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120VDC Solar Panel

Discussion in 'Renewable Energy' started by ignisuti, Aug 17, 2009.

  1. ignisuti

    ignisuti New Member

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    Can I string enough solar cells in series to output 120VDC? Will voltage this high damage the cells?

    Just thinking that if I did this, then I might be able to build my own inexpensive inverter.
     
  2. Hero999

    Hero999 Banned

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    120V is still quite a low voltage so no it won't break over voltage the cells.

    Do the cells have a metal enclosure?

    Just make sure the negative isn't connected to it.

    Also beware that if the cells are rated to 12V each, the open circuit voltage in full sun will be much higher.

    I hope you know that you won't be able to power mains devices unless they're resistive or have a switched mode power supply.
     
  3. ignisuti

    ignisuti New Member

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    For the time being, we're using a wood frame.

    I'm not sure what you mean by the open circuit voltage in full sun being greater than 12V. What do I need to be careful of? I'm not sure of the cell rating. I just bought the bunch from eBay.

    I'm currently learning about the difficulties of connecting the mains line. I was really interested in purchasing a Grid Tie Inverter so that I could supplement my energy bill until I found out that it cost the same $/Watt as I just spent on the panel itself! So, I'm just tossing around ideas of building my own inverter and thought starting with 120VDC might make things simpler and cheaper...
    Why would I only be able to power something that has a resistive or switched mode power supply?

    Thanks for the advice!
     
  4. dave

    Dave New Member

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  5. Hero999

    Hero999 Banned

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    When the solar panel doesn't have a load connected to it, its output voltgae will be higher than the rated voltage.

    I would advise using the panels to charge batteries.

    Just configure them to give whatever voltage is suitable for the inverter.
     
  6. ignisuti

    ignisuti New Member

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    Okay. So you're saying, if I design it to provide 120VDC to the batteries (or inverter), then I should expect the voltage to be much higher (possibly high enough to damage the cells) if I disconnect a lead (possibly for maintanence). Is my understanding correct? If it's open circuited, then I wouldn't think there would be enough current to do any damage.

    That is my long term goal, but I wanted to get a small system started now that provided some immediate benefit. That would be with solar panels directly powering the Inverter. As I save more money, then I'd like to buy batteries and improve my system efficiency.
     
  7. blueroomelectronics

    blueroomelectronics Well-Known Member

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    You may want to check out a Grid Tie Inverter if you want it to tie into your home AC.
     
  8. ignisuti

    ignisuti New Member

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    Yes, I have. Please read my responses to this post. The cost is too high.

    I simply want to know if I can safely string enough solar cells together to output at 120VDC from the solar panel.
     
  9. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Sure but the voltage will vary wildly.

    Currenty Solar energy and cheaply don't go together. It's a long term savings but has a high initial cost.
     
  10. ignisuti

    ignisuti New Member

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    Great. That's exactly what I'm trying to figure out.
    So, IF I decided to go this route. I'd want to design it so the max voltage is say 140VDC. That way in cloudy conditions, I'd still have 120VDC.

    Now, this still leaves the question: Do I need to be concerned with Open circuit voltages damaging the cells?

    I've never been one to follow the already paved road. I like to explore un-cleared paths in hopes of maybe perhaps stumbling upon a way to lower costs... :)
     
  11. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I know what you mean! The 'End Of The Road' sign stops most people from ever traveling any further. Yet for me it just means I am getting to the fields I go to work in. :)

    You are going to run into some problems with trying to keep the voltage stable with just a solar array as the power source. Realistically you need to put that power into a battery bank to keep the voltage stable under varying loads. Or grid tie it and use it in the AC system.

    Depending on what you are powering you may run into a rather limited range of devices that will actually work on 120 VDC. As I understand solar panel voltage rating they are rated at the nominal voltage they produce their peak power at. They will go much higher without any load but will drop to zero when shorted.
    Isolating 120 volts is not a problem even 400 volts open circuit would be reasonable to insulate but rather dangerous to work around if your not knowledgeable about it.
    I would shoot for a 120 volt nominal output rating myself. Your peak power would be available at or near that. If your solar panels not have the nominal or peak voltages listed you will need to do some experimenting to find the numbers.
     
  12. ignisuti

    ignisuti New Member

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    Great. I'm just getting started and learning a lot today!

    This was just a exploratory question. If I build a solar system, I may just go with the Grid Tie Inverter. I found a pretty cool one (OutBack GVFX3648) that looks like it'll let me start with just some solar panels and get an immediate supplement to my power usage. It'll also allow me to grow my system later on and add batteries and a sub-panel of loads I want to run during power outages. The thing I havn't figured out yet is if it'll use the battery power at night or if it'll continue to charge the batteries from the grid instead.

    Anyone have experience with this inverter system?
     
  13. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Thought you wanted something cheap, that OutBack is over $2,000
     
  14. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I personally build my own Grid tie equipment.;)

    However thanks to our ever so diligent bureaucrats all non UL or government recognized certified Grid tie devices, solar panel, wind and micro hydro systems may be getting put in the illegal category. If you buy a factory made unit make sure that it is in fact UL or like certified or you will most likely not be allowed to have it legally hooked up and working much longer.:mad:

    Also I dont care for the outrageous price Vs what goes into the actual making of one of these systems anyway. You will not likely ever pay for a factory made system with avoided costs in it working life time.:mad:

    We have reached a point where cost of production is cheap enough to put alternative energy into much more private usage. However the politics, bureaucratic red tape and manufactures greed is holding it back more than anything now. :mad:

    Sorry to sound discouraging but as you learn and find out more about real AE you will see its more true than you will care for.

    But then you could go pirate AE too! Illegal as all hell but far cheaper, viable and very cost effective! ;):D:)
     
  15. ignisuti

    ignisuti New Member

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    When I first posted, I was looking at the 200W Grid Tie inverters for $200 each. Meaning you pay $1/Watt just for power inversion. While I was researching today, I came across the Outback. You can get them for $1800 on eBay. Its still not cheap by any means, but the cost ends up being half ($0.50/Watt) of the others ones I was looking at.

    I'm now considering buying one of these along with enough cells from eBay to generate 3000W of solar power which would cost approx. $3000. I could get a low interest loan and make monthly payments that may be near my monthly energy savings. So if my math is right, it'd take me approx. 6 years to repay the loan, but then I'd be saving approx. $800/year after that.

    MATH:
    3000W * 4.8 hours of avg. sun hours for my location = 14.4kW/Day on avg.
    14.4kW/Day * $0.15/kW * 365Days/year = $788/year
    $5000 / ($788/year) = 6.3 years

    My understanding is that the 4.8 sun hours is without a tracking system. Is that correct? If so, I could add a tracking system and/or batteries to significantly increase my savings.
     
  16. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Hmm, seems cheap. The always cheap & cheerful Chinese 3000W kit ($15,000) with all the bits is somewhat more. Also solar is only going to give you lots of power on those hot sunny days and only at noon. Moving large solar arrays may or may not be cost efficient.
    3000w Solar Home System Solar Home System CN;HEI products

    I would find a solar contractor in your area and get an idea of size and cost of a system large enough for what you need.

    Spending $$$$ based on forum advice is probably not the safe bet.
     
    Last edited: Aug 17, 2009
  17. ignisuti

    ignisuti New Member

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    Interesting...
    1.) Have you shared/posted your schematic and design notes anywhere online. I'm an EE and would be very interested in studying them. As long as your system is designed to shut-down when grid power is lost, then no one would ever know the difference! :)
    2.) Pirate AE? How would you do that, steal panels off road construction equipment? ;)
     
  18. ignisuti

    ignisuti New Member

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    If I actually have to pay someone to do this project for me, then it looses all it's sex appeal. :D

    I'd never stick my tongue to a 240VAC line (120VAC maybe... :p) just because you guys said so. But, you guys are the ones who have already done all the research and have experience with this technology. Who better to learn from?
     
  19. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    The write up on the basic no frills bare bones GTI concept is right here in the AE section. :)

    Its not my best technical writing work by any means. I purposely wrote it to make people think about how it works. I had to work to learn how to do it and I make anyone else who really wants to learn how it works work for it a bit too. My intentions were to point the way to wards where to start and what are the basic but critical points that need to be addressed in the actual design of a system.
    It does give you the basic concept of how it can be done simply and cheaply. Safety and efficiency are basically what you build into it. Its not the most technical design but and explains the basics of what needs to be addressed in the design and implementation and well... hey its free, so dont complain too much. ;)
    It was basically a way for me to get a feel for technical writing and to see if there was a potential market for a do it yourself type CD I plan to sell some day when I get time to work on it again this winter or whenever.

    Pirate AE is basically doing it without all the legal and bureaucratic red tape that limits the products out there and drive the prices to the ridiculous numbers that they are now.
    That is you build it with what you can get thats cheap and works. What you build could very well be of a higher quality and capacity than of what any recognized system on the market is but without the pieces of bureaucratic paper and certification behind it is what makes it pirate by definition.
    You generate your own power with what you built yourself and grid tie that power to your home without being legally recognized to do it.
    It could be also called outlaw AE too! You fend for yourself and your needs first regardless of what some legalistic bureaucratic law may say. :)
     
  20. blueroomelectronics

    blueroomelectronics Well-Known Member

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    I would also be wary of legal advise you find in the forums too.
     
  21. Hero999

    Hero999 Banned

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    I'd say 120VDC is quite tame compared to 120VAC, which is really 170V before you even get into the debate about the safety of AC vs DC.

    Lots of devices will work off 120VDC: all incandescent lighting, heating and devices that use universal motors will certainly work, as long as they don't have phase controlled dimmers/speed controls, and lots of appliances that contain switched mode power supplies will work. I'd say if you're powering off a set of batteries fully charged to 138V all switched mode power supplies should work.

    If you're going to have a separate DC power supply in the house then use different connectors and appropriately label all the wiring.
     

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