Another Solar Wiring Scenario

I'm planning on adding some solar this Summer. I have been doing some research and I am starting to think through the project. I do not want to have the solar panels directly on my roof for different reasons. As a result, I plan to mount the panels on a shed "nearby". I measured the actual wire run and it is 200 feet from the shed to where the controller will be next to my battery bank. The roof on the shed is sheetmetal and relatively flat (maybe 10 degree slope). Because of high winds that we have here, I plan to mount them "flush" with the roof. I understand that there will be some losses since they are not angled ideally, but I want to do it this way. I feel it will be best for if/when the wind blows 100mph again!

I was using the Evergreen ES-A-210-FA3 to do some calculations.

http://evergreensolar.com/en/wp-content/themes/EvergreenSolar/images/techspecs/techspecs-es-a-na.png

Using the link that Neil has in his signature to the voltgae drop calculator that Solar Guppy made, I was getting around 6% voltage drop using 6 gauge wire.

I was entering 400 feet because my understanding was that I needed to double the distance. I plan to use a TriStar 45A MPPT controller. I plan to have 2 strings of 5 panels in order to fit my roof (2100W total).

We might get 20 below 0 F in the winters, but usually it's around single digits during cold snaps.

Thanks for any insights you might have. I know it's a long run, but 4 gauge wire could get expensive.

Edward

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Another Solar Wiring Scenario

    Sounds like you have an understanding of the problems involved: if you put more panels in series to up the Vmp in order to overcome the line loss you run the risk of exceeding the controller's Voc in cold temps. I tried to calculate this and got a maximum of four panels in series, but I can't run the V-drop calc on my linux netbook so not sure of the accuracy. With 5 I get a potential of 158 Voc in the cold. Pretty close but ... :confused:

    Someone can do the math more accurately I'm sure. :blush:

    Or if you haven't bought the Tristar, spring for a Midnight Classic 150. They have better V max in ratings (150 + system Voltage I believe).
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario

    Thanks for the feedback Marc. I really would rather have a Classic 150. About a year ago, I bought some panels (6x 130W) and a Tristar 45A MPPT controller. I was going to do a ground mount near my house. I never installed them. My plans changed, and I decided to sell the 130W panels and go with more solar. I still have the Tristar. I could sell it and buy another Classic 150. I am very happy with my Classic 150 for my wind turbine. Right now, I was trying to see if I could make things work with the Tristar controller I already have.

    Edward
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario

    Here's a picture of the shed where I plan to mount the panels. The sloped roof is facing towards due West.

    Shed.jpg

    Edward
  • solarvicsolarvic Solar Expert Posts: 1,052 ✭✭✭✭
    Re: Another Solar Wiring Scenario

    Edward. Did you consider polemounts near your battery bank? You might save about enough on wireing cost to go towards the cost of the mounts and pipe. Also you can adjust them for better yeild. I have Polemounts in Pa. and had trees blow down in my woods nearby but the polemounts survived. Also had the tale end of a hurricane a couple years ago. Another good thing is I can get to them to clean the snow off.
    :Dsolarvic:D
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario

    Vic,

    I have thought about pole mounts. I was expecting the price to be too high.

    How much did your pole mounts cost?

    On top of the shed, I plan to mount one 5 panel string along the east end and one 5 panel string along the west end of the roof. That way, I can easily set up a ladder and sweep the panels off with a broom, because they will be right along the edge. We don't have a lot of snow here, but it does usually snow some. We are in a semi-desert climate and don't get as much snow as many other places.

    I definitely do not want to be walking on a sheetmetal roof with snow/ice! The way I plan to lay out the panels, I can store a ladder in the shed and just take it out when I need to clear snow. Then I can climb up the ladder and use a push broom to clear off the panels (while standing on the ladder). At least that's the plan.

    Edward
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Another Solar Wiring Scenario
    but I can't run the V-drop calc on my linux netbook

    Check and see if it has a command line program called "bc". Handy little proggie that's been included with most Linux distros for a long time.
  • mike95490mike95490 Solar Expert Posts: 8,369 ✭✭✭✭✭
    Re: Another Solar Wiring Scenario

    re: Snow, if you get less than 2" at a time, it will likely melt the bottom layer, and may just slip right off as a mass, with the broom, dosent look like you have enough tilt for it to "self clear", but if adding tilt would improve your sun angle, that may be the trick. With MPPT, all panels in the array need to be at the same angle.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario

    Thanks Mike. With as little snow as we typically get here, I'm thinking that the broom idea will work fine. Some winters we almost get none (much to my kids' sledding woes).

    Guys, For those of you that have used the voltage drop calculator from Solar Guppy, is it true that I need to enter double the distance in the wiring length boxes? So, if it will be a 200' wire run to my controller, then I need to use 400' in the spreadsheet, right?

    Thanks,

    Edward
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Another Solar Wiring Scenario

    Which calculator for Solar Guppy?--Niel has an Excel spreadsheet in his signature.

    If you want, here is a very simple voltage drop calculator that uses "one way" length (not round trip). You can use its results to confirm if you are doing the other calculations correctly.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Another Solar Wiring Scenario

    I didn't create anything, its only hosted by me as it needed a new download home some time ago
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario
    I didn't create anything, its only hosted by me as it needed a new download home some time ago

    OK. Sorry about that. I misunderstood something that I read.

    Edward
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario
    BB. wrote: »
    Which calculator for Solar Guppy?--Niel has an Excel spreadsheet in his signature.

    If you want, here is a very simple voltage drop calculator that uses "one way" length (not round trip). You can use its results to confirm if you are doing the other calculations correctly.

    -Bill

    Yes, I was using the one in Niel's signature. Somehow I misunderstood and thought that Solar Guppy made it.

    I tried the voltage drop calculator (Thanks Bill) and it shows 3.7% drop using 6 gauge. Probably acceptable for what I am doing. I'll try to see if I can find a good deal on some 4 gauge, but I think I could live with a 3.7% voltage drop.

    Edward
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario
    Sounds like you have an understanding of the problems involved: if you put more panels in series to up the Vmp in order to overcome the line loss you run the risk of exceeding the controller's Voc in cold temps. I tried to calculate this and got a maximum of four panels in series, but I can't run the V-drop calc on my linux netbook so not sure of the accuracy. With 5 I get a potential of 158 Voc in the cold. Pretty close but ... :confused:

    Someone can do the math more accurately I'm sure. :blush:

    I took the Voc at STC of 22.8V and then increased it by 25% and multiplied by 5. This came out to around 144V. I read somewhere online about using the 25% for cold weather output, but it is a rough estimate. I'd like to know the exact Voc at -20F. This temperature is rare for around here and will not happen every year, but it has/could happen. Typically, when we drop down into the single digits, then this is considered very cold for around here. I see on the Evergreen spec sheet the various coefficients for temperature. The Voc temperature coefficient is -0.31 %/C. So, if I say that the lowest temperature I'll see around here is -30C in extreme cases, then that would be 17.05% increase in Voc over standard conditions (55 C x 0.31 %/C). This means a 5 panel string should be a little over 133V.

    Am I missing something here, or will the 150V max Tristar MPPT controller that I have work during cold snaps?

    Edward
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario

    After playing with PVWatts some, I am now thinking about changing my panel location. I have a large shop (100' long) that has a one face of the roof facing south. It's not ideal at only 20 degrees slope, but it's better than 0 degrees facing south on the small shed. According to PVWatts, if I went with a 0 degree flat installation, I'd lose 17% compared to a more ideal 45 degree tilt. On the shop roof, the 20 degree would only cost me 2% over the whole years total power. Much better trade off. I'm actually glad that my shop roof is not much steeper, because it would make it much more difficult to work on it.... for me, at least. I'm not real fond of heights.

    Shop.jpg

    This shop is big enough, that I could have a massive solar array, but cost is a big issue, and so I plan to start out with 2.1kW. If I was just going to do grid-tie, then I'd have a very short run to the power panel in the shop, but my set up is off-grid battery bank charging and using excess power to heat water. In any case, I measured out the wire run and it will be around 180 feet to reach the battery bank in my utility room. Not much shorter than the 200' from the shed. I originally chose the shed because it seemed like it would be easier to trench for the conduit. Also, the back of my shop faces some foothills where people occasionally hunt, and I was afraid some nut shooting my panels. In any case, hopefully that never happens.

    Edward
  • mike95490mike95490 Solar Expert Posts: 8,369 ✭✭✭✭✭
    Re: Another Solar Wiring Scenario

    I think that shop roof is a good site, if it's sturdy enough to walk on to install the panels.

    I think Midnight Solar has a high voltage (250V?) input charge controller, and Xantrex is going to have a 600VDC controller by this summer.

    I don't know the spec limit for the MS tristar MPPT, it would be in the manual, or on their site.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario

    True, Mike. I was thinking about the Classic 250 this morning. I could run all 10 panels in series that way. The rare 268Voc I might experience on a -20F winter day would still be within the HyperVoc rating of the Classic 250. The HyperVoc would be around 300 volts. Going with the higher voltgae would make 6 gauge wiring more than adequate.

    I do get a little nervous with higher voltage DC power.

    Edward
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Another Solar Wiring Scenario

    The Tristar has a 150 Volt max in. I'd be leery running it close to that Voltage, as from personal experience I've seen three in series "24 Volt" panels push Voc over that. Shuts down the system and it doesn't restart automatically. Toss in some snow reflection, a bit of edge-of-cloud ... it could be bad. The margin for error is small here. And remember that really cold temps will reduce the Voltage drop through the wires as well.

    Even though the DC Voltage would be high, the current would be low. Not entirely safe, but then electricity never is. I like the Midnight solution. :D (Yeah, I know; I'm not paying for it.)
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario

    Marc, The Classic 250 would be nice. By the time I pay for freight, it looks like it'd be close to $800. I'm not saying that's too much to ask for a quality controller, but right now I'm making various big purchases and have to be careful.

    I calculated Voc of 134V at -20F. I've only heard of -20F once around here. Typically, in the 20's and very cold dips into the single digits. Is that 134V dangerously close to the Tristar's 150V max input?

    Edward
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Another Solar Wiring Scenario

    I would not worry about it... Even at -40F, you are still at 137 volts with 5 panels in series.

    Assuming that MorningStar did their job, you are under their Voc 150 volt limit.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Another Solar Wiring Scenario

    I've never had a Tristar, but if they're as well made as the Outback (like Bill said - if they did their job) the worst you could expect is for the system to shut down from over-Voltage and have to be manually restarted. Sounds like you're in a safer locale for this than me. -40 is -40 on either scale, and we can expect near that regularly around here. I had an array configuration with a Voc of 130 Volts and it did shut down my MX60 when it got real cold. Reconfigured it, and bought new batteries.
  • icarusicarus Solar Expert Posts: 5,223 ✭✭✭✭
    Re: Another Solar Wiring Scenario

    Even if you have -40 over night, the likely hood (in most locations mind you) if it is going to be sunny, by the time the panels begin to put out significant current, the panel temp is likely to rise way above -40, unless they are subjected to lots of wind.

    I suppose it is proper to design for the worst case scenario (see also Japanese Nuke plants!) but designing for the real world probably fine in this case.

    Tony
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario

    Thanks for the input Bill, Marc, & Tony.

    I did the Excel voltage drop spreadsheet again with the 180' distance (might be a little shorter in reality, because when I measure I try to "round up").

    Using 6 gauge shows a 3.9% voltage drop under Standard Test Conditions (STC) conditions and 3.3% using Normal Operating Cell Temperature Conditions (NOCT).

    Upgrading to 4 gauge would drop that to 2.5% under STC conditions and 2.2% under NOCT conditions.

    For the small decrease in efficiency, I opted for 6 awg. I found someone selling a 500' spool of Southwire XLPE 6 awg wire on eBay and got it for $329 and that also includes shipping the heavy spool here. When I searched online for the same Southwire XLPE wire in 4 gauge, I was seeing prices of $700 - $1300 for a 500' spool (not including freight)! I'll save the money and use it to buy some of the other components I need to complete the system. In the future, if I ever add some more panels, then I'll need a new controller anyway. Then, I'll probably reconfigure for a Classic 250 and run with higher voltages and lower current.

    I always like to choose the most efficient route (would prefer 4 awg wire now), but I have to balance it with the reality of my bank account (or lack thereof)! :D

    Edward
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: Another Solar Wiring Scenario

    Edward if you are thinkning about going the Midnite route there is a home brew excel spreadsheet by KentO on Jan 13 in Re: Array sizing/configuration determination / Charge Controllers Discussion that compares the 3 Classics

    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • keyturbocarskeyturbocars Solar Expert Posts: 375 ✭✭
    Re: Another Solar Wiring Scenario

    Thanks Eric. Right now, I plan to use the Tristar MPPT controller that I bought a year ago. If I add to my array, then I'll outgrow the Tristar and will probably then go to the Classic 250.

    Edward
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Another Solar Wiring Scenario

    I think this is the thread from Midnite Solar's forum:

    Array sizing/configuration determination

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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