energy transition:

1. Turn targets into real opportunities and provide market visibility by accelerating the approval of wind power plant permits and establishing a visible project-pipeline for manufacturers and suppliers to load existing factories, and plan for new capacities.

2. Manage price risks and stabilize supply chains while compensating for inflation rises.

3. Support domestic innovation and foster technology competence. Energy security cannot be achieved through auctions solely based on price. Governments must get qualitative, not just quantitative, criteria correct in auctions.

4. Establish a level playing field across Europe to protect the European wind industry over the long term. This can be done through trade and/or fiscal policy instruments that would offset subsidies from other countries or through strict requirements in pre-qualification and participation conditions for tenders.

5. Consider the wind industry to be of strategic importance and invest today to secure its stability well into the future. 

The white paper is clear throughout that, while none of these measures are unfeasible, coordinated action on an EU, international, national and regional basis will be required. Successful implementation will deliver clean energy, GDP growth, a continuation of technological leadership within Europe and long-term employment for hundreds of thousands of European citizens.

It also warns that, while there is little time left to initiate the necessary steps, this opportunity is not yet lost and that, with decisive leadership and swift action, the tipping point may yet be avoided.