Can Solar Cells Reach 60 % Efficiency?

The theoretical maximum efficiency of Silicon based photovoltaic devices is in the neighborhood of 22-24% if memory serves, and this is a function of the bandgap of the material which controls the wavelengths of light that the cell is sensitive to and the percentage of the sun's energy that arrives at or near that frequency. Gallium Arsenide and Gallium Indium Arsenide have a larger bandgap and can therefore use higher frequency light. the current record holder AFAIK was a prototype cell made by a division of Boeing that achieved 42-43% efficiency under controlled laboratory conditions with lots of cooling capacity on the backside. it was a multi-layer design that used different layers sensitive to different wavelengths in order to maximize the wavelengths converted to electricity. but since it had multiple layers of different semiconductors with differing crystalline structures, it had long term stability issues, both from a corrosion and from a thermal expansion POV. There were also long term diffusion issues if memory serves too. If you have to ask how much it cost, you can't afford it. the ONLY thing it was even close to being cost effective for was satellite/space applications, but not until they solved the long term stability issues. Now will this quantum dot technology work? I'm betting it is going to be a while before it gets there, and then it is going to be a while before it becomes cheap enough to manufacture in quantity.

20 years? yeah sounds about right to me. but hey what do I know?

With CO2 sequestration estimated to cost between 2.5-4c / kWh and given "NREL reports that today this price difference [between "...green and non-green"] has fallen to a 1.75 cents per kWh" http://www.triplepundit.com/2010/05/850-utilities-offer-green-energy-price-parity-approaches/ seems that 14-20% is good enough!

Adam

The NREL statement seems to be political - same as the military going 'green'.

Without the massive subsidies that no one can afford solar and wind would not be doing much today.

It is not just the PV cells but all of the other costs associated with the system - electronics, cabling, design, installation etc.

Today every installation is a custom installation - that could be improved.

The best bet today is to own a share in a community owned system.

You say 20 years, and you may be correct. What aggrivates me is that all the new tech says they want to develope it for 5 to 10 years more before they put it on the market, and it appears to me that it is because they can collect R&D money for that period without having to invest in production. They want to ride out that reaseach money. Somebody correct me. I love the new batteries, we will get them in seven years. There is a great new solar cell, but no one is even thinking of mass producing it. I love the new supercar prototype, but sadly there are no plans for production, and the list goes on and on. We have the technology now to make so many things work, solar electric cars and planes and airships, motors and batteries and solar cells, but I cannot find a manufacturer. The joke is, however, that a start up company that has less money and faster researchers and built in planning for production will come up with a better solar cell, or cheaper and be ready for mass production in one year and make the other guys obsolete by the time their 20 year developemnet period is over. Competition is healthy.

Traditional power station ac wastes 10% or more over transmission lines as heat or leakage- photo voltaic will come of age- there are many new concepts being trialled & developed-even now they are looking at how photo synthesis in plants work in effort to improve photo voltaic. Things like dye sensitized panels- transparent- installed as windows- things like plastic roll up panels- the big draw back to pv is cost at this stage- the cynical among us may say "if oil co,s got out of the solar field(they are major owners), then pv would advance to replace oil- they won't let it till it suits em-ie oil wells all dry). Could be true!.

Since oil and other fossil fuels receive major subsidies already, and since none of these fuel or energy producers are really bearing the cost of the environmental damage they are causing, solar, at an average of a couple cents a kwh more expensive, is already cheaper if the big picture is looked at. We are all subsidizing cheap oil and coal with our taxes and our health.

Prices for power generation are not going down, nor is grid power becoming more reliable. There is ample evidence that solar is affordable already, and functional already if one looks at the process in other countries.

When calculating efficiency, one has to calculate overall efficiency within the environmental and tax structure. When calculating the current cost and efficiency of the coal, oil or nuclear powered grid systems, the same set of facts have to be acknowledged.

These may be called "political" considerations, but their factual nature makes them as scientific as any analysis of electron production at given wavelengths.

Is it likely that solar cells will reach 60 percent efficiency? No. Do they have to reach 60 percent efficiency to be cost effective compared to old school power production methodology? No. Take away the subsidies for fossil fuel production and/or give similar subsidies to solar cell production and the tables will turn immediately as production ramps up.

Production efficiency has much more to do with overall energy production efficiency/cost than increased electron output at this point. Some of these efficiencies in production have and will come from technical advances, but these technical advances still live under the false economic shadow provided by ignoring the huge subsidies feeding the current system.

The proof of the adequacy of the current efficiency overall, however, is as simple as the other entry stated: Even with the deck stacked against it, solar power is already operating at very nearly the same cost per kwh as grid power in many regions, without considering the environmental costs.

Laboratory prototypes multi-junction cells are at 42%, and 39% cells are stable and commercially available. While expensive per area, the efficiency IMPROVES under concentration up to around 500 suns, at which point their per-watt cost is much less even than thin film. Tracking is needed, but the high efficiency, reduces the area to track.

Multi-junction efficiency can theoretically reach over 60% by stacking a few more layers, but this is very difficult in practice. Quantum dots could be used to tune the band gaps of the junctions for a bit more efficiency, or potentially to squeeze more than one junction out of the same base material, eliminating some stress issues.

Another way in research is to generate multiple electrons from each photon. This gives the effect of a multi-junction cell within a single junction, bypassing the single-junction-single-electron limit (of roughly 30%). Still another avenue is to capture the excess energy the 'hot' electrons have left over after matching the band gap, which gives theoretical efficiencies in the 60% range even without concentrating the light. And there are CPV/thermonionic hybrids that might also reach 60%, and horizontally separated cells that have already reached 42%. But these are all still research so I expect stacked multi-junction cells to remain the efficiency leader for commercially available cells for a long time.

So will solar cells reach 60% efficiency?

Certainly under concentrated light as a laboratory curiosity (<20 years with current trends).

Almost certainly commercially under concentrated light (<25 years with current trends).

Probably not economically for un-concentrated light (60% is too near theoretical limits).

Cost is a wild subject when you consider what it really entails. for instance, what is the cost of oil and coal based energy systems? How efficient is the powerplant at converting that potential energy in a gallon of oil into electricity. It has to be better than combustion engines poor 30 to 35 percent, for it costs 10 to 20 cents to operate a gas car per mile but only 1 to 2 cents to operate an electric. Also how much money and man hours were spent in research and developement to find new oil? How much on clean up of spills? And how much is it costing the environment in oil slick roads, oil leaks, oil changes and the disposal of all the old cars? How much to powerplants cost? The list seems to go on and on. Now on the other hand, solar is considered renewable, but better to call it perpetual power. Solar panels last upwards of 20 years and still can opperate at lower efficiencies after that. So the question is, how much are we going to pay per watt for our panels? Costs for panels have been around $5 dollars per watt but they are coming down close to one dollar per watt with the new thin film tech and competition between companies who are gaining in either efficiency (over 40 percent) or gaining in lower cost of production. Oil is obsolete and complicated. Solar is new but simple. Eventually the cost will be about equal, but the benifits are already in favor of solar.