hydricity

Solarkraftwerk Waldpolenz, the first Solar 40-MW CdTe PV Array installed by JUWI Group in Brandis, Germany. Credit: JUWI Group

Researchers are proposing a new "hydricity" concept aimed at creating a sustainable economy by not only generating electricity with solar energy but also producing and storing hydrogen from superheated water for round-the-clock power production.

"The proposed hydricity concept represents a potential breakthrough solution for continuous and efficient power generation," said Rakesh Agrawal, Purdue University's Winthrop E. Stone Distinguished Professor in the School of Chemical Engineering, who worked with chemical engineering doctoral student Emre Gençer and other researchers. "The concept provides an exciting opportunity to envision and create a sustainable economy to meet all the human needs including food, chemicals, transportation, heating and electricity."

Hydrogen can be combined with carbon from agricultural biomass to produce fuel, fertilizer and other products.

"If you can borrow carbon from sustainably available biomass you can produce anything: electricity, chemicals, heating, food and fuel," Agrawal said.

Findings are detailed in a research paper appearing this week (Dec. 14) in the online early edition of Proceedings of the National Academy of Sciences.

Hydricity uses solar concentrators to focus sunlight, producing high temperatures and superheating water to operate a series of electricity-generating steam turbines and reactors for splitting water into hydrogen and oxygen. The hydrogen would be stored for use overnight to superheat water and run the steam turbines, or it could be used for other applications, producing zero greenhouse-gas emissions.

"Traditionally electricity production and hydrogen production have been studied in isolation, and what we have done is synergistically integrate these processes while also improving them," Agrawal said.

The PNAS paper was authored by Gençer; former chemical engineering graduate student Dharik S. Mallapragada; François Maréchal, a professor and chemical process engineer from École Polytechnique Fédérale de Lausanne in Switzerland; Mohit Tawarmalani, a professor and Allison and Nancy Schleicher Chair of Management at Purdue's Krannert School of Management; and Agrawal.

In superheating, water is heated well beyond its boiling point – in this case from 1,000 to 1,300 degrees Celsius - producing high-temperature steam to run turbines and also to operate solar reactors to split the water into hydrogen and oxygen.

"In the round-the-clock process we produce hydrogen and electricity during daylight, store hydrogen and oxygen, and then when solar energy is not available we use hydrogen to produce electricity using a turbine-based hydrogen-power cycle," Tawarmalani said. "Because we could operate around the clock, the steam turbines run continuously and shutdowns and restarts are not required. Furthermore, our combined process is more efficient than the standalone process that produces electricity and the one that produces and stores hydrogen."

The system has been simulated using models, but there has been no experimental component to the research.

"The overall sun-to-electricity efficiency of the hydricity process, averaged over a 24-hour cycle, is shown to approach 35 percent, which is nearly the efficiency attained by using the best photovoltaic cells along with batteries," Gençer said. "In comparison, our proposed process stores energy thermo-chemically more efficiently than conventional energy-storage systems, the coproduced hydrogen has alternate uses in the transportation-chemical-petrochemical industries, and unlike batteries, the stored energy does not discharge over time and the storage medium does not degrade with repeated uses."

Agrawal said, "The concept combines processes already developed by other researchers while also improving on these existing processes. The daytime and night-time systems would use much of the same equipment, allowing them to segue seamlessly, representing an advantage over other battery-based solar technologies."

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Inside a Cell Phone

On a "complexity per cubic inch" scale, cell phones are some of the most intricate devices people use on a daily basis. Modern cell phones can process millions of calculations per second in order to compress and decompress the voice stream. If you have readHow Cell Phones Work, you know that they can transmit and receive on hundreds of FM channels, switching channels in sync with base stations as the phone moves between cells.

If you ever take a cell phone apart you will find that it contains just a few individual parts:

• A microscopic microphone
• A speaker
• An LCD or plasma display
• A keyboard not unlike the one we saw in a TV remote control
• An antenna
• A battery
• An amazing circuit board containing the guts of the phone

The circuit board is the heart of the system. Here is one from a typical Ericsson cell phone:

In this picture several of the components are identified. Starting from the left you the see the Analog-to-Digital and Digital-to-Analog conversion chips. You can learn more about A-to-D and D-to-A conversion and its importance to digital audio in How CDs Work. The DSP is a "Digital Signal Processor" -- a highly customized processor designed to perform signal manipulation calculations at high speed. This DSP is rated at about 40 MIPS (Millions of Instructions per Second) and handles all the signal compression and decompression. The microprocessor (Ericsson phones use an ASIC version of the Z-80) and memory handle all of the housekeeping chores for the keyboard and display, deal with command and control signaling with the base station and also coordinate the rest of the functions on the board. The RF and power section handles power management and recharging and also deals with the hundreds of FM channels. Finally the RF (Radio Frequency) amplifiers handle signals in and out of the antenna.

What is amazing is that all of that functionality -- which only 30 years ago would have filled the entire floor of an office building -- now fits into a package that sits comfortably in the palm of your hand.