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Ultra-efficient photovoltaic designs

A four-junction solar cell, developed by Germany’s Freiburg-based Fraunhofer Institute for Solar Energy Systems, Soitec and two other research organisations, achieved a record breaking 44.7% efficiency converting sunlight to electricity in September 2013. The solar cell structure comprised four solar sub-cells made from different semiconductor materials, each designed for absorbing different wavelength ranges of the solar spectrum.

Prior to this breakthrough, a team led by Dr Harry Atwater, a physicist at California Institute of Technology, developed an ultra-efficient solar design prototype integrating a multi-junction cell concept using spectral beam splitting technology. The design enables efficient splitting of the sunlight spectrum into six to eight component wavelengths, each producing a different colour of light. Each colour of light passes through a cell made of a specific semiconductor that can absorb it. The design is believed to be capable of a minimum 50% conversion efficiency.

The prototype design used a reflective metal to collect sunlight and direct it at a specific angle to the solar panel with multiple solar cells. The broad spectrum sunlight is split into different colours as it passes through the structure, encountering a series of optical filters. Atwater’s team is also working on two other designs based on this path-breaking concept. One of these uses nanoscale optical filters to filter light coming from all angles. The other uses a hologram instead of filters to split the spectrum. Which of these designs will offer the best performance remains to be seen.

Breakthroughs in HVDC transmission

The Swiss-based power and automation company ABB introduced its fourth generation HVDC light transmission system, which is designed for underground and subsea transmission with a record high ±320kV voltage-sourced converter. The voltage level achieved in this system was 50% higher than the previous record set by ABB itself.

This is the latest breakthrough in HDVC technology paving the way for the evolution of interconnected HVDC super grids. In late 2012, ABB announced the development of a hybrid HVDC circuit breaker, which is critical for the reliable operation of interconnected HVDC grids. The HVDC circuit breaker can disconnect parts of the grid experiencing problems while ensuring continuous transmission in the rest of the grid.

ABB also created a simulation centre to develop controls for DC grids including DC to AC conversion stations. High-voltage DC power has traditionally been used for point-to-point transmission, and integrated transmission networks have been predominantly operated using AC power. These breakthroughs lead to the development of integrated HVDC networks that could efficiently route power from far-flung places to any part of the world with significantly less power-conduction loss.

Flow battery technology for low-cost and large-scale renewable energy storage

Researchers at Massachusetts Institute of Technology (MIT) designed a low-cost, rechargeable flow battery without expensive membranes to generate and store renewable electricity on a large scale. A prototype of this innovative battery technology demonstrated significantly higher performance than most lithium-ion batteries and other commercial and experimental energy-storage systems.

“Researchers at Massachusetts Institute of Technology (MIT) designed a low-cost, rechargeable flow battery without expensive membranes to generate and store renewable electricity on a large scale.”

The reactants used in the storage device are a less expensive liquid bromine solution and hydrogen fuel. The device uses laminar flow technology, which allows the liquids to undergo electrochemical reactions between two electrodes in two separate parallel streams without a membrane.

In January 2014, a team of scientists and engineers from Harvard demonstrated a new flow-battery technology using organic molecules called quinones abundantly available in crude oil and green plants, instead of precious metal electrolytes such as Vanadium and Platinum. The new flow-battery technology offers a cost-effective means of storing large-scale renewable energy generated from wind and solar sources in the grid.

Floating wind energy storage

MIT researchers developed an approach to store and use on-demand the electricity generated by floating wind farms. The new technology represents a major leap in mitigating the intermittent and unpredictable nature of offshore wind power generation.

The new offshore wind power storage concept involves the erection of a 30m diameter hollow-concrete sphere with 3m of wall thickness on the sea floor under the wind turbine, which can serve as an anchor to moor the floating turbines while also helping to store the extra energy produced.

The concept envisages a pump attached to the underwater structure, which can be driven by excess wind energy, to pump sea water from the hollow sphere. Water can be allowed to flow back into the sphere through a turbine attached to a generator when needed. The sphere can also be used to store energy from other sources as the system can be connected to the grid.

Breakthrough developments in nuclear fusion technology

Research in the area of nuclear fusion technology development reached a new milestone in September 2013, as an experiment by scientists at the National Ignition Facility, Livermore, California, confirmed that the amount of energy released from nuclear fusion reaction could be more than the energy absorbed by the fuel.

The nuclear fusion technology involves power generation through fusion of two or more lighter atoms to a larger one, unlike the conventional nuclear fission technology whereby energy is released through the splitting of atoms. The particles released by fusion are believed to be less radioactive but more energy-producing than those released by fission.

The commercial viability of the fusion technology may be a reality in the near future with ongoing innovations in the field. The world’s biggest experimental nuclear fusion reactor, called ITER, is being developed in the French scientific research centre Cadarache as a joint project of multiple countries including the US, Russia, India and Japan. The superconductivity research group of the University of Twente towards the end of 2013 developed a superconducting cable system which can help create a magnetic field strong enough to control the enormously hot plasma in the fusion reactor core.

Underwater kites for low-velocity tidal power generation

Swedish marine energy technology company Minesto developed a new generation technology to harness power from low-velocity tidal currents. The new technology uses a device called “Deep Green” that looks like an underwater kite. The technology opens up the opportunity for ocean power generation from many potential sites around the world, which cannot otherwise be exploited with existing technologies.

“Minesto is planning a full-scale installation of Deep Green with 3MW capacity in 2015.”

The innovative marine power device is equipped with a hydrodynamic wing and a gearless turbine anchored to the ocean bed with a tether. The device is allowed to float at least 20m below the water surface along a controlled trajectory to maximise energy output. Water passing over the device lifts up the wing and rotates the turbine to generate electricity.

A pilot project based on this technology started power production towards the end of 2013 off Strangford Lough in Northern Ireland. It demonstrates the ability to produce power from currents with velocity of less than 2.5m/s. Minesto is planning a full-scale installation of Deep Green with 3MW capacity in 2015.

Multiple-zone stimulation from single wellbore for enhanced geothermal system

The enhanced geothermal systems (EGS)-focused renewable energy development company AltaRock Energy achieved a major breakthrough by creating multiple stimulated zones from a single well at the Newberry EGS demonstration site in Bend, Oregon, US. The new technique paves the way for cost-competitive electricity generation from EGS.

EGS are the geothermal reservoirs created by drilling wells deep into the ground and fracturing the hot rocks by injecting cold water. Injected water, heated by contact with the hot rock, is brought to surface for through production wells. The EGS technology expands the scope of geothermal energy exploitation from different geographical locations, unlike the traditional geothermal systems that are limited to places with naturally occurring geothermal reservoirs.

The multiple-zone stimulation technique with the use of a single well can lower the cost of EGS energy production by approximately 50%. The technique involves the use of thermally degradable zonal isolation materials (TZIM), AltaRock Energy’s patented materials made from a biodegradable non-toxic polymer. TZIM added to the injection water propels stimulation from one zone to the other.

Hydrogenie power generator passes trials successfully

GE announced the successful trial of its innovative compact power generation technology “Hydrogenie” in Rugby, England, in April 2013. The technology allows for higher electricity generation from renewable resources, such as water and wind, using superconductors running at relatively high temperatures.

The 1.7MW Hydrogenie generator spinning at 214rpm makes use of high-temperature superconductors (HTS) rather than copper for the rotor windings on the motor. Although superconductivity for similar purposes could only be achieved at approximately 4 Kelvin (-269°C), the new HTS power generation technology demonstrated its capacity to run at temperatures up to 50 Kelvin (-223.15°C).

The Hydrogenie generator features a cryonic cooling system, thermal insulation and a rotor located inside a vacuum. The breakthrough could lead to the development of more efficient superconducting machines for power generation. The technology can also help in upgrading older run-of-river power plants, as well as the high-torque and slow-speed wind machines in use.

NRI Energy Technology