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When a pinch is problematic: Detecting pertechnetate in groundwater

pertechnetate

A PNNL researcher holds a redox sensor in the project’s lab in the Radiochemical Processing Laboratory.  Andrea Starr | PNNL

PNNL develops an effective tool for measuring a tricky contaminant

March 30, 2020
March 30, 2020
Highlight

Imagine trying to detect and measure a pinch of salt in an Olympic-size swimming pool. Now pretend the tools you are using don’t work well. Some can detect the salt but can’t tell you how much is in there, and others confuse salt with chlorine.

Now swap the swimming pool for a source of groundwater and the salt for a radioactive contaminant called pertechnetate.

ACS Journal Pertechnetate
The future of groundwater contamination measurement? The large thiol claws of PNNL’s subsurface probe with custom gold tips detect and measure pertechnetate in aqueous environments. Cover illustration by Rose Perry, PNNL

Pertechnetate is a byproduct of nuclear waste. If it ends up where it is not supposed to be—like, in groundwater—it could impact human health, which is why researchers and regulators keep a close lookout for it. The environmental safety limits for pertechnetate are roughly equivalent to a pinch of salt in an Olympic pool. And there are only a few technologies to measure it, each with limitations.

PNNL research tackles this challenge with new technology to detect and accurately measure pertechnetate at super low levels in groundwater. This research, “Redox-Based Electrochemical Affinity Sensor for Detection of Aqueous Pertechnetate Anion,” was the cover article for the March 2020 edition of ACS Sensors (DOI: 10.1021/acssensors.9b01531). 

Why it matters: The Environmental Protection Agency drinking water standard for pertechnetate is 0.000000052 grams per liter (that’s roughly 1/6000th the weight of a single poppy seed). While techniques exist for detection of pertechnetate in the environment, many have their drawbacks. PNNL’s technology can accurately measure low levels of pertechnetate in groundwater. Additionally, this proof of concept has the potential to be applied to other target contaminants simultaneously, increasing efficiency for environmental sensing.

Summary: The new technology acts like a coin counter, but at a microscopic level. It sorts one type of chemical from another, providing the total amount of a target chemical at the end. The tool uses custom probes with a gold electrode that only allows the target groundwater contaminants to stick while the other chemicals bounce off.

Sulfur likes to bind to gold and it also tends to react with pertechnetate, making sulfur-containing compounds an ideal intermediate in tool development. The sulfur sticks to the gold probe, then reacts with the pertechnetate, which forms a precipitate. The precipitate inhibits an electric current pulsing through the probe, providing an inverse measurement of pertechnetate concentration.

What’s Next: While this work was specifically focused on pertechnetate, there is potential to expand the technology to simultaneous multiple targets with the goal of increasing the efficiency of environmental measurements.

Sponsors: This research was funded by the Laboratory Directed Research and Development program at PNNL and by the Deep Vadose Zone program under the U.S. Department of Energy’s (DOE’s) Office of Environmental Management. Part of this research was performed at the Environmental Molecular Sciences Laboratory, a national user facility at PNNL managed by the DOE Office of Biological and Environmental Research.

PNNL Research Team: Sayandev Chatterjee, Meghan S. Fujimoto, Yingge Du, Gabriel B. Hall, Nabajit Lahiri, Eric D. Walter, Libor Kovarik. ACS Sensors cover illustration by Rose Perry, PNNL.

 

March 27, 2020
MARCH 12, 2020
Web Feature

Tracking Toxics in the Salish Sea

With the help of a diagnostic tool called the Salish Sea Model, researchers found that toxic contaminant hotspots in the Puget Sound are tied to localized lack of water circulation and cumulative effects from multiple sources.

PNNL Launches Marine Renewable Energy Database

Logo of Tethys Engineering

PNNL created an online database to share information related to the marine renewable energy industry.

Tethys Engineering addresses industry’s technical and engineering challenges

November 18, 2019
November 18, 2019
Highlight

Marine renewable energy (MRE) has the potential to provide 90 gigawatts of power in the United States through waves and tidal and ocean currents.

To harness the ocean’s energy, the MRE industry needs to understand how to address technical and engineering challenges such as efficient power takeoff, device survivability, and grid integration.

PNNL developed Tethys Engineering in September 2019 to allow sharing resources around the deployment of devices in corrosive, high-energy marine environments. The recently launched Tethys Engineering online database includes collected and curated documents surrounding the technical and engineering development of MRE devices. Users can search and filter results to intuitively identify information relevant to developers, researchers, and regulators.

Tethys Engineering includes more than 3,000 journal articles, conference papers, reports, and presentations related to wave, current, salinity gradient, and ocean thermal energy conversion technologies. The database contains information from around the world.

The Tethys Engineering database was created as a companion to the already established Tethys website, which focuses on the environmental effects of the MRE industry.

November 18, 2019

Understanding the Grid Value Proposition of Marine Energy: A Literature Review

July 1, 2019
November 1, 2019
Report

Summary 

In 2018, the US Department of Energy’s Water Power Technologies Office Marine Hydrokinetics Program directed two national laboratories, Pacific Northwest National Laboratory and National Renewable Energy Laboratory, to investigate the potential of marine renewable resources to contribute the U.S. electric system. Due to the innovative nature of marine renewable energy and the transformation of the US electric system resource mix, there is a lack of insight about the future potential role and grid value proposition of marine energy.

An initial step in this technical project is to review available literature to inform and help characterize the portfolio of potential marine energy resource contributions. This literature review summarizes the energy fundamentals of marine resources; the performance and operational characteristics of energy conversion devices; grid opportunities and integration challenges most applicable to marine energy; storage coupling to achieve grid opportunities; and offshore wind energy competition and collaboration. It provides the context and the state of knowledge in which the grid value proposition of marine energy should be further researched and explored.

Notable findings from the review include the following:

  • Very little work has been conducted to connect the grid and fundamental marine energy development. Few technical papers attempt to demonstrate grid value from marine energy or, conversely, illustrate how grid applications may have an effect on device size and scale, convergence of device types, and location of marine energy technologies. Those that have done so relied on numerous estimations and assumptions and target very specific potential benefits.
  • Aggregation of tidal generation for baseload—the concept of distributing tidal generators to accomplish complementary phase shifts in generation that, when summed, would provide relatively stable power—faces challenges from a cost perspective. One study evaluated three geographically separate, complementary locations off the Scottish coast. The study concluded that aggregate power generated from sites with varying resources is sensitive to the characteristics of the individual sites and some irregularity should be expected in aggregate power output due to natural variation in successive tides. Ultimately, the study suggests that using complementary sites and limiting the capacity of the turbines, particularly during neap tides, could create baseload power, or a constant power output; but the research team expressed concerns regarding whether such a deployment would be cost effective. Decreasing the turbines’ rated capacity and therefore not capturing the resource to its fullest extent would cause economic losses.
  • Tidal energy-generating profiles may be well matched for storage. Energy storage is a fast-growing resource in the energy industry. It can provide value in a multitude of grid situations, including supporting marine energy technologies. One report suggests that because tides are predictable, tidal technologies are ideal for pairing with energy storage to create a steady output of power. In fact, Nova Innovation recently integrated a Tesla battery storage system with the Shetland Tidal Array in Scotland and expanded the generating capacity and enabled dispatchability at the site.
  • There is a potential match between resource peak and electric demand. When considering a seasonally peaking resource, like wave energy, there is an opportunity for the generation patterns to be well matched with energy demand. For example, one study noted that British Columbia’s energy consumption peaks in the winter when the available wave resource is also at its strongest; this same characteristic is true along the rest of North America’s Pacific Northwest coast.
  • Co-location may deliver grid benefits. A study evaluating a portion of the North Sea showed that there could be significant benefits to co-locating wave devices and offshore wind turbines. When wind and waves are negatively correlated, this decreases variability and can help mitigate grid integration concerns that are sometimes associated with variable generation. Being proactive in the siting process and performing quantitative spatial planning can avoid potential conflicts between sea uses, while harnessing the most useful energy.
  • The availability and cost of land was used in utility decision-making for resource selection and resulted in a portfolio selection that included marine energy development. In a 2017 Integrated Resource Plan for the Caribbean Utilities Company (the public electric utility for Grand Cayman in the Grand Cayman Islands), a contractor evaluated land use associated with different generation technologies and found a significant advantage to using marine energy, specifically ocean thermal energy conversion (OTEC). Accordingly, and despite a higher capital cost for OTEC relative to other resource options, the resource plan containing OTEC was among the two recommended portfolios. In the portfolio, OTEC resources replaced onshore solar development, which requires a relatively high land commitment proportional to total generation, as well as natural gas-fired backup generation and battery storage. Although OTEC is not considered in this report, connections can be drawn to the technology, and research from that field is applicable to other marine energy resources in particular instances.

As the marine energy industry grows, there is a corresponding increase in the body of literature about both the potential value of harnessing marine resources as well as the requisite technical work to integrate the resource into the grid. Due to the unique aspects of marine energy resources, especially their offshore location, volume, and predictability, there are many reasons to consider marine energy a viable potential renewable resource in the future electric system.

July 1, 2019

Understanding the Grid Value Proposition of Marine Energy: An Analytical Approach

September 2, 2019
November 1, 2019
Report

Summary

The US Department of Energy’s Water Power Technologies Office (WPTO) has tasked two national laboratories, Pacific Northwest National Laboratory (PNNL) and National Renewable Energy Laboratory (NREL), to develop an understanding of the grid value proposition for marine renewable energy (MRE): how harnessing the energy of waves, tides, and ocean currents could be a meaningful and competitive source of renewable energy in the future grid.

This work will provide insights to the conditions under which MRE technologies offer unique benefits for the electricity system. PNNL and NREL will conduct a project to comprehensively review the grid value for marine renewable energy development at scale on an intermediate- to long-term horizon. The project will dovetail with nationally-accelerating valuation efforts to characterize and quantify specific services from energy resources and assess the value of those services over time. It will capitalize on the emerging concept of locational value, especially for distributed energy resources (DER), referencing adopted frameworks and related laboratory analysis. And it will take advantage of laboratory expertise in a variety of disciplines – ocean physics, mechanical and electrical engineering, energy economics – chained together in order to ensure that benefits and services assessed are realistic for MRE technologies and ocean energy resources.

The purpose of the immediate analytical approach is to outline the landscape of MRE attributes and their potential value and, at a high-level, discuss methods to quantify these values. For purposes of this investigation, the words grid value should be broadly construed. The term is meant to include, but not be limited to, provision of a defined grid service, measurable benefit to grid performance, avoided costs to system investments or operations, revenue capture, and contribution to desired grid qualities (e.g. reliability or low carbon intensity). Value can also accrue to a range of entities.

The authors intend to consider use cases and system benefits where MRE may have a competitive or unique role; and where there is a distinct and measurable value additional to energy production. To do this, the authors look beyond the typical values of energy production (a payment of cents per kilowatt-hour produced) and instead to “grid services,” those services required for the grid to operate and deliver energy to customers (i.e. unit scheduling and dispatch, reactive power and voltage control, and frequency control). Certain grid services are captured in the traditional suite of ancillary services that may be directly compensated in an organized market, and as a result many of these benefits already have highly competitive contributing generators or other electricity system assets. Therefore, in this initial exercise of considering competitive and unique benefits, the authors are less concerned with the energy (or grid service) production itself but the timing, the location, or the system condition that form measurable and distinct value.

September 2, 2019
OCTOBER 31, 2019
Web Feature

The World’s Energy Storage Powerhouse

Pumped-storage hydropower offers the most cost-effective storage option for shifting large volumes of energy. A PNNL-led team wrote a report comparing cost and performance factors for 10 storage technologies.