September 15, 2008
Slicing Method Cuts Cost of Germanium Solar Cells
A new cutting method for processing germanium photovoltaic (PV) solar cells will cut their cost.
SALT LAKE CITY – University of Utah engineers devised a new way to slice thin wafers of the chemical element germanium for use in the most efficient type of solar power cells. They say the new method should lower the cost of such cells by reducing the waste and breakage of the brittle semiconductor.
The expensive solar cells now are used mainly on spacecraft, but with the improved wafer-slicing method, "the idea is to make germanium-based, high-efficiency solar cells for uses where cost now is a factor," particularly for solar power on Earth, says Eberhard "Ebbe" Bamberg, an assistant professor of mechanical engineering. "You want to do it on your roof.
Higher efficiency of germanium PV will allow a roof to collect a larger fraction of all power used in a home. But cost is a problem because germanium is so expensive.
Germanium serves as the bottom layer of the most efficient existing type of solar cell, but is used primarily on NASA, military and commercial satellites because of the high expense – raw germanium costs about $680 per pound. Four-inch-wide wafers used in solar cells cost $80 to $100 each, and the new cutting method may reduce the cost by more than 10 percent, says Grant Fines, chief technology officer for germanium wafer-maker Sylarus Technologies in St. George, Utah.
On orbital satellites and other space applications where weight is such a huge cost the higher cost of germanium solar cells is justified by their higher efficiency.
Silicon-based solar cells on Earth have maximum efficiency of 20 percent, Fines says. In space, germanium solar cells typically convert 28 percent of sunlight into electricity, but on Earth where solar concentrators are used, they can convert more than 40 percent of sunlight into electricity, and their efficiency theoretically exceeds 50 percent, he adds.
The ability to slice these wafers thinner will both cut production costs and reduce weight which is so critical for space applications.
Although this is a forum/site for solar news, it is frustrating. I'll soon be building in the high desert of NM. Solar, of course. And I'll have to choose from the options available even though better choices are on the horizon.
Hopefully one of these products will break through to the retail market in a year or so because that which is available for purchase seems either antiquated or dressed-up versions of yesterday's technology.
Hopefully one of these products will break through to the retail market in a year or so
None of the products you read about here will break through to the retail market in a year or so. Some (most?) will never break through, but those that do will be after a long, painful gestation period.
First Solar has production costs that are way below their selling costs. I expect that as First Solar and some competitors scale up their production capacity PV costs will take a big dive in a few years. But demand has been growing fast enough to prevent price declines that reflect production cost declines.
Concentrators do show a lot of potential and this might make a bit of difference, but a 30% cost reduction for 4inch wide wafers that cost $80 to $100 each doesn't sound like the kind of leap forward that will make solar cheaper than coal. Concentrators need to get lots cheaper and the tracking mirror systems need to be simple and mass produceable at low cost, like Ausra is doing with solar thermal. Ausra's mirror system fitted with PV might be an improvement but would the power actually end up cheaper than the same mirror system set up for steam production or PV/steam cogeneration? Meanwhile thin film PV using new technology is just getting into mass production, enough to see crystalline silicon - PV's most familiar form - up against competition that it won't be able to keep up with. Ultimately concentrators face competition from the same source and the kind of improvement here might be too small an increment to make it the low cost technology of choice.
I see 3 forms of solar power in competition:
1) Thin film PV.
2) Concentrators + Silicon PV (and other higher conversion efficiency PV).
3) Concentrators + Steam engine.
Thin film has a lower conversion efficiency. So it makes more sense to use silicon PV with concentrators. It even makes sense to use germanium PV if you are concentrating 10-20-30 times the area's light onto a PV cell. At a high enough level of concentration the PV cell's cost becomes pretty small.
I expect PV to gain ground against the steam engine approach. Certainly thin film PV is gaining ground against other forms of PV. But will this trend hold?
I mentioned Ausra because of their low cost approach to concentrating solar thermal and can't see any reason the same mirror system can't be used for concentrating PV as well. Used for thermal it has the advantage of being able to use thermal storage directly but the disadvantage of having to convert to electricity before being usable.. the inverse being true of PV. I have to say I'm doubtful of the scalability of true parabolic 2-axis tracking systems even if they are generally higher in conversion efficiency - more complex and needing to be very strongly built to withstand strong winds when they're tower mounted as many seem to be. The smaller, multiple, fully enclosed ones that can be roof mounted look more appropriate but that may be just my impression of them. Real relative costs may only be revealled with time and experience - and hopefully some honest accounting.
The challenge is to make solar the low cost logical choice, not merely on par with coal-fired power but clearly superior enough that demand for coal plummets and that industry collapses. That coal prices have shot up does make that goal closer but I'd prefer it were solar costs plummeting rather than coal prices soaring that drive the shift to solar.