Turning Humble Seaweed to Biofuel

The sea has long been a source of Norway’s riches, whether from cod, farmed salmon or oil. Now one researcher hopes to add seaweed to this list as he refines a way to produce “biocrude” from common kelp.

Kelp can be turned into a kind of "bio-crude" that can be further refined into a biofuel. Credit: Rune Petter Ness, NTNU Communication Division

“What we are trying to do is to mimic natural processes to produce oil,” said Khanh-Quang Tran, an associate professor in Norwegian University of Science and Technology's (NTNU) Department of Energy and Process Engineering. “However, while petroleum oil is produced naturally on a geologic time scale, we can do it in minutes.”

Tran conducted preliminary studies using sugar kelp (Laminaria saccharina), which grows naturally along the Norwegian coast. His results have just been published in the academic journal Algal Research.

Learn about more kelp biofuel initiatives here.

The Breakthrough

Using small quartz tube “reactors” — which look like tiny sealed straws — Tran heated the reactor containing a slurry made from the kelp biomass and water to 350 degrees C at a very high rate of 585 degrees C per minute.

The technique, called fast hydrothermal liquefaction, gave him a bio-oil yield of 79 percent. That means that 79 percent of the kelp biomass in the reactors was converted to bio-oil. A similar study in the U.K. using the same species of kelp yielded just 19 percent. The secret, Tran said, is the rapid heating.

Falling Short on Biofuel Production

Biofuel has long been seen as a promising way to help shift humankind towards a more sustainable and climate friendly lifestyle. The logic is simple: petroleum-like fuels made from crops or substances take up CO2 as they grow and release that same CO2 when they are burned, so they are essentially carbon-neutral.

In its report “Tracking Clean Energy Progress 2014,” the International Energy Agency (IEA) says that biofuel production worldwide was 113 billion litres in 2013, and could reach 140 billion litres by 2018.

That may sound like a lot — but the IEA says biofuel production will need to grow 22-fold by 2025 to produce the amount of biofuel the world will need to keep global temperatures from rising more than 2oC.

The problem is the biomass feedstock. It’s relatively easy to turn corn or sugar beets into ethanol that we can pump right into our petrol tanks. But using food biomass for fuel is more and more problematic as the world’s population climbs towards 8 billion and beyond.

To get around this problem, biofuel is now produced from non-food biomass including agricultural residues, land-based energy crops such as fast-growing trees and grasses, and aquatic crops such as seaweed and microalgae.

All of these feedstocks have their challenges, especially those that are land based. At least part of the issue is the fact that crops for biofuel could potentially displace crops for food.

However, seaweed offers all of the advantages of a biofuel feedstock with the additional benefit of growing, not surprisingly, in the sea.

Scaling Up

But turning big pieces of slippery, salty kelp into biocrude is a challenge, too. Some studies have used catalysts, which are added chemicals that can help make the process go more quickly or easily. However, catalysts are normally expensive and require catalyst recovery.

The UK study that resulted in a 19 percent yield used a catalyst in its process.

Tran says the advantage of his process is that it is relatively simple and does not need a catalyst. The high heating rate also results in a biocrude that has molecular properties that will make it easier to refine.

But Tran’s experiments were what are called screening tests. He worked with batch reactors that were small and not suitable for an industrial scale. “When you want to scale up the process you have to work with a flow reactor,” or a reactor with a continuous flow of reactants and products, he said. “I already have a very good idea for such a reactor.”

The Outlook

Even though the preliminary tests gave a yield of 79 percent, Tran believes he can improve the results even more. He’s now looking for industrial partners and additional funding to continue his research.

All-in-One Solution: Solar that Stores Its Own Power

Columbus, Ohio — Is it a solar cell? Or a rechargeable battery? Actually, the patent-pending device invented at The Ohio State University is both: the world’s first solar battery.

In the October 3, 2014 issue of the journal Nature Communications, the researchers report that they’ve succeeded in combining a battery and a solar cell into one hybrid device.

Key to the innovation is a mesh solar panel, which allows air to enter the battery, and a special process for transferring electrons between the solar panel and the battery electrode. Inside the device, light and oxygen enable different parts of the chemical reactions that charge the battery.

The university will license the solar battery to industry, where Yiying Wu, professor of chemistry and biochemistry at Ohio State, says it will help tame the costs of renewable energy.

“The state of the art is to use a solar panel to capture the light, and then use a cheap battery to store the energy,” Wu said. “We’ve integrated both functions into one device. Any time you can do that, you reduce cost.”

He and his students believe that their device brings down costs by 25 percent.

Researchers at The Ohio State University have invented a solar battery — a combination solar cell and battery — which recharges itself using air and light. The design required a solar panel which captured light, but admitted air to the battery. Here, scanning electron microscope images show the solution: nanometer-sized rods of titanium dioxide (larger image) which cover the surface of a piece of titanium gauze (inset). The holes in the gauze are approximately 200 micrometers across, allowing air to enter the battery while the rods gather light. Image courtesy of Yiying Wu, The Ohio State University. 

The invention also solves a longstanding problem in solar energy efficiency, by eliminating the loss of electricity that normally occurs when electrons have to travel between a solar cell and an external battery. Typically, only 80 percent of electrons emerging from a solar cell make it into a battery.

With this new design, light is converted to electrons inside the battery, so nearly 100 percent of the electrons are saved.

The design takes some cues from a battery previously developed by Wu and doctoral student Xiaodi Ren. They invented a high-efficiency air-powered battery that discharges by chemically reacting potassium with oxygen. The design won the $100,000 clean energy prize from the U.S. Department of Energy in 2014, and the researchers formed a technology spinoff called KAir Energy Systems, LLC to develop it.

“Basically, it’s a breathing battery,” Wu said. “It breathes in air when it discharges, and breathes out when it charges.”

For this new study, the researchers wanted to combine a solar panel with a battery similar to the KAir. The challenge was that solar cells are normally made of solid semiconductor panels, which would block air from entering the battery.

Doctoral student Mingzhe Yu designed a permeable mesh solar panel from titanium gauze, a flexible fabric upon which he grew vertical rods of titanium dioxide like blades of grass. Air passes freely through the gauze while the rods capture sunlight.

Normally, connecting a solar cell to a battery would require the use of four electrodes, the researchers explained. Their hybrid design uses only three.

The mesh solar panel forms the first electrode. Beneath, the researchers placed a thin sheet of porous carbon (the second electrode) and a lithium plate (the third electrode). Between the electrodes, they sandwiched layers of electrolyte to carry electrons back and forth.

Here’s how the solar battery works: during charging, light hits the mesh solar panel and creates electrons. Inside the battery, electrons are involved in the chemical decomposition of lithium peroxide into lithium ions and oxygen. The oxygen is released into the air, and the lithium ions are stored in the battery as lithium metal after capturing the electrons.

When the battery discharges, it chemically consumes oxygen from the air to re-form the lithium peroxide.

An iodide additive in the electrolyte acts as a “shuttle” that carries electrons, and transports them between the battery electrode and the mesh solar panel. The use of the additive represents a distinct approach on improving the battery performance and efficiency, the team said.

The mesh belongs to a class of devices called dye-sensitized solar cells, because the researchers used a red dye to tune the wavelength of light it captures.

In tests, they charged and discharged the battery repeatedly, while doctoral student Lu Ma used X-ray photoelectron spectroscopy to analyze how well the electrode materials survived — an indication of battery life.

First they used a ruthenium compound as the red dye, but since the dye was consumed in the light capture, the battery ran out of dye after eight hours of charging and discharging — too short a lifetime. So they turned to a dark red semiconductor that wouldn’t be consumed: hematite, or iron oxide — more commonly called rust.

Coating the mesh with rust enabled the battery to charge from sunlight while retaining its red color. Based on early tests, Wu and his team think that the solar battery’s lifetime will be comparable to rechargeable batteries already on the market.

The U.S. Department of Energy funds this project, which will continue as the researchers explore ways to enhance the solar battery’s performance with new materials.

How to Make a “Perfect” Solar Absorber

Cambridge, Mass. -- The key to creating a material that would be ideal for converting solar energy to heat is tuning the material’s spectrum of absorption just right: It should absorb virtually all wavelengths of light that reach Earth’s surface from the sun — but not much of the rest of the spectrum, since that would increase the energy that is reradiated by the material, and thus lost to the conversion process.

This rendering shows the metallic dielectric photonic crystal that stores solar energy as heat. Credit: Jeffrey Chou

Now researchers at MIT say they have accomplished the development of a material that comes very close to the “ideal” for solar absorption. The material is a two-dimensional metallic dielectric photonic crystal, and has the additional benefits of absorbing sunlight from a wide range of angles and withstanding extremely high temperatures. Perhaps most importantly, the material can also be made cheaply at large scales.

The creation of this material is described in a paper published in the journal Advanced Materials, co-authored by MIT postdoc Jeffrey Chou, professors Marin Soljacic, Nicholas Fang, Evelyn Wang, and Sang-Gook Kim, and five others.

The material works as part of a solar-thermophotovoltaic (STPV) device: The sunlight’s energy is first converted to heat, which then causes the material to glow, emitting light that can, in turn, be converted to an electric current.

Some members of the team worked on an earlier STPV device that took the form of hollow cavities, explains Chou, of MIT’s Department of Mechanical Engineering, who is the paper’s lead author. “They were empty, there was air inside,” he says. “No one had tried putting a dielectric material inside, so we tried that and saw some interesting properties.”

When harnessing solar energy, “you want to trap it and keep it there,” Chou says; getting just the right spectrum of both absorption and emission is essential to efficient STPV performance.

Most of the sun’s energy reaches us within a specific band of wavelengths, Chou explains, ranging from the ultraviolet through visible light and into the near-infrared. “It’s a very specific window that you want to absorb in,” he says. “We built this structure, and found that it had a very good absorption spectrum, just what we wanted.”

In addition, the absorption characteristics can be controlled with great precision: The material is made from a collection of nanocavities, and “you can tune the absorption just by changing the size of the nanocavities,” Chou says.

Another key characteristic of the new material, Chou says, is that it is well matched to existing manufacturing technology. “This is the first-ever device of this kind that can be fabricated with a method based on current … techniques, which means it’s able to be manufactured on silicon wafer scales,” Chou says — up to 12 inches on a side. Earlier lab demonstrations of similar systems could only produce devices a few centimeters on a side with expensive metal substrates, so were not suitable for scaling up to commercial production, he says.

In order to take maximum advantage of systems that concentrate sunlight using mirrors, the material must be capable of surviving unscathed under very high temperatures, Chou says. The new material has already demonstrated that it can endure a temperature of 1,000 degrees Celsius (1,832 degrees Fahrenheit) for a period of 24 hours without severe degradation.

And since the new material can absorb sunlight efficiently from a wide range of angles, Chou says, “we don’t really need solar trackers” — which would add greatly to the complexity and expense of a solar power system.

“This is the first device that is able to do all these things at the same time,” Chou says. “It has all these ideal properties.”

While the team has demonstrated working devices using a formulation that includes a relatively expensive metal, ruthenium, “we’re very flexible about materials,” Chou says. “In theory, you could use any metal that can survive these high temperatures.”

“This work shows the potential of both photonic engineering and materials science to advance solar energy harvesting,” says Paul Braun, a professor of materials science and engineering at the University of Illinois at Urbana-Champaign, who was not involved in this research. “In this paper, the authors demonstrated, in a system designed to withstand high temperatures, the engineering of the optical properties of a potential solar thermo photovoltaic absorber to match the sun’s spectrum. Of course much work remains to realize a practical solar cell, however, the work here is one of the most important steps in that process.”

The group is now working to optimize the system with alternative metals. Chou expects the system could be developed into a commercially viable product within five years. He is working with Kim on applications from this project.

The team also included MIT research scientist Ivan Celanovic and former graduate students Yi Yeng, Yoonkyung Lee, Andrej Lenert, and Veronika Rinnerbauer. The work was supported by the Solid-State Solar Thermal Energy Conversion Center and the U.S. Department of Energy.

Researchers Develop Faster, Cheaper Way to Make Solar Cells

A faster, cheaper way to manufacture silicon solar cells, partially funded by the Energy Department and fine-tuned at its National Renewable Energy Laboratory (NREL), has won a coveted R&D 100 award as one of the top technology innovations of 2013.

Crystal Solar's approach to growing high-quality, high-efficiency silicon wafers at 100 times the usual throughput and half the cost could be a game-changer, creating American jobs and stemming the flow of solar cell manufacturing overseas, says T.S. Ravi, chief executive officer of the Santa Clara, California-based company.

The monocrystalline silicon solar cells made by Crystal Solar are much closer to true squares than most other silicon solar cells. The shape is one of the reasons the wafers can be stacked vertically during the gas-deposition process — and one of the reasons that the cells can be produced at about 100 times the typical rate. Credit: Crystal Solar

Even before he founded Crystal Solar, Ravi set a goal to speed up the manufacturing process. In 2011, his nascent company applied for the Energy Department's SunShot Initiative's Photovoltaic (PV) Incubator Program, which at that time was run out of NREL. The PV Incubator Program has a very competitive selection process, searching for ideas that are truly disruptive in terms of lowering costs.

"We applied for the program and were selected in late 2011," Ravi said, recalling a conversation he had several years ago with NREL's Harin Ullal. "I knew that if I could bunch a lot of wafers together, and find a way to remove the epitaxial wafer with a simple mechanical process, it could actually change the game in the solar industry."

Crystal Solar's direct gas-to-wafer method is epitaxial, which means it grows a layer of material on top of another material that has the same crystal structure. In the direct gas-to-wafer method—the official name is Direct Monocrystalline Silicon Wafer Growth by High-Throughput Epitaxy—gaseous layers of semiconducting silicon material are grown directly on reusable silicon substrates. The method has several advantages, including eliminating the waste incurred in the traditional approach, which involves sawing thin slices from a large ingot or block of silicon. In the new approach, wafers can be made thinner without compromising their quality or efficiency.

However, semiconductor material using the epitaxial approach typically grows very slowly—about two wafers an hour for the thickness needed for solar wafers.  That's much too slow — and therefore costly — for solar cells. The Energy Department's SunShot Initiative has set a goal for solar energy of less than $1 per watt system price by 2020, as a way of making it cost competitive with fossil-fuel-based electricity.

Incubator Program at NREL Helped Drive the Technology

Crystal Solar's Epireactor can make up to 500 silicon solar cells an hour, about 100 times faster than previous methods. Scientists from NREL collaborated with Crystal Solar on the new approach. Credit: Crystal Solar

Crystal Solar worked closely with NREL into 2013. "NREL pointed us in the right direction," Ravi said. "All these things we wanted to prove—that we could grow these wafers at a high growth rate, that we could do it without compromising the quality of the wafers—required the silicon defect expertise at NREL."

"We helped them understand the nature of the defects and thus improve performance at the wafer and cell level," said NREL Principal Scientist Bhushan Sopori, who, along with Ullal and NREL's Steve Johnston, worked with Crystal Solar on the process.

Ullal noted that the efficiency of the rapidly made cells is greater than 20% in the lab, so once in panels on rooftops, they should compare favorably to the best solar modules being installed today. "The SunShot PV Incubator Program is very competitive," Ullal added. "Clearly, Crystal Solar had a unique process that really stood out. Compared to the traditional silicon technology that involves slicing, this eliminates several steps that have an impact on the cost of the final PV product."

Solar Wafers at 13 Cents per Watt

NREL researchers Harin Ullal, left, Steve Johnston, and Bhushan Sopori were part of the team that won the R&D 100 award with Crystal Solar. Credit: Dennis Schroeder, NREL

The new epitaxial system can produce up to 500 wafers per hour and sells for less than $5 million, while replacing traditional reactors and pullers. That translates to a wafer cost of about 13 cents per watt, less than half the typical cost of 30 cents per watt for high-end wafers, Ravi said. The entire module cost is projected to be less than 50 cents per watt — a reduction that could help nudge the installed cost of the solar system to less than $1 per watt.

Crystalline silicon commands 90 percent of the solar market, and despite the rapid success of thin films and other materials such as perovskite, will likely remain the leading technology in the near future.

Interest in the solar cells is huge, Ravi said. Crystal Solar is in the pilot manufacturing stage, and "we're struggling to keep up with the people who want our wafers. We want to set up a factory in the United States somewhere."

Ravi said the process lends itself to automation, which means labor costs — much cheaper in Asia — won't be such a big factor. "We don't have to go to a low-labor country—I'm very proud of that," he said. Even though the approach requires less manpower, it will mean numerous good-paying American jobs.

"We believe this technology will probably thrive in the United States, that it will be cheaper to do it here than anywhere else in the world," Ravi said. If the process continues to make high-quality efficient solar cells when ramped up to full manufacturing scale, it's a testimonial to the partnership between Crystal Solar, the Energy Department, and NREL, Ravi said.

Approach Eliminates Several Steps, Is Less Expensive

This schematic shows how silicon wafers are stacked vertically in Crystal Solar's Epireactor, allowing gas to flow to more wafers at the same time, which greatly increases the throughput. Credit: Crystal Solar

The approach is cheaper and faster because it eliminates several steps, Ullal said. The device is actually built as gaseous silicon is deposited on a solid silicon substrate. A dopant or impurity can create the junctions that force current flow much more easily than in traditional solar cell manufacturing, Ravi said.

Another advantage: The material doesn't have to be rotated as it does in the ingot-growth process, which means the wafer remains a true square — and that makes for better and more efficient packaging of the PV module.

The approach also incorporates less oxygen in the silicon layer, which has been shown to eliminate oxygen-related defects. That's important because it gives the photons that hit the cells a tiny bit longer to form into the electron-hole pairs that are essential to establishing a carrying current for electricity, and makes it less likely that the electron and hole will recombine. The difference is tiny — 1.3 milliseconds versus a bit less than 1 millisecond — but crucial in the world of photons and electrons.

"Most silicon wafers are made in Asia," Ullal said. "But this epitaxy process gets you there. And 30 percent of the overall cost of a solar module is the cost of the silicon wafer."

Typically, for epitaxial growth, wafers are arranged horizontally as layers are added. Crystal Solar arranges them vertically, for a smaller footprint, and passes the gas through a narrower space for a much higher growth rate.

"The key challenge was how to hold that wafer vertically and still get uniformity," Ravi said. "That took us 2 and a half years of researching for just the right material, the right shape, and so forth. There are so many advantages of the epitaxial method that it seems like a no-brainer. But the reason no one has really done it before is that it is a very hard thing to do in practice."

His company is looking for a site with low-cost access to electricity and a well-trained technical workforce. "There's great demand for solar energy. We're taking about hundreds of gigawatts in the next couple of decades."

NREL's collaboration with Crystal Solar is just one of dozens of working agreements with industry. "Partnerships with innovative private companies are part of the lifeblood of NREL," said Kristin Gray, director of NREL's Technology Transfer Office. Gray and colleague Anne Miller noted that NREL, year after year, has more cooperative research and development agreements (CRADAs) with private companies than any other federal laboratory. For every dollar that the Energy Department invests in a CRADA, it attracts another $6 in total value from all industry contracts. During the past year, NREL signed 20 new license agreements and filed more than 60 new patent applications.

"NREL scientists and engineers, working with companies with innovative ideas for sustainable energy, are accelerating the move toward a clean energy economy," Miller said.

The Power of Salt

Cambridge, Mass. -- Where the river meets the sea, there is the potential to harness a significant amount of renewable energy, according to a team of mechanical engineers at MIT.

Pressure retarded osmosis (PRO) is a method of producing renewable energy from two streams of a different salinity. Illustration: Jose-Luis Olivares/MIT.The researchers evaluated an emerging method of power generation called pressure retarded osmosis (PRO), in which two streams of different salinity are mixed to produce energy. In principle, a PRO system would take in river water and seawater on either side of a semi-permeable membrane. Through osmosis, water from the less-salty stream would cross the membrane to a pre-pressurized saltier side, creating a flow that can be sent through a turbine to recover power.

The MIT team has now developed a model to evaluate the performance and optimal dimensions of large PRO systems. In general, the researchers found that the larger a system’s membrane, the more power can be produced — but only up to a point. Interestingly, 95 percent of a system’s maximum power output can be generated using only half or less of the maximum membrane area.

Leonardo Banchik, a graduate student in MIT’s Department of Mechanical Engineering, says reducing the size of the membrane needed to generate power would, in turn, lower much of the upfront cost of building a PRO plant.

“People have been trying to figure out whether these systems would be viable at the intersection between the river and the sea,” Banchik says. “You can save money if you identify the membrane area beyond which there are rapidly diminishing returns.”

Banchik and his colleagues were also able to estimate the maximum amount of power produced, given the salt concentrations of two streams: The greater the ratio of salinities, the more power can be generated. For example, they found that a mix of brine, a byproduct of desalination, and treated waste water can produce twice as much power as a combination of seawater and river water.

n this simplified PRO system, permeate from a dilute feed stream enters a concentrated draw stream in a pressurized state via osmosis — after which useful power can be extracted from the draw-permeate mixture. Image: Leonardo Banchik

Based on his calculations, Banchik says that a PRO system could potentially power a coastal wastewater-treatment plant by taking in seawater and combining it with treated waste water to produce renewable energy.

“Here in Boston Harbor, at the Deer Island Waste Water Treatment Plant, where waste water meets the sea … PRO could theoretically supply all of the power required for treatment,” Banchik says.

He and John Lienhard, the Abdul Latif Jameel Professor of Water and Food at MIT, along with Mostafa Sharqawy of King Fahd University of Petroleum and Minerals in Saudi Arabia, report their results in the Journal of Membrane Science.

Finding Equilibrium in Nature

The team based its model on a simplified PRO system in which a large semi-permeable membrane divides a long rectangular tank. One side of the tank takes in pressurized salty seawater, while the other side takes in river water or wastewater. Through osmosis, the membrane lets through water, but not salt. As a result, freshwater is drawn through the membrane to balance the saltier side.

 

“Nature wants to find an equilibrium between these two streams,” Banchik explains.

As the freshwater enters the saltier side, it becomes pressurized while increasing the flow rate of the stream on the salty side of the membrane. This pressurized mixture exits the tank, and a turbine recovers energy from this flow.  

Banchik says that while others have modeled the power potential of PRO systems, these models are mostly valid for laboratory-scale systems that incorporate “coupon-sized” membranes. Such models assume that the salinity and flow of incoming streams is constant along a membrane. Given such stable conditions, these models predict a linear relationship: the bigger the membrane, the more power generated.

But in flowing through a system as large as a power plant, Banchik says, the streams’ salinity and flux will naturally change. To account for this variability, he and his colleagues developed a model based on an analogy with heat exchangers.

“Just as the radiator in your car exchanges heat between the air and a coolant, this system exchanges mass, or water, across a membrane,” Banchik says. “There’s a method in literature used for sizing heat exchangers, and we borrowed from that idea.”

The researchers came up with a model with which they could analyze a wide range of values for membrane size, permeability, and flow rate. With this model, they observed a nonlinear relationship between power and membrane size for large systems. Instead, as the area of a membrane increases, the power generated increases to a point, after which it gradually levels off. While a system may be able to produce the maximum amount of power at a certain membrane size, it could also produce 95 percent of the power with a membrane half as large.

Shown here is the maximum power that can be produced for a 4:1 seawater to river water combination. As the dimensionless area gets very large, the overall maximum power can be produced. Image: Leonardo Banchik

Still, if PRO systems were to supply power to Boston’s Deer Island treatment plant, the size of a plant’s membrane would be substantial — at least 2.5 million square meters, which Banchik notes is the membrane area of the largest operating reverse osmosis plant in the world.

“Even though this seems like a lot, clever people are figuring out how to pack a lot of membrane into a small volume,” Banchik says. “For example, some configurations are spiral-wound, with flat sheets rolled up like paper towels around a central tube. It’s still an active area of research to figure out what the modules would look like.”

“Say we’re in a place that could really use desalinated water, like California, which is going through a terrible drought,” Banchik adds. “They’re building a desalination plant that would sit right at the sea, which would take in seawater and give Californians water to drink. It would also produce a saltier brine, which you could mix with wastewater to produce power. More research needs to be done to see whether it can be economically viable, but the science is sound.”

This work was funded by the King Fahd University of Petroleum and Minerals through the Center for Clean Water and Clean Energy and by the National Science Foundation.

New Software Modeling Tool a Boon for Wind Industry

Wind energy is blowing away skeptics — it's so close to achieving cost parity with fossil fuels that just a little extra efficiency is all that is likely needed to push it into the mainstream and past the Energy Department's goal of 20 percent wind energy by 2030.

Wind energy is blowing away skeptics — it's so close to achieving cost parity with fossil fuels that just a little extra efficiency is all that is likely needed to push it into the mainstream and past the Energy Department's goal of 20 percent wind energy by 2030.

That extra efficiency may be realized with the help of a software tool built by the Energy Department's National Renewable Energy Laboratory (NREL). It's called Simulator for Wind Farm Applications (SOWFA), and it can calculate how undulating ground, whipping blades, surface temperatures, and other variables alter the air flow and energy production at wind farms.

In the Energy Systems Integration Facility (ESIF) Insight Center, NREL Senior Engineer Pat Moriarty, left, and NREL Senior Engineer Paul Fleming review velocity (blue) and turbulence (yellow) in a simulation of the Lillgrund Wind Farm in Denmark. The researchers have written the open-source software tool Simulator for Wind Farm Applications (SOWFA), which can calculate how undulating ground, whipping blades, surface temperatures, and other variables alter the air flow and energy production at wind farms. Photo by Dennis Schroeder, NREL

SOWFA's key innovation is that it simulates an extensive range of scales—from regional weather patterns down to the space between turbines and all the way to the movement of electrons. It gives a complete picture of an active plant, showing how controlling each turbine can influence the direction of the wakes, and detecting the effect on downwind turbines. And it helps researchers understand how local atmospheric conditions affect local wind around the wind farm.

SOWFA is the first tool that enables developers to improve the performance of not only one wind turbine, but the entire wind farm. And because it is an open-source "community" software platform available for free to academics, investors, wind developers, and manufacturers, users have the support of an online forum where they can discuss problems and solutions with other SOWFA users.

One application of SOWFA is the simulation and design of coordinated control of individual turbines in order to maximize plant-wide output. Using these controllers, upstream turbines can yaw their rotors to redirect their wakes away from downstream turbines, substantially improving power capture. Wake losses at wind farms can reduce total power production by 10%. If SOWFA can be used to design controllers that cut those losses in half, that's a huge benefit. If employed at wind farms across the country and the world, the additional revenue could add up to billions of dollars.

SOWFA Simulates Wake Effect for Turbines Downwind

NREL Senior Engineer Pat Moriarty, left, explains a wind turbine model at the ESIF Insight Center to Secretary of Energy Ernest Moniz, right, during a tour for the dedication of the ESIF last year. Photo by Dennis Schroeder, NREL

Across the Great Plains and at many spots offshore, if you see one wind turbine, you're likely to see a dozen or a hundred. A wind farm provides economies of scale—contract with a farmer or win a permit for offshore wind, and it makes sense to erect multiple turbines all tied to a single system.

However, those rows of giant turbines can be problematic. As the turbine's blades are turned by the wind, they also disrupt the wind, causing a wake similar to a calm spot behind a tree or building. If that wake heads straight for the next turbine downstream—maybe 800 meters away—its churn will mean weaker wind and less power produced by that second turbine.

But SOWFA shows turbine manufacturers, wind farm developers, or investors how a yaw can impart a thrust that curves that wake around the downwind turbine. "Wake, from a power perspective, is lower-energy wind," said NREL Senior Engineer Paul Fleming, one of the engineers using SOWFA in his research. "If you can move away that deficit of energy, you will have faster winds and more overall production at the wind farm."

"In the past, wind farms have relied on dissipation to control that energy loss—they just move the turbines farther away from each other," said NREL Senior Engineer Pat Moriarty, a leader of the SOWFA team. "Now, we can control it in a different way. And there are other ways to achieve more control."

SOWFA was created to model all the different variables at a wind farm—the topography, the air, surface and air temperatures, even the effects of the turbines themselves. Other models have looked at pieces of the whole, but now that the wind industry is maturing and the cost margins are decreasing, it's increasingly important to model the whole system and maximize energy production

Turbines and Central Controller Talk to Each Other

NREL Senior Engineer Paul Fleming, left, and NREL Senior Engineer Pat Moriarty review wind farm data in SOWFA. SOWFA can simulate and design coordinated control of individual turbines in order to maximize plant-wide output. Photo by Dennis Schroeder, NREL

With SOWFA, the central super-controller can receive information from individual turbines and send command messages to them. In other words, the central controller and the turbines can talk to each other. SOWFA's central controller can send a message asking a turbine to adjust its yaw—but the turbine can override that command if conditions at the turbine are such that adjusting the yaw would be unsafe. This architecture is designed to mimic as closely as possible how wind plant controls might be implemented at a real wind farm.

Another reason SOWFA is unique among wind modeling tools is that it has the capacity to incorporate the heat on the earth's surface into its calculations. The sun is the main reason that air moves. It causes different air temperatures and pressures, coaxing the wind in a particular direction at a particular speed and at different heights above the ground. The varying temperature of the ground and the hills and vales of the farm also influence how the wind moves through the atmosphere. In the daytime, when the ground is hot, the wind tends to be more turbulent, rising from the surface. At night, when the ground is cooler than the air, the wind becomes more horizontal and speeds up. The same rules apply offshore, except instead of the ground there is the water surface, and instead of hills and vales, there are the size and motion of the waves.

The software tool also can deliver the numbers to show a possible overall net benefit if that first row of turbines reduces the capture of wind so the second row can capture more.

Reducing Uncertainty Can Lower Financial Risk, Interest Rates

SOWFA has drawn acute interest from manufacturers, developers, and utilities. "One of the most important outputs of SOWFA is the reduced uncertainty," Moriarty said. "The finance community cares not just about energy production, but about the uncertainty of energy production over the next 20 years that wind farm would be operating. They particularly want to know what the worst-case energy production can be."

SOWFA's improved look at physics will help the community better understand the uncertainty gap between the average energy production and the worst-case energy production. That, in turn, should lower the interest rates for financing a wind farm, which can be a huge part of the total cost.

Supercomputers Make the Modeling Possible

Supercomputers made SOWFA possible, said Moriarty, noting that he and his NREL colleagues started work on the project in 2005, but that its success accelerated as computers reached the ability to do trillions of calculations per second. To accurately predict the motions of wind at a wind farm, computers need to simulate the dynamics in the space occupied by up to a hundred turbines — and model the flows, counterflows, cross flow, and temperatures in every square meter.

Of course, the goal is to arrive at the most accurate forecasts of wind energy production before the turbines are erected. Moriarty, Fleming, and the rest of the team use NREL's Peregrine high performance computer to simulate the movement of air through rows of turbines.

Understanding the dynamics of a wind farm means analyzing the effects of everything from clouds to rises and dips in the terrain, and even the height of surrounding  crops.

Researchers can use SOWFA to study how new control schemes can increase power production and reduce fatigue from wake effects, and developers can use SOWFA to move turbines like chessmen on a chess board to maximize output — all before construction begins.

The Energy Department, which provided funding for the SOWFA project, is in the process of developing experiments to test that the modeling predicted by SOWFA matches real-life conditions and energy output at the wind farms.

Offshore Wind Power Can Save US Billions On Electricity, Recent DOE Study Finds

Offshore wind power isn’t usually associated with lower-cost energy, at least not in the public imagination. But it turns out that installing 54 gigawatts of offshore wind power off America’s coasts can cut the cost of electricity in the U.S. by an astounding $7.68 billion a year. That’s right: $7.68 billion annually. (If utilities and grid operators pass those savings onto consumers, that’s about $100 a year per family of four.)

As the American Wind Energy Association’s Offshore WindPower 2014 conference begins today in Atlantic City, that’s just some of the good news to report about pollution-free, offshore wind power. This news is out in a recent U.S. Department of Energy study that proves offshore wind power’s potential in the U.S. is far more than theoretical: The National Offshore Wind Energy Grid Interconnection Study.

The study itself was designed to assess technical capacity and the possibility that offshore wind power can become a major component of the U.S. energy system — “to identify and help address the market barriers to the large-scale introduction of offshore wind energy into the U.S. energy portfolio,” its authors say. Just as other experts have noted, that potential is simply waiting to be realized, with about a dozen U.S. projects in some stage of development. The right state and federal policies can help move these projects off of their drawing boards and into the water, the study authors say, and with that, help create a promising clean-energy future for all of us. 

To begin with, there isn’t just 54 gigawatts of cost-effective, accessible wind power potential within 50 miles of U.S. coastlines. There’s more than 134 gigawatts of potential at 209 sites, the NOWEGIS authors conclude. The Atlantic coast, all on its own, has enormous wind resources. And there is substantial potential in the Gulf of Mexico, the Great Lakes, and the Pacific, too. In scouting these areas, the authors were sure to exclude important habitats and marine sanctuaries. (NRDC continues to work with both the U.S. Department of the Interior’s Bureau of Ocean Energy Management and with offshore wind power developers to ensure that one environmental good (pollution-free wind power) doesn’t come at the expense of another (important ocean wildlife and habitat protections.))

More good news from the study: Thanks to the popularity of offshore wind power in both Europe and Asia, the technology is evolving fast, meaning its becoming more powerful and less expensive simultaneously.

The report confirms what other researchers have discovered: Offshore wind power can be an especially important resource for densely populated coastal areas, like the Northeast, the Mid-Atlantic, and northern California, where energy prices are high and land available for generation and transmission is generally limited. All of this means that offshore wind power can help meet peak power needs while reducing grid congestion and fighting the risk of blackouts, especially on hot summer days and cold winter nights when energy demand is highest.

State and federal policies will be key to advancing this promising industry, the study found. State renewable energy standards and other state policies, particularly those that require that a certain percentage of a state’s electricity come from offshore wind power, are essential to making offshore wind power a reality here in the U.S. And the report praises innovations from both the DOI and the DOE — including BOEM’s “Smart from the Start” siting program that can protect vulnerable habitats while expediting permitting and leasing, and the DOE’s Offshore Wind Innovation and Demonstration Initiative, designed  to advance offshore wind power technology, remove market barriers, and demonstrate advanced technologies.

Federal tax policies will be pivotal, too. Conventional, fossil-fuel-powered electricity is highly subsidized by the federal government, NOWEGIS’s authors note. “Policy makers will need to determine whether offshore wind should likewise receive tax credit support to encourage its development….Enacting tax credit support that will extend through 2020 will help support the first generation of offshore wind projects.”

Of particular importance is extension of the now-expired Investment Tax Credit for Offshore Wind Power. It’s due for Congressional consideration as part of a package of so-called tax extenders during the post-elections lame duck session this November. It’s time this and other clean-energy provisions pass.

As an advocate, I’ve promoted many of offshore wind power’s benefits: It can provide reliable, pollution-free energy to the coastal states where a full three-quarters of America’s population lives. It can create tens of thousands of good-paying, permanent jobs. Now, the DOE’s NOWEGIS highlights the substantial amount of money offshore wind power can save all of us — if we enact policies that jumpstart this promising industry now. 

Renewable Energy Storage Gains Critical Mass

A host of U.S. renewable energy storage executives recently gathered here in the Silicon Valley are referring to the rapid expansion of the storage industry by comparing it to the solar power industry six or eight years ago, before that companion sector became the juggernaut it is now.

These storage advocates were assembled for the Energy Storage North America exposition, which doubled in size compared with last year, according to conference chairperson Janice Lin. Also co-founder of the California Energy Storage Association, Lin said that “energy storage is a game changer for the electric power system, and this year’s ESNA event truly represents that.” 

Storage Belatedly Following PV Growth Curve

A number of investors in energy storage touted the wisdom of their bets. “Energy storage is one of the holy grails of renewable energy; the main issue is that costs still have to come down,” commented Andrew Chung, a partner at the venture capital firm Khosla Ventures, based in Menlo Park. “Energy storage wasn’t invented for grid-scale applications, but with it getting acceptance in solar, more states and nations will start to move toward implementing policy,” he said. Khosla lists six energy storage start ups within its portfolio now.

Similarly, Peter Rive, the co-founder of SolarCity said, “In three to five years, storage will be a standard component of residential solar power, not optional, but deployed with every solar system.” He continued, “It won’t look that different to the customer, but the fundamental value proposition will be cleaner and cheaper.” Rive also said that electric vehicle (EV) charging capability was likely to become a feature of the energy storage rollout.

Standout Projects Raise Storage Profile

Among standout energy storage projects highlighted at the show was the City of Santa Clara’s Levi Stadium, which features over 1,000 solar panels and six electric vehicle charging stations. The stadium also has installed Green Charge Networks' GreenStationsystem to help curb its power demand and lower electric bills, which spike during certain hours on game days, compared with minimal power and energy consumption throughout the remainder of the year.

Developers like AES also are building a global network of pioneering energy storage projects associated with renewable energy. “We now have 200 MW of energy storage online, mostly in the United States and Chile, including four utility scale plants built, and 2,000 MW on order,” said John Zahurancik, the president of AES Energy Storage, based in Arlington, Va. “There is a demand for 30 GW of new peaker plants by 2024, and by that year, battery production capacity will exceed the peaker need by a factor of four,” he added, suggesting energy storage would be well positioned to compete.

Solar panel manufacturers now moving into energy storage also will drive adoption more rapidly. Kyocera, for example, recently has forged new strategic relationships with both Stem, the energy storage developers, and with Healthy Planet Partners, a clean energy solutions fund that finances, implements and maintains distributed energy and energy. Many energy storage companies have begun offering financing through their own balance sheets or through such partnerships with financial companies. 

Ontario a North American Storage Leader

Apart from the now well-know U.S. state programs in California and Hawaii, the current energy storage initiative for the Canadian Province of Ontario is “to purchase 35 MW of varying storage at a rough cost of $42 million, “which will show up in couple of years,” says Kim Warren, the vice president of operations for the Independent Electricity System Operator (IESO) of the province, based in Toronto.

“We received 431 applications for 12 projects, with differing technologies, and we are doing a three to five year study of the combined storage system to see how storage will value, like California is doing; we may even conduct it in consultation with California,” Warren said. Describing the limitations of pumped hydro storage, and provincial plans to shut down 13,000 MW of nuclear power within five years, He suggested that wind and solar fit the ISO’s needs better. “We already have 9,000 MW of wind and solar contracted,” he said.

The Ontario IESO is studying the use of renewable energy storage not only for the primary grid, but for microgrids and remote off-grid locations, which abound in Canada. “We have purposely put renewables and storage in both congested and uncongested areas,” Warren said. “It is inevitable that as we move toward microgrids, especially with solar parity, we will need more intelligent conversation between the grid operators and the microgrids. The regulators will have to decide who pays for what,” he said.

Does the Psychological Effect of Oil Prices Impact the Solar Industry?

NEW YORK -- Plunging oil prices are shifting investor sentiment away from renewable power and helping pull down shares for solar companies, said Gordon Johnson, an analyst at Axiom Capital Management in New York.

Oil prices have plunged as growing production and slowing demand trigger concern of a global oversupply. The Bloomberg Global Large Solar Index of 21 companies has slipped 25 percent over the past month, more than triple the 7.4 percent decline in the Nasdaq Composite Index over the same period.

“Countries that aggressively expand solar have significantly higher costs than their neighbors” for energy, said Johnson, who has sell ratings on five of the six solar manufacturers he covers.

Solar power doesn’t compete with oil as a source of electricity except on small islands and in some crude exporting countries. Oil generates less than 1 percent of U.S. power supplies and 5 percent globally.

That link may be more emotional than based on fundamentals, said Josh Baribeau, an analyst at Canaccord Genuity Inc. in Boston.

“We believe that part of the solar sell-off may also be driven by the fall in oil prices,” he said in a note to clients on Oct. 14. “We have never liked the psychological correlation between solar stocks and oil, but it exists to some degree.”

All but two companies in the solar index have declined in the past month. Yingli Green Energy Holding Co., the biggest panel maker, slipped 17 percent and Trina Solar Ltd., the No. 2 producer, declined 24 percent. The index rebounded to gain 2 percent at the close yesterday in New York.

“A drop in oil doesn’t affect our space,” David Crane, chief executive officer of NRG Energy Inc., said yesterday in an interview. This year, the largest U.S. independent power producer acquired three solar power supply companies.

European Commission Studies Renewable Costs

LONDON -- New analysis commissioned by the European Commission concludes that renewables such as onshore wind and solar PV are close to that of conventional technologies like coal, gas and nuclear in terms of costs a subsidy levels.

Furthermore, by including external factors, which are not currently not reflected in market prices, such as climate and health costs, renewables are comparable if not even.

Interim findings from the Ecofys study commissioned by the EC deliver the first full dataset on costs per megawatt-hour (MWh) as well as subsidies for all forms of electricity generation. According to this analysis the total value of public interventions in energy, aside from transport fuels, was between €120-140 billion in 2012 for the 28 countries of the European Union.

“Unsurprisingly, given the efforts to expand the share of renewable energy in the EU’s overall energy consumption, the largest amounts of current public support in 2012 went to renewables,” said the Commission, noting that in 2012 subsidies for solar power were €14.7 billion, onshore wind €10.1 billion, biomass €8.3 billion and hydropower at €5.2 billion.

Conventional power generation technologies received subsidies of a similar order though, with €10.1 billion for coal, nuclear at €7 billion and natural gas at € 5.2 billion.

Furthermore, the Commission notes, these subsidy figures do not reflect the free allocation of emission certificates nor tax support for energy consumption.  Including these elements would inevitably narrow the subsidy gap still further.

Presenting figures on levelized costs per MWh, electricity from coal is around €75, onshore wind is marginally higher while nuclear and natural gas are around €100. Solar power costs have fallen to about €100-€115 depending on the size of the specific installation.

In addition, the commission estimates the impact of external costs at between €150 and €310 billion, a figure which if included, say renewable energy trade groups, would put such technologies economically more beneficial than conventional fuels.

European Wind Energy Association (EWEA) analysis of the data in the report puts onshore wind at around €105/MWh and offshore wind at €186, compared with gas at up to €164, nuclear at €133 and coal at €162-€233.

Commenting on the figures Justin Wilkes, EWEA deputy CEO, said: “This report highlights the true cost of Europe's dependence on fossil fuels. Renewables are regularly denigrated for being too expensive and a drain on the taxpayer. Not only does the Commission's report show the alarming cost of coal but it also presents onshore wind as both cheaper and more environmentally-friendly."

He added: "We are heavily subsidizing the dirtiest form of electricity generation while proponents use coal's supposed affordability as a justification for its continued use. The irony is that coal is the most expensive form of energy in the European Union.”

The European Photovoltaic Industry Association (EPIA) noted that the Ecofys study “proves that solar energy is cost effective today, and is improving competitiveness at a rate that conventional technologies will never be able to achieve.”

"Despite decades of heavy subsidies, mature coal and nuclear energy technologies still rely on similar levels of public support as innovative solar energy is getting today. However, support to solar electricity is already coming down, in line with the rapid technology cost reduction, as opposed to coal and nuclear energy, which remain locked into subsidies as they have been for the last 40 years. With its increasing cost-effectiveness, solar is set to overtake conventional technologies in the short term," said Frauke Thies, EPIA Policy Director.