the real waste problem, solar edition

Previously, we produced an infographic on the amount of waste produced by coal powered electricity compared to nuclear powered electricity.  We also examined the many (50+) dangerous chemicals used in solar panel production.

But what of the volume of waste a solar powered world would create?  

Research on electricity generation and land use (paper, referenced here previously), estimates that solar power to produce 100% of world electricity generation would require 5,500,000,000,000 square meters (5.5 x 10^12 m^2).

Even with thorough research, this is a number that has to be reached with a number of assumptions.  Whether the panels are produced properly, whether they are functioning at their maximum efficiencies, whether they are appropriately maintained, and whether the weather is behaving and there is not an unusually cloudy year.  All of these decrease production significantly.  Solar panel lifetimes are about 15-30 years.  We will conservatively assume that the solar panel electricity production is at its maximum production over its entire lifetime, a full 30 years.

Assuming that the land use is the approximate area of the solar panels, and that the panels are a minimum of 1 inch thick (2.54 cm), the volume of PV panels as waste would be 139,700,000,000 cubic meters.

Used nuclear fuel produced by all US reactors is 2,000 metric tons annually.  This is about 100 cubic meters per year.  Multiplying the amount of US nuclear electricity production to produce the same amount as worldwide electricity production (data from EIA), this becomes about 37,000 cubic meters worldwide per year.  After the same 30 years, a nuclear powered world would produce 2,220,000 cubic meters of used fuel.

This means that a solar powered world produces 63,000 times the waste of a nuclear powered world. 

And the solar world produces no energy at night.  And used nuclear fuel actually still contains 95% of its energy- it is not just "waste".  On top of this, radioactivity decreases with time, whereas solar panel components including cadmium and lead, do not go away.  Yes, there is the potential for both to be recycled.  There would be significant energy lost in recycling solar panels versus the energy produced from recycling nuclear fuel in fast reactors.

How to illustrate this?  Nuclear waste after 30 years of powering the whole world would take up roughly 1.5 "Panamax" sized container ships (the largest container ships that can go through the Panama canal).  Solar waste would take roughly 95,000 Panamax ships.

That amount of difference is near impossible to illustrate.  Here's a 1/100 model of the aircraft carrier USS Enterprise, and a photo of the real Enterprise.  The size of the solar waste would be the real Enterprise, and the volume of the used nuclear fuel would be maybe the size of one of the model planes on the model Enterprise.  (Not to mention that the amazing achievements of the Enterprise would not be possible without nuclear power!)

Solar power could be a supplement, but never a substitute for nuclear power.

***NOTE:  Alert reader Eric Hanson made a good point that the value used for nuclear density was used roughly as uranium as opposed to uranium oxide, which would reduce the multiple.  The total size of all the supporting structures for solar were not taken into account either, but if we wanted to take into account the density of uranium oxide along with the geometry of the fuel- spacers, cladding, etc, the density might be closer to 3,500 kg/m3, so maybe you could divide by a factor of 6. This still leaves solar with over 10,000 times more volume of waste than nuclear. Either way, one can see that the amount of waste is significantly greater with solar than nuclear per energy produced.








25 comments

  1. Nice website! Saw the link on Meredith's. Have a great holiday. mary

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  2. A typical solar panel for generation of electricity contains 36 solar cells of different sizes, depending on the wattage or amperage of the panel. A strong aluminum panel serves as a rest for the solar panels and is mounted in a tough frame. The yield of the electricity depends on the type of material that goes in making the solar cells. Monocrystalline or polycrystalline solar cells are used to make rigid solar panels.

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  3. Hi Caroline,

    A few years ago I did my masters in a solar cell lab and I thought I’d run the numbers.

    The active bit is either 40-100 microns of silicon, or for us it was 5 microns of CdTe. All the other electronic junk, including electrodes, the window layer, buffer layers etc brought the entire active thickness up to about 7 microns.

    So the active and potentially nasty parts of a solar cell is about one-three-thousandth of an inch. A full module is mostly glass, and usually under a quarter of an inch thick.

    The biggest CdTe company is FirstSolar, who put aside money from each module sold to pay for the future reclaiming & recycling of the panel. In Europe we have the WEEE directive and nearly 70% glass recycling rates, so we should expect most of the panel and its aluminium frame to be recycled.

    This should reduce the energy demand of building the next round of solar power stations and improve their life cycle analysis results. There’re obviously other energy costs like access roads, substations, concrete etc, but that’s true of a nuclear station and refining its ore, so I’ll leave it to the Literature to work that one out!

    To calculate how much you need, I find it simpler to think in terms of power demand. Take an average capacity factor and an average efficiency (15% and 15% is fair), meaning that a square metre of panels rated at 150 W would average 22.5 W output. World electricity demand of 2.3 TW would need 100 billion sq m, or 100,000 sq km of solar panels if I have my numbers right.

    In terms of panels, that’s 500 million cubic metres of material, about 225 times the nuclear fuel. If you used cadmium telluride or other thin film materials, then the active material would be 0.7 million cubic metres, about a third of the uranium fuel used.

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    1. Thanks for the comment. I haven't had time to go over the numbers, but here are our initial comments:
      1) You cannot use those units for world electricity demand. It cannot be taken in a snapshot in time, it must be integrated over 24 hr days for a year to be reasonably accurate (in other words, kW-h, not just kW). The reasons for this are obvious- not all of the world is at peak demand at the same time, and demand fluctuates over a year substantially.
      2) The full panel has to be recycled and separated from the nasty stuff. Even if the nasty stuff is only microns thick, the whole thing is waste which must be transported and separated and recycled.
      3) The capacity factors and efficiencies you list are optimistic but may be reasonable ballparks.
      4) from our reading, we were not aware of any major PV company paying for recycling, especially compared to the $25 billion US nuclear have put aside. Will have to read further.
      *5) ULTIMATELY, you still have NO POWER at night or on cloudy days, meaning, there is a LOT, LOT more waste that would have to be generated using batteries or other storage mechanisms which were not even touched here. The chemicals and metals in batteries are a waste post for another day.

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    2. The 2.3 TW figure I used is the average power production, equivalent to global demand of just over 20 TWh/year. I just find it easier to run the numbers that way. :)

      Solar does produce power somewhere at night, except during a total solar eclipse!

      I suspect a purely solar world would need more attached gubbins than a purely nuclear one, but no-one is suggesting either of them afaik. After all, demand isn't flat and swinging nukes to match demand isn't particularly cost effective either, so maybe you'd end up building battery banks anyway (or fuel cells, pumped storage, CAES, flywheels or isentropic banks). Or maybe we'd use our new electric cars as batteries, I dunno.

      I think that's getting a little too complicated for our rough number crunching though!

      My problem with solar is that I live in the UK. Most of our demand is in the winter, but panels produce ~5 times as much in summer. Solar's never going to be more than a way of suppressing daytime peak prices unless we import it from the south. So that's why we're building wind turbines and interconnectors instead, which mostly produce in winter.

      Mark

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    3. Hi Mark,

      I should have read your comments closer. There are several major issues that have mainly to do with an understanding of engineering and the power industry that must be cleared up.

      1) It would be a dream world for electric utilities if they could use a yearly average as the spot demand. At peak on a hot summer day, the demand would be multiples of the demand on a winter evening. Since people aren't too keen on blackouts every afternoon, electricity has to supply for this maximum amount, not just an average. This is probably one reason your estimate of area of solar panels needed is significantly lower from the Lincoln institute.

      2) Nuclear does not require batteries (fuel cells, pumped storage, flywheels, etc) in order to produce electricity at all times unlike solar or wind. The main question in this post is how much waste would be produced while meeting world energy requirements. Yes, it is not economical to have nuclear producing at peak demand 24/7 all year for the whole world, and the extra power would have to be sunk somewhere, but at least it could meet those requirements all of the time. Theoretically, BWRs or fast reactors could load follow too.

      3) 1 kWh of solar does not displace 3 kWh of coal. or of nuclear. You are speaking of thermal efficiency, which is already taken into account with most other power sources. When a nuclear or coal powered steam plant is rated as 1000 MW, *it means it PRODUCES 1000 MW of electricity,* (all the time). Sometimes it is specified as 1000 MWe (MW electric), as opposed to MWth (MW thermal) which is less frequently specified. This is the crux of the problem with solar. When a solar panel says it will produce such-and-such Watts, it does not mean total electric production. First, it is a peak possible production, without taking into account capacity factor. Then after capacity factor, the efficiency of producing electricity must be factored in. If anything, 0.02 kWh of coal replaces 1 kWh of solar.

      4) yes, there is sunlight somewhere in the world at any given time, but any electricity produced by it must be transported. TRANSMISSION LOSS is another major factor affecting the usefulness of solar power (and other distributed sources) that the Lincoln Institute probably took into account which you did not. Losses are so significant that after transporting over more than a couple hundred miles with conventional methods, the losses eat up all of the production. Other methods are extremely expensive, which is the main reason why the whole world can't effectively be powered by the Sahara (yes, among other reasons- waste, stability, maintenance, safety...)

      5) in engineering, a factor is something multiplied to a number in order to adjust it. A "derating factor" of 0.77 would not cut solar by 77%, it would multiply it by 77%. This would cut it by 23%, as you mentioned. This is reasonable, probably to take into account the distributed nature of the electricity production or other issues such as lifetime.

      6) i haven't seen numbers, but I doubt the most of the UK demand for electricity is in the winter. Maybe for energy as a whole, which include heating oil, natural gas, and etc.

      7) good luck with powering your grid with any significant portion of wind. Please check out what that did to Denmark- the volatility has become so costly that they actually have to both pay expensive rates to import when there is no wind production AS WELL AS pay larger countries to take their overproduction. Out of their installed capacity of 20%, it has met as low as 5% of their energy needs. http://thingsworsethannuclearpower.blogspot.com/2012/03/windfall.html

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    4. Hi Caroline,

      1/3 – The Lincoln Institute are quite clear about this part of their methodology and you can read it on p92. They give land used to produce 148,922 TWh, i.e. global primary energy consumption. For your nuclear figure you cited the EIA who give a 2009 figure of 18,979 TWh of electricity consumption.

      The Institute use McDonald et al’s 2009 figures of about 39 sq km per TWh, referenced to two other articles, only one of which mentions solar and cites a 2001 US DOE report that gives 28 sq km of solar plant per TWh. But this is land use for the plant and access requirements, not module area. Using NREL and figures from my previous references, a value of 100,000 sq km of modules, instead of the 5.5 million you used is more realistic IMO. Although you could comfortably double it if you think that a combination of losses would halve the power output I estimated.

      I calculated including capacity factor, and I expect that the peer reviewed references I gave and the NREL guys were probably aware of efficiency and capacity factor too when they calculated figures that were close to mine, but ~98% smaller than the Lincoln Institute’s.

      5 – we agree, I was just speculating that perhaps the LI had done it the other way round!

      6 – you might find this interesting then, UK national grid monthly demand:
      http://www.nationalgrid.com/uk/Gas/Data/Operational_Summary/other_info.htm
      Monthly demand only ever exceeds 100 TWh between November and March. In summer it often falls below 70 TWh/month.

      7 etc – as I said, this is just a thought experiment. There’re no plans to make a purely nuclear or a purely solar or a purely wind world. I just think that if we’re going to be putting numbers to things, then it’s our duty to try and make sure we get the figures right. And I’m pretty sure that your figures for solar waste need a pretty hefty correction.

      A factor of between 27.5 and 55 for module area versus the land area you got from the Lincoln Institute. A factor of about 7.25 for the thickness. And a factor of 5-10 if you include recycling.

      I think the solar waste figure you calculated for modules is off by a factor of between 1,000 and 4,000 (including recycling) unless you can pick a hole in my figures.

      Module thicknesses are now typically 35 mm apparently:
      http://www.swithenbanks.co.uk/shop.php?action=full&id=11293
      http://www.swithenbanks.co.uk/shop.php?action=full&id=12312

      All the best,
      Mark

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  4. Hi again Caroline,

    I should have mentioned why my numbers are so different from your source’s. The Lincoln Institute gets 5.5 million square kilometres, I get 100,000. What’s going on?!

    You used electricity use for your nuclear comparison, so I did too. This is about 7 times smaller than the total energy value the Lincoln Institute use. Their choice is a bit funny IMO as 1 kWh of solar PV output should displace 3 kWh of coal, since coal power stations are only ~33% efficient.

    Next up, they assume worse panels than I do. You could double my estimate, or you could halve it based on these assumptions. Combined with the above, this explains a factor of 12 or so.

    What about the rest? I don’t know. They talk about a ‘derating factor’ of 77%, so maybe they cut solar production by 77% when the NREL report says it should be 23%.

    Who’s right? Denholm & Margolis in Energy Policy, 2008 say that US electricity demand needs 180 sq m of PV per person. US per capita electricity use >4 times higher than the global average so globally it should be ~40 sq m per capita – but the Institute gives 780 sq m.

    Love et al, 2003 got 41,000 sq km to provide 2000’s US electricity demand of ~3.6 trillion kWh. Based on modern global demand of ~20 trillion kWh you’re looking at 225,000 sq km. A 2004 DoE report ‘How much land will PV need to supply our electricity?’ gave ~40,000 sq km which is 7% of land designated as ‘cities and residences’. From the table, they appear to consider ‘packing density’, and if so then my figures are the right ones to use here because you want module area, not solar farm area including the pathways etc.

    Based on Denholm & Margolis, Love et al and the DoE figures, I think I’m pretty close to the mark. If so, then you need to cut your volume estimate by a factor of about 250.

    All the best,
    Mark

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    1. Thank you, Mark. This is an extremely well written comment and we sincerely appreciate your research. It is always encouraging when people are willing and capable to look into something and really know what they are talking about. I will have to look more closely at it soon.

      Even if we cut our volume estimate by a factor of 250, this still leaves solar as producing over 250 times the amount of waste of nuclear, right?

      And that's not even touching it, since we know that a solar powered world would be at least half the time a battery powered world, and those lifetimes and recycling and metal/chemical waste look much worse than panel recycling.

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    2. I believe one aspect that is missing from all these solar panel area requirement, is that they are based on averaged demands. By taking an annual demand and figuring out the requirements, there is the aspect of Peak Demand Load; when everyone is utilizing large amounts of electricity at the same time, or when everyone has their air conditioners on. Usually measured in kVA, this demand load should be taken into consideration as these solar panels would need to account for peak demand loads, not just the average load, which would most likely increase their footprint that much more.

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  5. Can any of the solar panel materials be reused? I know there is also at least 1 process for regenerating spent nuclear fuel as well.

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    1. As mentioned by Mark, above, the aluminum mounts and the glass are certainly the majority of the panel, and can be recycled.

      Right now there is little regulation in the U.S. on how to dispose of the PV panels properly (mainly because of the lead and cadmium content). In many cases they can be thrown in regular landfills which leaves no incentive to recycle. Europe has declared them as hazardous e-waste and set forth plans for recycling. (http://www.energytrend.com/EnergyTrend_PV_20120315)

      However, PV recycling is complicated and is neither economical nor done on a large scale anywhere (to my knowledge) although the costs are expected to come down as the industry continues to mature.

      paper on PV recycling and waste issues
      http://digitalcommons.law.ggu.edu/cgi/viewcontent.cgi?article=1064&context=gguelj

      article on PV recycling and remaining "green"
      http://www.greentechmedia.com/articles/read/solar-waste-recycling-can-the-industry-stay-green/

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    2. For a 100% solar world to work (not just electricity but the whole 20TW), you have to have a global transmission and distribution system. Some years ago I have attempted to calculate the cost of this (assuming redundant HVDC bi-polar transmission backbones of 120.000 km length and HVDC subnets at 500 km gridspacing in all populated regions) I concluded it would cost at least 400 trillion euro's. Allowing for world primary energy demand of 50TW in the future, the figure would rise to 1000 trillion euro's. Annual maintenance and replacement costs would be 1% = 10 trillion euro's annually. That would amoount to between 5% and 10% of global GDP.

      All this just just for the global renewable energy transmission network!

      So you would still need to buy your solar panels and windfarms, etc, at a total installed capacity of between 100 and 250 TW, assuming a 20% average capacity factor for wind/solar. Assuming a 1€/W installed cost for solar and wind, you would need another 100 to 250 trillion euro's for your PV panels and windturbines.

      But of course, average power loss due to resistance (HVDC also has resistance) from sending power across on average about 3/8 the circumference of the earth would probably be between 25% and 50%(!), so you would have to build between 130 TW and 375 TW of solar panels/wind farms, at a cost of somewhere between 100 and 400 trillion euro's. And you would need to rebuild them every 15-30 years of course.

      That is assuming that we can position our solar and wind so that together it counts as enough firm capacity so you don't need backup (which remains a dangerous assumption even if the system is globally connected)

      Doing the same thing with nuclear power would only require between 20TW and 50TW of nuclear power plants (= about 25.000 NPP sites), and you would save the 400 to 1000 trillion euro cost of the global transmission grid. Since these plants would probably last between 60 and 100 years, you would save a couple hundred trillion euro's every 15-30 years due to *not* having to build new windturbines and PV systems.

      Just saying: calculating the waste of solar/wind power should include the waste of this massive global transmission network, since such a global network would not be needed in a nuclear powered world.

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  6. "solar power to produce 100% of world electricity generation would require 5,500,000,000,000 square meters"

    Also known as 5.5 million km^2. Don't be a drama queen: http://xkcd.com/558/.

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    1. You are good at units (and sexist generalizations).

      However, since the volume of nuclear waste doesn't even make a cubic kilometer, for comparison we made the units the same in meters. It sounds like a lot, because it is.

      Just promise me you aren't one of the people that uses Becquerels for units of radiation when Curies will do.

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  7. While I am a big supporter of nuclear power, I think you have to check some of your numbers. You state that;

    “Used nuclear fuel produced by all US reactors is 2,000 metric tons annually. This is about 100 cubic meters per year.”

    Density = mass/volume. 2000 tonnes/100 cubic metres = 20 tonnes/cubic meter or a Specific Gravity (SG) of 20 i.e. 20X more dense than water. That's impossible. Uranium metal itself has a SG of 19.1 according to wikipedia. Ceramic uranium oxide fuel pellets have a density of 10.97.

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

    However, the spent nuclear fuel isn't just the fuel pellets. It is the fuel pellets inside the fuel rods that form part of a fuel bundle with space between the rods. So overall bulk density, maybe about 5? A long way from 20.

    I had a similar discussion on another energy blog. See the following.

    http://canadianenergyissues.com/2012/09/02/one-gram-of-garbage-per-day-we-should-be-so-lucky/

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    1. We are glad you did check the numbers, and glad to have your support. I used the density of uranium, at 18,900 kg/m3 for a very rough estimate. The total size of all the supporting structures for solar were not taken into account either, but if we wanted to take into account the density of uranium oxide along with the geometry of the fuel- spacers, cladding, etc, the density might be closer to 3,500 kg/m3, so maybe you could divide by a factor of 6. This still leaves solar with over 10,000 times more volume of waste than nuclear. Either way, one can see that the amount of waste is significantly greater with solar than nuclear per energy produced.

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  8. I am new to the science included in solar panels and the effect it has on our planet, I was all for solar panels but reading this has made me re-consider as I just want a better planet for my children and grandchildren!

    Good Read.

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  9. I am a past Nuclear Process Engineer that worked for a decade on the Treatment of Nuclear Waste at Hanford, WA. I always believed if Environmentalists truly understood the science on Nuclear energy they would be the biggest proponents. Also, those crazy canucks to the north use the CANDU reactor which utilizes natural uranium and heavy water which actually has less of the "bad"/highly radioactive isotopes than does a processed uranium fuel. And yes, with 95% of the waste being able to be reprocessed, it is interesting that there hasn't been more push for Nuclear energy.

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  10. Hi,

    As soon as you factor in the thousands and possibly millions of years nuclear waste has to be cared for till it is safe for the environment, then solar waste looks very clean indeed.

    Give me cold-fusion and then this debate would be worth having.

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    1. Hi there,
      The truth is that with recycling, you would only need to store for a couple hundred years. And, as mentioned above, it would actually produce energy while being recycled. So, is it "waste" or just very slightly used (5% of energy utilized) fuel?
      Check out our most recent article about waste here which talks about these points and more: http://www.thingsworsethannuclearpower.com/2013/05/10-cool-things-about-nuclear-waste.html
      Thanks for your comment.

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    2. The waste from discarded solar panels never breaks down. Cadmium and lead remain in the environment forever and never break down to safer elements. A solar powered world would have thousands of times of these heavy metals dumped in the environment.

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  11. Sorry, but this calculation is well-known nonsens. A correct calculation would not reduce the nuclear-waste to its reactor-fuel, it would include the waste of liquid and solid nuclear waste that is produced by the mining- and transforming-processes too! (about 100 000 - 200 00 tons per year for a 1000 MW-reactor)

    It has to include the waste and energy-needs for storing the waste.

    It has to include the waste oft the building and its energy-demand, including the deconstrution.

    It has to include the demand and waste of running the power supply systems, which is in a centralized sturcture much more higher, than i a decentralized structure, bringing up all the economy-activities to the same structure of long or short ways of trading products and moving ressources. (Mainly globalization or regionalisation of economy)

    It has to include the coming transformation in traffic, which is bringing more effizient e-motors than Cl-engines and with them a juge capacity of storage-potential, making lots of power supply systems needless.

    You will never understand how to organize the energy supply of a society correct, if you just look at the technical element, ignoring the social conditions.

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  12. "Assuming that the land use is the approximate area of the solar panels, and that the panels are a minimum of 1 inch thick (2.54 cm), the volume of PV panels as waste would be 139,700,000,000 cubic meters."

    I have panels on my garage. They are not an inch thick. They're about 0.2 inches thick.

    That frame is made of aluminum, and 100% recyclable. The main panel consists largely of glass and silver, also 100% recyclable. The only portion that isn't is a small amount of glue, the insulation on the wires, and the plastic backsheet which is the thickness of saran wrap. It is more recyclable than a car, which is one of the most recycled items in the world.

    "Cadmium and lead"

    There is no cadmium and lead in a typical solar panel. SOME thin-film systems use these, but they too completely recyclable.

    "Also, those crazy canucks to the north use the CANDU reactor"

    I'm a Canadian that lives within the Pickering exclusion zone. There's a warning horn down the street. Ironically, it's solar powered.

    The Pickering plant is sitting on prime beachfront real estate. When it was built it was in the middle of nowhere, today it's in the middle of a growing and extremely valuable housing area, with commuter train access to downtown Toronto.

    Due to the problem that we have no long-term storage solution, the waste from Pickering is stored on-site. That means that when the generator turns off in a few years (currently slated for 2018) the plant cannot be dismantled. There are some plans to try to move the spent fuel to other sites, but much of it is still to hot, the plant is now surrounded by homes, and none of the other plants have much leftover storage room either. So basically that land, worth hundreds of millions, has been removed from the economy, for a very very long time.

    This is precisely the sort of "support" that nuclear doesn't need: one that is formed largely on bad numbers that is so easily picked apart by anyone, which then leads the casual reader to think that *all* the pro-nuke numbers being presented are a lie.

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  13. Your first fundamental statement is incorrect: "Research on electricity generation and land use (paper, referenced here previously), estimates that solar power to produce 100% of world electricity generation would require 5,500,000,000,000 square meters (5.5 x 10^12 m^2)."

    Re-read the article and it says this are of land is needed for total world wide energy demand from all sources, not just electricity (coal, oil, natural gas, all forms of electricity generation ,etc.... everything, not just current electricity demand):

    "Some 5.5 million km2 of land area would be
    needed to supply 100 percent of current energy demand with solar photovoltaics.
    This amount of land would easily fit within the desert regions of the world."

    Electricity represents only about 15% of total energy use. Also in rereading the report, it's clear they are talking about current systems and total land use, not just that covered by the panels but total enclosed areas for odd shaped parcels. Some of this land use will be mitigated through use of existing wasted land (rooftops, parking lot covers), multiuse, more efficient total land area usage, improved efficiency, and improved panel lifespans. A forward looking view on nuclear should be compared to a forward looking view of Solar to be fair as solar is also an evolving technology and it would be clearly optimized before such a huge level implementation would be seriously considered:

    For example, you state panel life at 30 years, but panel degradation is being improved and will continue to be:
    The National Renewable Energy Laboratory (NREL) performed a meta-analysis of studies that examined the long term degradation rates of various PV panels. They found that the 1% per year rule was somewhat pessimistic for panels made prior to the year 2000, and today’s panels, with better technology and improved manufacturing techniques, have even more stamina than their predecessors. For monocrystalline silicon, the most commonly used panel for commercial and residential PV, the degradation rate is less than 0.5% for panels made before 2000, and less than 0.4% for panels made after 2000

    Solar cell type Output loss in percent per year
    Pre 2000 Post 2000
    Amorphous silicon (a-Si) 0.96 0.87
    Cadmium telluride (CdTe) 3.33 0.4
    Copper indium gallium selenide (CIGS) 1.44 0.96
    Monocrystalline silicon (mono-Si) 0.47 0.36
    Polycrystalline silicon (poly-Si) 0.61 0.64

    Yes, there is still work to do in all these areas before large scale deployment, but reasonable projections of technology advancements should be made in your comparisons.

    - S. Miller

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