Cable from inverter to utility meter

palmtree
palmtree Registered Users Posts: 12
We are considering a PV system for our home. The only suitable location for the panels is about 250 - 300 feet from the utility meter. Is that considered too far? Maybe the long run should be from the panels to the inverter. I could have the utility company come out and move the transformer and meter if I have to but that would be costly I'm sure.
Any help is greatly appreciated.
Brett

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Cable from inverter to utility meter

    How many watts of solar are you looking at and have you picked a particular GT inverter yet?

    It can certainly be done--but you will end up spending a fair amount of extra money to lay down the copper/aluminum cable from the array to the home/inverter (depending on size of system).

    There are some tax breaks that the extra costs can be offset with (30% federal tax credit is one).

    Moving your transformer/mains is probably something you should try to avoid.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Cable from inverter to utility meter

    You want to turn it to AC as close as possible to the panels, the AC will carry farther with less losses, Consider your wire size over that much distance to minimize voltage drop.
  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter

    Thanks for the quick replies.
    We are looking at about 7KW system. Maybe something like this http://sunelec.com/index.php?main_page=7140_watt_grid_tie_system

    The real kicker is that we just had the electric company install the line and set the transformer last week. I just got in a hurry, screwed up and didn't think about how far away it ended up form the only sunny, south facing place on the property when I told them where I wanted it.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Cable from inverter to utility meter

    just get them to mount the inverter close to the panels as possible and run a AC line to the service entrance panel, maybe increase the wire size a bit just to make sure the loss is at a minimum.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Cable from inverter to utility meter

    I am going to be a bit contrarian here...

    It is not an easy choice to put the GT inverter close to the solar panels and run the AC drop the long distance to the Array/GT Inverter... Several issues:
    1. 240 VAC vs 250-480 VDC for solar array wiring--The current is, typically, less for the DC side of the system--So smaller wire/less drop is typical.
    2. You need to monitor the voltage at your home and estimate how much resistance there is from your main panel to the transformer. Basically, your AC Mains have to operate from ~212 volts to 264 volts AC... If your home runs ~250+ VAC during parts of the day, and you add the 30 amps from your GT Inverter, you could have enough voltage increase to kick the GT Inverter off-grid. If the end of your AC run is a shop--you could have heavy starting currents (saws, compressor, welder, etc.) drop the mains below 212 VAC and also kick the GT inverter off-line (typically a 5 minute time-out before it reconnects).
    3. The voltage drop on the DC side is just a "loss of power"--Functionally, it is usually pretty easy to design the Vmp-array to operate comfortably with the GT inverter's solar input. You don't have any utility hi/low line voltage to worry about.
    -Bill

    By the way:
    • 7,000 watts / 240 vac = 29 amps
    • 29 amps * 1.25 derating = 36.35 amps -- round up to 40 or 50 amps
    Voltage Drop Calculator: 300 feet of one way wiring running 40 amps would require about 4 awg copper wire for a 3% maximum drop (7.2 volts)... Many folks aim for 1-2% loss...
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter

    Thanks again for the great info.
    Smaller wire and less loss sounds good to me.
    I'm a total rookie at this stuff. I have read up a bit but still have a long way to go. Our meter is mounted right next to the transformer (underground service line). From there it goes about 60 ft to the barn/shop (100 amp service) and also from the meter about 60 ft to the house (probably 200 amp service). The meter is between the house and the barn. The house is not built yet and the barn is still under construction.

    Has anyone had experience with kits from sunelec.com? The prices seem pretty good.

    Thanks again again,
    Brett
  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter
    BB. wrote: »
    I am going to be a bit contrarian here...

    It is not an easy choice to put the GT inverter close to the solar panels and run the AC drop the long distance to the Array/GT Inverter... Several issues:
    1. 240 VAC vs 250-480 VDC for solar array wiring--The current is, typically, less for the DC side of the system--So smaller wire/less drop is typical.
    2. You need to monitor the voltage at your home and estimate how much resistance there is from your main panel to the transformer. Basically, your AC Mains have to operate from ~212 volts to 264 volts AC... If your home runs ~250+ VAC during parts of the day, and you add the 30 amps from your GT Inverter, you could have enough voltage increase to kick the GT Inverter off-grid. If the end of your AC run is a shop--you could have heavy starting currents (saws, compressor, welder, etc.) drop the mains below 212 VAC and also kick the GT inverter off-line (typically a 5 minute time-out before it reconnects).
    3. The voltage drop on the DC side is just a "loss of power"--Functionally, it is usually pretty easy to design the Vmp-array to operate comfortably with the GT inverter's solar input. You don't have any utility hi/low line voltage to worry about.
    -Bill

    By the way:
    • 7,000 watts / 240 vac = 29 amps
    • 29 amps * 1.25 derating = 36.35 amps -- round up to 40 or 50 amps
    Voltage Drop Calculator: 300 feet of one way wiring running 40 amps would require about 4 awg copper wire for a 3% maximum drop (7.2 volts)... Many folks aim for 1-2% loss...

    Wow! 4 awg copper. That's a lot of pennies. Any suggestions on the best place to buy wire?
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Cable from inverter to utility meter

    I just did something about the same, 900' underground wire run. I used #6 aluminun, much less than copper, but to replace #4 copper, you need #2 aluminun.
    That needs a larger condouit to pull through.

    Or - you run your DC the long run. Many inverters can take 500VDC on the array input, 7KW @ 500V = 14A Hello # 8 wire (or # 6 aluminum) That puts the inverter close to the shop or wherever, and solves some problems.
    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 ,

  • jcgee88
    jcgee88 Solar Expert Posts: 154 ✭✭
    Re: Cable from inverter to utility meter
    palmtree wrote: »
    We are considering a PV system for our home. The only suitable location for the panels is about 250 - 300 feet from the utility meter. Is that considered too far? Maybe the long run should be from the panels to the inverter.

    OK, I hope I am not being too dense on this...

    The PV array ties into your circuit breaker box, not into
    the electric meter. Often those two are close by, i.e.,
    the meter sits on an outside wall of your house and the
    circuit breaker box sits only a few feet away but on the
    inside of that same wall.

    Is your circuit breaker box next to the meter? If not,
    how far is the circuit breaker box from the PV panels?

    John
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Cable from inverter to utility meter

    It is not really possible to run the inverter at Vmp-array = 500 VDC...

    Solar panel voltage falls with increasing temperatures... Your inverter's optimum range is around 250-480 VDC (300 volts minimum to start) and a maximum Voc of 600 VDC...

    With Evergreen modules, it appears that you would need between 17 minimum to 22 maximum modules in series (Vmp hot to Voc cold 100F to 0F). This range of panels will give you an operating voltage Vmp range of ~250-370 VDC (cool to hot days) depending on how many panels you choose to put in series.

    If you try for Vmp=500VDC, then Voc Cold will be >>> 600 VDC and you run the risk of damaging the inverter (at least how I see the issues).

    You can play with SMA's array sizing tool here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Cable from inverter to utility meter

    I forgot he already had an inverter picked out.
    34 evergreen ES-A-210-xxx in 2 strings of 17 (only way you can run the array)
    gives you 420VDC cold start (0f), and 258VDC hot afternoon (104f)
    so 7100W @ 258VDC = 28 amps DC
    6 of one, half dozen of the other.

    Or you could add 3 more PV panels (and required racking) each string to get up closer to the higher voltage. Or maybe a different panel, if the vendor cares to swap them (maybe 195's at a lower price)
    Massage it around, also our board's host, WindSun, has a couple DIY kits too:
    http://store.solar-electric.com/capr.html
    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 ,

  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter
    jcgee88 wrote: »
    OK, I hope I am not being too dense on this...

    The PV array ties into your circuit breaker box, not into
    the electric meter. Often those two are close by, i.e.,
    the meter sits on an outside wall of your house and the
    circuit breaker box sits only a few feet away but on the
    inside of that same wall.

    Is your circuit breaker box next to the meter? If not,
    how far is the circuit breaker box from the PV panels?

    John

    Hey. This could be good news. I just assumed that the inverted tied into the electric meter. The house isn't built yet, so I could put the breaker box on the inside of the house closest to the PV array. That would be about half the distance or maybe less.
    The meter is next to the transformer which is between the shop and the future house site. This would put the meter about 120 - 150 feet from the circuit breaker box in the house. Is that OK?
    This forum has already been a wealth of information for me. Thanks!
    Brett
  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter
    mike90045 wrote: »
    I forgot he already had an inverter picked out.
    34 evergreen ES-A-210-xxx in 2 strings of 17 (only way you can run the array)
    gives you 420VDC cold start (0f), and 258VDC hot afternoon (104f)
    so 7100W @ 258VDC = 28 amps DC
    6 of one, half dozen of the other.

    Or you could add 3 more PV panels (and required racking) each string to get up closer to the higher voltage. Or maybe a different panel, if the vendor cares to swap them (maybe 195's at a lower price)
    Massage it around, also our board's host, WindSun, has a couple DIY kits too:
    http://store.solar-electric.com/capr.html

    I haven't purchased anything yet. Just trying to get things figured out. I will surely check with you guys before making a purchase. And I will check the store of the host company too.
    Thanks
    Brett
  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter

    OK. This is lookng much better now. Since the iverter ties into the breaker box my wire run from the array is only about 80-90 ft. Does it pose any problems that my breaker box is about 80 feet from the meter and transformer?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Cable from inverter to utility meter

    Should be pretty easy... I still like to put the inverter near the meter--but any place that has weather protection and shaded to keep the inverter cool and dry is probably fine.

    I have a cool garage and keep mine inside (outside AC disconnect for the utility when they used to require one here).

    Others with hot garages probably should not keep it inside--although there is at least one person here that just uses a small AC fan to keep his inside inverter cool in the summer (just throw the fan on an inexpensive lamp timer).

    Are you planning on doing this install yourself, or a contractor?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter
    BB. wrote: »
    Should be pretty easy... I still like to put the inverter near the meter--but any place that has weather protection and shaded to keep the inverter cool and dry is probably fine.

    I have a cool garage and keep mine inside (outside AC disconnect for the utility when they used to require one here).

    Others with hot garages probably should not keep it inside--although there is at least one person here that just uses a small AC fan to keep his inside inverter cool in the summer (just throw the fan on an inexpensive lamp timer).

    Are you planning on doing this install yourself, or a contractor?

    -Bill

    We set the meter next to the transformer which is smack in the middle between the barn and the "soon to be" house. We did this because we are living in the barn while the house is being built. This way we could run 100 amp service to the barn right now and then run 200 amp service to the house when it is built. Otherwise we would have had install the meter on the barn and that would have put it even further away from the house breaker box when we eventually move in there.
    I am planning to do the install myself. I am a bit nervous since I have limited experience with stuff like this. I do however have a pretty good relationship with the electrician. Also, I can tell already that this forum will be very valuable to me.
    The other thing that makes me anxious is the rebate system from the utility company. They offer $2 per watt rebate. That really makes it pretty affordable if I build my own ground mounts. The thing is that it kind of seems too good to be true -- so I worry that there may be a catch somewhere along the road to the rebate check. I guess we'll find out.
    Thanks again for you time and help.
    Brett
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Cable from inverter to utility meter

    You are very welcome...

    Some rebates do require a "licensed installer" -- but it depends on the local regulations/programs. You can check out this website for information:

    www.dsireusa.org

    IF you have a chance, see if you can watch / help one or two other local installs... It will make things much clearer.

    There are also some videos/threads here that have lots of details about installs:
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter
    BB. wrote: »
    You are very welcome...

    Some rebates do require a "licensed installer" -- but it depends on the local regulations/programs. You can check out this website for information:

    www.dsireusa.org

    IF you have a chance, see if you can watch / help one or two other local installs... It will make things much clearer.

    There are also some videos/threads here that have lots of details about installs:
    -Bill

    that's what gets me concerned. It doesn't say a professional installer is required in the agreement. But there is a space to fill in the name and company of the installer. I guess we will find out.
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,729 ✭✭✭✭✭✭
    Re: Cable from inverter to utility meter
    palmtree wrote: »
    that's what gets me concerned. It doesn't say a professional installer is required in the agreement. But there is a space to fill in the name and company of the installer. I guess we will find out.

    Keep in mind that the federal 30% is just a couple lines in turbo tax and your done. It is the utility/local that can be a small pain.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter

    Yes. I think you're right. I can tell that the utility company is not going to make it easy on me. Unfortunately, they are also the one that will make or break the deal. $2 a watt rebate will save me a lot more than the 30% federal tax credit. In fact, we couldn't afford to even think about it if it weren't for the utility company rebate.
    We are trying to get all of the forms and agreements approved by KCP&L before we buy anything. I hope we can pull it off.
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,729 ✭✭✭✭✭✭
    Re: Cable from inverter to utility meter

    You just have to wear them down! I thank my stars that I am not in your shoes! Good Luck!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter
    You just have to wear them down! I thank my stars that I am not in your shoes! Good Luck!

    Thanks. I report how it eventually turns out.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Cable from inverter to utility meter

    Since the OP wasn't aware that the PV hooks into the breaker panel, I'm going to mention for his benefit that there is a limit to how much you can hook up.

    The max feed IN (feed breakers connected) to a panel is 120% of the panel's rating, or 240a in the case of a 200a rated panel. So, if you have a 200a panel, and a 200a main breaker feeding IN to it from the utility meter, the biggest breaker that you can install for a feed IN from the PV would be 40a.

    Note that that breaker itself has to be rated at 125% of the load it is servicing - so if you have a 200a panel with a 200a main breaker, you can add up to a 40a breaker for the feed in from the PV - BUT the PV feed has to be 32a or less (32a x 125% = 40a).

    So, if you are planning to feed more than 32a into the panel from the PV, you are going to need MORE THAN a 40a breaker, but you can't do that if you have a 200a panel with a 200a main breaker from the utility meter.

    Make sure that's going to be enough for what you are doing. If it isn't, you'll likely have to install a larger main panel - and since you haven't bought one yet, now would be the time to figure it out.


    Note also that this is different from the rule about how much you can tap off to feed OUT of that panel. You can connect LOAD breakers of up to 125% of the panel's capacity, but you can only connect FEED breakers of up to 120% of the panel's capacity.

    Also, different panels also have an absolute limit on how many breakers can be installed, so make sure you get a panel that can supply enough slots for the number of breakers you're going to need.
  • palmtree
    palmtree Registered Users Posts: 12
    Re: Cable from inverter to utility meter
    dwh wrote: »
    Since the OP wasn't aware that the PV hooks into the breaker panel, I'm going to mention for his benefit that there is a limit to how much you can hook up.

    The max feed IN (feed breakers connected) to a panel is 120% of the panel's rating, or 240a in the case of a 200a rated panel. So, if you have a 200a panel, and a 200a main breaker feeding IN to it from the utility meter, the biggest breaker that you can install for a feed IN from the PV would be 40a.

    Note that that breaker itself has to be rated at 125% of the load it is servicing - so if you have a 200a panel with a 200a main breaker, you can add up to a 40a breaker for the feed in from the PV - BUT the PV feed has to be 32a or less (32a x 125% = 40a).

    So, if you are planning to feed more than 32a into the panel from the PV, you are going to need MORE THAN a 40a breaker, but you can't do that if you have a 200a panel with a 200a main breaker from the utility meter.

    Make sure that's going to be enough for what you are doing. If it isn't, you'll likely have to install a larger main panel - and since you haven't bought one yet, now would be the time to figure it out.


    Note also that this is different from the rule about how much you can tap off to feed OUT of that panel. You can connect LOAD breakers of up to 125% of the panel's capacity, but you can only connect FEED breakers of up to 120% of the panel's capacity.

    Also, different panels also have an absolute limit on how many breakers can be installed, so make sure you get a panel that can supply enough slots for the number of breakers you're going to need.

    OK. Thanks. That is all very helpful and I, myself did not realize that. It is very good to have as much info as possible going into things.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Cable from inverter to utility meter

    I probably also should have mentioned that these "over rated capacity" rules only apply to residential installations. For commercial installations you can't install breakers over 100% of the panel's rated capacity for either feed or load.

    There are a few tricks as well. For instance many main panels are rated at 225a, so if you used one of those but only put in a 200a breaker from the utility feed, you'd have some extra feed capacity for the PV.

    225a * 120% = 270a
    270a - 200a utility feed = 70a
    56a * 125% = 70a

    So you could use a 225a rated panel, but with only a 200a breaker from the utility feed, and use up to a 70a breaker for the PV feed, which would allow you to feed in up to 56a from the PV.


    And to clarify what I said about the number of slots in the panels. Many panels will let you install 120v OR 240v breakers in any slot - i.e., you could have a panel completely full of nothing but 240v breakers.

    But some panels are designed so that only *some* of the slots can be used for 240v. So you might have 30 slots, but only 8 of them will accept 240v breakers. Since a 240v breaker uses two slots, that would limit you to 4 240v breakers. If that's all you'll ever need, then fine, but if not, then you'd need a different panel.