Solar Cells for Cheap

Not everyone gets a solar cell named after them: but Michael Gratzel did. He says his novel technology, which promises electricity-generating windows and low manufacturing costs, is ready for the market.

Michael Grätzel, chemistry professor at the Ecoles Polytechniques Fédérales de Lausanne in Switzerland, is most famous for inventing a new type of solar cell that could cost much less than conventional photovoltaics. Now, 15 years after the first prototypes, what he calls the dye-sensitized cell (and everyone else calls the Grätzel cell) is in limited production by Konarka, a company based in Lowell, MA, and will soon be more widely available.

Grätzel is now working on taking advantage of the ability of nanocrystals to dramatically increase the efficiency of solar cells.

Technology Review asked him about the challenges to making cheap solar cells, and why new technologies like his, which take much less energy to manufacture than conventional solar cells, are so important.

Technology Review: Why has it been so difficult to make efficient, yet inexpensive solar cells that could compete with fossil fuels as sources of electricity?

Michael Grätzel: It's perhaps just the way things evolved. Silicon cells were first made for [outer] space, and there was a lot of money available so the technology that was first developed was an expensive technology. The cell we have been developing on the other hand is closer to photosynthesis.

MG: That has to do with the absorption of light. Light generates electrons and positive carriers and they have to be transported. In a semiconductor silicon cell, silicon material absorbs light, but it also conducts the negative and positive charge carriers. An electric field has to be there to separate those charges. All of this has to be done by one material--silicon has to perform at least three functions. To do that, you need very pure materials, and that brings the price up.

On the other hand, the dye cell uses a molecule to absorb light. It's like chlorophyll in photosynthesis, a molecule that absorbs light. But the chlorophyll's not involved in charge transport. It just absorbs light and generates a charge, and then those charges are conducted by some well-established mechanisms. That's exactly what our system does.

The real breakthrough came with the nanoscopic particles. You have hundreds of particles stacked on top of each other in our light harvesting system.

TR: The dye absorbs the light, and the electron is transferred to the nanoparticles?

TR: The image of solar cells is changing. They used to be ugly boxes added to roofs as an afterthought. But now we are starting to see more attractive packaging, and even solar shingles (see "Beyond the Solar Panel"). Will dye-sensitized cells contribute to this evolution?

MG: Actually, that's one of our main advantages. It's a commonly accepted fact that the photovoltaic community thinks that the "building integrated" photovoltaics, that's where we have to go. Putting, as you say, those "ugly" scaffolds on the roof--this is not going to be appealing, and it's also expensive. That support structure costs a lot of money in addition to the cells, and so it's absolutely essential to make cells that are an integral part.

[With our cells] the normal configuration has glass on both sides, and can be made to look like a colored glass. This could be used as a power-producing window or skylights or building facades. The wall or window itself is photovoltaicly active.

TR: The cells can also be made on a flexible foil. Could we see them on tents, or built into clothing to charge iPods?

MG: Absolutely. Konarka has a program with the military to have cells built into uniforms. You can imagine why. The soldier has so much electrical gear and so they want to boost their batteries. Batteries are a huge problem--the weight--and batteries cost a huge amount of money.

Konarka has just announced a 20-megawatt facility for a foil-backed, dye-sensitized solar cell. This would still be for roofs. But there is a military application for tents, and Konarka is participating in that program.

MG: I expect in the next couple of years. The production equipment is already there. Konarka has a production line that can make up to one megawatt [of photovoltaic capacity per year].

TR: How does the efficiency of these production cells compare with conventional silicon?

MG: With regard to the dye-cells, silicon has a much higher efficiency; it's about twice [as much]. But when it comes to real pickup of solar power, our cell has two advantages: it picks up [light] earlier in the morning and later in the evening. And also the temperature effect isn't there--our cell is as efficient at 65 degrees [Celsius] as it is at 25 degrees, and silicon loses about 20 percent, at least.

If you put all of this together, silicon still has an advantage, but maybe a 20 or 30 percent advantage, not a factor of two.

MG: A factor of 4 or 5 [lower cost than silicon] is realistic. If it's building integrated, you get additional advantages because, say you have glass, and replace it [with our cells], you would have had the glass cost anyway.

MG: People say you should be down to 50 cents per peak watt. Our cost could be a little bit less than one dollar manufactured in China. But it depends on where you put your solar cells. If you put them in regions where you have a lot of sunshine, then the equation becomes different: you get faster payback.

TR: Silicon cells have a head-start ramping up production levels. This continues to raise the bar for new technologies, which don't yet have economies of scale. Can a brand-new type of cell catch up to silicon?

MG: A very reputable journal [Photon Consulting] just published predictions for module prices for silicon for the next 10 years, and they go up the first few years. In 10 years, they still will be above three dollars, and that's not competitive.

Yes, people are trying to make silicon in a different way, but there's another issue: energy payback. It takes a lot of energy to make silicon out of sand, because sand is very stable. If you want to sustain growth at 40-50 percent, and it takes four or five years to pay all of the energy back [from the solar cells], then all of the energy the silicon cells produce, and more, will be used to fuel the growth.

And mankind doesn't gain anything. Actually, there's a negative balance. If the technology needs a long payback, then it will deplete the world of energy resources. Unless you can bring that payback time down to where it is with dye-cells and thin-film cells, then you cannot sustain that big growth. And if you cannot sustain that growth, then the whole technology cannot make a contribution.

MG: The silicon people need to make silicon out of silicon oxide. We use an oxide that is already existing: titanium oxide. We don't need to make titanium out of titanium oxide.

TR: An exciting area of basic research now is using nanocrystals, also called quantum dots, to help get past theoretical limits to solar-cell efficiency. Can dye-sensitized cells play a role in the development of this approach?

MG: When you go to quantum dots, you get a chance to actually harvest several electrons with one photon. So how do you collect those? The quantum dots could be used instead of a [dye] sensitizer in solar cells. When you put those on the titanium dioxide support, the quantum dot transfers an electron very rapidly. And we have shown that to happen.

TR: You are campaigning for increased solar-cell research funding, and not just for Grätzel cells.

I am excited that the United States is taking a genuine interest in solar right now, after the complete neglect for 20 years. The Carter administration supported solar, but then during the Reagan administration, it all dropped down by a factor of 10. And labs like NREL [National Renewable Energy Laboratory in Golden, CO] had a hard time surviving. But I think there is going to be more funding.

Terrorists could target them. They would become targets in an all out war, and as safe as they are there is always the possibility of something unexpected going wrong, whether caused by an accident or some natural disaster like an earthquake, or an intentional act. I feel like my family is safer living far away from any nuclear power plants. Odds are high that no one currently living near a nuclear plant will ever be affected by a nuclear disaster, but the risk for them is certainly greater than it is for those who don't live anywhere near one. Those living near nuclear power plants have one additional risk my family does not have.

Like I said though I probably wouldn't live in a big city like New York City either. That place is a major target for terrorists and it would be a major target in an all out war. I probably wouldn't live in a place like San Francisco either because aside from being a target, that area is prone to major earthquakes. Others are free to live in those places if they want, and if they want nuclear power plants there or anywhere else that's fine by me too, just as long as it's not near where I live. I'd be opposed to one going up anywhere near my hometown. Maybe I'm being overly cautious on this, but that's the way it's going to be for me.

I'm not opposed to nuclear power, just leery of it. The more plants that are built around the world the greater the likelihood there will be accidents, or natural disasters, or man made events at nuclear plants that lead to disastrous consequences. The more nuclear waste generated around the world and shipped here and there for storage, the greater the likelihood of major contaminations that could negatively affect us in a major way. And of course there is the problem of nuclear weapons. The more nuclear plants there out there the easier it will be for bad guys to enrich nuclear materials to weapons grade quality, or at least for bad guys to gain access to that material enriched by those who were more or less the good guys. I do not believe that we or the international community at large are capable of 100% effectiveness in policing nuclear activity throughout the world. Irresponsible zealots of some sort are going to get ahold of nuclear weapons at some point and cause a lot of problems with them. Sooner or later that's going to happen, and the more nuclear power plants there are throughout the world the sooner it will be.

It is true that nuclear plants alleviate the need for coal and natural gas fired power plants and that would reduce pollution. I'm no environmentalist but there is no sense in unnecessarily polluting our environment when there is a simple fix. As for electricity being available at a reasonable cost from nuclear power plants, I wonder if it is true that it ends up being any cheaper to consumers from those plants as opposed to other types of power plants? Nuclear plants are incredibly expensive to build and they have a lot of ongoing costs. Without considering up front costs, regulatory costs and the costs in keeping the process safe it may be considerably cheaper to produce energy with nuclear power, but is it so much cheaper when you consider all the costs involved? And how much money are taxpayers out because of nuclear power? The government has always been heavily involved in the process from the day the applications were filed to build each plant. I don't know how all this works but my guess would be that significant tax dollars go to regulating and policing the nuclear power industry.

Nuclear plants are incredibly expensive to build and they have a lot of ongoing costs.

A HUGH chunk of the cost of building the plants in the 70's was the legal costs from the suits brought by the nuke wackos. Seabrook actually had TWO plants under contruction, but ended up only finishing one and bringing it online because it took 10 years of legal wrangling and all those costs involved just to get that ONE up and running. It would have taken them another 10 to get the second one going, and they just didn't want to spend that money that was essentially down the drain.

Terrorists could target them.

I'd rather have a compact reactor to defend than a monstrous LNG terminal (which is where we are heading).

I feel like my family is safer living far away from any nuclear power plants.

Contrary to your feelings nukes are far safer in terms of human life than coal mining or propane.

Remind me how many people were hurt in Three Mile Island?

ZERO. That's what you get when you design for the worst possible case, a core melt, which is a tractable problem.

Which is to say you will still need a grid with a very similar capacity regardless of your solar cell investment.

Yup.Fortunately, we already have one.

Now where shall that capacity come from? Solar cells ? Wind (same lousy energy density as Solar).

Where it's cost-effective, yes. Most of our energy for the foreseeable future will continue to come from the same sources as today; my point is that there isn't, and won't be soon, a single replacement.

"When is the last time we built a reactor in this country?

Now when is the last time the government subsidized solar and wind in this country?"

Nuclear reactors are subsidized too:

"The Energy Policy Act, signed by the President on August 8, 2005, has a number of articles related to nuclear power, and three specifically to the 2010 Program. First, the Price-Anderson Nuclear Industries Indemnity Act was extended to cover private and DOE plants and activities licensed through 2025. Also, the government would cover cost overruns due to regulatory delays, up to $500 million each for the first two new nuclear reactors, and half of the overruns due to such delays (up to $250 million each) for the next four reactors. Delays in construction due to vastly increased regulations were a primary cause of the high costs of some earlier plants. Finally, 'A production tax credit of 1.8 cents per kilowatt-hour for the first 6,000 megawatt-hours from new nuclear power plants for the first eight years of their operation, subject to a $125 million annual limit. The production tax credit places nuclear energy on equal footing with other sources of emission-free power, including wind and closed-loop biomass.' (ibid, copyright, permission obtained to use in Wikipedia - see discussion)

The Act also funds a Next Generation Nuclear Plant project at INEEL to produce both electricity and hydrogen. This plant will be a DOE project and does not fall under the 2010 Program"

http://en.wikipedia.org/wiki/Nuclear_Power_2010_Program

The cost of building nuclear power plants is enormous. Several are on the market today because the companies that own them can't make ends meet. They sell for millions, as opposed to the billions it costs to build one. The government is offering subsidies to build more plants, because utility companies can't afford to do it on their own. While fuel costs may be lower than with traditional power plants, the ongoing operation and maintenance costs coupled with principle and interest payments on the exorbitant up front costs are too high. Nuclear power is not exactly cheap.

Nuclear reactors are subsidized too:

What better way to destroy it?

Also, the government would cover cost overruns due to regulatory delays, up to $500 million each(!!!!!)

Delays in construction due to vastly increased regulations were a primary cause of the high costs of some earlier plants.

The Act also funds a Next Generation Nuclear Plant project at INEEL to produce both electricity and hydrogen.

Oh God, make it stop.

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