Tidal-power research under way

By Knight Ridder Tribune


Protective Relay Training - Basic

Our customized live online or in‑person group training can be delivered to your staff at your location.

  • Live Online
  • 12 hours Instructor-led
  • Group Training Available
Regular Price:
$699
Coupon Price:
$599
Reserve Your Seat Today
Researchers will have to wait several weeks before they can adequately begin studying tidal information in Puget Sound.

The Snohomish County Public Utility District and the University of Washington are waiting for results from ongoing acoustic Doppler testing at Admiralty Inlet and Deception Pass. The PUD is considering how well each site might perform as a tidal-power location, while the UW hopes to use the information to continue mapping tidal flows throughout Puget Sound.

About two weeks ago, the two began collecting data, and it won't be until mid-September that enough information has been collected to start giving them a sense of how the waters move through both areas. Admiralty Inlet, about three miles wide, could be the PUD's best option for a tidal-power plant, says Craig Collar, the PUD's senior manager of energy-resource development.

But fast currents at Deception Pass make it too good not to study, despite other problems at the location, he said. "We're looking for strong, predictable tidal currents," Collar said. "Deception Pass, while having the highest current in Puget Sound, could be too turbulent."

Plus, environmental and aesthetic concerns would force the PUD to reconcile with several parties, including the state of Washington, before any tidal plant would be built at the state park. The PUD is counting on adding tidal power to its array of energy production in light of Initiative 937, which requires a mix of conservation measures and renewable-energy sources to make up a utility's energy base.

Under the initiative, utilities serving more than 25,000 customers - the PUD has more than 300,000 - need to get at least 15 percent of their energy from renewable resources, not including hydropower, by 2020. The PUD also needs to meet new energy needs associated with continued growth in Snohomish County.

"We estimate we'll need to add 140 average megawatts by 2020," Collar said. That's enough power for about 100,000 more homes. The seven sites scheduled for tidal-power testing could produce about 100 megawatts, according to the PUD's federal permit applications. The acoustic Doppler tests are the first completed to see how useful a location might be in providing enough wave energy to turn underwater propellers attached to turbines.

The PUD will do one round of testing this year at Admiralty Inlet and Deception Pass, then test five more sites sometime next year. Those sites are at Speiden Channel and San Juan Channel off San Juan Island, Guemes Channel near Anacortes, and Agate Passage and Rich Passage along Bainbridge Island. The first Doppler testing was done by boat and measured how tidal currents bounce off the shoreline at each site. Now, stationary devices have been placed in the water to measure currents over the course of a month. It's this long-term data that interests UW researchers as they develop a model of tidal currents throughout Puget Sound.

"Anytime you're modeling something as complex as Puget Sound, you like to have measurements to verify that modeling," said Philip Malte, a UW mechanical-engineering professor. "We're getting an initial impression now, and then as we begin to look more deeply at the data we should learn quite a bit quickly."

Ocean currents are continually shifting, so to be successful in its modeling, the UW needs to see how measurements change over time. The stationary tests will measure two tidal cycles. After tidal testing, if sites prove to have potential, the PUD will study the economics of operating tidal-power plants at those locations and begin to look at available technologies and conduct environmental tests.

The field of tidal energy is relatively new in the United States, and much will need to be done to get federal approval for any power plant, Collar said. Any tidal-power plant run by the PUD is still years away, he said.

"These are the Kitty Hawk days for tidal energy," he said, referencing the Wright Brothers' initial airplane flight in 1903. "There are still many questions to be answered."

Related News

Clorox accelerates goal of achieving 100% renewable electricity in the U.S. and Canada to 2021

Clorox Enel 70 MW VPPA accelerates renewable energy, sourcing Texas solar from the Roadrunner project to support 100% renewable electricity, Scope 2 reductions, and grid decarbonization through a virtual power purchase agreement starting in 2021.

 

Key Points

A 12-year virtual power purchase agreement for 70 MW of Texas solar to advance Clorox's 100% renewable electricity goal.

✅ 12-year contract supporting 100% renewable electricity by 2021

✅ Supplies 70 MW from Enel's Roadrunner solar project in Texas

✅ Cuts Scope 2 emissions via grid-delivered virtual PPA

 

The Clorox Company and a wholly owned subsidiary of Enel Green Power North America announced today the signing of a 12-year, 70 megawatt (MW) virtual power purchase agreement (VPPA) for the purchase of renewable energy, aligned with carbon-free electricity investments across the power sector beginning in 2021. Representing about half of Clorox's 100% renewable electricity goal in its operations in the U.S. and Canada, this agreement is expected to help Clorox accelerate achieving its goal in 2021, four years ahead of the company's original plan.

"Climate change and rising greenhouse gas emissions pose a real threat to the health of our planet and ultimately the long-term well-being of people globally. That's why we've taken action for more than 10 years to measure and reduce the carbon footprint of our operations," said Benno Dorer, chair and CEO, The Clorox Company. "Our agreement with Enel helps to expand U.S. renewable energy infrastructure, reflecting our view that companies like Clorox play an important role in addressing global climate change, as landmark policies like the U.S. climate deal further accelerate the transition. We believe this agreement will significantly contribute toward Clorox achieving our goal of 100% renewable electricity in our operations in the U.S. and Canada in 2021, four years earlier than originally planned. Our commitment to climate stewardship is an important pillar of our new IGNITE strategy and part of our overall efforts to drive Good Growth – growth that's profitable, sustainable and responsible."

The 70MW VPPA between Clorox and Enel Green Power North America for the purchase of renewable energy delivered to the electricity grid is for the second phase of Enel's Roadrunner solar project to be built in Texas, and complement global clean energy collaborations such as Canada-Germany hydrogen cooperation announced recently. Roadrunner is a 497-direct current megawatt (MWdc) solar project that is being built in two phases. The first phase, currently under construction, comprises around 252 MWdc and is expected to be completed by the end of 2019, while the remaining 245 MWdc of capacity is expected to be completed by the end of 2020. Once fully operational, the solar plant could generate up to 1.2 terawatt-hours (TWh) of electricity annually, while avoiding an estimated 800,000 metric tons of carbon dioxide emissions per year.

Based on the U.S. Environmental Protection Agency Greenhouse Gas Equivalencies Calculator[i], this VPPA is estimated to avoid approximately 140,000 metric tons of CO2 emissions each year. This is equivalent to the annual impact that 165,000 acres of U.S. forest can have in removing CO2 from the atmosphere, and illustrates why cleaning up Canada's electricity is central to emissions reductions in the power sector, or the carbon impact of the electricity needed to power more than 24,000 U.S. homes annually.

"We are proud to support Clorox on their path towards 100% renewable electricity in its operations in the U.S. and Canada by helping them achieve about half their goal through this agreement," said Georgios Papadimitriou, head of Enel Green Power North America. "This agreement with Clorox reinforces the continued significance of renewable energy as a fundamental part of any company's sustainability strategy."

Schneider Electric Energy & Sustainability Services advised Clorox on this power purchase agreement and, amid heightened investor attention exemplified by the Duke Energy climate report, supported the company in its project selection, analysis, negotiations and deal execution.

 

Clorox Commits to Scope 1, 2 and 3 Science-Based Targets

For more than 10 years, Clorox has consistently achieved its goals to reduce greenhouse gas emissions in its operations. Clorox is focused on setting emissions reduction targets in line with climate science. As a participant in the Science Based Targets Initiative, Clorox has committed to setting and achieving science-based greenhouse gas emissions reduction targets in its operations (Scopes 1 and 2) and across its value chain (Scope 3), and consistent with national pathways such as Canada's net-zero 2050 target pursued by policymakers. The targets are considered "science-based" if they are in line with what the latest climate science says is necessary to meet the goals of the 2015 Paris Agreement – a global environmental accord to address climate change and its negative impacts.

Clorox's climate stewardship goals are part of its new integrated corporate strategy called IGNITE, which includes several other environmental, social and governance (ESG) goals and reflects lessons from Canada's electricity progress in scaling clean power. More comprehensive information about Clorox's IGNITE ESG goals can be found here. Information on Clorox's 2020 ESG strategy can be found in its fiscal year 2019 annual report.

 

Related News

View more

Scientists generate 'electricity from thin air.' Humidity could be a boundless source of energy.

Air Humidity Energy Harvesting converts thin air into clean electricity using air-gen devices with nanopores, delivering continuous renewable energy from ambient moisture, as demonstrated by UMass Amherst researchers in Advanced Materials.

 

Key Points

A method using nanoporous air-gen devices to harvest continuous clean electricity from ambient atmospheric moisture.

✅ Nanopores drive charge separation from ambient water molecules

✅ Works across materials: silicon, wood, bacterial films

✅ Predictable, continuous power unlike intermittent solar or wind

 

Sure, we all complain about the humidity on a sweltering summer day. But it turns out that same humidity could be a source of clean, pollution-free energy, aligning with efforts toward cheap, abundant electricity worldwide, a new study shows.

"Air humidity is a vast, sustainable reservoir of energy that, unlike wind and solar power resources, is continuously available," said the study, which was published recently in the journal Advanced Materials.

While humidity harvesting promises constant output, advances like a new fuel cell could help fix renewable energy storage challenges, researchers suggest.

“This is very exciting,” said Xiaomeng Liu, a graduate student at the University of Massachusetts-Amherst, and the paper’s lead author. “We are opening up a wide door for harvesting clean electricity from thin air.”

In fact, researchers say, nearly any material can be turned into a device that continuously harvests electricity from humidity in the air, a concept echoed by raindrop electricity demonstrations in other contexts.

“The air contains an enormous amount of electricity,” said Jun Yao, assistant professor of electrical and computer engineering at the University of Massachusetts-Amherst and the paper’s senior author. “Think of a cloud, which is nothing more than a mass of water droplets. Each of those droplets contains a charge, and when conditions are right, the cloud can produce a lightning bolt – but we don’t know how to reliably capture electricity from lightning.

"What we’ve done is to create a human-built, small-scale cloud that produces electricity for us predictably and continuously so that we can harvest it.”

The heart of the human-made cloud depends on what Yao and his colleagues refer to as an air-powered generator, or the "air-gen" effect, which relates to other atmospheric power concepts like night-sky electricity studies in the field.

In broader renewable systems, flexible resources such as West African hydropower can support variable wind and solar output, complementing atmospheric harvesting concepts as they mature.

The study builds on research from a study published in 2020. That year, scientists said this new technology "could have significant implications for the future of renewable energy, climate change and in the future of medicine." That study indicated that energy was able to be pulled from humidity by material that came from bacteria; related bio-inspired fuel cell design research explores better electricity generation, the new study finds that almost any material, such as silicon or wood, also could be used.

The device mentioned in the study is the size of a fingernail and thinner than a single hair. It is dotted with tiny holes known as nanopores, it was reported. "The holes have a diameter smaller than 100 nanometers, or less than a thousandth of the width of a strand of human hair."

 

Related News

View more

Ontario rolls out ultra-low electricity rates

Ontario Ultra-Low Overnight Electricity Rate lets eligible customers opt in to 2.4 cents per kWh time-of-use pricing, set by the Ontario Energy Board, as utilities roll out the plan between May 1 and Nov. 1.

 

Key Points

An OEB-set overnight TOU price of 2.4 cents per kWh for eligible Ontarians, rolling out in phases via local utilities.

✅ 8 of 61 utilities offering rate at May 1 launch

✅ About 20% of 5M customers eligible at rollout

✅ Enova Power delays amid merger integration work

 

A million households can opt into a new ultra-low overnight electricity rate offered by the Ministry of Energy, as province-wide rate changes begin, but that's just a fraction of customers in Ontario.

Only eight of the 61 provincial power utilities will offer the new rate on the May 1 launch date, following the earlier fixed COVID-19 hydro rate period. The rest have up to six months to get on board.

That means it will be available to 20 percent of the province's five million electricity consumers, the Ministry of Energy confirmed to CBC News.

The Ford government's new overnight pricing was pitched as a money saver for Ontarians, amid the earlier COVID-19 recovery rate that could raise bills, undercutting its existing overnight rate from 7.4 to 2.4 cents per kilowatt hour. Both rates are set by the Ontario Energy Board (OEB).

"We wanted to roll it out to as many people as possible," Kitchener-Conestoga PC MPP Mike Harris Jr. told CBC News. "These companies were ready to go, and we're going to continue to work with our local providers to make sure that everybody can meet that Nov. 1 deadline."

Enova Power — which serves Kitchener, Waterloo, Woolwich, Wellesley and Wilmot — won't offer the reduced overnight rate until the fall, after typical bills rose when fixed pricing ended province-wide.

Enova merger stalls adoption

The power company is the product of the recently merged Kitchener-Wilmot Hydro and Waterloo North Hydro.

The Sept. 1 merger is a major reason Enova Power isn't offering the ultra-low rate alongside the first wave of power companies, said Jeff Quint, innovation and communications manager.

"With mergers, a lot of work goes into them. We have to evaluate, merge and integrate several systems and processes," said Quint.

"We believe that we probably would have been able to make the May 1 timeline otherwise."

The ministry said retroactive pricing wouldn't be available, unlike the off-peak price freeze earlier in the pandemic, and Harris said he doesn't expect the province will issue any rebates to customers of companies that introduce the rates later than May 1.

"These organizations were able to look at rolling things out sooner. But, obviously — if you look at Toronto Hydro, London, Centre Wellington, Hearst, Renfrew — there's a dynamic range of large and smaller-scale providers there. I'm very hopeful the Region of Waterloo folks will be able to work to try and get this done as soon as we can," Harris said.

 

Related News

View more

US Electricity Market Reforms could save Consumers $7bn

PJM and MISO Electricity-Market Reforms promise consumer savings by enabling renewables, wind, solar, and storage participation in wholesale markets, enhancing grid flexibility, reliability services, and real-time pricing across the Midwest, Great Lakes, and Mid-Atlantic.

 

Key Points

Market rule updates enabling renewables and storage, improving reliability and lowering consumer costs.

✅ Removes barriers to renewables, storage, demand response

✅ Improves intermarket links and real-time price signals

✅ Rewards flexible resources and reliability services

 

Electricity-market reforms to enable more renewables generation and storage in the Midwest, Great Lakes, and Mid-Atlantic could save consumers in the US and Canada more than $6.9 billion a year, according to a new report.

The findings may have major implications for consumer groups, large industrial companies, businesses, and homeowners in those regions, said the Wind-Solar Alliance, (WSA), which commissioned the Customer Focused and Clean report.

The WSA is a non-profit organisation supporting the growth of renewables. American Wind Energy Association CEO Tom Kiernan is listed as WSA secretary, amid ongoing debates about the US wind market today.

"Consumers are looking for clean energy, affordable and reliable energy that will keep their monthly electricity bills low," said Kristin Munsch, president of the Board of the Consumer Advocates of the PJM States, which represents over 65 million consumers in 13 states.

"There is great potential to achieve those goals with the cost-effective integration of wind, solar and battery storage plants into our wholesale power markets."

The report found the average residential customer in the PJM and Midcontinent Independent System Operator (MISO) regions, covering 29 US states and the Canadian province of Manitoba, could each save up to $48 a year as lower wholesale electricity prices materialize with significantly more wind, solar and storage on the grid.

The average annual home electricity, for example in New Jersey, in the PJM region, was just over $106 in 2018, according to the US Energy Information Administration.

The latest report quantifies the findings of a previous one for the WSA, published in November 2018, which found that outdated wholesale market rules in the US were preventing full participation by renewable energy, including wind power.

 

Outdated rules

"The existing wholesale power market rules were largely developed for slower-to-react conventional generators, such as coal and nuclear plants," said Michael Milligan, president of Milligan Grid Solutions and co-author of the new report.

"This report demonstrates the benefits of updating the rules to better accommodate the characteristics and potential contributions of wind and solar and other newer sources of low-cost generation."

With more renewables generation on the grid, customers would benefit the most from increasing power-system flexibility through market structures, the new report concluded. It called for the removal of artificial barriers preventing renewables, storage and demand response from participating in markets.

The report also advocated improving the connections between markets, thereby lowering transaction costs of imports and exports between neighbouring systems.

"There are currently artificial barriers that are preventing the full participation of renewables, storage and other new technologies in the PJM and MISO markets," said Michael Goggin, vice president of Grid Strategies and co-author of the report.

"Providing consumers with a real-time price signal that allows them to adjust their demand, rewarding flexible resources for their capabilities through improved market design, and allowing renewable and storage resources to participate in reliability-services markets would yield the greatest consumer benefits," he said.

PJM and MISO, which incorporate some of the windiest areas of the country, are currently reviewing their market designs as part of a broader grid overhaul underway.

 

Related News

View more

New fuel cell concept brings biological design to better electricity generation

Quinone-mediated fuel cell uses a bio-inspired organic shuttle to carry electrons and protons to a nearby cobalt catalyst, improving hydrogen conversion, cutting platinum dependence, and raising efficiency while lowering costs for clean electricity.

 

Key Points

An affordable, bio-inspired fuel cell using an organic quinone shuttle and cobalt catalyst to move electrons efficiently

✅ Organic quinone shuttles electrons to a separate cobalt catalyst

✅ Reduces platinum use, lowering cost of hydrogen power

✅ Bio-inspired design aims to boost efficiency and durability

 

Fuel cells have long been viewed as a promising power source. But most fuel cells are too expensive, inefficient, or both. In a new approach, inspired by biology, a team has designed a fuel cell using cheaper materials and an organic compound that shuttles electrons and protons.

Fuel cells have long been viewed as a promising power source. These devices, invented in the 1830s, generate electricity directly from chemicals, such as hydrogen and oxygen, and produce only water vapor as emissions. But most fuel cells are too expensive, inefficient, or both.

In a new approach, inspired by biology and published today (Oct. 3, 2018) in the journal Joule, a University of Wisconsin-Madison team has designed a fuel cell using cheaper materials and an organic compound that shuttles electrons and protons.

In a traditional fuel cell, the electrons and protons from hydrogen are transported from one electrode to another, where they combine with oxygen to produce water. This process converts chemical energy into electricity. To generate a meaningful amount of charge in a short enough amount of time, a catalyst is needed to accelerate the reactions.

Right now, the best catalyst on the market is platinum -- but it comes with a high price tag, and while advances like low-cost heat-to-electric materials show promise, they address different conversion pathways. This makes fuel cells expensive and is one reason why there are only a few thousand vehicles running on hydrogen fuel currently on U.S. roads.

Shannon Stahl, the UW-Madison professor of chemistry who led the study in collaboration with Thatcher Root, a professor of chemical and biological engineering, says less expensive metals can be used as catalysts in current fuel cells, but only if used in large quantities. "The problem is, when you attach too much of a catalyst to an electrode, the material becomes less effective," he says, "leading to a loss of energy efficiency."

The team's solution was to pack a lower-cost metal, cobalt, into a reactor nearby, where the larger quantity of material doesn't interfere with its performance. The team then devised a strategy to shuttle electrons and protons back and forth from this reactor to the fuel cell.

The right vehicle for this transport proved to be an organic compound, called a quinone, that can carry two electrons and protons at a time. In the team's design, a quinone picks up these particles at the fuel cell electrode, transports them to the nearby reactor filled with an inexpensive cobalt catalyst, and then returns to the fuel cell to pick up more "passengers."

Many quinones degrade into a tar-like substance after only a few round trips. Stahl's lab, however, designed an ultra-stable quinone derivative. By modifying its structure, the team drastically slowed down the deterioration of the quinone. In fact, the compounds they assembled last up to 5,000 hours -- a more than 100-fold increase in lifetime compared to previous quinone structures.

"While it isn't the final solution, our concept introduces a new approach to address the problems in this field," says Stahl. He notes that the energy output of his new design produces about 20 percent of what is possible in hydrogen fuel cells currently on the market. On the other hand, the system is about 100 times more effective than biofuel cells that use related organic shuttles.

The next step for Stahl and his team is to bump up the performance of the quinone mediators, allowing them to shuttle electrons more effectively and produce more power. This advance would allow their design to match the performance of conventional fuel cells, but with a lower price tag.

"The ultimate goal for this project is to give industry carbon-free options for creating electricity, including thermoelectric materials that harvest waste heat," says Colin Anson, a postdoctoral researcher in the Stahl lab and publication co-author. "The objective is to find out what industry needs and create a fuel cell that fills that hole."

This step in the development of a cheaper alternative could eventually be a boon for companies like Amazon and Home Depot that already use hydrogen fuel cells to drive forklifts in their warehouses.

"In spite of major obstacles, the hydrogen economy, with efforts such as storing electricity in pipelines in Europe, seems to be growing," adds Stahl, "one step at a time."

Financial support for this project was provided by the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and by the Wisconsin Alumni Research Foundation (WARF) through the WARF Accelerator Program.

 

Related News

View more

DBRS Confirms Ontario Power Generation Inc. at A (low)/R-1 (low), Stable Trends

OPG Credit Rating affirmed by DBRS at A (low) issuer and unsecured debt, R-1 (low) CP, Stable trends, backed by a supportive regulatory regime, strong leverage metrics, and provincial support; monitor Darlington Refurbishment costs.

 

Key Points

It is DBRS's confirmation of OPG at A (low) issuer and unsecured, R-1 (low) CP, with Stable outlooks.

✅ Stable trends; strong cash flow-to-debt and capital ratios

✅ Provincial financing via OEFC; Fair Hydro Trust ring-fenced

✅ Darlington Refurbishment on budget; cost overruns remain risk

 

DBRS Limited (DBRS) confirmed the Issuer Rating and the Unsecured Debt rating of Ontario Power Generation Inc. (OPG or the Company) at A (low) and the Commercial Paper (CP) rating at R-1 (low), amid sector developments such as Hydro One leadership efforts to repair government relations and measures like staff lockdowns at critical sites.

All trends are Stable. The ratings of OPG continue to be supported by (1) the reasonable regulatory regime in place for the Company's regulated generation facilities, including stable pricing signals for large users, (2) strong cash flow-to-debt and debt-to-capital ratios and (3) continuing financial support from its shareholder, the Province of Ontario (the Province; rated AA (low) with a Stable trend by DBRS). The Province, through its agent, the Ontario Electricity Financial Corporation (rated AA (low) with a Stable trend by DBRS), provides most of OPG's financing (approximately 43% of consolidated debt). The Company's remaining debt includes project financing (31%), including projects such as a battery energy storage system proposed near Woodstock, non-recourse debt issued by Fair Hydro Trust (Senior Notes rated AAA (sf), Under Review with Negative Implications by DBRS; 11%), CP (2%) and Senior Notes issued under the Medium Term Note Program (12%).

In March 2019, the Province introduced 'Bill 87, Fixing the Hydro Mess Act, 2019' which includes winding down the Fair Hydro Plan, and later introduced electricity relief to mitigate customer bills during the COVID-19 pandemic. OPG will remain as the Financial Services Manager for the outstanding Fair Hydro Trust debt, which will become obligations of the Province. DBRS does not expect this development to have a material impact on the Company as (1) the Fair Hydro Trust debt will continue to be bankruptcy-remote and ring-fenced from OPG (all debt is non-recourse to the Company) and (2) the credit rating on the Company's investment in the Subordinated Notes (rated AA (sf), Under Review with Negative Implications by DBRS) will likely remain investment grade while the Junior Subordinated Notes (rated A (sf), Under Review with Developing Implications by DBRS) will not necessarily be negatively affected by this change (see the DBRS press release, 'DBRS Maintains Fair Hydro Trust, Series 2018-1 and Series 2018-2 Notes Under Review,' dated March 26, 2019, for more details).

OPG's key credit metrics improved in 2018, following the approval of its 2017-2021 rates application by the Ontario Energy Board in December 2017, alongside the Province's energy-efficiency programs that shape demand. The Company's profitability strengthened significantly, with corporate return on equity (ROE) of 7.8% (adjusted for a $205 million gain on sale of property; 5.1% in 2017) closer to the regulatory allowed ROE of 8.78%. However, DBRS continues to view a positive rating action as unlikely in the short term because of the ongoing large capital expenditures program, including the $12.8 billion Darlington Refurbishment project, amid ongoing oversight following the nuclear alert investigation in Ontario. However, a downgrade could occur should there be significant cost overruns with the Darlington Refurbishment project that result in stranded costs. DBRS notes that the Darlington Refurbishment project is currently on budget and on schedule.

 

Related News

View more

Sign Up for Electricity Forum’s Newsletter

Stay informed with our FREE Newsletter — get the latest news, breakthrough technologies, and expert insights, delivered straight to your inbox.

Electricity Today T&D Magazine Subscribe for FREE

Stay informed with the latest T&D policies and technologies.
  • Timely insights from industry experts
  • Practical solutions T&D engineers
  • Free access to every issue

Download the 2025 Electrical Training Catalog

Explore 50+ live, expert-led electrical training courses –

  • Interactive
  • Flexible
  • CEU-cerified