Maximizing Solar Energy: Multi-Layer Cells & Silicon Absorption

[Jake]

Ok so right now the best solar cells get only about 20-30% of the energy available to it from the sun. This is because for each photon that knocks off an electron, any excess energy not needed to knock off the electron in the silicon is wasted.

And I read in howstuffworks.com that really good solar cells do use multi-layer cells which absorve the light differently at different layers, and thus make efficient use of the light at each layer.

So my question is, what's stopping the creation of a cell that has like let's say, 30 layers, each for a specific level of photon energy, thus extracting a much higher amount of energy from the sun?

I also read an article in Discover/SCIAM I forget which which talked about how silicon, when made right, has the property to absorb light differently at different depths of the same piece of silicon. Now this article was how it could be used for better digital cameras, but could it be used for solar cells? Each layer absorbing photons with different energy levels.

Thanks!

 

[DaVinci]

The lack of money due to the oil industry not wanting solar power to happen as their empire will collapse overnight?

:rofl:

 

[hitssquad]

the oil industry ... solar power ... happen ... their empire will collapse overnight

Could you show the math for this?

 

[russ_watters]

Could you show the math for this?

Yes, please.

Jake, one problem is absorption - not all the excess light will be transmitted to the next layer. Another is that if 30% is converted to electricity, there isn't as much light available for he second layer to absorb. So the law of diminishing returns applies (in 2 ways, actually).
Say 30% is converted to electricity, 70% transmitted by each layer: in the second layer, you'd convert 30% of that remaining 70% or 21% of the total light. Third layer is 30% of the remaining 51% or 15% of the total light. So the 3rd layer only collects half as much light as the first layer - and probably costs just as much to manufacture. So it would actually increase the cost per kW of the cell.

 

[DaVinci]

This is a pretty good explanation of the whole PV effect: http://www.renewableenergyaccess.com/rea/tech/solarenergy;jsessionid=abtm-DyFL_F_

The US Department of Energy has more funding for other energy research besides Solar power. I tried to find the numbers on the internet (as they must be available) but have been unable to locate them in my 10 minute search. My comment stems from a discussion I had with a distant family member that works for the DoE. But that is not enough information to 'prove' my case and I cannot find the numbers on the web at this time.

 

[Jake]

Yes, please.

Jake, one problem is absorption - not all the excess light will be transmitted to the next layer. Another is that if 30% is converted to electricity, there isn't as much light available for he second layer to absorb. So the law of diminishing returns applies (in 2 ways, actually).
Say 30% is converted to electricity, 70% transmitted by each layer: in the second layer, you'd convert 30% of that remaining 70% or 21% of the total light. Third layer is 30% of the remaining 51% or 15% of the total light. So the 3rd layer only collects half as much light as the first layer - and probably costs just as much to manufacture. So it would actually increase the cost per kW of the cell.

4 layers then could absorb about 70% of the energy, and then some lose to electrical resistence and lost space for the metal conductors. So say at best youd get 60% out of four layers...an incredible amount by today's standards.

Are you saying this is actually possible? As in, we have the technology today? As far as cost, its actually a lot cheaper if you think about it...Oil will run out, but solar won't, no matter how much it costs to make a cell. And it won't destroy the enviroment. And given enough demand, I'm sure mass-production could lower costs.

So what, other than costs, is stopping someone from making 3-4-or 5 layer solar cells, be interested to know, thanks!

 

[Jake]

Another question

What is it about a photon that causes it too have too much or to little energy for a precise one-electron knock off? Is it the photons frequency? (IE color) Or is it some other aspect?

 

[hitssquad]

Oil will run out

Oil can be manufactured with the help of nuclear energy, and there remain thousands of years worth of fissile uranium in the world's oceans.
http://groups-beta.google.com/group/alt.security.terrorism/msg/baf44b5dae522945

but solar won't, no matter how much it costs to make a cell. And it won't destroy the enviroment.

The lifecycle of a solar cell has environmental impacts. Solar energy also, since it is so diffuse, tends to be more dangerous for maintenance crews than nuclear.

And given enough demand, I'm sure mass-production could lower costs.

Ditto for nuclear power plants and their accompanying oil-production facilities. No one that I am aware of who is knowledgeable about grid solar pretends that implementing it might involve PV cells. PV cells are used to power satellites and remote radio repeater towers. For grid power production, thermal solar (powering turbines) is envisioned.

This is a solar-trough concentrator:
http://happy.emu.id.au/neilp/solar/solartrough.htm

It heats up oil which can then be used to power rankine-cycle (steam) turbines.
http://www.google.com/search?q=solar+trough+rankine

 

[Jake]

Oil can be manufactured with the help of nuclear energy, and there remain thousands of years worth of fissile uranium in the world's oceans.
http://groups-beta.google.com/group/alt.security.terrorism/msg/baf44b5dae522945



The lifecycle of a solar cell has environmental impacts. Solar energy also, since it is so diffuse, tends to be more dangerous for maintenance crews than nuclear.



Ditto for nuclear power plants and their accompanying oil-production facilities. No one that I am aware of who is knowledgeable about grid solar pretends that implementing it might involve PV cells. PV cells are used to power satellites and remote radio repeater towers. For grid power production, thermal solar (powering turbines) is envisioned.

This is a solar-trough concentrator:
http://happy.emu.id.au/neilp/solar/solartrough.htm

It heats up oil which can then be used to power rankine-cycle (steam) turbines.
http://www.google.com/search?q=solar+trough+rankine

Please, they were just passing comments, I see no validity in your logic, but let's not go off topic...

 

[russ_watters]

4 layers then could absorb about 70% of the energy, and then some lose to electrical resistence and lost space for the metal conductors. So say at best youd get 60% out of four layers...an incredible amount by today's standards.

Are you saying this is actually possible?

That was an example (and a generous one, at that), I don't actually know what they are capable of today - probably not.

As far as cost, its actually a lot cheaper if you think about it...Oil will run out, but solar won't, no matter how much it costs to make a cell. And it won't destroy the enviroment. And given enough demand, I'm sure mass-production could lower costs.

So what, other than costs, is stopping someone from making 3-4-or 5 layer solar cells, be interested to know, thanks!

Well, cost ($/kW) is everything here. Whether you use 10% or 20% efficient solar panels, the payback for setting up an array on your roof is about the same - about 20 years, with generous assumptions. Currently, that fact alone is what keeps people from doing it. Presumably, as technology improves, costs will drop, but higher efficiency cells will always be more expensive than low efficiency ones - so efficiency is always going to be secondary to $/kW.

Also, you must remember that nothing is maintenance free - not even solar cells. They also don't last forever. So its not like you can set up a plant today and forget about it.

Regarding the environment, you'd be surprised what environmentalists will oppose. Windmills are clean to, but...

You are right, however, that mass production would lower costs. Economically, though, they need to come down by about a factor of 4 before they begin to become viable. Most individuals and business still have a much shorter time horizon than a 5 year payback though. I've seen businesses balk at a 5 month payback.

 

[Jake]

Well when oil is running low and costs $15 a gallon and we start choking on the air we breath, it might seem rather a good deal to them

 

[willib]

i believe if the solar cells were ecthed properly they could yeald a lot more power , say they were ecthed in a W shape or something similar , wouldn't that give more surface area?

what about wind energy http://www.otherpower.com/

 

[Chronos]

PV technology is not quite as gloomy as it sometimes appears. Depending on location and factors like subsidies, the break even point can be reached in 5 years or less. See
http://www.eere.energy.gov/solar/cf...hotovoltaics/cat=Financial Considerations#Q69
http://www.ecotopia.com/apollo2/pvlever.htm

 

[Jake]

Energy Towers are also very promissing, an indirect solar power method, gathers the energy from the air itself.

 

[hitssquad]

PV technology ... the break even point can be reached in 5 years or less.
http://www.eere.energy.gov/solar/cf...hotovoltaics/cat=Financial Considerations#Q69
http://www.ecotopia.com/apollo2/pvlever.htm

Russ was talking about monetary breakeven. Those links discuss energy breakeven.

 

[russ_watters]

i believe if the solar cells were ecthed properly they could yeald a lot more power , say they were ecthed in a W shape or something similar , wouldn't that give more surface area?

Specific surface area of the cell itself is largely irrelevant: if you angle-in some cells to increase the surface area, you don't increase the amount of light that hits it.

Russ was talking about monetary breakeven. Those links discuss energy breakeven.

Yeah - energy break-even is a pretty much useless measure. It may actually be designed to fool people into thinking its the same thing as a financial payback period.

I can't stress enough that barring a government mandated switch from coal and oil (not happening in our lifetime, even with coal), economics will continue to drive the issue. Scarcity will drive up the price of oil, but I doubt its going to $15 a gallon (today's dollars) in my lifetime. People have been crying wolf on scarcity for decades and we're still not seeing it. Government regulations on emissions and taxes will also drive up prices, but mabe 50%-100% tops.

But like I said before - photocells need to drop in price by a factor of 4 before they can even be worth considering. And they aren't moving down that fast.

RE: "Energy Towers" - if you mean solar towers, we had a thread on that a while ago and I poked into it a little bit. Its a sound concept - it would work - trouble is, they require some engineering like we've never seen. If you notice, every big skyscraper is 10, 20, or 50 feet higher than the last: this is supposed to be 1km high - around twice the height of any existing skyscraper. Maybe in 50 years. Oh, and the company that says they are going to build it is a fraud.

 

[willib]

I can't stress enough that barring a government mandated switch from coal and oil (not happening in our lifetime, even with coal), economics will continue to drive the issue. Scarcity will drive up the price of oil, but I doubt its going to $15 a gallon (today's dollars) in my lifetime. People have been crying wolf on scarcity for decades and we're still not seeing it. Government regulations on emissions and taxes will also drive up prices, but mabe 50%-100% tops.

you seem to think that the supply of oil will last forever , it won't .. it is finite , not infinite.. and the sooner that we all realize this the better off we all will be..
and the sooner that we look into alternative energy sources , the better..
we need to design better batteries ..
we need more wind energy production , more and better solar cells .. and less SUV's
and we need to do this now..
thanks for reading , my little rant is over , go about your business.

 

[Locrian]

The lack of money due to the oil industry not wanting solar power to happen as their empire will collapse overnight?

As a huge proponent of solar and wind energy, whenever I see arguments like this, I cannot help but think to myself

"With friends like these, who needs enemies?"

 

[brewnog]

you seem to think that the supply of oil will last forever , it won't .. it is finite , not infinite.. and the sooner that we all realize this the better off we all will be..
and the sooner that we look into alternative energy sources , the better..
we need to design better batteries ..
we need more wind energy production , more and better solar cells .. and less SUV's
and we need to do this now..
thanks for reading , my little rant is over , go about your business.

You are correct, except that Russ does not believe that there is an inexhaustable supply of oil. The thing you don't understand is that for the time being, it's about money. There is plenty of oil left underground for politicians not to have to worry about it, on a short-term basis. Currently, fossil fuels provide the most economically viable source of energy. Not many people would argue that developments have to be made in terms of renewable sources, but these developments ARE being made, and I doubt you're currently running a solar-powered car, or have a wind turbine on your house. Let me guess, you fill up with petrol, and are connected to the grid like everyone else, right?

 

[Francis M]

Jake, I have to agree with Russ and some of the others in this post. Now please don't take some of these peoples posts as an anti-enviornmental rant. It's just that right now right or wrong it's a matter of economics and politics. IT's cheaper to power our vehicles with petrolium. It's also cheaper to power/heat our houses with petrolium. Most people (myself included) can't afford the higher initial upfront expenditure for solar/wind & battery power equipment, and then wait for the economic payoff which they'll never see unless they do number chrunching and comparisons for 5-10 or 20 years down the road. Also as pointed out these things while probably better in the long run don't come without enviornmental detractions, some of which come from the very people that want cleaner energy and build some of this stuff. THere's the beef that there's an impact to the enviornment form manufacturing processes, also the beef about what to do with these cells and batteries when they break or wear out, and also complaints about solar farms and windmills wrecking the view. THere'll also be a higher mainteanence cost involved as the infrastructure for servicing this equipment isn't as established (common) as plumbers and HVAC businesses.
Russ and a few others were simply pointing out to your question earlier that due to current technology and the property of materials it's not economically better to build the type of solar cell you suggested than the ones they build currently. NO one said it couldn't be done, it was just said that at a certain point you're going to spend more money manufacturing/engineering that cell than you'll ever see back efficiancy wise which will make the retail cost higher, which will make whoever buys it have to wait even longer for the system to pay for itself.

 

[russ_watters]

you seem to think that the supply of oil will last forever , it won't .. it is finite , not infinite.. and the sooner that we all realize this the better off we all will be..

Its not infinite, its just that stories of its demise are greatly exaggerated. And while its true that at some point that scarcity will be an issue, its still primarily an economic issue. That's just the reality of the world we live in: people do and don't do things related to energy primarily because of money - and even then, its mostly today's money (meaning, they don't tend to consider payback from investments. But back to the scarcity: what do we use oil for in the first place? We use it to run the economy. Oil (and energy itself) is commodity: energy is a form of money.

Think about it this way: why does any company ever do anything? Money! Even government mandated pollution control and conservation is a stricly economic matter for a company: they obey the law because if they don't they'll get fined or shut down and either way, it'll cost them money. Many large boilers and some generators, those that heat and power large buildings, are dual-fuel - they can use natural gas or oil. Which to use? Whichever costs less!

But like I said before, even then, companies and people (often knowingly) make bad decisions that will cost them $2 simply because it saves them $1 today. Almost no one pays extra for high efficiency air conditioning - but it has a payback of 1 cooling season! It should be a no-brainer. But spending $300 today to make $600 over the next two years just isn't something people consider.

 

[chroot]

The future of mankind's use of energy is almost certainly going to be fusion supplemented by renewable sources, with cars sporting fuel cells or high-capacity batteries. No one doubts this; these technologies are better than the ones we have today for myriad reasons, the least of which is the threat of running out of fossil fuel. This shift in technology will happen eventually, regardless of the activity of environmentalists and alarmists.

When the automobile was first introduced, no one had to ban horse-drawn buggies, did they?

- Warren

 

[Locrian]

Unfortunately sustained, efficient fusion is turning out to be a bigger leap than automobiles were. :(

 

[chroot]

Is it? People have been riding horses for millenia, but we've had cars for fewer than a hundred years.

- Warren

 

[Locrian]

The first engine was a leap. The first automobile followed shorty after, on those time frames.

I suppose it depends on whether you think ITER is utilizing something really new or is just improving something we already had. I don't see much chance there will be a functioning fusion generator before 2050, and it certainly won't be common until the end of this century.

So I'll be dead before we have a fusion economy. I suppose it isn't really that long. The whole death thing makes it feel like an eternity of waiting.

 

[chroot]

We knew how to make machines out of metal during the entire length of the industrial revolution, which began in the 18th century. It still took at least a hundred years before anyone figured out how to put the metal bits together to make an engine. I discredit the ICE as being a leap, in the sense that the supporting technologies -- machining, etc. -- were already in place before it, and those all took time to mature. The ICE was just the killer app that came out of all that machining technology. If it took people hundreds of years to get a decent ICE even when surrounded by the tools to make one, why should fusion's progress be considered slow in comparison? IMO, it's been going along quite well, comparably or perhaps even faster than the development of the technologies needed for the ICE.

- Warren

 

[willib]

i have thought about how to reply to all this..
Russ do you think its not going to be an economic issue when we run out of oil ?
i used to think that the Tocamac was The answer , now i an not so sure that it will even work, this is not to say that we shouldn't try, we should , as i am as big a proponent of R&D that am of wind and solar energy..i am just not sure it is , the way to go..no pun intended..

 

[Locrian]

I can't speak for Russ, but I don't think anyone thinks it would not be an economic issue if we ran out of oil given our current technological level. The problem is that focusing on that particular point without viewing the big picture is not useful. There are even others in this thread who make wild accusations that have no supporting evidence at all (see the first reply).

It is true that, without improvements in technology, there will be a huge economic problem encountered when we run out of oil. It is also true that right now, if we stopped using oil, we'd see huge economic reprocussions. People seem to think that the answer to a limited supply of oil is to stop using it. They don't always seem to realize that stopping now would be even more painful than running out later.

Most of people's problems with oil are due to a misguided opinion that work is not being done to suplant oil. Work is being done, and great progress is being made. Solar and wind have made huge progress in the last twenty years, and nuclear is more safe and effective than ever. The reason we aren't using most of those is mostly because, although they've improved, they haven't quite improved enough.

They are, however, getting closer. Funding further R&D is good, and I don't think anyone in this thread has argued otherwise. The question of whether there is an alternative to fossil fuels has, to me, been answered. It is just a matter of when.

All evidence I see shows it occurring long before we fully run out of oil. Heck, if gasoline prices continue to rise as they have, alternatives may be economically efficient sooner than anyone guessed.

 

[russ_watters]

Regarding "running out of oil," precisely what does that mean? Its not like we'll wake up one day and there will be no more oil. Production will level off, then start to fall over a span of decades. As demand outstrips supply, prices will rise - this will make it economical to recover oil that to this point is too expensive to mine (such as in Canada), helping offset the shortfall. But the new production won't make up for the shortfall and prices will continue to rise. During this period, economics, again, will drive consumers toward alternate forms of energy.

Warren is right - everyone knows oil's days are numbered. Hydrogen will likely replace it for cars, but this shift is still decades away.

 

[willib]

Hydrogen hmmm nice point.. fuel cells seem to be the way to go with hydrogen..
http://www.fuelcells.org/info/fclib.html#stationary


this is a "demo car" that runs on solar power and water..
http://www.bpa.gov/Energy/N/projects/fuel_cell/education/fuelcellcar/