Tuesday, August 26, 2008

NREL beats Boeing Spectrolab efficiency record; Harnessing untapped infrared

The National Renewable Energy Laboratory of the U.S. Department of Energy announced that it has achieved what it claims to be a world record photovoltaic cell conversion efficiency of 40.8%.

According to NREL, its new solar cell differs significantly from those of the previous record holder, Boeing Spectrolab, which boasted an efficiency of 40.7 and was also based on an NREL design:
Instead of using a germanium wafer as the bottom junction of the device [as per a the previous design], the new design uses compositions of gallium indium phosphide and gallium indium arsenide to split the solar spectrum into three equal parts that are absorbed by each of the cell's three junctions for higher potential efficiencies. This is accomplished by growing the solar cell on a gallium arsenide wafer, flipping it over, then removing the wafer. The resulting device is extremely thin and light and represents a new class of solar cells with advantages in performance, design, operation and cost.

The following diagram, courtesy of NREL (via Semiconductor Times) depicts the improvements in NREL's new solar cell design:

It is also worth noting that this new observed efficiency mark was measured under concentrated light of 326 suns. One sun is about the amount of light that typically hits Earth on a sunny day. As a result, NREL notes that the new design is suited for "the space satellite market and for terrestrial concentrated photovoltaic arrays, which use lenses or mirrors to focus sunlight onto the solar cells."

Readers of this blog may recall that in July 2007, we reported that a group of researchers form the University of Delaware had claimed the world record for solar cell efficiency at 42.8%. In trying to reconcile these competing claims to the world record, spokespeople from both camps agree that comparing both systems is like comparing apples to oranges. Greentech Media details the reasons why.

Tapping into Infrared

In other research, scientists have developed new semiconductor materials that can tap into the previously unharnessed infrared spectrum of light in order to boost theoretical efficiencies to 63%.

Conventional semiconductors are silicon based and are only able to absorb light from the visible spectrum. Researchers led by Perla Wahnón at the Institute for Solar Energy at the Polytechnic University, and José Conesa at the Institute of Catalysis of the Spanish Higher Scientific Research Council, both in Madrid, Spain, have added titanium and vanadium in order to alter the electronic properties of semiconducting material to boost its theoretical conversion efficiency from 40%. The researchers emphasized that real-world conversion efficiencies would be less than these theoretical efficiencies.

Tuesday, August 12, 2008

The MIT Solar Revolution

Watch out Silicon Valley! The Massachusetts Institute of Technology is steadily making a name for itself as the solar R&D hub America (and thus the world). In noticing one solar news story after another emerging from the venerable university, I decided to provide a summary of MIT’s recent solar activities in one single post.

Announced this April, the Solar Revolution Project at MIT is research program funded by a $10 million gift by the Chesonis Family Foundation. The Project “will focus on three elements—capture, conversion and storage—that will ultimately make solar power a viable, near-term energy source.”

Here at the solar coaster, we previously discussed an MIT spin-off company called 1366 Technologies, which recently won a solar startup competition. But that is just one of several innovations to have gushed out of the MIT solar R&D pipeline. Let's take a look at a few other solar research and business developments emerging from the venerable Cambridge-based research university:

  • Energy Storage

MIT researchers have developed a new water-splitting (electrolysis) catalyst that is easily prepared from earth-abundant materials (cobalt and phosphorous) and that for the first time, potentially operates in benign conditions, i.e. pH neutral water at room temperature and 1 atm pressure. This finding has massive implications for the development of fuel cells as effective energy storage devices and hence address the intermittency problem that solar power faces. Green Tech blog reports that the Masdar City in Abu Dhabi could be a testing ground for the technology.

Separately, A123 Systems, an MIT spin-off and maker of lithium ion batteries for application to electric vehicles, electric grids (with implications for solar and wind) and consumer electronics have filed a registration statement for a $175 million initial public offering on Nasdaq.

  • Solar Concentrator

Covalent Solar, an MIT spin-off, has unveiled a new solar concentrating technology, which consists of organic dyes painted onto glass or plastic that effectively absorb and re-emit light that so that they are then trapped inside and travels within the plane of the glass/plastic and channeled to the edges where it is capture by strips of PV cells. Some light passes through the concentrator, and is absorbed by lower voltage solar cells underneath. Because such an arrangement does not require tracking or cooling features, it is more cost effective compared to other solar concentrating technologies such as those from Sungri, SolFocus or Energy Innovations. According to this video, early tests have demonstrated that use of Covalent’s technology can yield a 20% boost in performance, but the company is hopeful that this will increase to 40 – 50% with further tweaks. GreentechMedia identifies certain technical challenges that the Covalent team will have to address, such as the relatively short lifespan of the organic dyes

  • Solar Thermal Dish

Another MIT spin-off company, RawSolar, has developed a 10 kW solar thermal dish which the company claims it can produce more cheaply than its competitors “because it will use simple, standard materials and components, which can be ordered from local distributors anywhere in the U.S.,” according to Earth2Tech. The dish can concentrate sunlight1,000 times onto an aluminum tube emerging from the center of the dish, thereby heating water held in the tube to produce steam power.

According to RawSolar’s website, its “patented design flexes flat mirror into precisely the right shape without any special tooling or skilled labor, achieving incredibly high performance, long lifetime, and at a very low cost.” Citing the technology’s inventor, David Wood, MIT News reports that the modest scale of the dishes work to their advantage:

Unlike many technologies where economies of scale dictate large sizes, a smaller dish requires so much less support structure that it ends up costing only a third as much, for a given collecting area.

  • Solar Cooling

Promethean Power Systems, yet another MIT spin-off company, boasts an energy efficient hybrid solar powered thermoelectric refrigerator. The company claims their products, suited for rural off-gird or partially electrified area, can provide cooling at an operating cost that is 66% lower than that of conventional units. The company’s vision is to “develop a complete, stand-alone rural refrigeration system that stimulates businesses, reduces dependency on fossil fuels and increases the quality of life in emerging markets by enabling its users to reliably store food, vaccines and other perishable items.” Green Tech blog provides an excellent write-up.

Friday, August 8, 2008

First Solar Goes Big

Recall how we previously discussed that utilities are the stakeholders that should be driving the solar revolution in order to get the U.S. to the dream of “10% solar by 2025.” But First Solar, the Google of solar and the world’s leading thin-film manufacturer is beating the utilities at their own game by going into the utilities business as well. Last month, it announced that it had inked a twenty year purchase power agreement with Southern California Edison to build and maintain a 7.5 MW (expandable to 21 MW) thin-film power plant in Blythe, California. When completed, it would be the largest PV power plant in the Golden State. According to some sleuthing by the Green Wombat, the plant site spans some 120 acres.

Very shortly after, First Solar announced another 10 MW PV power plant project in Boulder City, Nevada for Sempra Generation, the San Diego-based natural gas production company. The PV plant will be built across 80 acres of land adjacent to an existing Sempra natural gas power plant, presenting a unique energy supply proposition in a solar-natural gas hybrid system whereby the natural gas plant supplies the base-load and the thin-film PV system provides the peak load. Such hybrid systems may be the way of the future as they reflect the understanding of the true value proposition of solar today—i.e, solar has already achieved grid parity in many geographic areas during peak demand periods and serve as an effective complement to base-load power supply.

Unlike the case with Southern California Edison, Sempra will actually take over ownership and maintenance of the power plant once construction is completed. However, these two deals are indication of First Solar’s ambitions to vertically integrate its operations, moving from PV module manufacturing to the actual delivery of solar generated power.

As far as utility-scale solar power plants are concerned, thin-film PV, because of their relative conversion inefficiencies, require far more land area than solar thermal systems or non-thin-film PV, and lack the molten-salt storage technologies that some solar thermal systems have. On the other hand, there are no moving parts in a thin-film solar power plant so maintenance demands are reduced and much less water is consumed compared to solar thermal systems that rely on conventional steam turbines to generate electricity (a key consideration in water-scarce desert areas where solar power plants are typically located). And of course, as long as polysilicon supply remains constrained and thin-film conversion efficiencies continue to improve, thin-film PV will continue to gain market share against crystalline-based PV. First Solar is not the first thin-film company to announce plans to build PV power plants; OptiSolar previously announced plans to build a massive 550 MW plant.

One utility that is heeding the call to go solar is Florida Power & Light, which has engaged SunPower to build two PV power plants totaling 35 MW in Florida.


- First Solar announces blow out Q2 financial results.
- Thin-film to grab 28% solar market share by 2012, projects Lux Research.