Monday, September 29, 2008

SolFocus in Focus

SolFocus, based in Google Land (Mountain View, California), has been making all sorts of news in recent days. It announced the completion of its first commercial installation, consisting of 500 kw worth of concentrating photovoltaic (CPV) equipment in Spain. SolFocus’ installation is part of a larger 3 MW project spread across two power plants that three different companies are building for its first phase at the Institute of Concentration Photovoltaic Systems (ISFOC) in Puertollano.

SolFocus also announced that it was forming a CPV industry consortium with other participatnts of the ISFOC project, including Concentrix Solar, Emcore, Isofoton and ISFOC itself with the goal of accelerating the development of CPV into the mainstream. One of the practical steps the consortium may undertake is to set standards within the CPV for measuring efficiencies:

People measure it every which way," [Nancy Hartsoch, vice president of marketing for SolFocus] said. "Some talk about panel efficiency, some talk about system efficiency, and some will only talk about [a mirror or lens]. It can be very confusing to developers trying to figure out 'How much energy do I get at the end of the day?' We will work to figure out standards so they can compare apples to apples."

Separately, SolFocus announced that its CPV modules have met the safety and reliability standards of the California Energy Commission and have been placed on the list of approved equipment suppliers for the California Solar Initiative, which will allow SolFocus to participate in the Golden’s State’s solar rebates. According to GreenTech Media, this announcement sets the stage for a possible future announcement of a Californian desert project scheduled for the second quarter of next year.

Let’s take a closer look at their technology.

SolFocus Technology

A review of SolFocus technology on their website is broadly reminiscent of the technology of Nevada competitor, Sunrgi, which we reviewed in May. Essentially, SolFocus’ systems adopt mini-dish designs, concentrating sunlight by some 500 times through arrarys of primary and secondary mirrors onto an optical rod which channels the light onto an area of high efficiency, multi-junction solar cell material (with efficiencies approaching 40%). The systems are mounted onto their proprietary dual-axis (i.e. x and y axis) tracking systems to optimize their alignment to the sun.

The winning features of their design, according to company’s website, is that their systems use just 1/1000th of active material found in standard solar cells, that 95% of the systems is made of aluminum and glass which is readily sourced globally, and that it the systems are designed for durability by being fully enclosed so as to protect its internal components from the elements.

Unlike Sungri’s systems, which rely on special heat dissipating technology, SolFocus’ cells are so small, they can be cooled passively without fans, according to this article.

The following YouTube video throws more color to the SolFocus story:

In the meantime, SolFocus is seeking capital to ramp up its production towards fulfilling its mission of achieving grid-parity (“The SolFocus mission is to enable solar energy generation at a Levelized Cost of Energy (LCOE) competitive with traditional fossil fuel sources”) for CPV.

Tuesday, September 23, 2008

Suniva's Light-Trapping Pushes Effiiciency to Over 20%

Suniva, an Atlanta-based startup, announced that is has produced high efficiency monocrystalline solar cells with a conversion efficiency of 20%, representing a significant improvement over the efficiency of 18.5% of its current line of ARTisun cells and close to the industry's leading efficiencies (23.4% by SunPower).

According to its website, Suniva has a three-prong approach to making efficient cells:

  • An improved set of screen-printed contacts. While screen-printing of solar cell gridlines is now a standard practice in the industry, Suniva has adjusted processing parameters and paste to improve contact performance.
  • An improved high sheet-resistance emitter to increase response from the blue end of the solar spectrum (where photons are more energetic) and raise the current level of the device.
  • An improved dielectric passivation layer to minimize recombination of electrons with holes and reflect light for a second pass through the active layer. By improving this passivation, fewer photogenerated carriers are lost at the surfaces and the power output of the cell is increased.

Translating the above bullet points into English, Technology Review ran an excellent piece discussing in greater detail how Suniva achieves higher efficiencies by "light-trapping" through the use of additional texturing on the surface of the silicon layer coupled with the addition of a reflective layer at the back of the silicon surface. This results in the ability to halve the thickness of the solar cell while achieving the same level of light absorption, which in turn allows Suniva to make do with not only a reduced amount of expensive silicon material but also with a lower quality, less pure and cheaper grade of silicon.

In a conventional solar cell, which can have a silicon layer 200 micrometers thick, impurities within the material can easily trap electrons before they reach the surface and escape to generate a current. In a layer of silicon just 100 micrometers thick, however, the electrons have a shorter distance to travel, so they're less likely to encounter an impurity before they escape.

Suniva’s website currently has stated goals of achieving 20% conversion efficiencies by, depending on which specific webpage you are on, 2010 or 2011. It seems that they have already handily outdone themselves. On the other hand, perhaps these are dates by which they hope to have 20% efficient cells fully commercialized, in which case some challenges lie ahead, according to Technology Review:

The results [of Suniva’s cells achieving 20% conversion efficiency] have been confirmed by the National Renewable Energy Laboratory, in Golden, CO. But for those tests, Suniva used cells with 200-micrometer-thick silicon wafers, and reaching 8 cents a kilowatt [i.e. grid-parity] will require 100-micrometer wafers. That this is technically possible has been established. The challenge lies in acquiring large amounts of such silicon, since wafers that thin aren't commercially available, [Founder and CTO Dr. Ajeet] Rohatgi says. What's more, factories will need to be retooled to handle 100-micrometer cells, which machines designed to handle thicker wafers could break.

Suniva's approach thus seems to be dispelling the myth that high conversions efficiencies and lower production costs are necessary trade-offs. (As an aside, the silicon-based solar guys aren’t the only kids in the block trying to get wafer thickness down. Utah scientists have devised cutting edge methods to slice germanium-based wafers resulting in less waste, and thus more usable wafers and ultimately lower costs per watt.)

Suniva was spun out of Georgia Institute of Technology's Center for Excellence in Photovoltaics, a research group founded in 1992 by the university. According to Venture Beat, the company received US$50 million in a second round of financing earlier this year, and expects to achieve the holy grail of producing cells at US$1 per watt (generally agreed as the cost level corresponding to grid parity) in two to three years time. Suniva ranked #9 in GreentechMedia's list of Top Ten Startups this year.

Suniva has been wheeling and dealing quite a bit for a two-year old (and not heavily capitilized) startup. In June, it announced it would begin production on a 32 MW pilot plant (and expects to add another 100 MW over the next two years) and signed up to a US$300 million wafer supply deal with REC. Just last month, it sealed a US$500 million deal to supply Solon AG, Europe's largest solar photovoltaic module manufacturer, with high-efficiency monocrystalline solar cells through 2012. In the same month, it tappws its India connections through its founder and CTO, Dr. Ajeet Rohatgi (pictured), Suniva entered into a long-term supply contract to supply Titan Energy Systems, one of India's largest and longest-standing manufacturers of solar modules, more than US$480 million worth of high-efficiency monocrystalline silicon solar cells through 2013 to be used in Titan's highest efficiency product lines.

We'll try to keep tabs on the progress of Suniva's ongoing RD&D.

Wednesday, September 3, 2008

SOLION--Energy Storage Solutions for Grid-Tied PV

In the U.S., much of the solar buzz over the past week has been centered around the series of blockbuster fundraising rounds for thin-film startups, namely AVA Solar ($104 million) and Nanosolar ($300 million). Xunlight also got into the action with a more modest $11 million capital injection.

However, the announcement that Saft is tying up with Conergy and Tenesol launch SOLION, a large scale energy storage deployment project to supplement residential photovoltaic systems, was a more meaningful development for me, simply because I have argued for some time that the development of effective energy storage solutions is going to be one of the keys to a solar revolution. GreenCarCongresss sums up the role of energy storage quite nicely:

The role of energy storage in an on-grid application—such as that of a residence with solar panels connected to the grid—is to store excess PV energy until it is needed. Effectively, energy storage will ‘time-shift’ PV energy produced during the day, peaking at noon, to make it available on demand. This will both maximize local consumption and enhance the efficiency of the PV system. Surplus energy can also be fed back into the grid, for which the owner of the PV system would be remunerated at a higher tariff.

Energy storage will also increase security of supply while making individual consumers less dependent on the grid and help to boost the development of energy self-sufficient houses and buildings and contribute to the continuous growth of PV as part of the global energy mix...

The main benefit of on-grid energy storage for utilities is that it will reduce the peak load on their grid while at the same time making PV a source of predictable, dispatchable power that they can call on when needed.

Critics of renewable energy and the fossil/nuclear energy establishment like to highlight the intermittent nature of renewable energy sources like wind and solar, e.g. click here. I will leave it to the words of Hermann Scheer, one of the most forceful and eloquent advocates for renewable energy, for a insightful rebuttal in his book, Energy Autonomy:

In a strongly centralized and internationalized nuclear/fossil energy supply system, this simultaneity [of production and utilization of energy] is, on principle, not possible. The storage warehouse for petroleum is the oil tanker, for coal it is the coal heap, for natural gas the major storage caverns and the gas tank, for nuclear energy the fuel rod store, and for water power (if necessary) the reservoir. Transport and distribution systems--pipelines, tanker ships and trucks--take on supplementary storage function. Or else it is the power plants themselves that operate as steam power plants, that is, they produce steam, which they must then keep holding in side the power plants as a reserve in case there is a rapid increase in production. All nuclear power plants and all large fossil power plants are of this type...

In its campaign against renewable energy, the energy business never mentions its own storage capacity, as if this were not as easily usable as a reserve for solar- and wind-based electricity...The possibility that the sun might not be shining or the wind might stop blowing just when these sources are most needed to produce electricity is presented as an insurmountable obstacle--as if, by way of contrast, extra coal or uranium could be hauled out of the mines at the very moment there is a spike in demand for coal- or nuclear-based electricity.
Saft, an established name in the battery business, will develop lithium ion battery modules, while Conergy and Tenesol will develop ancillary components. In pilot trials, 75 SOLION energy storage systems will be deployed--25 in Germany and 50 in France--in order to validate the performance of these systems.

It is innovative game-changing initiatives, such as SOLION, that can fully harness the true potential of solar power. We'll be keeping tabs on the progress of SOLION right here at the solar coaster.