Help on panel sizing and number

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  • racsw
    racsw Solar Expert Posts: 26
    Re: Help on panel sizing and number

    Did you see my Post #60?

    The issue is factoring in "days of no sunshine" .
    According to your math, one day of "no sunshine" is already included, which is not true I believe.

    The multiplier works with two or more days, but not if you just want one.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number
    racsw wrote: »
    Did you see my Post #60?

    The issue is factoring in "days of no sunshine" .
    According to your math, one day of "no sunshine" is already included, which is not true I believe.

    The multiplier works with two or more days, but not if you just want one.

    Did you see my post #61?

    For 1500 Watt hours per day you need a total battery bank capacity of 138.8 Amp hours, if you draw down to 50% DOD. (You will actually use 62.4 Amp hours.)

    Now a lot of people will argue about "you're only drawing on the batteries for 20 hours" but in reality we are talking about the 20 hour Amp hour rate.

    You can "trade off" DOD for days without sun by sizing the bank for 25% DOD, knowing you can go to 50% if needed. This has the same effect either way:

    ~140 Amp hours for one day @ 50% DOD
    ~280 Amp hours for one day @ 25% DOD
    ~280 Amp hours for two days @ 50% DOD

    And yes you will always get some charging even on the cloudiest days. Just ignore that as it is impossible to factor in. Any extra power achieved through that or extra conservation is an incidental bonus.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number

    I'm going to address a couple of points here directly.
    racsw wrote: »
    Lets construct the formula and see if it works, it's in two steps for clarity:

    Whr/D = Watt Hours per day.
    Vn = Nominal system voltage
    Ie = Inverter Efficiency
    DOD = Battery discharge limit
    DNS = Days of no sunshine

    1. Whr/D / Vn /Ie = Amp Hours Consumed per day (AHC)

    1500 / 24 /.9 = 69.4 (round up to 65)
    This figure represents a battery draw down limit of 100% and does not contain any buffer of days without sun, which is impractical. So...

    Actually the problem is you can not take a battery below 50% State Of Charge (50% DOD) without ruining it. So this is where you need to insert the first "2X" factor on Amp hours. "4X" if you want to keep the DOD to 25%. This is the total Amp hour capacity.
    2. Now we factor in the limit of battery draw down we need to maintain good battery life (15% - 30% normally) and factor in the amount of days we need as a buffer of "no sun". The formula is:

    ((100/DOD) x AHC) x DNS =Total amount of battery capacity in Amp Hours.

    ((100/25) x 65) x 1 = 260 Total amount of battery capacity in Amp Hours.

    Here's where i have a slight problem with the formula. Actually "DNS" should be represented as (DNS + 1), because if you want one (1) day without sunshine factored using a multiplier of 1 doesn't compute. Correct?

    Now if you want to factor for Days of No Sun you need to multiply again. In other words if you expect the battery bank to supply for two days you take the total Amp hour capacity from the first calulation and multiply it by two.
  • racsw
    racsw Solar Expert Posts: 26
    Re: Help on panel sizing and number

    icarus,
    You never say what your watt hours per day is on the system you are using.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    From post # 44


    As a side note, we live in a very small cabin in far northern Ontario. We have 400 watts of panel, 450 ah of battery. Daily we use ~ 5-800 wh of power for everything. We don't have a TV, but we have two lap tops, sat modem, wireless internet router etc. We almost never have to run a generator to charge. We fire it up for the vacuum and for power tools.

    Tony
  • racsw
    racsw Solar Expert Posts: 26
    Re: Help on panel sizing and number

    Marc,
    All you guys were complaining about the pump. Now that the pump is gone, what did we gain in the system configuration and why?

    With the pump gone, and a 1500 WH/D load, can we get by with 4 - 215 amp panels for 4 hrs per day?

    icarus,
    5800 WH/D?? Are you kidding me? And you're replacing 5800 WH/D with 400 watts of panel? Doesn't compute.

    Robert
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    I believe some pages back I made mention of going back to 12vdc, using a Xantrex 1800 watt inverter that only draws ~1.5 watt at idle. As for the panel sizing, since you loading is ~ double of mine, then about double the PV would certainly work. (and double the batteries. Personally I might add a few hundred watts for growing loads, and figure that into the battery calcs and the head room of the charge controller.

    That would give you 860 watt of PV and by my napkin calc, would yield out the inverter ~ 1700 wh/per day on average over the course of the year.

    That panel configuration, into 12 volt should deliver ~ 55-60 amps. So a 900 ah battery would be a bit better than 5% of Ah capacity. Sounds all doable to me. Like I said earlier, keep it simple.

    Tony

    PS: You could probably pump your water with this size system if you change out the pump as discussed if you choose to do so in the future.
  • racsw
    racsw Solar Expert Posts: 26
    Re: Help on panel sizing and number

    icarus or Marc,
    For a 12 volt system, it appears that 600 A/Hr's of batteries would work with 4 - 215 Watt panels and a Magnum 2012 inverter to handle a 1500 WH/D load with 4 hours of charge time. (and no pump motor)

    The 200 A/Hr batteries are $275 each, so it'll cost him $825.00.
    Panels @ $700 will be $2800
    Inverter for $1600.
    Blue Sky SB50DL Charge controller for $508.

    Does this work by your calcs?
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    I think the BS50 controller is a bad choice. If memory serves it is limited to 50 amps. Your ~830 watts of panels might routinely put out ~ 55-60 amps, A: wasting power that it can't put through, and probably limiting the life of the hardware. A Xantrex C 60 conventional controller is only ~ $175

    http://www.solar-electric.com/tracc6060amp.html

    Or an Outback FM 60 is ~ $550

    http://www.solar-electric.com/oupofl60mpso.html

    The Bluesky controller is generally considered to be somewhat outdated technology by most folks. Running one so close to it's limits is not something I would be comfortable with.

    http://www.blueskyenergyinc.com/products/details/solar_boost_50_and_3048/[/u
    rl]


    All things being equal, I would buy a Outback FM 80 so I had some room to grow. One of the very real issues with off grid systems is that because you have 24/7 ac power available, the loads almost always grow with time. Spending the extra on the larger controller and the large battery bank now would be cheap insurance. You could then add PV as required up to some certain point. As I'm sure you know from reading the battery FAQ links, battery banks don't grow well,, mixing newer and older batteries.

    1.5 kw out of 600 ah of battery would be 125 ah. That would be ~ 20% on a daily draw. Personally, I would prefer the bigger battery bank of ~ 900 but price considerations would allow the 600 to work.

    Tony

    PS Interestingly enough, if you go back to the very beginning responses in this thread, the first three or four responses by Bill and 'Coot had it about dialed to where we are now.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    Don't forget you will need a good 4 stage battery charger:

    http://www.solar-electric.com/dls-45.html

    Also, a transfer switch if you are ever going to plug the generator into the house.

    http://www.solar-electric.com/ioitauactrsw.html

    I think the Xantrex and the Magnum inverters have a built in transfer switch.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number

    Tony was saying 500 to 800 Watt hours per day. He just wrote it oddly. :p

    1500 Watt hours on a 12 Volt system is basically the 24 Volt Amp hours X2:

    1500 / 12 = 125 / 0.9 = 138.8 *2 = ~ 280 Amp hours total for one day @ 50% DOD.

    I don't know where you got your 600 Amp hours from, but that's almost 3 days worth for this size system.

    (NOTE: I got interrupted while writing this and don't know if I completed it. :confused: again!)
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    I didn't write it "oddly" I wrote it wrong! In the original I said 5-600 and corrected it to be 5-800.

    That however does not strictly include "time shifting loads" because they don't measure through the Tri-metric. The Tri-metric reads only net ah in/out, so if yo draw power while charging that is less than the amount the controller (or genny) provide, it doesn't register.

    We are routinely down ~ 30-50 amp hours by first thing in the morning, (360-600 wh) so it is a WAG to estimate how much power we use during sun hours. On cloudy days we tend not to do things like charging tool batteries, or we use the laptop batteries more, and we turn off the Sat Modem and router when we aren't using it.

    Power management is pretty simple, but it comes down to discipline. My wife often forgets to turn off the modem/router and to un plug her laptop. I tend to be obsessive/compulsive about keeping power use down, even though I really don't need to.

    Tony
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number
    Tony was saying 500 to 800 Watt hours per day. He just wrote it oddly. :p

    1500 Watt hours on a 12 Volt system is basically the 24 Volt Amp hours X2:

    1500 / 12 = 125 / 0.9 = 138.8 *2 = ~ 280 Amp hours total for one day @ 50% DOD.

    I don't know where you got your 600 Amp hours from, but that's almost 3 days worth for this size system.

    (NOTE: I got interrupted while writing this and don't know if I completed it. :confused: again!)

    Marc,

    I have to say, this is a confusing post. (Not that I don't do so nearly all the time).

    I think he is going back to 12 vdc, so 600 ah is ~ 1.5 day at the DoD he is

    1500/12=125ah 125 ah is ~ 20% of 600 ah. (600 ah@ 12 vdc=~ 7200 wh

    1500/24=62.5 ah (600 ah @ 24 vdc is 14.4 kwh) (twice as many batteries though)

    Please note, that in all my calcs I am not including any derate for efficiencies of charge controllers/battery charging/inverters etc. so my numbers will vary a bit from 'Coot's.
    I just find it is simpler to keep the numbers simpler, and then add in the fudge factor. That is why I like the 50%X4 rule. (Name plate rating/2 to account for all cumulative system loses, 4 being the average hours of good sun one might expect on a daily basis over the course of the year).

    So, in the OP's case, 860 watts of PV/2=430*4=1720 wh/day average,, right in line with what his expected loads are likely to be. (with no reserve for no sun days) Now that everything is clear as mud!

    Tony
  • racsw
    racsw Solar Expert Posts: 26
    Re: Help on panel sizing and number

    icarus,
    You like to throw me curve balls :roll:
    I certainly would not think of a battery charger if I have a charge controller. Besides, the Magnums all have genset input for charging.

    Also, we got the 600 amp hours because we were dealing with a 25% discharge limit, which doubles the A/Hr I believe.

    OK, guys, this is it for me. I have one final question, but first, let me express my sincere appreciation for all your time and patience. You guys have a wealth of knowledge, and I learned a hell of a lot. I knew absolutely nothing about this stuff.
    I am surprised, and I would hope that down the road, you and marc would collaborate on a line by line calculation sheet that someone could use who only knew how much much wattage per day they needed to have on solar. It probably would have saved 60 posts.

    Did I learn enough to confidently calculate a solar system? No way. But I learned enough to get somewhat close, and i learned the function, in and outs, of the major pieces, like panels, charge controllers, Sin Wave inverters, MPPT charge controllers, etc, etc. I just told the wife that for our camp in the Adirondacks of NY, I'm going to get a couple of panels, a couple of batteries, a 300 Watt inverter and a Morningstar charge controller that will power the lights, radio, a DVD player, the small stuff. I use it for lights myself.

    Also, I know just enough to ask the right questions when something doesn't look right. That's worth a lot.

    Here's a nifty site:
    http://www.se-renbu.com/support/xwsizing/disclaimer_SE.aspx

    I also uploaded a battery sizing sheet much in the same vein that I would propose you and Marc create for an entire system.

    So anyhow, I'm backing out of this for my friends. I got them the information they wanted and they said it was too much. So I'm not going to play this game called "Is this too much?".

    What I decided to do was to ask you guys your recommendations for qualified and reputable solar distributors ( 2- 3) that they could call with their load evaluation sheet. These people would then put together the components they needed, and if they want to change it, it's up to them. I'll answer a question they might have, but that's about it.

    So if you would, could you please suggest a few places you know?
    And thanks very, very much for all your time,
    Robert
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    Robert,

    No worries,


    You are beginning to get the gist of how this all works. I didn't mean to throw curve balls, only wishing to inform that different choices reveal different issues. The Manums have on board battery chargers, others do not. Some inverters have on board transfer switches other do not. I just didn't want you to be surprised if you changed the hardware in the design stage.

    Your idea of getting a small inverter, a couple of batteries, couple of panels and a CC and you will have joined the club in much the same way that most of us did.

    Did you find the way to calculate PV? Just remember the 50%*4 rule and you have a great start.

    Good luck and keep in touch,

    Tony
  • racsw
    racsw Solar Expert Posts: 26
    Re: Help on panel sizing and number

    To calculate the number of panels needed:

    WH/W = Watt hours per Week
    WH/D = Watt Hours per day
    AH/W = Amp Hours per Week
    AH/D = Amp Hours per day

    WH/W x 1.15 (Inverter loss) = DC Watt Hours per Week
    DC WH/W / System Voltage (12/24 etc) = Total AH/W
    AH/W / 7 = AH/D
    AH/D x 1.2 (Battery loss) = AH/D / Sun Hours per Day to charge = Total array amps required. (TAA)
    TAA / Amps per Panel = Number of panels needed. Round up.

    Got any suggestions for distributors who know what they're doing?

    Thanks,
    Robert
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help on panel sizing and number

    This forum was started by our host Northern Arizona Wind & Sun. (and still funded/admin+software support by them).. They have 30+ years of experience.

    As I understand they are a stocking retailer/distributor--which is becoming quite rare (many places these days simply manage retail orders and fulfill from some regional warehouse).

    I, and the rest of the moderators here, are not connected with NAWS in any way other than for spam control here plus an exchange of information related to solar and conservation (with the occasional bump to threads to keep them on topic--sometimes bad jokes that take them off topic. :roll::blush:).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number

    I can't recommend any installer because I've never used one.

    As for calculating system size ... I hope you've learned that the kind of load is important and not just the Watt hours. Nothing points this out better than the options we've explored here.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    Here is a list of installers in the Timmins area. (Northeastern ON.

    http://www.solar-panel-installers.ca/CompanyList/Timmins_Ontario---North/Solar-Photovoltaic-Energy-(Electricity)/Residential/