Cheap and enviromentally friendly: Tofu ingredient could revolutionize solar panel manufacture

ScienceDaily
The chemical used to make tofu and bath salts could also replace a highly toxic and expensive substance used to make solar cells, a new study has revealed. Cadmium chloride is currently a key ingredient in solar cell technology used in millions of solar panels around the world. This soluble compound is highly toxic and expensive to produce, requiring elaborate safety measures to protect workers during manufacture and then specialist disposal when panels are no longer needed. (Original paper)

3D PV

R&D Mag
Building cubes or towers that extend the solar cells upward in 3D configurations. Amazingly, the results from the structures they've tested show power output ranging from double to more than 20 times that of fixed flat panels with the same base area. The biggest boosts in power were seen in the situations where improvements are most needed: in locations far from the equator, in winter months and on cloudier days. The new findings, based on both computer modeling and outdoor testing of real modules, have been published in Energy and Environmental Science. (...) "Even 10 years ago, this idea wouldn't have been economically justified because the modules cost so much," Grossman says. But now, he adds, "the cost for silicon cells is a fraction of the total cost, a trend that will continue downward in the near future." Currently, up to 65% of the cost of photovoltaic (PV) energy is associated with installation, permission for use of land, and other components besides the cells themselves.
Check the original paper for details.

Hybrid PV cell with up to 44% efficiency

SolarServer
Researchers at Cavendish Laboratory have developed a "hybrid" solar photovoltaic (PV) cell which can reach up to 44% efficiency by utilizing a greater portion of the spectrum of sunlight.
The new cells not only absorb both red and blue light, but by adding the organic semiconductor pentacene the cells are able to generate two electrons for every photon from the blue light spectrum. Cambridge University Professors Neil Greenham and Sir Richard Friend led the team, which published its research in the journal NanoLetters concurrent with the announcement.
Paper at NanoLetters

Paint-on solar cells developed

Science daily
A team of researchers at the University of Notre Dame has made a major advance toward this vision by creating an inexpensive "solar paint" that uses semiconducting nanoparticles to produce energy.(...) [D]escribed in the journal ACS Nano, centered on nano-sized particles of titanium dioxide, which were coated with either cadmium sulfide or cadmium selenide. The particles were then suspended in a water-alcohol mixture to create a paste. When the paste was brushed onto a transparent conducting material and exposed to light, it created electricity. "The best light-to-energy conversion efficiency we've reached so far is 1 percent, which is well behind the usual 10 to 15 percent efficiency of commercial silicon solar cells,".

Full paper here.

NREL achieves 114% external quantum efficiency with quantum dots

KW51
NREL states that it has reached an external quantum efficiency of 114% with sub-microscopic semiconductor crystals, also called quantum dots, photo-excited with photons from high-energy light. The results of the organization's research have been originally published in the December 16th, 2011 issue of Science Magazine [co-authored by Octavi E. Semonin, Joseph M. Luther, Sukgeun Choi, Hsiang-Yu Chen, Jianbo Gao, Arthur J. Nozik and Matthew C. Beard.](...) Researchers constructed the 114% external quantum efficiency cell from a layered PV cell consisting of anti-reflection coated glass, a thin layer of transparent conductor, a nano-structured zinc oxide layer, a quantum dot layer of lead selenide treated with ethanedithol and hydraizine, and a thin gold top electrode layer.
NREL states that the mechanism for producing a quantum efficiency greater than 100% is based on a process called Multiple Exciton Generation (MEG). In this process, a single high energy absorbed photon can produce more than one electron-hole pair per absorbed photon.
Here is the full article (for those with a Science subscription).

Solar Grid Parity Is Here Today

Greentech Media
The price of solar energy-generated electricity, calculated by a legitimate levelized cost of energy (LCOE) method, is now competitive in many regions with the price of electricity generated by conventional sources.

Paper: K. Branker, M.J.M. Pathak, J.M. Pearce, A review of solar photovoltaic levelized cost of electricity, Renewable and Sustainable Energy Reviews, Volume 15, Issue 9, December 2011, Pages 4470-4482

Residential Solar Systems Increase Sale Prices, Study Finds

NYTimes.com
All those homeowners who have been installing residential solar panels over the last decade may find it was a more practical decision than they thought. The electricity generated may have cost more than that coming from the local power company (half of which, nationwide, comes from burning coal), but if they choose to sell their homes, the price premium they will get for the solar system should let them recoup much of their original capital investment. (...) Homeowners who install solar on existing houses get nearly three times the premium of homeowners whose house came with solar panels. The study speculates about the reasons, suggesting that “new home builders may also gain value from PV as a market differentiator, and have therefore often tended to sell PV as a standard (as opposed to an optional) product on their homes and perhaps been willing to accept a lower premium in return for faster sales velocity.”

More details at the Lawrence Berkeley National Lab site:
Hoen, B., R. Wiser, P. Cappers and M. Thayer. LBNL-4476E. April 2011
An Analysis of the Effects of Residential Photovoltaic Energy Systems on Home Sales Prices in California

Reconsidering solar grid parity

Chi-Jen Yang in Energy Policy, Volume 38, Issue 7, July 2010, Pages 3270-3273
Grid parity–reducing the cost of solar energy to be competitive with conventional grid-supplied electricity–has long been hailed as the tipping point for solar dominance in the energy mix. Such expectations are likely to be overly optimistic. (...) [C]ost-effectiveness may not guarantee commercial competitiveness. Solar hot water technology is currently far more cost-effective than photovoltaic technology and has already reached grid parity in many places. Nevertheless, the market penetration of solar water heaters remains limited for reasons including unfamiliarity with the technologies and high upfront costs. These same barriers will likely hinder the adoption of distributed solar photovoltaic systems as well. The rapid growth in PV deployment in recent years is largely policy-driven and such rapid growth would not be sustainable unless governments continue to expand financial incentives and policy mandates, as well as address regulatory and market barriers.

Energy from solar ballons
Solar balloons are hot air balloons in which the air is heated directly by the sun, by means of a black absorber. The lift force of a tethered solar balloon can be used to produce energy by activating a generator during the ascending motion of the balloon. The hot air is then discharged when the balloon reaches a predefined maximum height. (...) The efficiency is lower than what can be achieved with conventional photovoltaic or thermal systems, due to the limited temperature difference that can be exploited. However, the system requires simple technologies and low cost materials, and the final cost per unit power output can be competitive.

Solar Panel Productivity Boosted by Origami
Three-dimensional solar panels could in principle absorb more light and generate more power than a flat panel of the same area footprint, which could prove useful in circumstances where the available space is limited. The idea is that any light that might normally reflect unused off a solar panel surface could then get trapped on another panel.
Original paper at Applied Physics Letters

Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications
To achieve competitive conversion efficiencies, [silicon nano-]wires must absorb sunlight over a broad range of wavelengths and incidence angles, despite occupying only a modest fraction of the array’s volume. Here, we show that arrays having less than 5% areal fraction of wires can achieve up to 96% peak absorption, and that they can absorb up to 85% of day-integrated, above-bandgap direct sunlight. In fact, these arrays show enhanced near-infrared absorption, which allows their overall sunlight absorption to exceed the ray-optics light-trapping absorption limit for an equivalent volume of randomly textured planar Si, over a broad range of incidence angles. We furthermore demonstrate that the light absorbed by Si wire arrays can be collected with a peak external quantum efficiency of 0.89, and that they show broadband, near-unity internal quantum efficiency for carrier collection through a radial semiconductor/liquid junction at the surface of each wire. The observed absorption enhancement and collection efficiency enable a cell geometry that not only uses 1/100th the material of traditional wafer-based devices, but also may offer increased photovoltaic efficiency owing to an effective optical concentration of up to 20 times.

43% composite split-spectrum concentrator solar cell efficiency
One way of improving photovoltaic efficiency is to subdivide the solar spectrum into small energy ranges and to convert each range with an appropriate bandgap cell. Most implementations use monolithic or mechanical cell stacks, with earlier approaches based on steering different wavelengths to non-stacked cells recently re-explored. The present work extends this by putting measurements on a more rigorous basis and by improving the composite experimental efficiency of selected cells to beyond 43%, the highest reported for photovoltaic conversion.

“Near Perfect” Absorption of Sunlight, From All Angles
To harness the full spectrum of solar energy, Fresnel reflection at the surface of a solar cell must be eliminated over the entire solar spectrum and at all angles. Here, we show that a multilayer nanostructure having a graded-index profile (...) can accomplish a near-perfect transmission of all-color of sunlight. An ultralow total reflectance of 1%-6% has been achieved over a broad spectrum, λ=400to1600 nm, and a wide range of angles of incidence, θ=0°-60°. The measured angle- and wavelength-averaged total reflectance of 3.79% is the smallest ever reported in the literature, to our knowledge.


Typical antireflective coatings are engineered to transmit light of one particular wavelength. Lin’s new coating stacks seven of these layers, one on top of the other, in such a way that each layer enhances the antireflective properties of the layer below it. These additional layers also help to “bend” the flow of sunlight to an angle that augments the coating’s antireflective properties. This means that each layer not only transmits sunlight, it also helps to capture any light that may have otherwise been reflected off of the layers below it. The seven layers, each with a height of 50 nanometers to 100 nanometers, are made up of silicon dioxide and titanium dioxide nanorods positioned at an oblique angle — each layer looks and functions similar to a dense forest where sunlight is “captured” between the trees. The nanorods were attached to a silicon substrate via chemical vapor disposition, and Lin said the new coating can be affixed to nearly any photovoltaic materials for use in solar cells, including III-V multi-junction and cadmium telluride.

Germany's solar cell promotion: Dark clouds on the horizon
[Frondel et al, Energy Policy, Nov 2008; also available from here] This article demonstrates that the large feed-in tariffs currently guaranteed for solar electricity in Germany constitute a subsidization regime that threatens to reach a level comparable to that of German hard coal production, a notoriously outstanding example of misguided political intervention (...) For the first scenario [if it had ended in 2007], we have estimated real net cost of approximately 26.5 Bn€, while an abolition in 2010 [after the next federal election] comes at similarly large additional net cost of about 27 Bn€ (in prices of 2007) (...) We argue that in the early stages of development of noncompetitive technologies, it appears to be more cost-effective to invest in research and development (R&D) to achieve competitiveness, rather than to promote their large-scale production.

Ultrathin silicon solar microcells for semitransparent, mechanically flexible and microconcentrator module designs
[Nature Materials, Rodgers at al, Illinois] The authors carve their microcell arrays from a rectangular block of silicon. They begin by etching the outlines of the microcells (the tops and sides) onto the upper surface of the silicon block. They then make electronic junctions and electrical contacts by doping the silicon, adding boron and phosphorus, and using an inert mask to define the regions to be doped. A further round of etching exposes the final three-dimensional shape of the microcells, retaining a thin sliver of silicon to anchor the cells to the block. Finally, the base of the wafer is doped with boron, to yield functioning solar microcells. To make bendable, large-scale solar cells, Rogers and colleagues use a printing technique. They press a flat stamp onto the arrays of microcells on the silicon block, breaking the anchors that tether them to the silicon. The microcells stick to the soft surface of the stamp, and are transferred to a flexible substrate simply by pressing the stamp onto the substrate. The authors then construct electrodes to connect the microcells to each other, using one of various established methods. [more details on Semprius]

Printing Highly Efficient Organic Solar Cells
[Nanomaterials, N. Hoth, Konarka] The technological attraction in organic solar cells is their compatibility to printing processes. However, up to today, nearly no literature on “printed” organic solar cells have been published and the major body of the research work was done by spin coating or blading techniques. Transferring the spin-coating or doctor blading process currently used for the fabrication of bulk heterojunction solar cell to a printing process holds morphological challenges that have not been observed or reported up to today. We highlight these challenges and we show that inkjet printing of organic bulk heterojunction solar cells requires completely novel approaches and skill sets compared to the current state of the art (...) report a new record power conversion efficiency of 3.5% for inkjet printed poly(3-hexylthiophene):fullerene based solar cells.

A High-Efficiency Solution-Deposited Thin-Film Photovoltaic Device
[Advanced Materials, Mitzi et al, IBM] In an effort to significantly reduce fabrication costs relative to vacuum-based approaches (e.g., no vacuum requirements, less energy intensive deposition, better materials utilization efficiency), as well as known solution-based approaches (e.g., fewer processing steps, no high-temperature selenization treatment, more facile Ga incorporation), we are pursuing a simple molecular-based approach for solution-depositing CIGS layers. (...) yielding a short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor, and total area power conversion efficiency of 25.7 mA cm2, 605 mV, 0.66, and 10.3%, respectively.