Help on panel sizing and number

racsw
racsw Solar Expert Posts: 26
Hello,
I'm helping some friends that have a cabin in Canada. They don't have the technical background to either choose a solar system, install one, or know if someone is giving them inaccurate information.
I've contacted two solar distributors with the same information, and I get two wildly different estimates of panel needs. So I'm here to help sort this out if possible.

Our daily watt/hrs are 1827. The place in upper Ontario gets about 4 hrs of good sunshine per day.
We want to have a 3 day battery "no sunshine" factor.

One person figures i need two 230 watt panels, the other says I need six 180 Watt panels. Not only do the total wattage differ greatly, but why one prefers to have a lot of smaller panels I can't discern. The estimate of batteries is between 4 - 6 155 Amp/hr batteries for a 12 volt system, and we prefer the gel type, if that is ok.

Can someone who knows this stuff help me out here? The charge controller and inverter are not an issue right now. Picking the correct number of panels, their size in wattage output and the batteries are.


Thanks,
Robert
«13

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number

    Welcome to the forum.

    Good news! There's a few of us cabin-dwelling Canucks on here who actually use solar. Much better people to get advice from than someone whose trying to sell you something, eh? :D

    First off, forget about trying to supply 3 days without sunshine. You'll buy a lot of extra panels and battery that will sit there doing nothing while the sun shines. A more practical plan is to size the battery bank for one day at 25% DOD, know that you can take it to 50% for two days, and buy a back-up generator. You're going to need one of those anyway. Bet they didn't mention that!

    Let's use Icarus' fast estimate plan: you need 1825 Watt hours daily, over about 4 hours of 'harvest time' so you'd need 912 Watts of panel on the roof. How does that compare with the proposed plans? Not very good. One says 460 Watts, the other says 1080 Watts. Which is correct? The 1080 is closest.

    Let's use my nominal calculation plan: 1825 Watt hours @ 12 VDC = 152 Amp hours * 2 (50% DOD) = 304 Amp hours. This sounds like a reasonable albeit smallish battery bank. To charge that you want 30 Amps of peak current @ 14.2 VDC = 426 Watts, less a typical derating factor (77%) gives a need for 553 Watts. Round up to the nearest practical configuration. The battery estimate is close for this, but both batteries and panels would need to be doubled for 25% DOD. This is simple math.

    Now for the really interesting bit: is this actually what you need? If you want some good advice on that we'll need to know what the loads actually are. Icarus gets away with the record for minimal electricity use. This is partly due to his propane 'frige.

    So if you could provide some info on what will be used, preferably with some Kill-A-Watt power consumption figures, we can get you some good, solid figure. The first advice is always to reduce consumption as much as possible when off-grid living. It also is important to know if this will be full-time or weekends/one week living.

    The loads are the most important factor in correctly sizing a system. From the type of loads and the maximum Watts you can determine the best inverter type/size. The daily Watt hours gives the information needed to size the battery bank. From that you can determine how many panels and what charge controller are needed to recharge them.

    Frankly it sounds like both installers pulled the numbers out of a hat and wanted to sell what they make the most profit on. This is, unfortunately, all too typical.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    Sorry 'coot, but you got some math wrong some where. My quick napkin calc is PVwatt rating/2*4=harvest in wh/day

    So if the OP's loading is ~ 1800 wh,

    900/2=450*4=1800.

    That would be 900 watts of PV to provide an average of 1.8 kw. If you wish 3 full days of autonomy you might look to 2700 watts see my following post(s).

    I'll write more in a bit.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help on panel sizing and number

    Welcome to the forum Robert!

    You did the first part fine:
    Our daily watt/hrs are 1827. The place in upper Ontario gets about 4 hrs of good sunshine per day.
    We want to have a 3 day battery "no sunshine" factor.
    Knowing your usage is 1/2 the battle. I will assume that this is relatively small loads (no deep well pump, etc.) and just powering a few lights and a TV/DVD player, laptop computer, etc. Also assume that 1,287 watts is the AC load. (note the unit is Watt*Hours, not Watts/Hours--a very common mistake--We want 100 watts * 4 hours of use = 400 Watt*Hours total energy used).

    Note, I am going to have lots of very accurate numbers (like your 1,827 WH)--I am just showing the math. If you are within 10-20% of those numbers (battery size, panel size, etc.), that is certainly close enough for solar work.

    First, lets size the battery bank. Aim at maximum of 50% discharge on the battery bank for long life and to allow it to age/lose capacity and still support your needs. 3 days of no sun, 12 volt battery, with 85% efficient inverter:
    • 1,827 Watt*Hours * 1/12 volt * 1/0.85 * 3 days no sun * 1/0.50 max discharge = 1,075 Amp*Hour battery bank
    That is a pretty large battery bank for 12 volts--You might want to consider a 24 volt or 48 volt battery bank to keep current down--But worry about that later.

    Next, sizing the solar array. We can size it two different ways. One is based on the battery bank size and the other based on your power needs. I will do both and we can see what the results are.

    First, a battery bank should have a minimum of 5% rate of charge for proper charging (flooded cell). AGM's can go lower rate, but it is still good for several reasons to have the 5% floor.

    The maximum rate of charging can be as high as 20-30%--but that is a lot of solar panels and wasted power as most of the time the panels will not be supplying full power. So, 10% rate of charge is a good number and 13% is a good cost effective maximum for solar charging, and 0.77 derating (for solar panel and charge controller losses):
    • 1,075 AH * 14.5 volts charging * 1/0.77 system derating * 0.05 rate of charge = 1,012 watts minimum of solar panels
    • 1,075 AH * 14.5 volts charging * 1/0.77 system derating * 0.10 rate of charge = 2,024 watts nominal
    • 1,075 AH * 14.5 volts charging * 1/0.77 system derating * 0.13 rate of charge = 2,632 watts maximum cost effective solar array
    So, we can see from using 3 days of no sun and 50% maximum discharge really pushes up the solar array requirements.

    Another way of sizing your solar array is to supply 100% of your power for 9 months of the year, and use a genset for 3 months of the year.

    Using a website like PV Watts to predict your sun for 12 months a year. Try Thunder Bay, 0.52 over all system derating (yes, 1/2 of panel name plate rating for all system losses), 1 kW of solar panel (round number), fixed array:
    "Station Identification"
    "City:","Thunder"
    "State:","ON"
    "Lat (deg N):", 48.37
    "Long (deg W):", 89.32
    "Elev (m): ", 199
    "Weather Data:","CWEC"

    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 48.4"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 0.1 Can$/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (Can$)"
    1, 3.80, 67, 0.06
    2, 4.83, 74, 0.06
    3, 5.58, 92, 0.08
    4, 5.41, 81, 0.07
    5, 5.57, 82, 0.07
    6, 5.41, 75, 0.06
    7, 5.64, 80, 0.07
    8, 5.14, 73, 0.06
    9, 4.69, 67, 0.06
    10, 3.47, 53, 0.05
    11, 2.89, 44, 0.04
    12, 3.03, 52, 0.04
    "Year", 4.62, 840, 0.72
    The lowest power output for 9 months of the year is 67 kWH per month (120 VAC from inverter) for January:
    • 67 kWH * 1/31 days per month = 2.16 kWH = 2,160 Watt*Hours per 1,000 watts of solar panels per day in January
    Not a bad estimate from you for 4 hours of sun for your system.

    Realize that you cannot use 2,160 WH per day in January without needing to use a genset to make up for cloudy weather... You should plan on using 1/2 to 2/3 of that power on average and have the extra in your back pocket for growing loads (or use the genset).

    So for your usage, purely sizing the solar array for an average January:
    • 1,827 WH load / 2,160 Watt*Hours per 1,000 watts of panels = 846 watts of solar panels
    So, from a load point of view, you should be looking at around 846 watts to 1.5x more or 1,269 Watts (if you want some buffer).

    So, from a load point of view, you are looking at 850 watts of panels for "breaking even" in January.

    From a Battery Bank point of view, you would be a minimum of 1,000 watts of solar panels and better off with 2,000 watts of solar panels.

    Or, you have a choice to reduce your battery bank size by 1/2 (1.5 day of no sun) and plan on using a genset+AC charger and/or cutting back on your power usage during poor weather.

    If this where a full time home--You might be better off running the large bank and solar array. If this is a weekend/few months out of the year occupation, then you may want to think about the smaller battery bank/solar array and using a Honda eu2000i genset (or similar) with a ~40 amp 12 volt battery charger... Charge during the early morning and get the battery to 80-90% state of charge and let the solar array finish off the charging.

    Notice that if you go with a larger battery bank, even generator/battery bank charger needs can double too... (assuming 10% rate of charge)

    Lastly, picking the right AC inverter is important too. If your peak loads are small, getting a small inverter can save power too (large inverters have larger losses with light loads).

    For a 12 volt system, the MorningStar 300 Watt True Sine Wave AC Inverter is hard to beat. It has the "search mode" function which lets the inverter shut down most of the time (just turning on for a short time every second or so) to look for 6+ watt AC loads--If a load is found, it then turns on full until the loads are turned off. It also has a remote on/off input that you can wire to a simple low power DC switch, again puts it into a very low power standby.

    In the end, 850 watts of solar panel is a good sized system for a cabin if you are careful with loads. Keeping the battery bank smaller will save you quite a bit of money (batteries need to be replaced ~3-9 years, depending on how well you take care of them and the quality).

    For your use, I would suggest AGM's (sealed) are much better than Gel. If this is your first off-grid system, you may want to get some inexpensive "golf cart" batteries (flooded cell) and run those for 3 years. It will let you better understand your power usage and learn how to manage the system with "training batteries" before purchasing the expensive AGMs.

    Here are a couple of battery FAQ's you can read:

    Deep Cycle Battery FAQ
    www.batteryfaq.org

    Also, I would suggest getting a Battery Monitor for your system. The Trimetric is a good entry level unit. The Xantrex and Victron Energy are higher end units.

    Your thoughts?

    -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
    icarus wrote: »
    Sorry 'coot, but you got some math wrong some where. My quick napkin calc is PVwatt rating/2*4=harvest in wh/day

    So if the OP's loading is ~ 1800 wh,

    900/2=450*4=1800.

    I'll write more in a bit.

    Right you are, Tony; I left out the whole time function! :blush:
    That'll teach me to answer questions before breakfast. :p
  • Derik
    Derik Solar Expert Posts: 82 ✭✭✭✭
    Re: Help on panel sizing and number

    I would stick with fewer higher watt panels rather and a lot of little ones, much easier to install and monitor.

    I am not even going to commen about how many panels since you guys experience such a drastic difference in losses than what I do here.

    I am guessint that LagoonCoot your system would work in this application wouldn't it?
  • Derik
    Derik Solar Expert Posts: 82 ✭✭✭✭
    Re: Help on panel sizing and number

    Wow, sorry

    Cariboocoot, not Lagooncoot.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    Racsw,

    In point of fact, both your installers are "correct". It does illustrate the point that there is no "right"answer to your question, only a continuum of possible right answers.

    For example, one might logically decide that a building that is used weekends and occasionally holiday weeks might have a different design criterion than a full time building.

    (I see that Bill has posted so I won't repeat what he has said) .

    Other factors are three days of battery reserve is also a somewhat nebulous number, given the fact that there are few days where you get no solar harvest whatever, so trying to factor in a diminished harvest is difficult.

    For what it is worth, we live off grid in NWO. We have ~400 watts of PV, 450 ah of t-105 batteries. We routinely use ~5-800 wh/day. Our system keeps up nearly any day, and certainly on an average basis. We seldom if ever have to run a genny except in November and December before the lake freezes to give us reflection, and we might get a week of grey.

    I would suggest your first stop would be here:

    http://www.batteryfaq.org/

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

    Good luck and keep in touch,,,

    Tony

    PS Welcome to the forum. There are some very smart, helpful folks here. Where are you located in "upper ON"?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number
    Derik wrote: »
    Wow, sorry

    Cariboocoot, not Lagooncoot.

    :p The difference is you may find a coot in a lagoon but you won't find one in the Cariboo.
    'Cept me. :p
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    As for batteries, I would suggest stating our with cheaper flooded lead acid batteries, probably in the t-105 size. The reason being is that most people tend to early "kill" a starter set of batteries. T-105s are generic, easy to service, easy to buy replacements for.

    Another big mistake that beginners often make is going with too big a battery bank, on the theory that it gives them more reserve. What actually happens is that because the battery is bigger people use power with less regard, and they don't often up size the PV to properly charge, leading to very quick failure.

    Design your battery bank to draw a Max of 50% after ~ three day, say 5 kw, or ~15-20% per day. So in a 12 vdc system, your 1800 wh/day would draw ~ 150 AH, 3 days ~450 ah so a battery bank of ~ 900 ah would be about right,,, or 8 t-105s.

    900 ah of battery would require charging current in the 45-100 amp range, or ~ 550-1200 watts of PV to be ideal.

    If you reduced the battery bank by 1/3 and were content to run the genny a bit more often you could then reduce the PV size. (that is what I would do, as I suspect that even at three days, you will have some significant charging sometimes during those three day). What you don't want to do is leave the batteries partially discharged for more than a day or two regardless.

    Once again, Good luck and keep in touch,

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

    Regarding panel size... Typical, panels > 100 watts are cheaper on a $$$/watt basis.

    However, >100 watt panels tend not to come in "standard" voltage ratings... For example to charge a 12 volt battery bank the Vmp of the panel (Voltage maximum power) is around 17.5 volts...

    The larger panels may be Vmp 24-34-60 volts or more... To match those with a 12 volt battery bank, you need to use an MPPT (Maximum Power Point Tracking) charge controller.... MPPT charge controllers are around 3-5x more expensive vs the older/simpler PWM charge controllers.

    All About Charge Controllers
    Read this page about power tracking controllers

    MPPT charge controllers can give you a bit more power in winter (10% or so) over PWM--but their big advantage is you can use non-standard Vmp rated panels and higher Vmp Array Voltage to allow smaller gauge wire from the solar array to the charge controller (and longer distances)... Remembering that Power=Voltage*Current -- so if you double the voltage, you cut the current by 1/2...

    -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

    Okay now that the OP is even more confused than before ... :p

    Without knowing the type of loads, the size of loads, and how long they'll be used for you can not determine any aspect of the system design. We're all just shooting in the dark here.

    1825 Watt hours a day doesn't tell the whole story. That is an average of 76 Watts per hour, but that's not going to be how they're used. If you have to run a refrigerator you'll need an inverter capable of handling the start-up surge and preferably supply pure sine. If you're just running lights you might only need a very small, MSW type inverter.

    Once the load size(s) and type(s) is(are) established then you can calculate a battery bank size that will supply the needs over the given time of use. From that you can determine how best to recharge it. That's when you start to add in site specific info like PVWatts projected 'harvest' and compensations for line loss.

    It's better to figure out how much power you need and then come up with a way to supply it than to come up with a given amount of power capacity and then see how much you can do with it.

    Now I've got to go paint a closet. At least that doesn't require fancy calculations! :p
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Help on panel sizing and number

    What questions would be asked of Cariboocoot if he was looking for information here from the solar forum on painting his closet...
    How many square feet is that closet? Porous or sealed surface? One coat or two? Stain sealer/primer? Did California ban that oil based/fast dry sealer/stain killer you liked so much? Flat, semi-gloss, gloss paint (flat hard to clean, shows imperfections less; gloss easy to clean and longer surface life but does not look at good; semi-gloss easier to clean but still looks OK)

    Is the old paint lead based? Have it tested yet? How will you take it out? Full Hamat suits? Are you going to sand to prep?

    And does the ceiling have that pop-corn spray? Is there asbestos in the textured ceiling? If less than 1% you can do work or higher a Hazmat crew. If less than 0.1% any contractor can manage.

    Light colored walls so you can see better? Or does that clash with your spouses decorating style? Since you are in there, are you going to finally install a light? What kind of light? Battery, rechargeable (NiCad--haz-disposal, NiMH? Lead Acid flooded cell/agm/gel), solar, mains (building permit, UL listed), backup power? Manual switch, motion sensor, door switch, kids leave lights on? Filament (extra heat will keep mildew down)--oops being banned as we speak, CFL what color temperature (will fail sooner because of short on/off cycles; watch mercury if lamp gets broken). How about LED--20x more expensive for a light that runs less than 1 hour per year. Hmm., there are those nice Halogen bulbs in standard Edison based bulbs--have not banned them yet and only 5x more expensive--and they have nice color temperature...
    Would recommend using cheap paint and repainting again in three years after all above questions have been answered.:p:p

    -Bill "too much time on my hands" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    Off grid loading is a curious/complicated calculation(s).

    1.8 kwh over the day is, as 'Coot says, an average load of 75 watts.

    By time shifting as many loads as possible to daylight hours, one can get an immediate ~20% increase in efficiency by not having to discharge/charge the battery to supply the load. So by minimizing nighttime loads, and driving as many loads as possible when the Pv is at it's peak you can change the parameters significantly. You would still consume the same 1.8 kw, but you wouldn't have to charge as much.

    For example, we try not to pump water if we don't have to in the evening. By using a big enough P-tank we can do evening dishes and shower without the pump running until morning most days. We will also use the lap tops during the day plugged in, and unplug them at night. We also use the time when the batteries are going in absorb or float to charge everything else from tool batteries to cell phones et.

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

    Well, I didn't expect an answer this quickly, but thanks.
    It won't be necessary to go over all the small wattages (unless you feel it necessary) , which are pretty straightforward, but with the 1827 W/hrs/day includes one 1/2 hp well pump.
    The well pump (external) has a 9.2 FLA rating.

    Since the well pump only runs about 1 hr per week (5 min per session), the issue is the starting amps.

    OK, to answer some questions:
    We are in Rochester, NY, and the property is on the Black River in Matheson, ON.
    They are retired, and stay every day for 6 months, May - Oct.
    They come up for two weeks of snowmobiling in February. The rest of the season they are back home and the cabin is closed up.

    The one solar place has configured a 2800 watt Magnum inverter, and figured we would be talking about 4 -6 batteries, each 155 A/Hr. The only thing these two places seem to get close is a 45 Amp Charge controller.

    So let me know if you need any more info, and thanks for all your help. BTW, they were expecting about $6000 for their needs, but I'm not sure if we can stay in the neighborhood if we have to have 4 - 6 230 watt panels at $600 - $800 ea.
    That's why getting this right is important.

    Also, they do have a generator that has been running for 6 hrs a day to supply lights, the pump, etc. They are trying to go the solar route because of the price of gas, and the fact that the only way to get to the cabin is with their pontoon boat. He will probably be in a wheelchair next year, and this will become a real problem for them, as his wife is all that is healthy and able.

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

    I don't understand this forum. I replied, but it ended up in the middle somewhere, not at the end.

    To add to that reply:
    The solar place (2nd place) told us that because we (they) are not there during the winter, that the batteries would have to go inside for protection, rather than build something external attached to the cabin to hold the batteries. All the usable space inside is already taken, and especially if we're talking 4 - 6 batteries. So inside isn't possible. Won't the solar cells and charge controller keep the gel batteries from freezing?

    Also, we prefer gel type, for the safety and mounting choices. They don't want to deal with wet acid batteries.

    Robert
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number

    Ah, good ol' Rochester, NY; Cloud Capital of the World. :p Still running the ferry to Toronto or did they give up on that?

    Now you'll see why the type of load is important: that well pump. It's a killer. It will want pure sine wave and a very healthy Watt inverter to handle the start-up surge. It's hard to say just how much that will be, because pumps start with the load (weight of water) present. My 1/3 HP pump uses 800+ Watts running. It's a bear, but it only runs 6 minutes a day. This is one of those cases where you want to either continue pumping via generator, or else buy a 24 VDC system and at least 2 kW inverter. Just to run the pump.

    So they were suggesting the Magnum MS2812? In my opinion and inverter of that Wattage shouldn't be 12 Volt; over 2 kW and the system Voltage ought to go up to 24. Reason being that at minimum Voltage on a 12VDC system that 2800 Watts would be drawing nearly 300 Amps, and that's a lot of current to handle. Double the Voltage and you halve the current.

    For about $200 more you could get an Outback VFX3524 - 3.5 kW which will handle the pump and 24 Volt so the current isn't too extreme. The downside of the OB: no PF on the charger, only 120 VAC (Magnum has 240 VAC output), and a need for a MATE programmer (more money). Others may have different suggestions.

    Four T105 (or that type) 6 Volt 250 Amp hour batteries would give you 125 Amp hours max @ 24 Volts - about 3000 Watt hours to work with; nearly 2 days worth. But if maintenance is an issue then they'll have to spend extra $ for AGM's and be very sure they're set up right.

    It still looks like about 1000 Watts of panel, though.

    Let's let some of the other folk toss in their ideas.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number
    racsw wrote: »
    I don't understand this forum. I replied, but it ended up in the middle somewhere, not at the end.

    To add to that reply:
    The solar place (2nd place) told us that because we (they) are not there during the winter, that the batteries would have to go inside for protection, rather than build something external attached to the cabin to hold the batteries. All the usable space inside is already taken, and especially if we're talking 4 - 6 batteries. So inside isn't possible. Won't the solar cells and charge controller keep the gel batteries from freezing?

    Also, we prefer gel type, for the safety and mounting choices. They don't want to deal with wet acid batteries.

    Robert

    You are right: charged FLA's don't freeze. Not even in Ontario. Not even in the Cariboo (-40). A little shed outside and they'll be fine. Mine are left on charge all winter, unheated, unattended. Never had one freeze in 24 years.

    You want AGM - Absorbed Glass Mat - not gel cells.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    If the pump runs so rarely, forget running it on solar at all. If needed add some storage capacity and run the pump of the generator the few hours a week you need to store enough water. Since you will need a genny anyway you can fire up the genny, do some bulk charging and pump water and be done with it. That way you can significantly downsize the inverter and the inverter will run way more efficiently most of the time.


    I would vote again to start with the T-105s They are available from Canadian tire and are reasonably priced, (and like I said earlier) people will kill a set learning how to use them. I have a set on an unattended site that are still going strong and they were installed in 1999.

    I also would strongly suggest a good battery monitor like the Bogard Tri-metric because it is easy and simple to use that beginners have what is in essence a self explanatory "gas gauge" for the battery, telling them when they need to charge.


    Icarus,

    'Coot don't disparage Matheson as not being in the North. Northeastern ON can get genuinely cold. We chuckle when people in Muskoka refer to themselves as "in the north". (In fact the former Mike Harris provincial government changed the definition of "northern Ontario" to include places like Muskoka so that they could get more northern road allowances. For those that don't know Muskoka is ~ 100 kms north of Toronto, Matheson ~ 650 kms,, we are ~ 1600 km. (It's only ~ 1900 from TO to Florida!)
    http://www.solar-electric.com/tm2020.html
  • racsw
    racsw Solar Expert Posts: 26
    Re: Help on panel sizing and number

    We call it Rottenchester. Home of the best IFR pilots in the US.

    Anyhow, we seem to have established a few facts:
    We need to stay with AGM batteries.
    It appears that the panel size is about 1000 watts.
    We don't have to worry about having batteries inside, or winter issues.
    Good...making progress.

    Both solar places said to stay with 12 volts, because this system really is on the small size. That isn't set in concrete obviously, it's just about the only thing they agreed on. We have to try to keep the money reasonable. He's on disability and she is retired. This is a stretch for them I know, but it saves them (her) having to haul gas cans to the truck, to the pontoon boat, off the pontoon boat, and to the cabin.

    They don't want to operate the pump off the generator, it has to function off the batteries.

    Questions:

    1. Will the Magnum 2812, that has a surge of 3900 watts for 5 seconds, be ok for this system in 12 volts?

    2. Who makes T-105 batteries @ 250 Amp?

    3. If we stay with 12 volt, would the same amount of batteries be required, ie, 4 - T105 @250 Amp, 6 volt?

    4. I was attracted to the REC panels, although I don't know the difference between the black and silver. Anyhow, most all the panels are around 205 - 230 watts. In manageable pairs, that's either 4 - 230 watts for 920 watts, or 6 - 200 Watt for 1200 watts. But the difference is about $1000. Would the four 230 watt do the job?

    5. The Model SB50DL Blue Sky Solar Boost 50 charge controller seems like a good controller for this application. It's not overpriced, is an MPPT type, and seems to be good quality. Would you agree?

    6. For the moment, assuming we are close to the requirements for a 12 volt system, what specific changes are required to go to 24 volt?

    I have this info for 24 V:
    Same number of panels
    Same SB50DL charge controller
    Same number of batteries
    Outback VFX 3524 inverter

    One other thing. Nobody has told us what we need to connect the generator to this system. One told us we can connect the generator right to the Magnum Inverter, and the other said that because of the power factor loss of the inverter used with the generator to charge the batteries, we would be better off with a separate battery charger connected to the generator.
    After some reading, I gather that with this system, the object is not to use a transfer switch to go to generator power (which we figured to do originally) , but to have the generator supply power to charge the batteries to maintain our power. Can you guide us on this?

    Thanks again.

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

    Most T-105's are around 225 ah at the 20 20 hour rate at 6 volts, so a pair of them will produce ~ 225 ah at 12 vdc.

    The BlueSky series of controllers are fairly good units, but they are fairly dated technology.

    If you went to 24 vdc you could run close to 1000 watts on the Rogue 3024. You might have a bit of waste a few hours a few days per year, but since the cabin in the winter it won't be missed.

    Tony

    Ps I really would like to see a "work around" for the pump issue. We pump using a submersible Shurflo pump that draws ~ 10 amps whilst pumping into 60 psi and will pump ~ 3 gallons per minute into 60 psi. Is your pump a submersible or a surface jet pump? Changing the pump to a soft start low flow pump might result in a better over all performing system. You might pump longer net/net but draw less total power, and eliminate the high current starting. Even a DC pump would reduce the inverter loses, (like the shurflo for a small pump or a sunpump or grunfos.

    http://www.solar-electric.com/sodcwapu.html
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number

    I'm going to stick some bold type answers inside the quote box this time. :D
    racsw wrote: »
    We call it Rottenchester. Home of the best IFR pilots in the US.

    Anyhow, we seem to have established a few facts:
    We need to stay with AGM batteries.
    It appears that the panel size is about 1000 watts.
    We don't have to worry about having batteries inside, or winter issues.
    Good...making progress.

    Both solar places said to stay with 12 volts, because this system really is on the small size.
    That is perfectly true, except for the water pump. Its extra load throws a monkey wrench into the works. Having to up-size the system to handle that one thing really causes design problems.
    That isn't set in concrete obviously, it's just about the only thing they agreed on. We have to try to keep the money reasonable. He's on disability and she is retired. This is a stretch for them I know, but it saves them (her) having to haul gas cans to the truck, to the pontoon boat, off the pontoon boat, and to the cabin.

    They don't want to operate the pump off the generator, it has to function off the batteries.

    Questions:

    1. Will the Magnum 2812, that has a surge of 3900 watts for 5 seconds, be ok for this system in 12 volts?
    Yes, it would work. The important thing is to be certain line loss is kept to a minimum for when that pump draws its massive power requirement. This means DC cables from batteries to inverter should be kept as short as possible. This is going to require 0000 AWG wire I think.

    2. Who makes T-105 batteries @ 250 Amp?
    Disregard: this is a Trojan FLA battery (basic "golf cart" type) and you've stated you desire AGM to reduce maintenance. So you'd be looking for something like the Concorde PVX-2240T (6V, 220 Ah).

    3. If we stay with 12 volt, would the same amount of batteries be required, ie, 4 - T105 @250 Amp, 6 volt?
    Looking at total Watt hours, it doesn't matter if you put four 6 Volts 220 Amp hours in series for 24V @ 220 Ah (5280 Watt hours) or parallel two strings of two 6 Volts 220 Amp hours for 12V @ 440 Ah (5280 Watt hours). The total power available is the same.

    4. I was attracted to the REC panels, although I don't know the difference between the black and silver. Anyhow, most all the panels are around 205 - 230 watts. In manageable pairs, that's either 4 - 230 watts for 920 watts, or 6 - 200 Watt for 1200 watts. But the difference is about $1000. Would the four 230 watt do the job?
    Basically panels behave the same. The choice mostly comes down to $ per Watt. The 920 Watts should be enough for the 440 Amp hour bank, but someone should double-check my calculation on that. I get 50 Amps peak current and about 1840 Watt hours per day.

    5. The Model SB50DL Blue Sky Solar Boost 50 charge controller seems like a good controller for this application. It's not overpriced, is an MPPT type, and seems to be good quality. Would you agree?
    I can't find the specs on that model just now. BlueSky equipment is generally regarded as good stuff. But there may be an issue with input Voltage being limited? Some have a maximum input of 35 Volts, which means you can't use "24V" panels with them.

    6. For the moment, assuming we are close to the requirements for a 12 volt system, what specific changes are required to go to 24 volt?

    I have this info for 24 V:
    Same number of panels
    Same SB50DL charge controller
    Same number of batteries
    Outback VFX 3524 inverter
    I think we're disregarding the 24 Volt choice in favour of saving money.

    One other thing. Nobody has told us what we need to connect the generator to this system. One told us we can connect the generator right to the Magnum Inverter, and the other said that because of the power factor loss of the inverter used with the generator to charge the batteries, we would be better off with a separate battery charger connected to the generator.
    Hah! Magnum inverters have power factor corrected chargers! They're better than most inverters' chargers and regular battery chargers. Don't worry about that.

    After some reading, I gather that with this system, the object is not to use a transfer switch to go to generator power (which we figured to do originally) , but to have the generator supply power to charge the batteries to maintain our power. Can you guide us on this?
    Inverters have transfer switches built-in; when they sense the presence of generator input they switch loads to the generator feed and switch from inverting to charging. You may want to read the data sheet on the MS2800: http://lib.store.yahoo.net/lib/wind-sun/Magnum-MS-Inverters.pdf

    Thanks again.

    Robert

    Note to Tony: All of BC is further North than that! We don't quite have polar bears dropping by, but there aren't any palm trees either! :p
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Help on panel sizing and number

    'Coot, "The North" is a state of mind, as well as a climatological phenomena. Any where you get -30 is North! We get -40 routinely and I have seen -58F. We are much more influenced by the Arctic than you are. With the Pacific to your west serving as a huge moderating influence, and the Rockies to your east keeping the cold Arctic air at bay,,, ou are practically balmy.

    According to the EC website you are expecting ~-10 on tuesday, we are going to be -27, our OP's location ~-28. It's just a bit of climate elitism. LOL.

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

    OK :D

    We seem to be making great progress.

    However, because the original post was for panels, I need to nail this down a little closer.
    "The 920 Watts should be enough for the 440 Amp hour bank, but someone should double-check my calculation on that. I get 50 Amps peak current and about 1840 Watt hours per day."
    Could somebody check this to make sure, and tell me what your concern relates to? Personally, I would be interested in knowing how you arrived at the 1000 Watts for panels for this system.

    Also, I don't understand your comment about the input voltage of the panel. Will the REC work or do i need to select something else? Most of the panels I looked at were all between 28V and 35V output.

    On the 24V issue: That brings us down to a 220 A/Hr capacity. Is that OK?

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

    I forgot one question:

    if we go to the 24V system, and the Outback VFX-3524M, is this a Power factor corrected charger like the Magnum? (So it will accept a direct plug from the generator)

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

    OK, the decision has been made to go to 24 Volt.

    We will be using the Magnum 4024 MPPT Inverter.
    We will have 620 A/hrs of AGM batteries.
    We will be using the Solar Boost (Blue Sky) SB50DL charge controller w/display.

    If we can get this panel issue nailed down, that's all we need.

    Robert
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number
    racsw wrote: »
    I forgot one question:

    if we go to the 24V system, and the Outback VFX-3524M, is this a Power factor corrected charger like the Magnum? (So it will accept a direct plug from the generator)

    Robert

    Outback chargers are not power factor corrected. This doesn't mean that they can't be plugged directly in to the generator; it means they are less efficient at converting generator's output Watts into charging Watts. Something like this:

    Charging 14.2 Volts @ 20 Amps = 284 Watts / .80 (example) PF = 355 Watt draw on generator.

    This is usually not a problem, although it uses more fuel and can "marginalize" smaller gens as they are loaded near capacity.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Help on panel sizing and number
    racsw wrote: »
    OK, the decision has been made to go to 24 Volt.

    We will be using the Magnum 4024 MPPT Inverter.
    We will have 620 A/hrs of AGM batteries.
    We will be using the Solar Boost (Blue Sky) SB50DL charge controller w/display.

    If we can get this panel issue nailed down, that's all we need.

    Robert

    There's no doubt that's a good inverter choice. It will easily handle the pump and anything else. But remember it has a standby power draw that is higher than what a small inverter uses. It will draw 25 Watts all the time it is on. If that's 24 hours, that's an extra 600 Watt hours per day that must be factored in. So your daily usage figure is now more like 2.5 kW hours.

    So let's look at the 620 Amp hours of battery. At 50% DOD you get 310 * 24 = 7440 Watt hours. That's nearly triple the expected daily use. In that case you have to ask if you want to pay for that 3 day capacity or down-size a bit. Especially considering the next bit of bad news:

    The 50 Amp charge controller possibly won't do. You really want to run close to 10% of the Ah's for peak charge rate, and that would be 62 Amps. 50 Amps would be 8%, but the charge controller will be operating at its peak limit much of the time. We often find that shortens the life of any component. (An informal study found the venerable MX60's work most efficiently at 75% capacity: 45 Amps.)

    Panels.
    For the 50 Amp controller you'd be looking at this:
    50 Amps * 28.8 Volts charging = 1440 Watts / 77% efficiency = 1870 Watts total panel.
    For the 62 Amp "ideal" scenario its worse (including the need for an OB FM80 controller):
    62 Amps * 28.8 Volts charging = 1785 Watts / 77% efficiency = 2319 Watts total panel.

    All for running the pump. This is why both Tony & I questioned if there wasn't some other way of pumping the water and if the conversion of the pump system might not work out to be cheaper than buying this big of a solar electric set-up.

    Are you seeing the mathematical relationships here between Volts, Amps, and Watts? We seem to have gone from a system with a 1008 Watts of panels to double that size. It gains a lot of power, but is that really necessary? I can't answer that question for you; you have to work it out yourself for the particular circumstances.
  • racsw
    racsw Solar Expert Posts: 26
    Re: Help on panel sizing and number

    I'm trying, guys, I'm trying. (I rewrote this post 4 times now)

    If I understood the post at 21:02, you said that to supply our 1827 watt/hrs per day including our small 1/2 hp above ground pump, we would be OK using 920 watts of panel, 440 A/Hr batteries (4 - 220A/hr) with the Magnum 2812 inverter and the SB50DL controller. I figured we were done for a 12 volt system, but you said you wanted someone to recheck the calc for the panels.

    You suggested, and then I asked about changing to 24 volts, and you basically said it was a better move due to smaller wire size, and nothing had to be changed except the inverter and re-connecting the batteries for 24 Volt.

    I didn't quite understand if we have any "no sunshine" factor with that system. We were hoping for 3 days.

    Because you suggested the move to 24 volts, I made a mistake by not halving the A/Hr's to 220 at 24 V. So if you agree, we will stay with 220 A/Hr's of AGM batteries. We should still be balanced at this point. Agree?

    So if we go with 24 volts, what inverter would you suggest?

    How many DOD's does that give us? (I have no clue what DOD is. Days of Darkness?)

    I assume the SB50DL will be ok now that we are back to 220 A/hr. ( the 620 was a mistake)

    OBTW, dumping the pump is not an option, I thought I said that before. Try to understand this please. He is on disability and will most likely be in a wheelchair next year, so that leaves just the wife. They live on the river, which means hauling gas cans to run the generator, which becomes her task. She has to lift them into the truck, lift them out of the truck, haul them down to the pontoon boat, haul them onto the dock, and then carry them 50 yds to the cabin. She cannot do this. That's why the solar. Generator for emergency, but solar for the main power 95% of the time.

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

    My friends emailed me and are willing to do without some of the appliances they originally listed.
    So for that reason, I will list them here now. The last column is Watt/hrs per week:

    Eco Lights (3) 16W x3 = 48W 35 1680
    Water Pump 1104 W ** 1 1104
    TV 200 W 14 2800
    Stereo 50 14 700
    Hand mixer 300 1 300
    Vacuum 1440 1 1440
    Hair Dryer 1500 1 1500
    Drill Charger 80 1 80
    Misc Chargers*** 120 8 960

    10,564 Watt/Hrs per week or 1509 Watt/hrs/day.

    The bottom one is tough. That includes chargers for cell phones, ebook, netbook, portable two way radios, a chargeable lantern next to the bed, a chargeable floor sweeper, an Eliminator power box, electric razor. They don't run all the time, some don't take long to charge, so I don't know how to list this in watts. Understandably, we will do things differently. When something is charged, it is unplugged.

    So that's the latest.

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

    I don't want this to degrade into a shouting contest but here are my thoughts, and then I will shut up.

    By going to 24 vdc you will net/net use the same amount of power, but your wiring will be easier and cheaper to do. Remember, when you double the voltage, you half the current.

    12v * 10 amps= 120 watts

    24v* 5 amps= 120 watts,, the same amount of power consumed. An inverter big enough to start your pump running off 12 vdc requires large current and large wires. 24 vdc requires 1/2 the amperage and smaller wiring (with less loss).

    Batteries follow the same rules. 100 ah of battery at 12 volts =~ 1200 watt/hours.
    50 ah of 24 volts =~ 1200 wh. So 4 25ah 12 volt batteries wired in parallel would yield ~100 ah @ 12 volts or ~ 1200 watt. Or the same 4 batteries wired in series/parallel would yield 50 ah @ 24 vdc,, the same 1200 watts. The formula works for all voltages and all battery ah sizes.

    As for the pump situation. I understand the desire to get away from gasoline. That said, there MAY be other pump solutions that are better solutions that still can use the solar. Understanding that the pump you have is bought and paid for, if you can reduce the solar size by using a different pump configuration it might well pay for the cost and installation of a different pumping system. I don't know that, but it certainly (IMHO) would warrant a good look. For example, it is a much different situation using a 800 watt pump for 1 hour or a 100 watt pump for 8 hours.

    It might be of interest if you could provide some detail on your pumping situation. Are you, for example pumping from a deep well,, or a shallow well or cistern, or from the lake or river? All these present different pumping challenges for a solar installation, but an out of the box generic jet pump or deep well submersible MAY not be the right solution long term.

    OK, I will be silent on the subject until asked for further "advice".


    Tony