Power/Performance Bits: Dec. 18

Solar storage

Engineers at MIT, Georgia Institute of Technology, and the National Renewable Energy Laboratory designed a system to store renewable energy in vast amounts and deliver it back to the grid when power generation is low. The system stores excess electricity from solar or wind installations as heat using tanks of white-hot molten silicon, and then converts the light from the glowing metal back into electricity as needed. The researchers estimate that such a system would be much more affordable than lithium-ion batteries, and cost half as much as pumped hydroelectric storage.

The system, called TEGS-MPV for Thermal Energy Grid Storage-Multi-Junction Photovoltaics, consist of a large, heavily insulated, 10-meter-wide tank made from graphite and filled with liquid silicon, kept at a “cold” temperature of almost 3,500 degrees Fahrenheit. A bank of tubes, exposed to heating elements, then connects this cold tank to a second, “hot” tank.

Researchers propose a concept for a renewable storage system that would store solar and wind energy in the form of white-hot liquid silicon, stored in heavily insulated tanks. (Source: Duncan MacGruer / MIT)

When electricity from solar panels or wind installations comes into the system, the energy is converted to heat in the heating elements. Meanwhile, liquid silicon is pumped out of the cold tank and further heats up as it passes through the bank of tubes exposed to the heating elements, and into the hot tank, where the thermal energy is now stored at a much higher temperature of about 4,300 F.

When electricity is needed, the hot, glowing silicon is pumped through an array of tubes that emit that light. Multijunction photovoltaic solar cells then turn that light into electricity, which can be supplied to the grid. The now-cooled silicon can be pumped back into the cold tank until the next round of storage.

The researchers estimate that a single storage system could enable a small city of about 100,000 homes to be powered entirely by renewable energy.

Electron accelerator on chip

Engineers at TU Darmstadt have developed a design for a laser-driven electron accelerator so small it could be produced on a silicon chip.

The Accelerator on a Chip International Program (AChIP) aims to create an accelerator on a chip in an experimental chamber the size of a shoebox. The program, which has funding until 2020, hopes to produce electrons with one mega-electron volt of energy from the chip, as well as ultra-short electron pulses.

To build the chip, it was necessary to replace accelerator parts made of metal with glass or silicon, and to use a laser instead of a microwave generator as an energy source. Due to glass’s higher electric field load capacity, the acceleration rate can be increased and thus the same amount of energy can be transmitted to the particles within a shorter space, making the accelerator shorter by a factor of approximately 10 than traditional accelerators delivering the same energy.

Accelerator chip on the tip of a finger, and an electron microscope image of the chip. (Source: Hagen Schmidt / Andrew Ceballos)

However, the vacuum channel for the electrons on a chip has to be made very small, which requires that the electron beam is extremely focused. Conventional magnetic focusing channels are too weak, making developing a new focusing method a priority.

The TU Darmstadt group’s solution uses the laser fields themselves to focus the electrons in a channel only 420nm wide. The concept is based on abrupt changes to the phase of the electrons relative to the laser, resulting in alternating focusing and de-focusing in the two directions in the plane of the chip surface and creating stability in both directions.

The tiny accelerator could be used as part of a compact coherent X-ray beam source for the characterization of materials and photolithography, or as an accelerator-endoscope used in tumor treatment. Importantly, the researchers believe the chip could be produced inexpensively in large numbers, allowing every university to afford an accelerator laboratory.

Graphene for disease detection

Researchers at the University of Illinois at Chicago found a new use for graphene. The so-called “wonder material” shows promise in areas ranging from flexible electronics to batteries, and may now find a use in testing and diagnosis of amyotrophic lateral sclerosis, or ALS. ALS, a progressive, neurodegenerative disease, is currently diagnosed mostly by ruling out other disorders.

The test relies on the bonds between carbon atoms in graphene. The elasticity of these bonds produces resonant vibrations, or phonons, which can be very accurately measured.

The researchers found that when cerebrospinal fluid from patients with ALS was added to graphene, it produced a distinct and different change in the vibrational characteristics of the graphene compared to when fluid was added from a patient with multiple sclerosis or without neurodegenerative disease.

How graphene can be used to detect ALS biomarkers from cerebrospinal fluid. (Source: Berry Research Laboratory, UIC)

“We saw unique and distinct changes in graphene’s phonon energies depending on whether the fluid was from someone with ALS, multiple sclerosis or someone without neurodegenerative disease,” said Vikas Berry, associate professor and head of chemical engineering at UIC. “We were also able to determine whether the fluid was from someone over age 55 or younger than 55 when we tested cerebrospinal fluid from ALS patients. We think the difference we see between older and younger ALS patients is driven by unique biochemical signatures we are picking up that correlate to inherited ALS, which usually produces symptoms before age 55, and what’s known as sporadic ALS which occurs later in life.”

Berry believes the graphene is picking up on the unique biosignatures — combinations of proteins, and other biomolecules — present in the cerebrospinal fluid of individuals with different diseases.

“The electronic properties of graphene have been extensively studied, but only recently have we begun to examine its phononic properties as a way to detect diseases,” Berry said. “And it turns out that graphene is an extremely versatile and accurate detector of biosignatures of diseases found both in cerebrospinal fluids and whole cells.”

Since there is no definitive test for ALS, an objective diagnostic test would help patients start receiving treatment sooner to slow the disease.