Building my first Grid-Tie PV system (w/out batteries)

jfavalorajfavalora Registered Users Posts: 12 ✭✭
Hey guys, I'm planning out my first grid-tie solar panel system and was looking for a bit of help from the experienced.

I'm planning a grid-tie system with NO batteries. The panels will give me what I need and feed any excess to my power company.

The inverter I plan on using is the Fronius IG Plus 10kw which has an input range up to 500v with a max of 600v, and a MAX input of 46.7a. The recommended input is 8500w - 11500w.

I can wire a house any day of the week but when it comes to DC circuits and connecting them together, I get a little nervous. I understand the concept of series and parallel wiring and how each one will up the voltage or amperage depending on how they are wired.

My proposed panel layout is attached (in a sadly sketched MS Paint drawing).


My question is this:
How do I go about connecting the 3 strings shown in parallel to obtain my desired amperage? I have the voltage the way I want it by wiring the 7 panels in each string in series...I just need to wire the 3 strings in parallel to up my amperage.

Can I use regular old junction boxes to connect the 7 panels in series, the 3 strings in parallel and just wire them together or is there more advanced equipment to be used?

Also, I have been reading about Diodes and I haven't quite grasped the concept of using them....? Please enlighten me.

Thanks.
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Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Welcome to the forum.

    What you're looking for is called an array combiner:
    http://www.solar-electric.com/sopawiinco.html

    It gives you a nice place to tie the panel strings together, and provide over-current protection as well. Using breakers gives you a handy disconnect.

    But remember: you need to check your local code/building inspector in regards to what is necessary to be compliant. There can be issues about placement, et cetera. All grid-tie installs have to be done with the co-operation of the utility and the local government to be sure everything is wired properly and safely.
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)
    It gives you a nice place to tie the panel strings together, and provide over-current protection as well. Using breakers gives you a handy disconnect.

    Thanks for the info.

    I want to make sure I understand correctly...I would need 4 of these boxes; One for each string to connect the panels in series and then an additional box to wire the three previous boxes in parallel...?

    Forgive me for being a n00b with this, I just don't want my panels to go up in flames (I've seen pictures).
    But remember: you need to check your local code/building inspector in regards to what is necessary to be compliant. There can be issues about placement, et cetera. All grid-tie installs have to be done with the co-operation of the utility and the local government to be sure everything is wired properly and safely.

    Already covered with the parish inspector and utility co. :D

    Thanks again.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Well I don't know exactly what panels you have/will get, but generally you just plug the MC4 connectors together to create the series strings. Then the strings are tied together in the combiner box.

    It looks like Fronius has its own combiner box available, although I can't find a link to it.
    Also, the Fronius IG seems to have built-in DC & AC disconnects?
    Your input strings will exceed the 150 VDC limit of breakers, but no worries if the above is correct.

    Speaking of which, what panels are you going to be using? As the Fronius wants 150 VDC minimum input, up to 450. Keep in mind this is for Vmp, not Voc. I can't think of any panel that seven in series would give you more than 245 Volts.

    You might want to run the PVWatts program http://rredc.nrel.gov/solar/calculators/PVWATTS/version2/ to get some idea of how much power you can expect in your area, and possibly the Fronius configuration tool http://www.fronius.com/froniusdownload/tool.html to check your panel configuration.
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Well after discussing it with the inspector and utility co, I decided to build my own panels so I can get the voltage and amperage I want as the price per watts is more than I'm interested in paying.

    I was going to use 114 cells per panel, panels would probably be 4'x8' or somewhere close. Each cell has a peak of 0.614 volts and 7.7 amps.

    114 x 0.614= 69.996 volts per panel (cells wired in series).

    7 x 69.996= 489.972 volts per string (strings wired in series).

    3 x 7.7= 23.1 amps (3 strings wired in parallel).


    So I have a total output from the panels to the inverter of 489.972 volts and 23.1 amps.

    489.972 x 23.1= 11318.3532 watts...which is in the upper range of the recommended PV input.

    Still pretty far from the 600v maximum and from the 46.7a maximum.

    That's my idea anyways...will it work? I have no clue, that's why I'm here for support.

    I've heard that I wouldn't be allowed to build my own panels, but the inspector and utility co didn't seem to have a problem with it as long as I stay within their 20kw output range from the inverter.

    What's your thoughts or suggestions? Thanks.
  • solarvicsolarvic Solar Expert Posts: 1,053 ✭✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    We need to know the specs on your solar panels. I suspect you have too big of an inverter and not the right number of solar panels. I have a 3.1 fronius plus and have 158 watt 23.5 volt solar panels connected and it still could use a couple more. And I still am not that close to wattage capacity of inverter. Solarvic
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)
    solarvic wrote: »
    We need to know the specs on your solar panels.

    Just under 70 volts per panel, 539 watts.
    21 panels, 7 panels in series for each string, 3 strings in parallel.

    Further described the internals in my previous post. Thanks.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Well that's a first. Never before have I heard of an inspector/utility/insurance company that would allow homemade panels on a GT system. With good reason; you simply can not make as good a quality a panel as you can buy. No matter how good a job you do building them (and it is not easy) they will fail; it's a matter of when, not if. Nor is it necessarily cheaper than buying panels. I don't think you'll find any fans of homemade panels here. I certainly would not recommend you go this route.

    I have another question about your inverter: what is the exact model? The only 10kW Fronius I see is a 3-phase unit. It is highly unlikely your home has 3-phase service.
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Well, I'm assuming the main reason that they don't care is because our region doesn't really have that many solar setups.. either they just want to promote it or they are uneducated on why other companies won't allow it. Who knows?

    It's hard for me to justify spending $300 on a 200watt panel when I can build one twice the wattage for half the price.

    I can understand and appreciate the reasons why many people are not fans of home-made panels. A lot of people do not understand that these panels have to be engineered from different aspects as there are many factors that can cause it to fail.

    I don't claim to be an expert but when it comes to quality and efficiency I triple check everything.

    I intend to take every step necessary in engineering the panels for proper ventilation and efficiency, preventing moisture and oxidation/corrosion...while I'm looking to save money, I won't be cheap on the enclosure of the panels.
    I'll more than likely try to replicate an actual manufactured panel.

    Aside from that, the model of the inverter is the IG Plus 10.0-1 Uni.
    What page are you viewing the specifications from? I didn't notice where it showed the phase. Thanks again for your help.

    :cool:
  • icarusicarus Solar Expert Posts: 5,391 ✭✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Just my opinion, but I have never heard of a homemade solar panel that has any kind of real world longevity. It seems that with PV prices as low as they have ever been I don't see the long term justification to build ones own. New Pv at ~$2/watt when bought in quantity, with real world warrantees of 20+ years, UL/CSA listings etc makes it just seem rather penny wise and pound foolish.
    If I were going to embark on such a challenge, I would consider building a small beta system and see how it performs in the real world for a year or two before embarking on such an ambitious DIY project. The biggest issue that I can see is long term sealing of the panels given that they have to live in a harsh environment 24/7 365.

    Like I say,, just my opinion.

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Poring over their rather poorly written tech data :roll: ...
    Evidently the "Uni" designation indicates single phase. The same page lists other models with "Wye" and "Delta" designations - a sure sign of 3-phase output.

    You'll find several threads on this forum regarding homemade panels. They include discussions of how hard it is to solder the cells without a temp-controlled iron, the lack of low-iron glass for panels, the near impossibility of sealing the things against weather, and the costs versus purchased panels when all is said and done. Oh, and there's this one about a big fire ... Like I said; not a route I'd take. :roll:

    Look at the cost per Watt. Some commercial panels are under $3/Watt now. Check out the selection from the forum host: http://www.solar-electric.com/hiposopa.html

    Occasionally you can find even better deals if you're looking to buy case lots. Obviously you'd be looking for around 12 kW of panels. That's no small system. Why chance it?
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    I understand. If you can point me to a place where I can buy an equivalent panel to the ones I'd like to build for a close range in price, I'd be all over it.

    I'm not going to fight with building a good panel if I can buy one for roughly the same price.

    I calculated the entire system at costing me about $15,000...give or take. The inverter is a little less than $6000 of that and a the panels make up the majority of the $9,000.

    It pays for itself in 3 - 5 years after credits/rebates.

    Definitely let me know if your familiar with a company where I can find such panels in my price range.

    The wife is calling me to bed, I look forward to further discussing this tomorrow.
    Thanks again for all of your information and assistance. Have a great night and I'll talk to you later. :D

    -Josh
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)
    jfavalora wrote: »
    Well after discussing it with the inspector and utility co, I decided to build my own panels so I can get the voltage and amperage I want as the price per watts is more than I'm interested in paying.

    Really? That's surprising. Pretty sure that home made panels violate the National Electrical Code, the code requires all parts that carry electricity be either UL or CSA listed.

    I'd also be surprised if you could build a panel cheaper than you can buy one.
    You can buy quality panels for as little as $1.69 per watt or even less sometimes.

    Remember that commercial panels come with 20-25 year warranties and will last much longer than that, home made panels come with no warranty and it's doubtful that they will last 10 years.

    PV cells are hydroscopic, they will suck the water vapor right out of thin air. This degrades the cells and if they are subjected to freezing weather the moisture in the cells will freeze and crack the cells.
    It takes a fair amount of engineering to build panels that are air tight. You have to take into account the different coefficients of expansion between the aluminum, glass and whatever you use for backing.
    P.s. don't use wood. Water vapor will go right through wood.
  • johnljohnl Solar Expert Posts: 30
    Re: Building my first Grid-Tie PV system (w/out batteries)

    While I appreciate your DIY enthusiasm, here's a few thoughts that you may find helpful:

    1) Even if your local electrical inspector, building inspector, and utility company all sign-off on your use of non-UL approved panels for a grid-tied system, keep in mind your house insurance. If this is going to be roof-mounted on your house, your insurance company may consider your homeowners insurance to be voided if you install non-UL approved panels on your roof. (Ground mount might escape this issue...check with your insurance co).

    2) As others suggest, a quick google today shows me that there are UL-approved poly-si panels available at prices well under $2.00 per watt when purchased by the pallet in the quantities you need.

    3) If that's not inexpensive enough, but you want a panel that will last longer than home-brew and still be UL approved, consider thin-film UL-approved panels like the DuPont Apollo DA100-A2 or the Kaneka G-SA060. These are available from time to time in the $0.98 to $1.50 per watt price range. There is some doubt about whether thin-film panels will have as long a lifespan as crystalline silicon panels, and the conventional wisdom on this forum seems to be that the more expensive crystalline panels are still a better overall value when you consider the amount of power produced over the life of the panel. But even a thin-film panel like these will likely last many times longer than the best homemade panel. This may be a reasonable choice if your financial focus is on keeping the up-front install cost to a minimum, instead of looking at ROI over the life of the system.

    The other drawback to thin-film panels besides expected lifespan is square footage. Thin film panels generally require more area and more panels for the same amount of watts, which typically means that the slightly higher costs for racking and installation eat in to some of of the savings from lower per-watt panel costs.
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    I don't guess they make solar cell enclosures...? Hah.

    10kw - 16000 just for the panels at 1.69 /watt.
    I know that sounds cheap but damn...not to mention how many I would need at 60w per panel.

    But I guess if I'm getting 80% back on them it isn't so bad.
    50 state and 30 fed..

    So I guess I can give myself a 30k dollar budget.

    While paying twice the cost for panels, I suppose they would last twice as long, and in the long run I would pay the same amount.

    With that being said, I'm now considering the following panels:

    http://www.dmsolar.com/somo28perwa.html

    With 36 of those, is wiring them in series the same as mentioned before? Do they just connect to each other or will I need a junction box for each string?

    Other Suggestions?
    Thanks 8)

    Just out of curiosity, what if I were to use wax coated cells to protect from the weather?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    be careful as it always sends me a red flag when a company does not list a postal address.
  • BB.BB. Super Moderators, Administrators Posts: 29,812 admin
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Make sure that you will really be getting that 80% rebates/tax credits from the state and feds... And that if you are using tax credits, that you will have the income to use up the credits in time (jobs are not very stable out there right now).

    State and Federal budgets are pretty much in bankruptcy range right now--And I would hate to see you spend your hard earned money (or worse yet, some sort of loans) and see the rebates be pulled out from under you (as in Canada, Spain, and other countries now).

    Solar Power for a home is not really an investment (the value of your home will not increase much with solar GT, if at all)--it is more of a bet that:
    1. You will be living in your home for the next 5-15+ years
    2. the "state" will follow through on their promises
    3. power costs will increase dramatically
    4. the state PUC (public utility commission) does not change the rules about Net Metered systems a couple years down the road
    Sorry to sound like a broken record--You have addressed all possible conservation measures / improvements / upgrades possible before installign solar GT? Conservation is almost always a better investment vs solar PV power.

    Don't put yourself and your family in a position where other's non-performance of promises lands you in a financial hole.

    -Bill "Chicken Little" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    I hear ya on the Feds screwing people. Nah, I have the money from refinancing my home. I got a good rate and I'm pretty comfortable with my finances. I was just wanting to use half of the money to pay my wifes student loans off, but that can wait until next year.

    My goal here is to cut my electric bill down to a minimum and sell some power back to them. They allow 20kw.. Already confirmed with them... Even if I wasn't making anything off of them, it sure beats the he'll out of what I'm paying now.

    Push comes to shove, I'll switch to batteries or a natural gas gen and go off the grid.
    But yeah it would be a thorn if I didn't get the credits but it isn't something that's going to bury me. Excellent points though.

    I've already gone mostly to energy efficient appliances and lighting.

    Thanks.
  • icarusicarus Solar Expert Posts: 5,391 ✭✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Once again, not to sound like a stuck record:
    While paying twice the cost for panels, I suppose they would last twice as long, and in the long run I would pay the same amount.

    I would be hard pressed to believe that ANY DIY panel would last 1/2 as long as a good quality factory built panel.

    My suggestion is that you do some thorough research on both DYI PV as well as grid tie installations. There is a reason that UL/CSA/UBC/NEC rules exist. There have been several threads on these board about DIY panel failures including fires, as well as some pretty shoddy installs.


    It just seems that if you are willing to invest ~ $30k in a system, and you are willing to to take advantage of rebates equalling ~ 50% you really have to consider all your alternative. As in so many things, the initial price of something is not always a good indicator of total life time cost. A cheap tool may be fine for a one off application, but daily use is another matter. I know of no professional mechanic with a tool box full of Harbor Freight tools.
  • BB.BB. Super Moderators, Administrators Posts: 29,812 admin
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Personally, I would suggest paying off all student loans first. They are among the few debts that can't be discharged through bankruptcy... If things go upside down, student loans are as close to leglegalized slavery as one can get in the US.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Peter_VPeter_V Solar Expert Posts: 226 ✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)
    jfavalora wrote: »
    I don't guess they make solar cell enclosures...? Hah.

    10kw - 16000 just for the panels at 1.69 /watt.
    I know that sounds cheap but damn...not to mention how many I would need at 60w per panel.

    Maybe I missed it, but just out of curiosity...why do you think you'll need 10kw worth of panels?

    Where do you live and how much energy do you use in a day, on average?


    Seems to me that to need a 10kw array you'd have to use something like 40-50kwh per day, that's almost twice the national average.

    If that is actually how much you use, then you will be MUCH better off starting with reducing your use and THEN getting solar.

    With just some minor efforts at conservation we brought our average daily use down to about 19kwh. CFLs, high efficiency appliances, turning the computers off when not using them, etc.

    Just because you can sell power to the electric company doesn't mean that it makes sense to size your array way to large and sell your excess.
    I don't know about your power company, but mine only buys excess power at their "avoided cost" which runs less than 4 cents per kwh.
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    I use 35-45kw on average.
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)
    BB. wrote: »
    Personally, I would suggest paying off all student loans first. ...
    -Bill

    +++

    student-loans-3.jpg
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    I could do that first but then I'm without money for solar after the fact.
    50/50'chance they don't give me the credit.

    If I do the solar, get the credit, I still have plenty left to pay the loans.

    Am I wrong? Thanks :D
  • BB.BB. Super Moderators, Administrators Posts: 29,812 admin
    Re: Building my first Grid-Tie PV system (w/out batteries)

    We do not know your financial situation--At least for me, it is a personal opinion to pay off/avoid debt whenever possible. Not having ongoing loan payments can make life a bit nicer.

    More of an issue of not wanting folks to see solar PV systems as an "investment" that has a better return than paying off existing debt and other conservation measures.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,391 ✭✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    I might humbly suggest, that if you are using 35-45 kwh/day average, there are probably a significant number of things you can do, way more inexpensively to reduce loads, which in turn would yield much better energy efficiency. Solar hot water comes at ~1/4 the cost of PV for heating water as one example. If you have large A/C loads, consider upgrading your system to a ground source and or a hot water recapturing system, once again yielding much more bang for your buck. Not to mention all the simple things, like phantom loads, poor lighting choices, HVAC set too hot or too cold, using nat. gas or L/P for cooking, adding building envelope insulation. All these come cheaper net/net than PV.

    The first three rules of solar energy are, conservation, followed by more conservation, and then followed up by still more conservation. A BTU/KWH not needed is far and away cheaper than any BTU/KWH you have to produce.

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)
    jfavalora wrote: »
    I use 35-45kw on average.

    Uh, that's about 20X my cabin use. You sure there isn't room for improvement there?
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    That all makes a lot of sense. I was really just looking to profit from the utility co a bit at the same time, but I suppose conserving energy will allow me to use a smaller system in the future (after student loans are paid).

    Where might I find some of these fantastic energy efficient devices?
    ...and how does a solar hot water heater work. I bath at night... Does it use batteries or am I missing something there? I was considering a nat gas water heater or something similar.

    I have a 5000 btu AC unit w/ a heat pump... Any better alternatives or modifications to that? All of my lighting uses 15w fluorescent.

    If I had to guess I would bet that most of the electricity goes to the water heater and hot tub... We keep the AC/heat on a set temp between 65 and 70. All 3 appliances are 220v

    Thanks
  • icarusicarus Solar Expert Posts: 5,391 ✭✭✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Here is a Primer for solar hot water.

    http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12850

    Solar hot water is a much easier/cheaper DIY project than PV.

    For example, I have built small home made flat plate collectors, covered with discarded patio door glass (available nearly free) with ~100' of copper pipe, a simple controller and and discarded electric hot water heater, for a total cost of ~ $500. The last one I built, in the decidedly non sunny Pac. NW provided ~ 50 gallons of 135F water per day for about 9 months of the year. Use this in front of a demand gas water heater and you can reduce your water heating load to nearly zero KWHs, and very few BTUs of gas, and yet always have as much hot water as you need.

    http://www.takagi.com/index.php?product_id=3&page_id=2
    http://www.rinnai.us/tankless-water-heater/
    http://www.boschhotwater.com/
    http://www.palomatankless.com/

    There are a number of hot tub solutions, but the best and cheapest is to simply insulate the tub better. Going from an R-4 cover to an R-10 cover will save ~ 1/2 the energy. Hot tubs don't take a lot of energy to stay warm, as long as they are not losing their heat to the air.

    Do some homework before you embark on too much investment. As has been said, even with good rebates, and good FITs PV solar is at best a long term, break even investment. Every dollar you save on load, saves ~$10 on PV costs.

    T
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)

    Electric hot water is misery! 3500 - 4500 Watts. One full hour to heat a batch. May turn on 4 or 5 times a day even if no water is used. So there's a lot of kilowatts going to nothing!

    You could get a tankless gas fired heater. These are good if water usage is low. If you use a lot of hot water, the gas fired tank-type would be more efficient (and cheaper).

    Solar hot water usually works directly on the water. It's then stored in a tank until needed. The sun doesn't have to be shining at the moment the water is used. They can also be used to supplement/supplant other water heater types.

    A good site for DIY solar projects is Build-it Solar: http://www.builditsolar.com/

    It'll put ideas in your head. :D
  • jfavalorajfavalora Registered Users Posts: 12 ✭✭
    Re: Building my first Grid-Tie PV system (w/out batteries)
    Electric hot water is misery! 3500 - 4500 Watts. One full hour to heat a batch. May turn on 4 or 5 times a day even if no water is used. So there's a lot of kilowatts going to nothing!

    After reading that I went and pulled the circuit breaker....Won't need it for a couple of hours... by the way, it WAS heating.

    I'll check into some of the products you guys have recommended... I really appreciate all of the guidance.

    I'm going to attempt to lower my usage and see what kind of difference it makes.
    If not enough, I'll be back for some more info.

    By the way, I asked the same initial question on another 'popular' forum and got a ton of flack from them...trying to continue the discussion they completely ignored my post. I appreciate the hospitality you guys give.

    ;) Thanks again.
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