Isegoria

Introducing a simple, renewable chemical to the pretreatment step can finally make biofuel production both cost-effective and carbon neutral:

Lignin is one of the main components of plant cell walls. It provides plants with greater structural integrity and resiliency from microbial attacks. However, these natural properties of lignin also make it difficult to extract and utilize from the plant matter, also known as biomass.

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To overcome the lignin hurdle, [UC Riverside Associate Research Professor Charles] Cai invented CELF, which stands for co-solvent enhanced lignocellulosic fractionation. It is an innovative biomass pretreatment technology.

“CELF uses tetrahydrofuran or THF to supplement water and dilute acid during biomass pretreatment. It improves overall efficiency and adds lignin extraction capabilities,” Cai said. “Best of all, THF itself can be made from biomass sugars.”

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First-generation biofuel operations use food crops like corn, soy, and sugarcane as raw materials, or feedstocks. Because these feedstocks divert land and water away from food production, using them for biofuels is not ideal.

Second-generation operations use non-edible plant biomass as feedstocks. An example of biomass feedstocks includes wood residues from milling operations, sugarcane bagasse, or corn stover, all of which are abundant low-cost byproducts of forestry and agricultural operations.

According to the Department of Energy, up to a billion tons per year of biomass could be made available for the manufacture of biofuels and bioproducts in the US alone, capable of displacing 30% of our petroleum consumption while also creating new domestic jobs.

Because a CELF biorefinery can more fully utilize plant matter than earlier second-generation methods, the researchers found that a heavier, denser feedstock like hardwood poplar is preferable over less carbon-dense corn stover for yielding greater economic and environmental benefits.

Using poplar in a CELF biorefinery, the researchers demonstrate that sustainable aviation fuel could be made at a break-even price as low as $3.15 per gallon of gasoline equivalent. The current average cost for a gallon of jet fuel in the U.S. is $5.96.

On a clear night you’ll feel your body cool; some of that cooling is heat radiating into space:

Removing heat this way can cool that object down tens of degrees below the temperature of its surroundings.

We can exploit the temperature difference by turning it into electricity through thermoelectric power generation. The working principle behind a thermoelectric generator is the Seebeck effect, which describes how a material develops a voltage difference in response to a temperature differential across it. We can manipulate the Seebeck effect in semiconductors by the controlled addition of impurities, or dopants.

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With the ambient environment as a hot reservoir, we can use the coldness from deep space to create the cold reservoir. To do this, we send heat out to space using what we call an emitter, which cools itself to a lower temperature than its surroundings. That’s a phenomenon known as radiative cooling. Then, a thermoelectric generator situated between the cold emitter and the now-hotter ambient surroundings can produce electricity.

The emitter’s job is to radiate the heat out beyond Earth’s atmosphere. But the atmosphere is transparent only to photons of certain wavelengths. Within the mid-infrared range, which is where heat radiation from typical earthbound objects is concentrated, the most applicable atmospheric transmission band is in the 8- to 13-micrometer-wavelength range. Even some simple emitters send out heat radiation at these wavelengths. For example, if it’s insulated from ambient surroundings, black paint emits enough radiation within that band to cool a surface down by 10 degrees Celsius when exposed to the night sky.

In the wavelength range outside 8 to 13 mm, the atmosphere bounces back a substantial amount of radiation. During the daytime, solar radiation comes into the equation. More-advanced emitter designs aim to avoid the incoming radiation from the atmosphere and sunlight by ensuring that they absorb and emit only within the transparency window. The idea of using such a wavelength-selective emitter for radiative cooling dates back to the pioneering work of Claes-Göran Granqvist and collaborators in the 1980s. Just as an engineer designs a radio antenna with a specific shape and size to transmit over a certain wavelength in a certain direction, we can design an emitter using a library of materials, each with a specific shape and size, to adjust the wavelength band and direction for heat radiation. The better we do this, the more heat the emitter ejects into space and the colder the emitter can get.

Glass is a great material for an emitter. Its atomic vibrations couple strongly to radiation around the 10-micrometer wavelength, forcing the material to emit much of its heat radiation within the transmission window. Just touch a glass window at night and you’ll feel this cooling. Adding a metallic film to help reflect radiation skyward makes the emissions—and the cooling—even more effective. And structures can be specifically designed to strongly reflect the wavelengths of sunlight.

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Putting all these optimizations together, we calculated that the maximum achievable power density for this technology is 2.2 W/m². This power density is a lot lower than what can be generated with solar cells under sunlight. However, when sunlight isn’t readily available, this is pretty good; it’s significantly higher compared to what can be achieved with many other ambient energy-harvesting schemes. For example, it’s orders of magnitude more than the less than 1 mW/m² that can be harvested from ambient radio waves.

Geothermal offers a virtually limitless, always-on source of emissions-free heat and electricity:

If the US could capture just 2% of the thermal energy available two to six miles beneath its surface, it could produce more than 2,000 times the nation’s total annual energy consumption.

But because of geological constraints, high capital costs and other challenges, we barely use it at all: today it accounts for 0.4% of US electricity generation.

To date, developers of geothermal power plants have largely been able to tap only the most promising and economical locations, like this stretch of Nevada. They’ve needed to be able to drill down to porous, permeable, hot rock at relatively low depths. The permeability of the rock is essential for enabling water to move between two human-drilled wells in such a system, but it’s also the feature that’s often missing in otherwise favorable areas.

Starting in the early 1970s, researchers at Los Alamos National Laboratory began to demonstrate that we could engineer our way around that limitation. They found that by using hydraulic fracturing techniques similar to those now employed in the oil and gas industry, they could create or widen cracks within relatively solid and very hot rock. Then they could add in water, essentially engineering radiators deep underground.

Such an “enhanced” geothermal system then basically works like any other, but it opens the possibility of building power plants in places where the rock isn’t already permeable enough to allow hot water to circulate easily. Researchers in the field have argued for decades that if we drive down the cost of such techniques, it will unlock vast new stretches of the planet for geothermal development.

A noted MIT study in 2006 estimated that with a $1 billion investment over 15 years, enhanced geothermal plants could produce 100 gigawatts of new capacity on the grid by 2050, putting it into the same league as more popular renewable sources. (By comparison, about 135 gigawatts of solar capacity and 140 gigawatts of wind have been installed across the US.)

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Creating fractures in rocks with low permeability means that the water in the system can’t easily leak out into other areas. Consequently, if you close off the well system and keep pumping in water, you can build up mechanical pressure within the system, as the fractured rock sections push against the earth.

“The fractures are able to dilate and change shape, almost like balloons,” Norbeck says.

That pressure can then be put to use. In a series of modeling experiments, Fervo found that once the valve was opened again, those balloons effectively deflated, the flow of water increased, and electricity generation surged. If they “charged it” for days, by adding water but not letting it out, it could then generate electricity for days.

Researchers at Purdue have developed HADAR, or heat-assisted detection and ranging:

Because thermal waves constantly scatter, infrared cameras capture “ghostlike” images with no depth or texture:

For their experiment, the researchers chose an outdoor space in a marshy area, far from roads and urban illumination. They collected thermal images in the infrared spectrum across almost 100 different frequencies. And just as each pixel in RGB images is encoded by three visible frequencies (R for red, G for green, B for blue), each pixel in the experiment was labeled with three thermal physics attributes, TeX—temperature (T), material fingerprint or emissivity (e), and texture or surface geometry (X). “T and e are reasonably well understood, but the crucial insight about texture is actually in X,” says Jacob. “X is really the many little suns in your scene that’s illuminating your specific area of interest.”

The researchers fed all the collected TeX information into a machine-learning algorithm to generate images with depth and texture. They used what they call TeX decomposition to untangle temperature and emissivity, and recover texture from the heat signal. The decluttered T, e, and X attributes were then used to resolve colors in terms of hue, saturation, and brightness in the same way humans see color. “At nighttime, in pitch darkness, our accuracy was the same when we came back in the daytime and did the ranging and detection with RGB cameras,” Jacob says.

The biggest advantage of HADAR is that it is passive, Jacob adds. “Which means you don’t have to illuminate the scene with a laser, sound waves, or electromagnetic waves. Also, in active approaches like lidar, sonar, or radar, if there are many agents in the scene, there can be a lot of crosstalk between them.”

As a new technology, HADAR is in a fairly nascent stage, Jacob says. At present, data collection requires almost a minute. By comparison, an autonomous vehicle driving at night, for example, would need to image its surroundings in milliseconds. Also, the cameras required for data collection are bulky, pricey, and power hungry: “Great for a scientific demonstration, but not really for kind of widespread adoption,” according to Jacob. The researchers are currently working on these problems, and Jacob predicts another few years of research will be directed to address them.