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FCKGW posted:This is probably the weirdest thread I've even seen a slap fight take place Oh man, I get super annoyed by appeals to authority. It is one of my pet peeves. Claverjoe isn't doing it that badly but the sociology and political threads on this site are loaded with name-drops and appeals to authority in lieu of actual explanations or reasons and it drives me nuts. silence_kit fucked around with this message at 20:26 on Jun 12, 2013 |
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Jun 12, 2013 19:47
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silence_kit posted:You are assuming that all sand gets turned into silicon or needs to get turned into silicon to make an appreciable amount of solar cells. I doubt that this is true. quote:Do you have a source for this? I am going off of a recent presentation given by the founder of SunPower, where he gave 250-300um as normal thicknesses. Here, have a couple of 5 year old article where they have 180-150 as a quote. http://americas.kyocera.com/news/news_detail.cfm?key=1619 http://www.renewableenergyworld.com/rea/news/article/2008/11/silicon-genesis-starts-production-of-150um-kerf-free-pv-wafers-54055 Now, have a 2 year old journal article, with 43 um thickness. http://onlinelibrary.wiley.com/doi/10.1002/pip.1129/abstract If I recall correctly, Sunpower's big claim to fame is their ability to control wafer processing to a fantastic degree, and not making the ideal wafer thickness, it doesn't surprise me that they are using an older thickness. quote:This is not true in this case. The technique that the gallium arsenide company uses leverages the facts that 1) hetero-epitaxy is much more mature technology and is richer for the III-V semiconductors over silicon (this is actually a lot of the reason why gallium arsenide cells are higher performance than silicon cells) Uhh, GaAs are more efficient (per unit depth is what I'm assuming you are saying here) because they are direct band-gap semiconductor, full stop. Si solar cells are indirect band-gap semiconductors, and are a bit more wonky to deal with because of that. Lots of light trapping needs to be done to actually absorb the light. Saying "more efficient" is very vague. quote:and 2) that there is a huge difference in solubility of aluminum arsenide and gallium arsenide in hydrofluoric acid. There isn't a way to do what the gallium arsenide company is doing in silicon. There may be other ways to achieve thin silicon wafers without having to waste a lot of silicon though. quote:That company went out of business, although I think a lot of other silicon solar cell companies are looking into techniques to make thinner silicon solar cells without wasting so much material. It is a good idea. quote:One thing that I don't understand is how you can process these silicon cells which are exfoliated from the wafer (the technology that Twin Creeks tried to sell is similar to the highest quality way to make silicon-on-insulator wafers). Doping and oxidizing silicon traditionally are high temperature processes, and attaching the thin, fragile silicon films onto glass or plastic sort of prevents you from doing those processes after the fact. The gallium arsenide company puts the dopants in during the growth and the processing of the cells is simple and at low temperatures. This is pretty normal for III-V device processing. quote:I would also like to say that in this thread you've said multiple wrong things about solar cells, so I would knock it off with the condescending know-it-all crap. quote:Well, at least in silicon, half of the cost of solar cells is independent of their manufacturing cost, and improving efficiency allows you to recoup those costs in addition to the manufacturing costs so you can't just declare efficiency to be irrelevant. Obviously you also need higher areas of solar cells to get the same power output, so you aren't really saving on material cost per watt by making your cells too thin to be able to get all of the current that they could get from the sun. The ultimate measurement of solar cells is total cost/watt, assuming no materials scarcity. With anything above iron (element 26), you have to keep your material demands in mind over the amount or you will run into a major cost curve eventually for massive deployment. quote:I understand how it works. Spare me the lecture please. It is unusual in that all other III-V devices (okay, let's ignore the blue LED) are made on expensive III-V substrates. All projections on cost, material availability assume that you are attached to a substrate. The substrate is over 100x thicker than what you need to make a solar cell. quote:Technically, you are misreading the paper--the 30 tons number is for a low-efficiency CIGS technology. The 111 tons number that you cited is also the amount of gallium that they use, not that amount that is available. The paper notes that there is way more gallium available from aluminum refining that people currently don't have a use for and don't bother to use. Also, assuming that all gallium goes into making III-V semiconductors is not that unreasonable of an assumption--gallium isn't used that much. It is very possible that the factor of ten that you donate to the calculation may not be generous enough. There are a lot of uncertainties here. quote:I didn't check the numbers, but thank you for at least doing this calculation. Obviously solar cells aren't going to supply all of the world's electricity and probably gallium arsenide solar panels won't be more common than silicon, so this result doesn't bother me. silence_kit posted:Yes, I know that gallium arsenide wafers are expensive--however, you don't need the wafers to be incorporated into the solar cell and in principle, you could reuse the wafers to make other cells. They aren't my favorite solar cells--I am just challenging your assertion that GaAs will forever be doomed for high cost and pointing out that there are engineering approaches to lower the cost. In my first post in this thread I noted that it remains to be seen whether it can be cost-competitive with silicon. That estimation was assuming that all possible Ga was made into solar cells, with no downtime for recycling, no wastage, no panel degradation, no nothing negative whatsoever. It isn't going to be cost competitive. There isn't enough readily available for large scale production. What really bugs me is when somebody comes in against the scientific/engineering consensus and uses sources who he or she doesn't read thoroughly. I guess we both happened to punch each other's pet peeve. The internet is serious business after all. 
The Dipshit fucked around with this message at 21:57 on Jun 12, 2013 |
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Jun 12, 2013 21:39
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Its really goddamn weird to see someone arguing for GaAs so passionately.
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Jun 12, 2013 23:38
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I just discovered this thread today and I hope this is the right place to ask this, but what are the thoughts on the build quality of GoalZero's stuff? I like the fact that they have a whole range of stuff and their customer service seems pretty good. I was looking at potentially getting their Yeti 1250 inverter/generator because of the portability for camping and road trips, but I'm not really feeling their solar panels. After poking around Amazon a bit, the Grape Solar stuff seems to get good reviews. Would I be able to use something like Grape's 250 panel in conjunction with GoalZero's Yeti 1250? I wish I could do more with residential solar, but my roof has a lot of tree coverage. EDIT: To be clear, while I did ask for opinions on the brands, what I'm really interested in is finding out if the two products are compatible with each other. Hungryjack fucked around with this message at 01:37 on Jun 13, 2013 |
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Jun 13, 2013 01:24
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I've never looked at GoalZero before. Don't know anything about the place. On "Solar Generators" though... I personally cringe every time I hear the term. There are some decent ones at decent prices, but most of them have overstated marketing claims. Look at the battery: 1250 watthours; and they claim that will back up a frige, or c-pap, etc... Yeah for a day. Maybe. A modest energy star frige uses 1000-2000 watthours per day. With no sun, you'd drain the battery to 0% in a single day. I believe a c-pap uses around 800 watthours per night. You can do that if you want. And I'll call you a battery murderer. The battery can be recharged to full, but you will severely shorten its lifespan by discharging that heavily on a regular basis. If the sun is out, then you lessen the discharge some amount; but solar generators tend to be marketed for backup systems during power outages, when there are often storms, and very little sun for a couple of days. Gotta step away for a bit, I'll edit in more later. Edit: For a backup machine its okay, assuming it gets used for a couple of day once every month or two. Leave it plugged into utility power(you can, cant you?) when not being used, and it should be a nice bit of piece of mind for when you need it. In general, what you are paying for is the nice, portable, all-in-one package. For the same price range, I could get you similar equipment, twice as much battery capacity, all the necessary "nuts and bolts" pieces and a 250ish watt panel. It would be separate components though, and not portable in a tight package. It would require a bit of do-it-yourself to get it up and running(reputable vendors make themselves available for tech support on the phone to help with installation questions), rather than the plug and play aspect that you are paying for when you buy a solar generator. It's nice to see that Grape Solar is no longer stamping "Made in the USA!!!" all over their website. That was a bit of a peeve with a lot of other panel manufacturers for a while, as the panels were mostly NOT made in the USA. As far as I know their panels are fine though, but they are still a relatively new manufacturer by most standards. Seems to be a typical 30 volt panel, and the GoalZero box says it has a 20 amp MPPT charge controller in it. That combo should work fine for charging a 12 volt battery. 2nd edit: Holy poo poo! I just looked at Goalzero's panels. They are out of their loving minds! $240 for a 30 watt panel?!?!? I don't care what kind of package they put it in. A decent 30 watt panel should be at $100(high price) or less. Maybe you get a bag of the weed they are smoking with each panel. Internetjack fucked around with this message at 02:26 on Jun 13, 2013 |
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Jun 13, 2013 01:38
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Thanks for the response. You really hit on what I was wanting to hear. I know this is the residential solar thread, but I was looking for something mostly portable that I could use in place of a small gas generator for things like camping trips and tailgating. The ability to use it in the car or in the tent is handy. I can't see myself putting a lot of draw on it so 1250 should be more than enough capacity for me. You can indeed plug the Yeti 1250 into utility power and I guess at that point it would just act like an uninterruptable power supply for whatever is plugged into it. The ability to charge it from solar is an added bonus that appeals to me. You also detailed what I expected to hear about GoalZero's 30w panels. It just didn't add up how a 30w panel should cost $240.
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Jun 13, 2013 04:07
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Uncle Jam posted:Its really goddamn weird to see someone arguing for GaAs so passionately. Ain't that the truth. And here I thought the inevitable techno-fetishism would pop up with regards to plastic solar cells, which at least have the promise of not putting themselves into a corner with regards to materials, but have that damnable problem of keeling over and dying after less than five years.
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Jun 13, 2013 05:14
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Claverjoe posted:Ain't that the truth. And here I thought the inevitable techno-fetishism would pop up with regards to plastic solar cells, which at least have the promise of not putting themselves into a corner with regards to materials, but have that damnable problem of keeling over and dying after less than five years. You and silence_kit cool it down or take it to PMs. I can see how this conversation may be interesting to others so I am hesitant to shut it down completely, but keep it civil.
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Jun 13, 2013 12:17
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Claverjoe posted:That's what makes Si based solar cells so nice, we couldn't use up the world's reserve of Si if we tried, and it comes in such a highly refined state relative to things that come in ppm. Ga? In? Limited available quantities, low concentrations. You aren't getting my objection. The six order magnitude difference in availability would only be a relevant number if you actually needed all the silicon in the world to make appreciable amounts of solar cells. Your comparison between 10^6 and 10^2 is not relevant. Claverjoe posted:If I recall correctly, Sunpower's big claim to fame is their ability to control wafer processing to a fantastic degree, and not making the ideal wafer thickness, it doesn't surprise me that they are using an older thickness. No, their claim to fame is that they are committed to high solar cell efficiencies. Their solar cell designs are a little more complicated to make but have the best efficiencies. Claverjoe posted:Uhh, GaAs are more efficient (per unit depth is what I'm assuming you are saying here) because they are direct band-gap semiconductor, full stop. Si solar cells are indirect band-gap semiconductors, and are a bit more wonky to deal with because of that. Lots of light trapping needs to be done to actually absorb the light. Saying "more efficient" is very vague. More efficient isn't vague at all. The power efficiency of a solar cell under some calibrated spectrum is a pretty well-defined quantity. The flat plate single junction gallium arsenide cell efficiency is higher than the silicon single junction cell efficiency. This is one wrong thing in this post that you have said about solar cells. The following is another wrong thing that you have said about solar cells--gallium arsenide isn't more efficient because it is a direct gap semiconductor. Your worry about the longer absorption lengths in silicon isn't that relevant to the performance of silicon cells. Silicon, being an indirect band gap semiconductor, doesn't absorb light well--you just said that--but it also doesn't emit light well. Because it doesn't emit light well, its radiative recombination rate is much lower than in gallium arsenide, and thus minority carrier lifetimes and diffusion lengths are longer than in gallium arsenide. Good silicon cells have no problem absorbing all of the light. What they actually have a problem with and what holds them back from reaching their theoretical efficiency according to a report that I read from the founder of SunPower is actually recombination at the cell contacts, which lowers the voltage. This is because hetero-epitaxy is not well developed for silicon like it is for gallium arsenide, and there aren't 'normal' big bandgap semiconductors to coat the silicon with to repel the wrong carriers from the contacts, like there are for gallium arsenide. This is one of the reasons why gallium arsenide is a high efficiency technology. This was what I was trying to explain in my previous post. quote:There to do something similar (thin film epitaxy) if not the exact same manner. Don't be dense. There is no direct analogue to do in silicon what the gallium arsenide company is doing. But there is more than one way to skin a cat, and the proton implant and cracking technology that is currently used to make SOI wafers is being looked into to make thin silicon wafers. This is the technology used in some of the links that you shared with me. This is a minor point, so I will drop it. Claverjoe posted:They won't be as efficient at the theoretical best thickness (around 50 um or so, as I recall), but who cares if they work and are cheap. . . . Here is yet another wrong thing that you have said about solar cells in your post. There is little point in thinning the silicon solar cell down so much that it hurts their efficiency in order to save on material cost. What you end up needing to do is to make more solar cells, and thus use more material, to get the same power output. The materials cost isn't even the biggest cost in a silicon solar cell anyway, so being extreme about this can actually make your cells more expensive. There is value in thinning down the cell while keeping the same efficiency or improving the efficiency though, or at least doing the optimization where thinning down the cell makes the most sense. I suspect that there isn't much benefit to trading off efficiency for thin-ness because material cost isn't the biggest cost of a silicon solar cell. Claverjoe posted:111 tons is what people currently produce, so that is far and away the most sensible starting point for estimation. We aren't in the business of assuming a magical unicorn, because it is convenient. I don't think that the 111 tons number is that relevant, given that the next sentence in the report is basically "we throw away most of the gallium in the waste stream because currently there is no use for it." silence_kit fucked around with this message at 23:21 on Jun 13, 2013 |
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Jun 13, 2013 17:44
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silence_kit posted:You aren't getting my objection. The six order magnitude difference in availability would only be a relevant number if you actually needed all the silicon in the world to make appreciable amounts of solar cells. Your comparison between 10^6 and 10^2 is not relevant. quote:No, their claim to fame is that they are committed to high solar cell efficiencies. Their solar cell designs are a little more complicated to make but have the best efficiencies. quote:More efficient isn't vague at all. The power efficiency of a solar cell under some calibrated spectrum is a pretty well-defined quantity. The flat plate single junction gallium arsenide cell efficiency is higher than the silicon single junction cell efficiency. This is one wrong thing in this post that you have said about solar cells. quote:The following is another wrong thing that you have said about solar cells--gallium arsenide isn't more efficient because it is a direct gap semiconductor. Your worry about the longer absorption lengths in silicon isn't that relevant to the performance of silicon cells. Silicon, being an indirect band gap semiconductor, doesn't absorb light well--you just said that--but it also doesn't emit light well. Because it doesn't emit light well, its radiative recombination rate is much lower than in gallium arsenide, and thus minority carrier lifetimes and diffusion lengths are longer than in gallium arsenide. 1. band gap energy, read up on the Shockley-Queisser limit(http://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit) for an explanation. GaAs solar cells bandgap (at 1.45 eV, and about 32.8% power conversion efficiency) has a theoretical maximum a grand total of around 4% higher than that than of Si solar cells (at a band gap of 1.15 eV, and a theoretical maximum of 29%). 2. whether or not a given solar cell is a direct bandgap or indirect bandgap material. Read wikipedia on here, and read thoroughly the section of "implications for light absorption" (http://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps) Now current research goes into making photonic crystals, light traps for internal reflection, and other neat tricks to pass the same light through the material. Read that journal article using porous silicon from my last post, those are the "neat tricks" I'm talking about. Light emission doesn't factor into solar cells, just the absorption-> electron-hole pair generation. quote:Good silicon cells have no problem absorbing all of the light. What they actually have a problem with and what holds them back from reaching their theoretical efficiency according to a report that I read from the founder of SunPower is actually recombination at the cell contacts, which lowers the voltage. This is because hetero-epitaxy is not well developed for silicon like it is for gallium arsenide, and there are no big bandgap semiconductors to coat the silicon with to repel the wrong carriers from the contacts, like there are for gallium arsenide. This is one of the reasons why gallium arsenide is a high efficiency technology. This was what I was trying to explain in my previous post. quote:There is no direct analogue to do in silicon what the gallium arsenide company is doing. But there is more than one way to skin a cat, and the proton implant and cracking technology that is currently used to make SOI wafers is being looked into to make thin silicon wafers. This is the technology used in some of the links that you shared with me. This is a minor point, so I will drop it. There is a point to reach a sweet spot of thickness, material inputs, and efficiency to produce the lowest cost/watt solar cell. The winner so far is Si based solar cells, even the GaAs folk of Alta Technologies admits this at point blank. The rest of your statement goes in some weird circle, and I got nothing to say to that. Maybe you can crunch some numbers to explain your thoughts? quote:I don't think that the 111 tons number is that relevant, given that the next sentence in the report is basically "we throw away most of the gallium in the waste stream because currently there is no use for it." There is no economical use for it, which is what you are proposing making GaAs solar cells for, a producer of energy. Basically you have been saying this entire time that the people who work with using Ga in their solar cells are wrong, and that they should be able to produce it cheaper than the Si based solar cells, and that what going on in the real world *right now* is completely false. Look, there are many technically feasible things that nobody does (like build airships for transport) because there are easier, better ways to do things (like using regular ships, and building the occasional canal/harbor for the ships), and if you grew up playing Final Fantasy video games, airships sound pretty awesome, but it doesn't mean they should happen in the real world. I've been willing to go with you on doing some basic back-of-envelope material calculations, cost/watt discussions, and so on. Calculate me the cost/watt of a GaAs module, and we'll see if it lines up with the real world costs, and if not, we can see where your analysis breaks down. The Dipshit fucked around with this message at 00:07 on Jun 14, 2013 |
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Jun 13, 2013 23:44
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I am going to let the topic of scarcity go. I think that I have heard your spiel. You have done one calculation which sets a very loose upper bound on the availability of gallium. For that I applaud you. The other one I don't think is that relevant because there are uncertainties regarding the numbers you put into it. I still am not convinced that your claim is true and that gallium scarcity is that big of a problem. quote:Biggest things that go into a solar cell's efficiency: I made a subtle point about engineering a solar cell to improve the cell's open circuit voltage, and you respond with solar cells 101. I don't think that you are making an attempt to read what I am writing here. quote:Light emission doesn't factor into solar cells, just the absorption-> electron-hole pair generation. The point that I was making was that the longer absorption length in silicon isn't a problem because the minority carrier diffusion lengths are longer too. Minority carriers in silicon have long diffusion lengths because their bulk minority carrier lifetimes are long. The reason why the bulk minority carrier lifetimes are long is because radiative recombination in silicon is low. This is because silicon is an indirect bandgap semiconductor or in other words is a poor light emitter. With silicon, thicker cells are not a problem--the carrier extraction is still good because the diffusion lengths are longer. silence_kit fucked around with this message at 00:30 on Jun 14, 2013 |
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Jun 14, 2013 00:24
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silence_kit posted:I am going to let the topic of scarcity go. I think that I have heard your spiel. You have done one calculation which sets a very loose upper bound on the availability of gallium. For that I applaud you. The other one I don't think is that relevant because there are uncertainties regarding the numbers you put into it. I still am not convinced that your claim is true and that gallium scarcity is that big of a problem. I take it you now understand your imprecision with your usage of "efficiency". quote:I made a subtle point about engineering a solar cell to improve the cell's open circuit voltage, and you respond with solar cells 101. I don't think that you are making an attempt to read what I am writing here. quote:The point that I was making was that the longer absorption length in silicon isn't a problem because the minority carrier diffusion lengths are longer too. Minority carriers in silicon have long diffusion lengths because their bulk minority carrier lifetimes are long. The reason why the bulk minority carrier lifetimes are long is because radiative recombination in silicon is low. This is because silicon is an indirect bandgap semiconductor or in other words is a poor light emitter. With silicon, thicker cells are not a problem--the carrier extraction is still good because the diffusion lengths are longer. If you don't absorb the light in the first place, you don't ever worry about recombination, since no electron-hole pairs are produced. Minority carriers in Si or GaAs solar cells aren't a real issue, barring major cell defects that cause shunting. I mean, fill factors (where recombination is modeled) of most all decently made crystalline solar cells are pretty similar (Alta devices's tech brief is 84.2 for Fill factor, and Sunpower quotes an 81.2 for their current models), so the concern of charge carrier issues aren't really a thing to be worried about here. I don't see how this statement is remotely relevant to GaAs solar cells having any kind of possible superiority. Also: silence_kit posted:Here is yet another wrong thing that you have said about solar cells in your post. There is little point in thinning the silicon solar cell down so much that it hurts their efficiency in order to save on material cost. What you end up needing to do is to make more solar cells, and thus use more material, to get the same power output. The materials cost isn't even the biggest cost in a silicon solar cell anyway, so being extreme about this can actually make your cells more expensive. There is value in thinning down the cell while keeping the same efficiency or improving the efficiency though, or at least doing the optimization where thinning down the cell makes the most sense. I suspect that there isn't much benefit to trading off efficiency for thin-ness because material cost isn't the biggest cost of a silicon solar cell. Is still making no sense to me. Could you possible rephrase this so it has a point somewhere? I mean your last sentence has a "suspicion" but that's about all I got from that rambling. I invite you for a second time to offer up any analysis in terms of production, cost to produce, cost/watt, or any other metric you think would be relevant to offer that GaAs solar cells aren't a niche product for cost/weight considerations. The Dipshit fucked around with this message at 05:32 on Jun 14, 2013 |
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Jun 14, 2013 01:53
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Claverjoe posted:If you don't absorb the light in the first place, you don't ever worry about recombination, since no electron-hole pairs are produced. The high quality silicon and gallium arsenide solar cells have no problem absorbing all of the light and collecting all of the carriers to get their maximum short circuit current. It isn't an issue. What they have yet to do to achieve their theoretical efficiencies is to reach their highest open circuit voltages. Improving the efficiencies in these technologies is all about improving the voltage. Only in low efficiency technologies do they struggle with getting the full short circuit current. Claverjoe posted:Minority carriers in Si or GaAs solar cells aren't a real issue, barring major cell defects that cause shunting. The minority carrier lifetime (or the similar quantity the minority carrier diffusion length) is a really relevant quantity in solar cells. I am a little surprised that you don't believe this. The diffusion length dictates how far the photo-generated carriers can travel in a bulk semiconductor before they recombine. The reason why crystalline silicon and gallium arsenide are such high performance solar cells is because the ratio of diffusion length to absorption length is very good in those materials. This ratio dictates how easy it is turn photo-generated electrons and holes into electricity at the terminals of the cell. Having a short absorption length isn't good enough if your carriers still recombine before they reach the electrodes. You pointed out earlier that silicon has a longer absorption length than gallium arsenide, which is true, but for the same reason that sunlight in silicon has a longer absorption length, its carriers also have a longer diffusion length. For performance, the ratio and not only one or the other matters. Claverjoe posted:Is still making no sense to me. Could you possible rephrase this so it has a point somewhere? I mean your last sentence has a "suspicion" but that's about all I got from that rambling. The last sentence summarizes it well. Sacrificing efficiency to make really thin solar cells in an attempt to save on material cost is a dumb idea. If you do that, you will need to make more solar cells to get the same power output, which goes against the intended goal. This is sort of a fool's game to play because the material cost isn't even the biggest cost in a silicon solar cell. Let's do a hypothetical example. Assume that materials cost is 40% of the cost of making a c-Si cell. If we half our materials cost per cell (not per watt) by making our cells half as thick, which, say in this example, decreases their efficiency to four-fifths of what it used to be, we actually haven't done anything to the total cost per watt. The per-cell cost is now 80% of what it used to be, but now we require 1.25x as many cells to generate the same amount of electricity. We are using less material, but we aren't improving the cost per watt. There is value in making really thin solar cells and keeping the same or even improving efficiency, though. This is obvious.
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Jun 14, 2013 14:34
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silence_kit posted:The high quality silicon and gallium arsenide solar cells have no problem absorbing all of the light and collecting all of the carriers to get their maximum short circuit current. It isn't an issue. What they have yet to do to achieve their theoretical efficiencies is to reach their highest open circuit voltages. Improving the efficiencies in these technologies is all about improving the voltage. Only in low efficiency technologies do they struggle with getting the full short circuit current. Absorbing all the light in a Si solar cell is a much more complex question than that of a GaAs solar cell. You bring up processing costs in Si solar cells, and much of it is in light trapping techniques, patterning the light facing side to have an inverted pyramid look, playing with spacing at the back connections for reflection, stuff like that. quote:The minority carrier lifetime (or the similar quantity the minority carrier diffusion length) is a really relevant quantity in solar cells. I am a little surprised that you don't believe this. The diffusion length dictates how far the photo-generated carriers can travel in a bulk semiconductor before they recombine. The reason why crystalline silicon and gallium arsenide are such high performance solar cells is because the ratio of diffusion length to absorption length is very good in those materials. This ratio dictates how easy it is turn photo-generated electrons and holes into electricity at the terminals of the cell. Having a short absorption length isn't good enough if your carriers still recombine before they reach the electrodes. quote:You pointed out earlier that silicon has a longer absorption length than gallium arsenide, which is true, but for the same reason that sunlight in silicon has a longer absorption length, its carriers also have a longer diffusion length. For performance, the ratio and not only one or the other matters. quote:The last sentence summarizes it well. Sacrificing efficiency to make really thin solar cells in an attempt to save on material cost is a dumb idea. If you do that, you will need to make more solar cells to get the same power output, which goes against the intended goal. This is sort of a fool's game to play because the material cost isn't even the biggest cost in a silicon solar cell. Yeah, I think we were talking past each other then. There is an engineering sweet spot for any type of solar cell, and I don't find this statement controversial or germane to your belief that GaAs solar cells are somehow the superior option. quote:Let's do a hypothetical example. Assume that materials cost is 40% of the cost of making a c-Si cell. If we half our materials cost per cell (not per watt) by making our cells half as thick, which, say in this example, decreases their efficiency to four-fifths of what it used to be, we actually haven't done anything to the total cost per watt. The per-cell cost is now 80% of what it used to be, but now we require 1.25x as many cells to generate the same amount of electricity. We are using less material, but we aren't improving the cost per watt. The Dipshit fucked around with this message at 19:28 on Jun 14, 2013 |
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Jun 14, 2013 19:14
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Claverjoe posted:It is not as relevant as material properties. Minority carrier lifetime and absorption lengths ARE material properties. Minority carrier lifetime is also pretty important--CIGS, CdTe, and GaAs can all have similar bandgaps, but yet, cells made of the different materials have different open circuit voltages. Organic solar cells have higher bandgaps, but have really terrible open circuit voltages. The differences in voltage are largely due to different non-radiative recombination rates in those materials, which can be seen in the minority carrier lifetimes in the different materials. Minority carrier lifetime is a really important metric for semiconductors. Claverjoe posted:This has an effect on the thermal derate more than anything. See above. No, it is critical to the performance of a solar cell. See above. Claverjoe posted:Demonstrate that the 40% materials costs is a reasonable estimate, demonstrate that halving the current thickness will cause a decrease in efficiency. Your conclusion of needing more surface is fairly simple, but there is no reason to believe your numbers. You've asked of me to source my information, and I ask that whatever you ask of others, you demand of yourself. Even in the example you gave, it was a wash in terms of cost/watt, and in the general sense, we aren't exactly running out of surface are to put solar cells. First of all, I clearly stated that it was a hypothetical example. I used the numbers to illustrate the point. It wasn't a coincidence that it ended up as a wash. This is hilarious. Here is a presention by the founder of SunPower where he says that material costs are about 27% of the total costs of c-Si solar cells. https://www.youtube.com/watch?v=Qz_mUj0PbgE. Regarding the point that I am making that just taking a design and decreasing the thickness too much can decrease efficiency--you are the guy who keeps on trying to bring up that it is so hard for silicon cells to get their full short circuit current, so I don't know why you need to be convinced of this. This again is hilarious. silence_kit fucked around with this message at 00:31 on Jun 16, 2013 |
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Jun 14, 2013 22:42
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silence_kit posted:Minority carrier lifetime and absorption lengths ARE material properties. Minority carrier lifetime is also pretty important--CIGS, CdTe, and GaAs can all have similar bandgaps, but yet, cells made of the different materials have different open circuit voltages. Organic solar cells have higher bandgaps, but have really terrible open circuit voltages. The differences in voltage are largely due to different non-radiative recombination rates in those materials, which can be seen in the minority carrier lifetimes in the different materials. Minority carrier lifetime is a really important metric for semiconductors. quote:First of all, I clearly stated that it was a hypothetical example. I used the numbers to illustrate the point. It wasn't a coincidence that it ended up as a wash. This is hilarious. I suppose you can laugh all you want, but I still see your statement of GaAs as a potential type of solar cell to supplant Si based crystalline solar cells as indefensible. I guess we are getting to that point where you start claiming "puppetmaster" or something? The Dipshit fucked around with this message at 05:06 on Jun 17, 2013 |
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Jun 17, 2013 04:57
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I am going to bow out of this conversation. It is clear that you aren't bothering to read or are unable to understand any of my posts. I just pointed out that bandgap obviously doesn't uniquely determine the open circuit voltage of a solar cell--CdTe and GaAs have the same bandgap and yet the two cells have different voltages. You ignored that and decided to lecture me on an unrelated point. An additional point: silicon has a theoretical efficiency less than CdTe if you only look at band gaps, but yet silicon performs better than cadmium telluride. There is something else going on here that you seem uninterested or are uneducated about. I don't think that it is productive for me to continue talking with you. Have a nice day! silence_kit fucked around with this message at 15:16 on Jun 17, 2013 |
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Jun 17, 2013 14:56
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silence_kit posted:I am going to bow out of this conversation. It is clear that you aren't bothering to read or are unable to understand any of my posts. I just pointed out that bandgap obviously doesn't uniquely determine the open circuit voltage of a solar cell--CdTe and GaAs have the same bandgap and yet the two cells have different voltages. You ignored that and decided to lecture me on an unrelated point. An additional point: silicon has a theoretical efficiency less than CdTe if you only look at band gaps, but yet silicon performs better than cadmium telluride. There is something else going on here that you seem uninterested or are uneducated about. Oh, I am reading your posts, but I am not reading your mind. Happily telepathy does not exist, otherwise people would really know what they think of each other, and it'd probably doom civilization as we know it. If you want to talk about CdTe research, then so be it, but it was mostly left by the wayside back in the early 90s, which left out the optimization that has been performed in recent decades. We have been discussing the domain of mature GaAs R&D and mature Si R&D, where your concerns of minority carriers do not matter. Certainly the carrier lifetimes are an issue with CdTe solar cells, and with organic solar cells, and dye sensitized solar cells, and some other systems, but we weren't talking about those, now were we? If you wanted to open up a conversation about those systems, then I would have agree with you (and even discuss methods on how they are working on improving the system, especially for the dye solar cell which is where I specalized) but you had a bee up your nose about GaAs solar cells saying that they may and might be competitive due to some new technique you read on the internet. Any time you want to learn something about the mentioned platforms, I'll be happy to discuss things.
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Jun 17, 2013 16:28
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Every time I open this thread lately to find new posts, I'm disappointed in the resulting nerd arguments.  So I have a question about a standalone solar system for my garage. Long story short: I have a fairly small, 1 car garage that sits a long way from my house. Running electricity to it would be rather expensive as I would have to cut across my driveway to run it underground or I would have to put in a pole to support the wires above ground. I don't need a great deal of power. I just need a garage door opener, a couple of lights and an outlet or two just in case. I'm looking at a couple of cells on the roof and battery storage. The actual power usage would be fairly negligible, but I'm not sure what size of system I would need. Any suggestions?
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Jun 17, 2013 17:13
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JiimyPopAli posted:Every time I open this thread lately to find new posts, I'm disappointed in the resulting nerd arguments. I suspect the question will be what do you want to do with the outlets? That's probably going to drive what you need. Is it going to be a case of hobby working with some power tools, or running a TV (beer fridge?), and if so, for how long? Sorry about the nerd argument, there is no pleasing some people. The Dipshit fucked around with this message at 17:59 on Jun 17, 2013 |
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Jun 17, 2013 17:47
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Claverjoe posted:I suspect the question will be what do you want to do with the outlets? That's probably going to drive what you need. Is it going to be a case of hobby working with some power tools, or running a TV (beer fridge?), and if so, for how long? They're really more for just-in-case. Running an impact driver to put snow tires on/off, running a weed trimmer for a few minutes (as infrequently as I can manage), that sort of thing. Nothing that would run constantly, or require significant usage for more than 10 minutes or so. I think the highest drain thing I can think of would be running a waxing iron for skis, and even that wouldn't be for very long. I would also be willing to use LED lights to save on battery usage, despite the (significantly) higher initial cost.
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Jun 17, 2013 18:09
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JiimyPopAli posted:They're really more for just-in-case. Running an impact driver to put snow tires on/off, running a weed trimmer for a few minutes (as infrequently as I can manage), that sort of thing. Nothing that would run constantly, or require significant usage for more than 10 minutes or so. I think the highest drain thing I can think of would be running a waxing iron for skis, and even that wouldn't be for very long. So essentially your biggest demands will be in the winter time, but won't be for high up-times? I'd suspect you'd be able to get away with maybe a relatively small 500w array, but need to buy a enough batteries for 4-5kWh of usage to make it so that they don't drain heavily, though I think InternetJack would know better. I'd wager that the batteries would be the biggest single price, especially if you are fine with LED lights. garage door openers don't really eat up that much juice, really.
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Jun 17, 2013 18:19
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A garage as described wont take much in the way of panels and batteries. The trick will be sizing the inverter, and evaluating the phantom draw of the opener if you use a remote control. Get the owner's manual for the garage door assembly. The motor may be 1 hp or more. The run time is very short in terms of daily usage, but the 20 second draw of the motor may be very high in terms of wattage. A big heavy door requires more wattage. The higher the wattage, the bigger the inverter needed. It can be a sucky answer too, needing a $1000 - $2000 inverter to open and close a garage door once or twice a day, and massively oversized for running anything else. I believe a co-worker beat this problem by finding a unit that could be run DC direct off the batteries with some minor modification, removing the need for an inverter. It used a DC motor, and power supply for the circuitry. I'll make a note to myself to ask him about it again. The second part is that with a remote, the electronics may be "on" 24/7 waiting for an open/close signal. Even at a few watts, it can add up in a 24 hour period to a few hundred watt-hours. Not horrible, but it will impact the system size. With the garage door removed from the equation, you could do a simple system in the ballpark of $1000. One 12 volt marine battery, or two 6 volt golf cart batteries. An array of 100-200 watts would collect about 400-800 usable watt-hours on a sunny day. A small charge controller, a smallish pure or modified sine wave inverter, some simple fusing, and a battery charger for backup during overcast weather(take the batteries over to the house if need be?) would be all of the basics. Look at the wattage of the loads, and their estimated run-time on average, to estimate daily watt-hour usage, and then compare to the watt-hours collected I mentioned above for consideration. Fake edit: impact driver probably has a huge surge draw as well, similar to the motor on the garage door, requiring a decent sized inverter as well. Start with load evaluation.
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Jun 18, 2013 01:52
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Thank you both for your advice, it's very helpful I haven't bought the garage door opener yet (I'm not that optimistic on getting this done that quickly) but I'll look at the draw of it, and a couple of other things I could potentially use to get a handle on the requirements. $1000 is in line with what I was anticipating, I'll check to see if it matches my needs. Thanks again :-)
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Jun 18, 2013 03:01
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It may be possible to refit a garage door opener with a DC motor if an AC/DC unit cannot be found. It seems like the power requirement and duty cycle are similar to an automotive starter motor. It also sounds like the construction expenses associated with running wires from the house would be less than this inverter set-up.
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Jun 18, 2013 06:19
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That's worth looking into, thanks for the idea.  As for the construction, I'd rather not put it above ground since it would result in a small telephone pole in my front yard. Going underground would work, but my house and garage are separated by a paved driveway which I would have to cut to run the wires. I'm pretty environmentally friendly (I heat with wood, and it's a lot of work) so this would also be in line with how I live. It also sounds like a fun project. In the end it may be more work and cost more, but if it ends up costing a small fortune then I'll just live with having to manually lift the garage door, in the dark. I usually manage to get in the garage and back out before the grues get me anyways. :-p
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Jun 18, 2013 13:11
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JiimyPopAli posted:That's worth looking into, thanks for the idea. You can tunnel under a driveway with a piece of stiff pipe and a hammer, given some water and patience, assuming there aren't large rocks.
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Jun 18, 2013 23:26
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babyeatingpsychopath posted:You can tunnel under a driveway with a piece of stiff pipe and a hammer, given some water and patience, assuming there aren't large rocks. I had read about that, and it sounds interesting (even if it's just to say that I did it) but I also have some concerns about how long the wire would run from the house to the garage (about 200 feet, give or take). In the future I would like to get a dog and thought about one of those "invisible fence" setups, and this would be a very good idea for it.
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Jun 19, 2013 01:37
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Long story short, a relative died and left me 5 acres in a part of northern Texas with nothing but power going to a shack in an area that gets an average of 9-10 mph winds. First, What would keep me from putting 10-20 1.5 KW wind generators (effectively getting 1-1.2 KW in return) on 40 ft. towers and running them into a power inverter? Second, what sort of a return would that be? Third, would said return come in the form of power credit or in the form of bank deposit? I'm pretty sure I'm gonna sell it since Google maps shows it's a wasteland where the nearest town for supplies is 30 miles away, but if I can make it work for me, even better.
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Jul 3, 2013 01:21
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I'd guess that without some serious subsidies, your wind farm would have a lousy return on investment. First, the power: a 1-1.5k turbine in 9-10 mph winds, will actually generate something on the order of 100-200 watts. Turbines only hit their peak rating in maximum wind speeds, usually around 30 mph for something that size. Even at 24 hours a day, that'd be 2-5 kwh per day, per turbine. With 12 hours of wind a day, it'd be half as much power. Second, spacing: 5 acres is not that big. Each turbine should be 30 feet higher than anything within 300 feet. So, turbines must be spaced 300' apart for smooth wind flows. Third, cost: a single turbine and tower will probably cost about $5-6k each. The infrastructure to tie 10-20 turbines together and deliver it to the grid(I'm assuming grid-tie, not battery based) would be a small-scale construction project of its own. Lots of cost, probably at least equal to the cost of the turbines/towers would be my best uneducated guess. Maybe a $100-200k project at an optimistic guess is what you are describing, for a relatively small amount of power. There'd have to be some smoking good incentives to make it worth it. Wind speeds of 20+ mph, 16 hours a day, 300 days a year might make it worth it. Also, that money could buy a whole lot of solar that would generate a lot more power, and have a lot less maintenance.
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Jul 6, 2013 01:44
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Internetjack posted:Also, that money could buy a whole lot of solar that would generate a lot more power, and have a lot less maintenance. I think maintenance is gonna be a killer here. It sounds like keykey is thinking you can just install these, never come back, and count on a constant drip-feed income, which I really don't think is the case. Maintenance is gonna happen, and it's going to be annoying as hell if it's in podunk-nowhere Texas.
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Jul 6, 2013 02:42
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Maintenance is the key to this whole thing, because I live in CA. I'd be doing all the install/maintenance myself unless it was a really cheap fix. Even then, The cost of maintenance would have to factor in getting there/taking care of the turbines. As far as the grid-tie all that jazz, I'd be doing that myself as well. I've never installed either wind/solar but I've done quite extensive electrical work with bringing rentals/my own house to code so I'd be able to manage. I was looking at a 1.5 kw generator, the website showed around 1050-1200 watts in a 9 mph wind. I'd also be getting an internet connectable inverter with charge controller so I could monitor via dsl since that's an option there and I could set it for auto alert through smartphone should anything go wrong.
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Jul 8, 2013 07:47
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keykey posted:Maintenance is the key to this whole thing, because I live in CA. I'd be doing all the install/maintenance myself unless it was a really cheap fix. Even then, The cost of maintenance would have to factor in getting there/taking care of the turbines. As far as the grid-tie all that jazz, I'd be doing that myself as well. I've never installed either wind/solar but I've done quite extensive electrical work with bringing rentals/my own house to code so I'd be able to manage. I was looking at a 1.5 kw generator, the website showed around 1050-1200 watts in a 9 mph wind. I'd also be getting an internet connectable inverter with charge controller so I could monitor via dsl since that's an option there and I could set it for auto alert through smartphone should anything go wrong. Price out an open-return no reservation ticket plus rental car to get out there. Watch travel costs alone eat all your profit every time something breaks unexpectedly. Also, wouldn't a single larger windmill work better generally? At the very least, it will have fewer things to break.
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Jul 8, 2013 14:37
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keykey posted:I was looking at a 1.5 kw generator, the website showed around 1050-1200 watts in a 9 mph wind. Got a link? That much power at that low of a wind speed would require a turbine with a blade sweep on the order of 30-50+ feet, roughly. That's approaching industrial. I'm only familiar with residential units, with blade sweeps in the range of 8-12'.
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Jul 8, 2013 14:43
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Internetjack posted:Got a link? That much power at that low of a wind speed would require a turbine with a blade sweep on the order of 30-50+ feet, roughly. That's approaching industrial. I'm only familiar with residential units, with blade sweeps in the range of 8-12'. Actually, you're right. I was looking at the wrong number. The number I saw was M/S, I must have transposed MPH in my head. Yeah, the MPH of it for 9 is only like 200-300 watts. Looks like this wasteland is getting sold.
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Jul 8, 2013 16:02
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I'm about to sign up for a Solar Power Purchase Agreement from a SunRun reseller. I got a few bids from the 4 major companies and they seemed to be the best value. Before I sign up I wanted to run the numbers by you guys and see if there's anything I should be looking out for. I chose a PPA because it seems to be best deal going on right now that fits my needs. I would like to own the system outright but all financing options I've seen seem to end up paying about $5-10k more at the end of the 20 year term so from a near and mid term savings advantage this seems to make since. At the end of the term they can remove the system, I can buy the system at "fair market value", I can extend the lease for a couple more years or sign a new lease with new equipment. If I move the new buyer will assume the lease or I was just buyout the system and after it with the home price. I plan on staying in the home for 10+ years. Here's the system. pre:Site Assumptions Utility: SCE Current monthly SCE bill: $317 Annual electricity usage: 15,972 kWh Your System Sunrun Solar Service always includes 20 years of repairs, maintenance, insurance, and monitoring and a money-back performance guarantee Value of Sunrun Services: $6,215 5.00 kW (DC) Yingli Energy (China) system Equipment value: $21,120 Year 1 estimated production: 7,814 kWh Electricity usage offset: 49% Electricity bill offset: 58% Here's my SCE bill last month, totaled around $522  So as an example, with a solar PPA my tier 4 usage would be ~440kWh so I would end up saving around $77 over that particular month. Winter months would be little to no utility bill. Looking at past usage patterns I'm seeing about 8 months of the year I wouldn't go past tier 2 which is my main goal. I've already cut down energy usage where I can (switched to LEDs, replaced leaky windows, installed a whole house fan and window tinting) but with a wife and kids at home some things are just as they are. Here's the cost and terms. pre:PLAN DETAILS ESCALATOR NO ESCALATOR Upfront Payment $0 $0 Sunrun Rate $0.155 $0.195 SCE Rate $0.285 $0.285 Sunrun Annual Increase 3.5% 0.0% Sunrun Monthly Payment $101 $127 New SCE Monthly Bill $132 $132 Combined Monthly Bill $233 $259 20-Year Utility Savings $33,688 $37,463 The 0-down no escalator is a new program they started this month. Last month you had to make a down payment and a few other companies had a similar program. Pay $1,000 down and lock in no escalator. Another good deal with SunRun is that any overproduction of the solar system is free to me. The monthly rate is based on the promised 7814kWh production so if I produce 8014kWh the extra 200wWh I don't pay for. Underproduction is repayed as a credit at the solar rate agreed to. So that's where I'm at. It looks like I can save from day 1 of the install in either case. Anything other questions I should be asking? I'm in a great production area and with my usage patterns I don't see any major reasons not to go this route. FCKGW fucked around with this message at 19:52 on Aug 7, 2013 |
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Aug 7, 2013 19:48
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The power calculation numbers seem to make sense. You're averaging about 44kwh per day. It seems they are offering a 5kw array, which would hit 20kwh of production on a good sunny day; more or less depending on weather and location. So, the 50% coverage seems right. You mentioned a roof mount. Is it a new roof with a warranty? If so, check the warranty, because a roof mount solar install made void it. A lot of the financials, I simply don't follow or don't know. The value of $21k seems reasonable, but slightly high. The panels, mount, and inverters for a 5kw grid-tie could be purchased for around $15k delivered, but not installed. Does the estimated value include the installation cost? The $6k for their services, I assume some sort of remote monitoring, seems normal for a 20 year run. Does the pricing also include any fees from the utility company? Any extra metering that they may require to be installed? What type of warranty does Yingli have these days? I haven't seen that brand in a year or so. Honestly though, with de-rating of performance, and the aging of the equipment, I think it will be worth $5k at best in 20 years. Also, am I reading this correctly, "Another good deal with SunRun is that any overproduction of the solar system is free to me."? What? I would loving hope so. Do some of the lease programs actually penalize you if the system over-produces???? That's bonkers if so. Lastly, what type of inverter equipment are the using? Brand? Micros or strings?
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Aug 10, 2013 19:36
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Thanks for the response.Internetjack posted:The power calculation numbers seem to make sense. You're averaging about 44kwh per day. It seems they are offering a 5kw array, which would hit 20kwh of production on a good sunny day; more or less depending on weather and location. So, the 50% coverage seems right. This is a standard install size quote I got from all the companies. My roof can probably handle somewhere between 30-40 panels but it all depends how they work around some features and piping on the roof, so the actually system size would probably be a bit larger. I'd like to be in the 80% coverage range I think. quote:You mentioned a roof mount. Is it a new roof with a warranty? If so, check the warranty, because a roof mount solar install made void it. House was built in '05, we bought in '11. Flat concrete tile roof, no warranty but we're not expecting to replace the roof anytime soon. They provide a 10 year warranty on roof leaks. quote:A lot of the financials, I simply don't follow or don't know. The value of $21k seems reasonable, but slightly high. The panels, mount, and inverters for a 5kw grid-tie could be purchased for around $15k delivered, but not installed. Does the estimated value include the installation cost? The $6k for their services, I assume some sort of remote monitoring, seems normal for a 20 year run. Does the pricing also include any fees from the utility company? Any extra metering that they may require to be installed? Price includes all equipment, install and monitoring. Includes all wiring and painting of conduit, additional solar meter and any inverter replacement that may occur at the 10-year average mark. It's their equipment so they are responsible. Edison costs are just what I end up using from them at the end of the year beyond what I used from solar and any credit months. An ideal system would probably have around a $200 bill to my utility at the end of the year. quote:What type of warranty does Yingli have these days? I haven't seen that brand in a year or so. Honestly though, with de-rating of performance, and the aging of the equipment, I think it will be worth $5k at best in 20 years. Yingli is still one of the larger solar panel makers. The panels are warrantied for the 20 year term and have a .5% degradation estimate. quote:Also, am I reading this correctly, "Another good deal with SunRun is that any overproduction of the solar system is free to me."? What? I would loving hope so. Do some of the lease programs actually penalize you if the system over-produces???? That's bonkers if so. Solarcity and I think Verango had a "reconciliation" at the end of the year if your panels overproduced. If your system was rated for 8000kWh and it made 8100kWh (which you used), you would have to pay for the additional power you produced and used. This one has nothing like that, just a minimum production value. quote:Lastly, what type of inverter equipment are the using? Brand? Micros or strings?
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Aug 12, 2013 05:38
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How many people pair a PV setup for electric with a geothermal system for heating and cooling to get away from the electric and gas companies altogether? If I could "invest" $30-$50k and never pay a utility bill again, I might be interested.
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Aug 13, 2013 00:52
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adorai posted:How many people pair a PV setup for electric with a geothermal system for heating and cooling to get away from the electric and gas companies altogether? If I could "invest" $30-$50k and never pay a utility bill again, I might be interested. Geothermal heatpumps generally aren't cost effective compared to high efficiency standard HVAC systems and can be a giant pain, since they require a chunk of land and a lot of construction. Also, from the wording of your post not sure if you know this or not, but geothermal heatpumps still use a fair bit of electricity, it's just a lot lower than what a regular HVAC system would use, and a bit lower than a really good standard HVAC system. That said, there are people who do it, but their motives aren't generally just money (i.e. greenies and/or technophiles).
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Aug 13, 2013 03:35
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