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Solar Panel Questions...

Discussion in 'Energy, Environment, and Policy' started by EdA, Mar 24, 2011.

  1. EdA

    EdA Model S P-2540

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    Hello Tesla world,

    I'm a new member and a reservation holder for a Model S.

    I'm investigating solar panels for my house and have received 4 quotes (was going to go with 3 but then found out about Elon's involvement with Solar City...) for different systems.

    Only one of them has mentioned micro-converters, the other 3 are using "large" DC-to-AC converters next to my electrical box. Are micro-converters ready for prime-time? Are they more expensive/less efficient?

    I don't have all 4 quotes in front of my yet (the last guy just left my house a few hours ago) but already am having trouble comparing apples and oranges. With all the incentives in place (Federal and Mass.) this seems like the time to do it.

    I'd love to hear from other members who have gone solar recently.

    Thanks,
    /Ed
     
  2. TEG

    TEG TMC Moderator

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    They work. Overall costs is likely a bit more using them. But then you don't have a single point of failure so your whole system won't go down at once due to an inverter failure.
    Generally the panels are expected to last longer than the inverter(s).
    Also, one big inverter depends on all the panels working together, so partial shade can hurt. With the micro-inverters, the individual panels in direct sunlight are 'happy'.
     
  3. EdA

    EdA Model S P-2540

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    Thanks for the quick reply. What is the downside though, why did only 1 of 4 quotes offer them?
    Are they more expensive? Less efficient?

    /Ed
     
  4. Tommy

    Tommy Member

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    From the research I have done, Enphase is the major player in micro inverters. Their link: Home - Enphase Energy Besides the shade and single point of failure issues already pointed out, here are three more advantages I researched.

    1. The weakest panel's output does not drag down the entire system's output like a conventional inverter would. This is similar to the shade benefit; the difference being even in full sun, individual panels produce different output because of manufacturing tolerances; a micro inverter will sum the outputs of all the panels unlike a conventional inverter that must sum to the lowest panel's output on a given string.

    2. If you decide to expand your system, very simple to add panels.

    3. Because the micro inverters are attached to the panels, the wiring from the micro inverters is A/C rather than D/C. Much simpler code requirements and safer.

    If you got a bid from SunPower, they only grudgingly will use them and then only on their lower watt panels; I think most panel makers would rather you use their own branded inverters to get more profit and installers are not as familiar with micro inverters as they are somewhat new to the industry.

    The micro inverters are for all practical purposes just as efficient (96.5% I think) as conventional inverters.

    The downside is they don't have an established track record thou lab tests indicate they are very reliable.

    If a failure does occur, it means going up on the roof to replace, conventional inverters much easier to replace in this regard.

    Monitoring ALL the system's status can be a monthly expense, however a basic monitoring of the system is free.
     
  5. SByer

    SByer '08 #383

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    We went with the big inverters. Even if the micro inverters are less likely to fail, you have a lot more of them, so the likelihood of at least one of them failing goes way up. And, our roof is, uhm, not conducive to replacement (12/12 pitch, we had roofing companies drive up, call us from their cell, and say they wouldn't even bid when we were getting our roof done).

    The most likely part to fail in a big inverter is the fan. So, we went with the fan-less Xantrex inverters, and they got put where they are in the shade just about all day. With the big inverters, panels are ganged together by 8 to get the voltage, so if your roof and shading situation is such that you get little spikes of shade that hit one panel, you'll 'lose' that gang. A good installer can minimize that issue.

    I'm not sure where the micro-inverters go on the panel, but our installation is very low profile - barely off the roof, packed tight, with the black-on-black SunPower 225 panels, with the conduit going into the roof under the panels. It looks very slick - micro-inverters may affect how that could be done, but I don't know.

    So, I'm going to say it all depends on what the installation is going to look like, especially the shading profile.
     
  6. EdA

    EdA Model S P-2540

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    inverters


    Nice installation, and is that your Tesla on the driveway too?

    I have a basement which is about 50-60F and dust would be the biggest killer for the fan :)

    /Ed
     
  7. vfx

    vfx Well-Known Member

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    My research said Micro inverters were the way to go too. Another Tesla owner here has them on his house and he makes a good case for them.
     
  8. TEG

    TEG TMC Moderator

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    My system has been working flawlessly for over 5 years now.
    It has two strings of 10 going to a big "Sunnyboy" inverter.

    Having the inverter closer to ground level, more accessible will certainly make it easier to replace when the day comes.
    On the other hand, some people would probably prefer the "hidden inverter" aesthetic with the micro-inverters under the panels.

    Probably the biggest reason why more quotes show the big inverters is just that they are older, more established and more familiar.
    The micro-inverters are still relatively new. I wouldn't be surprised to see them become more commonplace in the future.
     

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  9. vfx

    vfx Well-Known Member

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    Indeed many of the panel makers are designing their own to include.
     
  10. roblab

    roblab Active Member

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    I would wonder if, since the inverter is the weak link, how does that affect lifetime? The panels on my roof are guaranteed for 30 years, will probably last much longer. The inverters will last, what, 10 years? My Trace Xantrex inverters died in two years! My batteries are guaranteed 18. So when the inverter dies, do you have to replace a perfectly good panel? Or pull off the micro inverter and replace it?
    Also, my strings are in gangs of 4, inverters don't care about shade, take whatever is handed them from one to over a hundred volts. I don't know much about how the panels work, but I do know that PGE here in CA has been racking up my excess power since January, with my true up in July.
     
  11. shark2k

    shark2k Member

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    #11 shark2k, Mar 25, 2011
    Last edited: Mar 25, 2011
    @roblab: Inverters might not "care" about shade, but because of the way the panels are wired (parallel vs series, I believe panels are wired in series, but somebody can correct me if I am wrong) shade does matter. Because of the way the panels are wired, if there is shade on one of the panels in the string it brings down the whole string. As to the micro inverters, you would just replace the inverter if it failed, same as you would replace the big inverter if that failed.

    @sbyer: The micro inverter gets mounted on the racking system directly under the panel. I believe it is pretty much flush with the bottom of the racking system, so you would more than likely have been able to get the same result. Micro inverters are used for the panels that are attached to light poles (at least around here) so I can actually get a good look. If I remember I'll take a picture on Monday with my cell phone and post it here. If you go here: GreenovationTV SLIDESHOW: America’s Oldest Net Zero House and go to the 7th picture in the slide show, under the video, you can see the micro inverter I believe. I'm pretty sure it is the silver piece attached to the mounting system. So you know, the guy has 36 panels, so 36 micro inverters. This is the monitoring site for his panels: GreenovationTV SLIDESHOW: America’s Oldest Net Zero House so you can see the output.

    General thoughts: If I knew about micro inverters when I convinced my parents to get solar panels two years ago, I would have asked the installer about them. I think they have definite advantages over conventional inverters. One nice thing is for areas where you get snow. Once one panel clears off you can start generating energy. We got hit with snow again on Tuesday/Wednesday and wednesday we didn't really generate much electricity (less than 1 kWh I believe). I tried clearing some of the snow off but it was that heavy wet snow that splash when you throw it, so that made it difficult to clear off. I did get some of the panels clear, but I don't believe I got any panel 100% clear. I think if we had micro inverters there is a chance the the panels I did manage to clear some snow off were have started producing better, helping melt the rest of the snow and generating more electricity.

    I also agree with Tommy that expanding the system at a later date with micro inverters is much easier than with conventional inverters. FYI, my parents have two SunPower inverters for our 4.725 kW system (21 panels) 3 strings with 7 panels per string and one inverter has two strings on it the other has 1 string.

    -Shark2k
     
  12. TEG

    TEG TMC Moderator

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    #12 TEG, Mar 25, 2011
    Last edited: Mar 25, 2011
    Series versus parallel terminology is stated as "strings". A particularly large inverter may support multiple "strings" of panels which are strung together in series. You effectively have multiple strings in parallel.
    The system design requires that you don't put too many panels in series in a string such that you run over the voltage rating of the inverter.
    Having strings helps a bit with the shade issue. One string can have panels in the shade, and the other strings can continue on normally if they have full sun. Micro-inverters isolate to individual panels instead of individual strings.

    Yes, I have read that inverters tend not to last as long as panels, and 10-15 years may be an estimate compared to 30 years for the panels. So it would be somewhat normal to consider at least one inverter change during the life of the panels.

    I had anecdotally heard some negative things about Xantrex, so perhaps they are less than average reliable? 2 years seems like premature failure.
     
  13. shark2k

    shark2k Member

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    TEG, not sure if that series vs parallel explanation was in response to my first paragraph, but I appreciate the information.

    -Shark2k
     
  14. DrComputer

    DrComputer Member

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    I guess I am the "other Tesla owner" that Eric is referring. My solar system does not use micro-inverters but intelligent modules on the back of each panel that are then controlled by a master unit that can bypass panels that are shaded. It does this in real-time and records everything to their website. The system is made by Tigo (www.tigoenergy.com) and, so far, has done what it says it will do. The problem with any system like this is that I have no comparison point. Since I installed my solar system from the beginning with the Tigo modules I can't say how much less efficient my system would be without them.
     
  15. SByer

    SByer '08 #383

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    Naw, that's actually the 911 that got replaced. Ironically, I believe those sat photos were taken during the few weeks of overlap when the old car got to stay outside ;-) !

    On Xantrex, they supposedly had issues a few years back but had worked to fix them. We went with them because at the time they were the only ones without fans. It's been over two years and they're doing well (knock on wood).
     
  16. richkae

    richkae VIN587

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    I recently put a 4kW system on my roof ( I would have done more but ran out of south facing roof ).
    One of the primary goals of the system was to turn the Tesla into a solar car.
    At the same time I got a TED 5000 and with the ability to carefully monitor my exact usage started trying to conserve.

    The result is that my Tesla is not powered by the sun. It is powerered by the off switch.
    My february 2010 bill showed 42 kWhr per day of usage, and it was down to about 30 kWhr per day in 2011 ( with significantly colder average temperature )
    The Roadster uses about 8 kWhr per day for my driving. ( included in that 30 kWhr )
    My conservation efforts have included some LED bulbs, some fixing of heating ductwork, insulation upgrades, some power bars and a lot of turning stuff off.
    If we use a room for more than a few minutes a day, it has CFLs or LEDs in it. If we aren't in it, everything gets turned off.

    Even without the solar panels, the power to drive my car is entirely "free", I'm buying it with the energy I've saved.
     
  17. felixtb

    felixtb RsEU502,Sp+14274,XpEUSig4

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    This statement is only true for you and your pocket book, since you are the one whom is saving. but sadly not true for the rest of us since you are still using power from the grid.......... not condemning you just not so impressed with the last statement as I was with the rest of your post. really good going saving more than 10kwH per day. i'm am building a new house and aiming for an energy positive house...... we'll see how it goes........
     
  18. Eberhard

    Eberhard #421 Model S #S32

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    an average household in germany consumes an around 3000kWh per year, that less then 10kWh per day. with my roadster i will triple this (30.000km * 0.17kWh/100km = 5100kWh). For that i would need a 6kW peak solar panels.
     
  19. EdA

    EdA Model S P-2540

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    micro-inverter is replacable

    Just the micro-inverter would need to be replaced, not the panel.

    /Ed
     
  20. richkae

    richkae VIN587

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    The statement about running the car on the energy I have saved is where I needed one of those sarcasm smileys.

    Since all energy is subsidised in the U.S. by income taxes ( in the form of massive tax breaks to energy companies ) most people here have little care about how much energy they waste.
    The energy monitor was a critical tool in my conservation, without the ability to measure it is hard to determine where to put the effort.

    If people could get the instant feedback that if they turned off a few things not being used - they would have 10 extra dollars in 5 days, they would be more incented.
    So far the conservation has yielded more power than the solar panels ( it has been a very cloudy couple of months, Seattle is a marginal location for solar in the winter ) and at a fraction of the cost.
    When I installed the solar system I was told that it would only produce a 1/3 of our power used over the year. I am going to try to get it to 2/3.

    We have dynamic signs that tell you the number of minutes a few destinations on the highway.
    I've wanted to mount a vision system that identifies cars, looks up their miles per gallon, computes the cost of the gas/other to go that distance, then shows them a dollar value next to the number of minutes.
    Jeep Grand Cherokee: 27 minutes $4.13
    Toyota Prius: 27 minutes $1.40
    Tesla Model S: 27 minutes $0.40
     

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