Figuring out service panel derate vs PV system size?

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  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    So at max it's using less than 1A? Even better, 23 amps saved! :D

    I'm going to look into have an electrician come out and do a formal loan analysis, that way I know exactly what is needed and also the inspector might need it or appreciate it.
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    Talked to an electrician real quick about a load analysis and he said the first thing to do was call the electric company and find out what was the most demand/load that we used in the past year. Called APS and they said in August last year, there was a point where we used 10.4kW. Seems pretty high but amps wise, if everything running was 120V, that would be 87 amps and if it were all 240V, it would be 44 amps...so that seems pretty low.
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Figuring out service panel derate vs PV system size?
    HX_Guy wrote: »
    So at max it's using less than 1A? Even better, 23 amps saved! :D

    I'm going to look into have an electrician come out and do a formal loan analysis, that way I know exactly what is needed and also the inspector might need it or appreciate it.

    Well it used 800w (about 6.6 amps) with the ignighter on for 5 seconds, then 275w (about 2.3) with just the motor and gas running.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?
    jcheil wrote: »
    Well it used 800w (about 6.6 amps) with the ignighter on for 5 seconds, then 275w (about 2.3) with just the motor and gas running.

    My bad, you're right, not sure how I messed up that calculation. :P
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?
    HX_Guy wrote: »
    Talked to an electrician real quick about a load analysis and he said the first thing to do was call the electric company and find out what was the most demand/load that we used in the past year. Called APS and they said in August last year, there was a point where we used 10.4kW. Seems pretty high but amps wise, if everything running was 120V, that would be 87 amps and if it were all 240V, it would be 44 amps...so that seems pretty low.

    Unless you have a smart meter that stores 15 minute demand figures, it is unlikely that APS has any idea at all what your demand really was. Typically only commercial meters will log a maximum demand figure. And the average kWH for one day is not going to do you any good as far as load analysis is concerned.

    If you do have a digital meter, then you can also just turn everything on and go look at the instantaneous demand figure. Unfortunately that will not cut any ice with an inspector though.
    SMA SB 3000, old BP panels.
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    Heh, that would be an interesting experiment. I do have a digital smart meter from APS.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    What city are you dealing with for permits? Hopefully not Glendale!
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    I'm in Peoria. I've actually heard they are pretty strict and for the heck of it, I actually took a look at random solar permits last night and of the 10 or so that I checked ok (Google satellite view then put the address in the permit search site) there was only 1 that didn't get denied initially, everyone else was denied on first attempt! Most took 1-2 months to finally get the permit it seemed.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?
    HX_Guy wrote: »
    I'm in Peoria. I've actually heard they are pretty strict and for the heck of it, I actually took a look at random solar permits last night and of the 10 or so that I checked ok (Google satellite view then put the address in the permit search site) there was only 1 that didn't get denied initially, everyone else was denied on first attempt! Most took 1-2 months to finally get the permit it seemed.

    Prepare for the worst and pray for the best then! :D:D:D
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    I installed a TED 5000 earlier this morning and it has a reading of Peak kW usage which is useful, somewhat, in figuring out the amps needed.
    The peak for the day was 10.464kW @ 1:51pm, which when you do the math, comes out to 87.2 amps. The problem there though is that's a figure at 120V, and since some of the items running were 240V, those amps are actually quite a bit less, but I guess it would give a worse case scenario?

    Maybe I should go turn everything on at once and see what it says? :)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Figuring out service panel derate vs PV system size?

    Conservation and optimizing your energy usage (both peak and average) is key to having any sort of "affordable" off grid power system.

    Can you design a system that will run 10-15 kWatt peak average load... Sure. It will just cost as much as a house in many parts of the country.

    And, there is a big difference between peak power, and average kWatt*Hours per day of loads. In general, if you design for your kWH per day loads, you will usually be able to manage your peak loads too (i.e., a system large enough to provide XX kWH per day will start/run most any specific combination of loads you "normally" run).

    If you have unusual needs (high peak loads, and low average loads)--Then that may be an issue. But until you start with the basics (how many kWH per day do you want to run)--A single peak load number is usually not enough to really get started on designing your system other in the most basic of rules of thumbs...

    For example, a 10 kWatt system will need a minimum of 1,000 AH @ 48 volt battery bank.

    A 48 volt battery bank will need 5% to 13% (roughly) to be properly charged:
    • 1,000 AH * 59 volts charging * 1/0.77 panel+controller eff * 0.05 rate of charge = 3,831 watt array minimum
    • 1,000 AH * 59 volts charging * 1/0.77 panel+controller eff * 0.10 rate of charge = 7,662 watt array nominal
    • 1,000 AH * 59 volts charging * 1/0.77 panel+controller eff * 0.13 rate of charge = 9,961 watt array "cost effective" maximum
    Assuming you are full time off grid and use the "nominal" array. And live around Phoenix Az, using PV Watts for fixed array tilted towards latitude:




    Month
    Solar Radiation
    (kWh/m2/day)


    1
    5.09


    2
    6.06


    3
    6.61


    4
    7.54


    5
    7.53


    6
    7.28


    7
    7.13


    8
    7.17


    9
    7.15


    10
    6.75


    11
    5.59


    12
    4.88


    Year
    6.57



    And you get a minimum of 5 hours of sun per day:

    7,662 kWH per day * 0.52 off grid system eff * 5 hours min sun = 19,921 WH = 19.9 kWH per day

    A 1,000 AH @ 48 battery bank used for 2 days of storage and 50% maximum discharge will supply:
    • 1,000 AH * 48 volts * 0.85 inverter eff * 1/2 days * 0.50 max discharge = 8,160 WH = 8.2 kWH of average daily storage
    If you live in the Phoenix area--You obviosly have a lot of sun--So, either a smaller array or larger battery bank would not be out of the question--Assuming ~20 kWH per day or 600 kWH per month is enough for your home.

    For my home, that would be 2-3x as much power as I currently use on grid (GT system--natural gas, no A/C or large electric appliances).

    However for somebody living in the desert south west--600 kWH per month is probably a fairly small monthly power usage if you have A/C, no natural gas, etc.

    What would work for you?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    Well Bill you've confused me. Not that such is a difficult thing these days.

    Sounds to me like he's planing a GT system since he mentions service panel derating in the title of the thread. I think he wants to figure out peak Amps drawn so he'll know how small a main breaker he can use to accommodate maximum solar back-feed while not running into any trouble supplying loads when there's no solar.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Figuring out service panel derate vs PV system size?

    Oh--OK--Still would want to know the approximate kWH per day/month/year that he would want to offset--So could size the array.

    I guess I got a little over the top here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    Haha yeah Cariboocoot is right, this is a grid-tied system that I'm doing, but I do appreciate the lengthy reply.

    As for usage, we're at about 21,000kWh per year over the past 12 months (still need June's numbers for I'm estimating) which a 12kW system should take care of for 100% coverage.
    The TED 5000 is a very useful tool though for figuring out where we can cut back, places that I didn't even really consider were really affecting energy usage significantly.
    For example, that my computer, and my wife's, never get turned off...they never even get put to sleep, we just let them run and run (except for the displays that go into sleep mode). I thought, eh, how much could it really use?
    I was able to figure that my computer, when just sitting there and not sleeping, uses 0.15kW, in sleep mode, 0 (or at least not registered). My wife's computer, .23kW when sitting the, 0 when sleeping. I can set timers on the computer to put them to sleep automatically every night for say, 8 hours. 8 hours x 365 days x 0.38kW = 1109.6kW per year! That's 5% of the energy we use all year! And, setting the computer to go to sleep anytime it's inactive for say 15 minutes will save even more...I can see saving 8%+ off our yearly energy usage from just this one change that doesn't affect us negatively in any way.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    You know what else will save power on computer use? Laptops. BIG difference.

    If you want to use the TED to get a max Watts that will work you'll need to take several sampling days, preferably half of them with the 240 VAC loads off. Yes, I know: that is not a convenient thing to do. Then you can analyze the data and see how much of the high Watts is from 240 (close enough for power estimating).

    BTW here where we are off-grid the Internet set-up is plugged into a power bar. Come the night the switch goes off and modem, router, and phone adapter all go off with it. Otherwise that little pile of electronic boxes would use as much in a day as the refrigerator does.
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    Yep, pretty much. When I was doing some testing earlier, everything with a switch in the house was off...except for things like modem, switches and who knows that else is on stand-by and sucking power, but with the computers off, the TVs off, lights off, A/Cs off...there were still being 0.40kW being consumed. That's 3,504kW per year of "phantom" use. Actually though, one or more of the fridges may have been running too, they were plugged in, just not sure if they were actually running.

    BTW, just to clarify for myself, if something is reading 0.400kW at that instant time, then that means if it ran for 1 hour without change, that would be 0.4kWh, correct?

    ted6.jpg

    Was a little nerve wracking clamping onto those live power feeds...
    ted3.jpg

    This was soon after install with both A/C units running...
    ted1.jpg

    I do have a problem though...when my pool pump turns on, the TED stops working. It's very weird...literally as soon as I turn the pool pump on (using an iPhone app), it registers it for a split second and then the online display freezes and the LED on the MTU stops blinking. As soon as I turn the pool pump off, everything resumes to normal, I don't have to unplug the MTU or reset anything, just starts working again. Same thing when I turn on the chandelier light in the dining room.
    Any ideas on that? I'll have to call tech support on Monday and see what they say.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    Yes; 400 Watts used for 1 hour is 400 Watt hours, or 0.4 kW hours.

    I've never used a TED and can't think of any logical reason why any load would shut it down. Especially with two such different loads. It should be interesting to see what the company says.
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    It has something to do with the powerlines. The TED uses PLC (power line communication) to send a signal from the sensors (connected to the power lines in the service panel) to the network gateway that then connects via ether cable to a router. If there is a lot of "noise", then it messed with the TED. What I don't get is why the pool would affect it...it has it's own subpanel so it's not using any of the house's power wires and it's even on the other side of the busbar from the breaker that I connected the TED to.
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    Find a different circuit to host the TED, any noise on the power line will render it not operable. When I did mine I picked the same circuit that the gateway is on.
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?
    solar_dave wrote: »
    Find a different circuit to host the TED, any noise on the power line will render it not operable. When I did mine I picked the same circuit that the gateway is on.

    That's what I did. I tapped into the breaker that controls the outlet which the gateway is in, which is an outlet close to where my internet router is. Don't really have a lot of choices where it would still reach the router. I also don't have anything else plugged into that outlet, just the gateway.

    BTW Solar_Dave I see from your TED 5000 system that you're pretty close to me in the Phoenix area, what rate plan are you under that you'r off-peak is 5.774¢? Mine is 6.118¢ with the 12-7 TOU plan.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Figuring out service panel derate vs PV system size?

    By the way--That top ~#14 awg white neutral wire on the right bus--Looks like it may be cooking a bit (loose/corroded connection?).

    Do not disconnect the neutral until you have turned off that circuit or killed power to the whole panel.

    And desktop computers--They can easily draw as much or more than a full size energy star refrigerator if left on 24x7:

    0.23 kWH * 24 hours = 5.52 kWH per day

    A good Energy Star fridge is around 1.2 to 2 kWH per day...

    Laptops can average almost 1/10th the power, and if set to sleep--even less.

    -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: Figuring out service panel derate vs PV system size?
    HX_Guy wrote: »
    That's what I did. I tapped into the breaker that controls the outlet which the gateway is in, which is an outlet close to where my internet router is. Don't really have a lot of choices where it would still reach the router. I also don't have anything else plugged into that outlet, just the gateway.

    BTW Solar_Dave I see from your TED 5000 system that you're pretty close to me in the Phoenix area, what rate plan are you under that you'r off-peak is 5.774¢? Mine is 6.118¢ with the 12-7 TOU plan.

    I am on the APS Time Advantage 9AM to 9PM (ET1) plan now frozen for new customers but grandfathered in for some of us. EPR6 for the solar.

    https://www.aps.com/en/ourcompany/ratesregulationsresources/serviceplaninformation/Pages/residential-sheets.aspx

    BTW do you have any X10 stuff running, like a remote for the pool pump?
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    Ah I remember that plan from back in the day.

    I don't have any X10 stuff, but my pool does have a remote interface gateway thing so it uses some sort of similar technology I assume. My alarm system is also wireless and X10 ready. The weird thing though is that the TED gets messed up even when I turn the pool on manually (not through the remote). I'm hoping the in-line filter solves it otherwise my kWh usage is going to be pretty inaccurate seeing how overnight when the pool is running, the TED measurement freezes up at whatever reading it was when the pool pump turned on. In last night's case, it was at 2.917kWH for 5 hours.

    ted10.jpg

    Weirder still though is the PVOutput shows something else? How is that even possible? Seems to be showing the A/C cycles and then just whatever the houses uses with almost no load...but it didn't register the pool pump running at all? Is that because it's on a sub-panel?
    ted11.jpg
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    In order to differentiate the solar from the loads you need a second MTU to measure the solar inputs to the panel. There is a setting to add/subtract the PV production from the overall load.
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    I dont have a PV system yet.
  • HX_Guy
    HX_Guy Solar Expert Posts: 296 ✭✭✭✭✭✭
    Re: Figuring out service panel derate vs PV system size?

    Thanks for that, these were the results. Looks like derating to 175A should be ok, at least according to this.

    amps.jpg
  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    Re: Figuring out service panel derate vs PV system size?

    That looks good. Your building dept and inspector should go with that because this worksheet is right out of the NEC.
    See - NEC is not so hard, just have to have the right cheat sheet.....