100 vs 200 Amp on Home PV

Vic99
Vic99 Registered Users Posts: 16 ✭
in Solar Beginners Corner #1
Looking at getting a ~5kW grid tied PV system for my home. We have no issues with breaker trips.
Any advantage to upgrading from 100 to 200 Amps? One the bidding companies suggested it. I'd love your input. Thanks.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #2
    Re: 100 vs 200 Amp on Home PV

    All of your bidding companies should have mentioned it. It's because of the 20% rule. On a 100A service (100A main breaker and 100A busbars) you are limited to a 20A backfed breaker for PV. That means your inverter cannot be bigger than 3840W. (3840W/240V X 1.25 = 20.0A)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: 100 vs 200 Amp on Home PV

    By the NEC regs it may be necessary. All about loading the bus bars to the max, you see? 5kW is about 20 Amps and if you've got a 100 Amp service that's maxed out ... No room! No room! Move up! Move up! *


    *As the Dormouse said.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
    Re: 100 vs 200 Amp on Home PV
    Cariboocoot wrote: »
    By the NEC regs it may be necessary. All about loading the bus bars to the max, you see? 5kW is about 20 Amps and if you've got a 100 Amp service that's maxed out ... No room! No room! Move up! Move up! *


    *As the Dormouse said.
    5000W/240V X 1.25 = 26A. Busted.
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #5
    Re: 100 vs 200 Amp on Home PV

    Coot, what about non GT systems? any need for more than 100A service?
     
    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
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  • Vic99
    Vic99 Registered Users Posts: 16 ✭
    #6
    Re: 100 vs 200 Amp on Home PV

    Does the answer change if all panels have microinverters?
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #7
    Re: 100 vs 200 Amp on Home PV
    westbranch wrote: »
    Coot, what about non GT systems? any need for more than 100A service?
    The rule is that a panel must not be fed with OCPD's totalling more than 120% of the rating of the busbar. For a grid tied PV, that means that you cannot backfeed a panel with a breaker bigger than 20% the size of the main breaker if the main breaker and the busbar are of the same rating. If you have an offgrid system the same rule applies, except that if the PV breakers are the only breakers feeding the busbar, so they can total up to 120% of the busbar rating and still be code compliant.

    Note that the load breakers do not figure into this at all.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #8
    Re: 100 vs 200 Amp on Home PV
    Vic99 wrote: »
    Does the answer change if all panels have microinverters?
    No. The microinverter trunk line feeds a breaker in the service panel, and that breaker is subject to the same rule.

    Note here that we are talking about AC rating. It's possible to have a system with a 5kW DC rating with an AC rating of less than 3840W. In the case of microinverters, multiply the rated output current at 240VAC by the number of micros and multiply that by 1.25. If that is less than 20A, you are good to go.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: 100 vs 200 Amp on Home PV
    ggunn wrote: »
    5000W/240V X 1.25 = 26A. Busted.

    You didn't read it right, ggunn. :D

    Eric;
    With an off-grid system all the power comes from the inverter, so there's no "back feed" and its associated rules: it's just straightforward power regs. Mind you a 100 Amp off-grid service would be pretty large by most installs: 24 kW. Usually the problem we run into off grid is inverters fault long before any circuit breakers trip!
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #10
    Re: 100 vs 200 Amp on Home PV

    Marc, that is what I thought, just wanted to be clear... Ya, a bit large but the Sq D QO 100A dist center is half the cost of anything else locally, due to volume buying...
     
    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
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #11
    Re: 100 vs 200 Amp on Home PV
    Cariboocoot wrote: »
    You didn't read it right, ggunn. :D
    How so? The 20% rule applies to OCPDs irrespective of what the incoming current actually is. A 5000W inverter at 240V requires a 30A breaker (5000W/240V = 20.83A; 20.83A X 1.25 = 26.04A; the next breaker size up is 30A), and no more than a 20A backfed breaker is allowed on a 100A service panel. What am I missing?

    Although... Now that I think about it I seem to remember reading somewhere that some 100A service entrance panels actually use 200A busbars because it is cheaper to make them all the same. In that case, if the OP has one like that and can prove it, he's golden.

    It's worth checking out, anyway; a service entrance panel upgrade ain't cheap. The cynical side of me suggests that an unscrupulous installer might not bring it up until the system is in place and then (oops) it takes an upgrade to interconnect.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #12
    Re: 100 vs 200 Amp on Home PV
    ggunn wrote: »
    Although... Now that I think about it I seem to remember reading somewhere that some 100A service entrance panels actually use 200A busbars because it is cheaper to make them all the same. In that case, if the OP has one like that and can prove it, he's golden.

    It is more likely that a 100A panel would have a 150A busbar, but that would still be enough to make the difference. If the busbar rating is not stamped on assembly itself, the AHJ will be justified in looking from some documentation from the breaker panel manufacturer to support the busbar rating.
    Similarly, a 200A panel may have a larger busbar too in some cases. The difference between busbar and panel rating really gets you a lot of benefit because there is no way that either the sum of the existing loads or the service (main) breaker can be above the panel rating.
    For best performance and best current distribution on the busbar, the Solar input breaker should be at the opposite end of the bus from the main breaker.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
    Re: 100 vs 200 Amp on Home PV

    That's exactly what I mean. The rule is on the bus bar rating, not the circuit main. And those pesky AHJ's tend to not "read it right" either. Remember a case not too long ago of someone looking for an 80 (or 75) Amp main breaker to derate his 100 Amp box with so he could get the GT hooked up?

    Really upgrading to a "200 Amp" service now is the safest way to insure the connection is allowed. Not cheap, but what is?
    Of course a line side tap may be allowed too.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #14
    Re: 100 vs 200 Amp on Home PV

    There is always the really worst case scenario. AHJ disallows a main down grade on a 200 amp panel because of loads and also declines a line side tap on residential. Only course to cure it is increase service entrance to 400 amp from the transformer an have a pair of 200 amp panels, one derated to 175 amps. Now layout $4300 to change out the whole nine yards.

    Ask me how I know! :D
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  • Vic99
    Vic99 Registered Users Posts: 16 ✭
    #15
    Re: 100 vs 200 Amp on Home PV

    The company mentioned a line side tap as an alternative to upgrading to 200 amp. They did say that upfront and I had a very positive read off of the sales guy, especially since I had dealt with two other companies before him. The side line would be ~$300 vs. ~$2,000 for the 200 Amps.

    I figured that 200 Amps would make more sense if I was going to hook an electric car in a 4-5 years with a level II charging station . . . . or something better if the tech changes. And I think I can take the 30% fed tax credit on the upgrade since that is part of the solar project installation.

    Also, what's a fair price for a 100 to 200 amp upgrade? House built 1920. Nothing crazy like knob and tube.
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