The past year has been one of disruptive technologies and markets, continuing a trend started nearly a decade ago. Driven by the nearly irresistible forces of convergence, our tools, vehicles, services, and infrastructures are integrating ever more functionality, communications (both wired and wireless), and intelligence.
The power- and energy-management segment has been a high-profile party to this relentless storm of change. From new materials such as wide-bandgap electronics, which are shaking up fundamental power-system design, to new packaging, passive designs, supply topologies, alternative power-source technologies, and advanced energy storage, the power industry is undergoing a fundamental evolution that is affecting every facet of society.
The area of alternative energy continues to grow, creating grid-integration issues as well as market disruption. Both solar and wind power are making major incursions into the grid as those technologies mature and improve. Renewable energy sources also create challenges for the power-engineering community, as both solar and wind must be closely managed and balanced with both stored and generated power to function properly and serve reliably.
In the area of traditional solar panels, Kaneka created a crystalline silicon solar cell with a conversion efficiency of 26.63%. The 180-centimeter-square demonstrator, a heterojunction back-contact crystalline silicon solar cell, shows how much further mainstream devices can be extended. Current solar conversion efficiencies in advanced devices are in the neighborhood of 20%, with some space to go before reaching the 35% max a single monocrystalline cell can achieve. There are other ways to harvest sunlight that can improve on this performance, though currently they are too costly to use in mainstream applications.
One of the methods, thermophotovoltaics (TPV), is moving closer to commercial reality as researchers work to resolve the cost and fabrication issues. Created by combining an absorber-emitter material and a photovoltaic cell, a TPV device operates at temperatures that can exceed 1,000°C. The emitter releases the absorbed heat as photons, which are then picked up by the PV cell, producing electricity.
In a boost to the future of solar-cell technology, researchers at Duke University (http://pratt.duke.edu) demonstrated an electromagnetic metamaterial for thermal energy conversion that they say is the first to be made without metal. The material’s thermal stability and conversion performance promise to breathe new life into alternative solar technologies.
The metal-free metamaterial dielectric has a surface dimpled with cylinders tuned to absorb terahertz waves (Figure 1). The Duke team used boron-doped silicon to make tiny cylinders of varying sizes on the substrate, each tuned to interact with the terahertz waves in a programmed manner. By aligning the little pillars properly, researchers demonstrated that the material absorbed 97.5% of the energy produced at 1.011 THz. The demonstrator operates outside of the visual spectrum (below infrared for the current iteration), but the technology can be tailored for other frequencies. Properly matched to the right PV technology, this development could be a game changer for solar.
Of course, creating or harvesting energy is just the first step; one must move the power to where it needs to go. Microgrids have been around for a while, but with the advent of smart-grid and alternative-energy technologies — combined with the recent spate of natural disasters and the general effort to improve the lives of people in developing countries — you could say 2017 was the year of the microgrid.
In what was arguably the biggest microgrid news this year, Elon Musk’s Tesla made good on its bet to build the Hornsdale Power Reserve, a huge battery farm to store energy from the neighboring Hornsdale Wind Farm near Jamestown, Australia (Figure 2). In the face of legacy-industry pressure and alternative-energy naysayers, Musk famously said in September he would build the 100-megawatt storage facility in less than 100 days or give it to the Australians for free. By making Musk’s target date, Tesla not only demonstrated the commercial viability of its core technologies but proved its ability to deliver.
Two microgrid projects announced in November further demonstrate that microgrids are a viable upward-migration path for facilities and municipalities. One will establish an ABB-furnished solar-based lithium-ion storage microgrid system, with more than 650 kW of output and over 800 kilowatt-hours (kWh) of storage, on Robben Island, off the South African coast. Hannah Solar Government Services, meanwhile, won a contract to build a renewable-energy microgrid to serve the U.S. Air Force base on Wake Island in the North Pacific.
There are a lot of ways to store energy, from hot rocks and compressed air to supercapacitors and reflow batteries. Lithium-ion battery technology remains the focus today because it is the commercially proven, go-to storage method for personal electronics and electric vehicles (EVs). There are mighty attempts to improve or replace Li-ion batteries, however, and some interesting breakthroughs were announced this year.
One loudly public challenger, EV developer Fisker, filed patents on a flexible solid-state battery technology created by a team that included the cofounder of Sakti3, an early pioneer in solid-state batteries. The patent filings describe the use of novel materials and manufacturing processes to make three-dimensional electrodes, reportedly yielding a surface area that is an order of magnitude greater than is possible with the flat elements currently used (Figure 3), as well enabling higher conductivity. The battery technology promises to deliver more than twice the energy density of legacy products, at a lower cost.
A more tangible breakthrough was reported in India, where researchers at the Indian Institute of Science Education and Research have synthesized an anode material that directly addresses the issues of speed and charging-cycle capacity. The multilayer anode has pores that are optimized to allow lithium ions to flow through the layered nanosheets, enabling easy discharge. The battery was run through 1,000 charge/discharge cycles in testing and still had double the capacity of a traditional graphite-anode, according to the researchers.
Startup SolidEnergy Systems is also working to improve anodes. Its cell uses an ultra-thin piece of lithium metal for the anode, along with a proprietary electrolyte and a novel cell design, to achieve a claimed capacity of 400 to 500 Wh/kilogram at a size of 1,200 Wh/liter. The company plans to release its Apollo battery for EVs in 2020.
In the most tangible example of the new tech, Toshiba has applied its SCiB technology to build batteries that it says are safer, more reliable, and longer lasting than legacy products (Figure 4). Using anodes based on lithium titanium oxide, SCiB can prevent thermal runaway from wear-related short-circuiting and can operate for more than 15,000 charge/discharge cycles, according to Toshiba. The technology’s ability to handle high currents is not only useful for storage quantity, but also lets the battery harvest regenerative energy from sources such as electrical test systems or braking trains and cars.
The most recent anode news is that researchers from Russia’s Siberian Federal University, Krasnoyarsk Research Center, and National University of Science and Technology are using graphene and vanadium disulfide as an anode. The approach increases unit capacity, according to the researchers, because lithium ions are bound not only at the surface, as in conventional batteries, but also between the material layers of graphene and vanadium disulfide. The team estimates the unit capacity could reach 569 milliamp-hours/gram, which is almost double that of graphite. The method also promises a high charge/discharge rate and ruggedness.
A promising upstart technology, sodium-based batteries, made news this year. Although not as high in energy density capability as Li-ion batteries, sodium-ion technology promises to be safer, more stable, less costly, and much less problematic for the environment.
In a move that could change the battery industry, Stanford researchers announced that they created a sodium-based design that is comparable to lithium ion but is expected to cost less than a quarter of the total for a lithium battery of the same capacity. The approach binds sodium to the common industrial organic material myo-inositol to make the cathode, which is paired with a phosphorous anode. Going forward, the team will address energy density and optimize the phosphorus anode.
Supercapacitors have been touted as battery replacements for some time, but cost has been a major factor delaying adoption. In a move that could accelerate that pace, researchers at the Center for Micro-Photonics at Australia’s Swinburne University of Technology released their design for the Bolt Electricity Storage Technology (BEST) battery. Not a real battery, but a supercapacitor using graphene oxide, the device is predicted to be less expensive than legacy solutions and opens the door to supercapacitors’ replacing batteries in a variety of applications (Figure 5). Recently the Swinburne researchers secured $3.45 million in funding as part of the Cooperative Research Center Projects commissioned by the Australian government.
Development of a new passive technology isn’t something that happens every day. The last real new passive tech was the memristor; it was a fundamentally new device, and we won’t see anything like that anytime soon. Better and newer passive topologies can and do emerge, however, and the smart transformer is one of them.
A logical extension of the solid-state transformer, a smart transformer takes the addition of silicon and adds functionality. Long brewing, the technology arguably came of age this year with the efforts of companies like Legend Power, whose product, actually a novel power converter, is a high-efficiency autotransformer and controller (Figure 6). In contrast to traditional transformers, a smart transformer can monitor and adjust the incoming voltage for the entire system in real time.
The coming year will almost certainly see its share of breakthroughs, from next-generation power topologies to sleeper technologies (like the zinc-acid battery work being done at the City College of New York) waiting in the wings. The common denominator is how you, the engineering community, can work with these developments and integrate them into your designs. Good luck in 2018!