How does one expand a system and make it work together

New_ClimberNew_Climber Registered Users Posts: 12
So, I am just thinking to the future....right now I have 2 grape solar panels that are 33v, total 375w (44voc). I want to connect all this though a charge controller and into a small battery bank...I have not decided on the charge controller or batteries as of yet. This initial setup would power CF lighting.

But my question is, if I want to add capacity, in both PV panels and battery storage capacity, what is the property way of doing this. If I were to get additional PV panels that are rated at different voltages, I would not want to connect all these together into the older panels...right?

What about adding batteries in the future, I have read it is not good to combine old and new batteries together...is this correct?

So, how would one increase capacity?? Would I need to just setup separate circuits...separate charge controllers, and seperate battery banks?

All would be going into a inverter to run AC lights in a barn/detached garage. With this said, wouldn't everything come together at some point, either though the inverter on the AC side?? Or would that need to be separated also...

Thx for the help, and sorry if this is a long winded question....I am just trying to in vision what a larger system would be...and if possible purchase equipment that might work then also...meaning a larger CC rather then something that only works now...

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: How does one expand a system and make it work together

    Expanding a system is one of the most difficult things to do, but if you plan in advance it is possible.

    Your first problem is that you don't have a fixed amount of power to supply. If you know you need X kW hours now and 2X kW hours later it's much easier to expand. Everything hinges on this: the inverter capacity, the size of the battery bank, and how much panel & controller you need for recharging.

    "I have not decided on the charge controller or batteries as of yet." That statement is indicative of backward planning. If you knew the Wattage of the CFL's and how long you wished to run them for you'd be much better off. Starting an off-grid system based on a couple of panels is bound to be a headache every step of the way.

    If you started the right way (sorry to keep harping on this but it is key) you would have so many kW hours from a battery bank of X Amp hours @ Y Volts and know that in the future that could be replaced with a battery bank of 2X Amp hours (and/or 2Y Volts which would necessitate changing the inverter) and add appropriate panels as needed.

    You are correct that panels with too different specifications are not going to work well together on the same controller. Multiple controllers can be connected to the same battery bank, however.

    The other option, which is sometimes necessary and sometimes desired, is to build a second completely separate system for additional loads. Often in off-grid situations someone might start with a small "lighting only" system and then add a larger "everything else" system later. The two would not be connected in any way.

    Last I will give a warning about AC connections. Unless the inverters are designed to have their outputs connected, do not do it.
  • New_ClimberNew_Climber Registered Users Posts: 12
    Re: How does one expand a system and make it work together

    Thanks again for the reply...

    I do have more planning involved...just have not decided on which model CC or batteries. At first I am in need to run 15-23watt CF lights. Not all the lights will be on at once, and they will not be used all the time..in fact they will only be used half the week.

    This gives me 345w*4hr per day * 3days a week. I have done some of the calculations, just don't have the numbers in front of me.

    But with you answer of "Multiple controllers can be connected to the same battery bank, however", this is the information I was looking for as I didn't now this. I didn't plan on connect the AC inverters to each other, but was not sure if the correct way was to keep the circuits apart.

    The idea of building a small system now for lighting and then expanding into a separate system I think will be what I want...or at least now that I know that you can connect different CC to the same batteries it allows me to deal with future CC and battery expansion as funds and capacity is needed.

    Thx again...
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: How does one expand a system and make it work together

    that a lot of power , 1.4Kwh per day, just for lights. have you considered using 9w CFLs or 3w LEDs?
    You might want to have a closer look at the max number of lights you will use mid winter at one time rather than the whole lot of 23 at one time. Conserve, conserve, conserve...

    The battery bank you will need is dependent on the load it has to supply/feed as is the array size.

    hth
     
    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
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: How does one expand a system and make it work together

    The problem is that off grid systems do not really scale up in size without issues.

    Loads drive battery bank selection (voltage/AH capacity). 1-3 days of storage and 50% maximum discharge is the usual "optimum" size (typically 2 days of no-sun and 50% max discharge for long life--Or ~4x your daily loads).

    Battery Bank drives min/nominal/maximum charging current range (typically 5-10-13%)--so this is one driver of the size of the solar array.

    And, the amount of sun (hours of sun per day) also drives the size of the solar array.

    More or less, you have about a 2-4x variation in power/charging/array/battery bank before you almost need to start from near scratch again on a system design.

    And some things don't really do a good job of expanding (battery banks--mixing old and new batteries and/or batteries of different makes/chemistries can create a lots of maintenance issues; solar charge controllers can support a 2-4x larger array at 2x to 4x battery bank voltage, 12 to 24 volt, 24 volt to 48 volt, etc.).

    Any way, Try to design the system you can use now--and then estimate your final system. And see what makes sense to migrate to the next system (vs sellings parts on Craig's List, etc.).

    So, 345 watts * 4 hours per day:
    • 345 watts * 4 hours = 1,380 WH per day

    Size of battery bank--Assume 2 days and 50% max discharge, with 85% efficient AC inverter--start with 12 volt battery bank:
    • 1,380 WH per day * 1/0.85 invrt eff * 2 days of no sun * 1/0.50 max discharge * 1/12 volts = 541 AH @ 12 volts

    Size of solar array based on Battery Bank capacity and 5/10/13% rates of charge:
    • 541 AH * 14.5 volts charging * 1/0.77 panel+controller derate * 0.05 rate of charge = 509 Watt array minimum
    • 41 AH * 14.5 volts charging * 1/0.77 panel+controller derate * 0.10 rate of charge = 1,019 Watt array nominal
    • 41 AH * 14.5 volts charging * 1/0.77 panel+controller derate * 0.13 rate of charge = 1,324 Watt array "max cost effective"

    Next, assuming your are near Portland Or, fixed array tilted to near 45 degrees:
    Month    Solar Radiation (kWh/m 2/day)
    1      2.07     
    2      2.59     
    3      3.89     
    4      4.35     
    5      5.29     
    6      5.29     
    7      6.01     
    8      5.55     
    9      5.00     
    10      3.79     
    11      2.00     
    12      1.46     
    Year      3.95
    

    Say we dump the lowest three months and assume genset or other power source, that leaves February with an average of 2.59 hours of sun per day. The array needed to break even would be:
    • 1,380 Watt*Hour per day load * 1/0.52 off grid sys eff * 1/2.59 hours of sun per day = 1,025 Watt array minimum (Feb)

    So, the optimum array for the loads you listed, for ~9 months of the year off grid (assuming 7 days a week) would be ~1,025 to 1,324 watts.

    If you pick the 1,025 watt array, the minimum charge controller (MPPT type) would be rated around:
    • 1,025 Watts * 0.77 panel+charger derating * 1/14.5 volts = 54 amps

    The larger MPPT charge controllers have a maximum output current rating of around 60-80-92 amps or so (depending on brand and model)--So, you are already pretty close to maximum useful charging output from a 60 Amp charge controller...

    If you doubled your loads/array/battery bank later--You would be looking at either 2x 60 amp charge controllers, or upping to a 60 Amp controller charging a 24 volt battery bank (i.e., reuse your existing controller to power a 2x higher voltage battery bank)--But this costs you a new 24 VDC input inverter--Or, no free lunch with off grid solar.

    The fact that you need only 3 days per week--It could drop your battery/array sizes a bit--But it does depend if these are M/W/F (day between) or Friday/Saturday/Sunday where you do not have time to recover between days of usage.

    You do want to recharge the batteries rather quickly--The more time the spend significantly discharged, the faster they will sulfate (why a small array charging a large battery bank will give you batteries that only last a few years).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: How does one expand a system and make it work together
    So, I am just thinking to the future....right now I have 2 grape solar panels that are 33v, total 375w (44voc).

    Are those panels positive or negative ground? You may have some headaches trying to expand a posative ground system. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: How does one expand a system and make it work together

    One thing I'll add is that if you had a very clear idea of your current and future needs, and these needs were, as BB said, something on the order of two to four times greater, you could keep most or all of your equipment, excluding batteries, when you upgraded.

    What I have in mind is that you'd build the system now using the expected final system voltage but smaller batteries to get that voltage. This is the idea Cariboocoot introduced above. So if, hypothetically, you needed 12 KWh of battery capacity now (which would be about 6 KWh usable), but expected to need 36 KWh in a few years, you'd set the system voltage now in terms of what would be appropriate for the expected need. If that was 48 volts (say), you'd build a 48 volt system now with a battery bank in the neighborhood of 250 amp hours to get the 12 KWh capacity at 48 volts. You'd thus buy a 48 volt inverter now, and choose a model that is 'stackable' (such as many Outback and Magnum model inverters are), so you could add a second or third one of the same type down the road while still using the original inverter. Wiring and fusing would all be done with an eye on expansion, and panels and controllers would be added as the system was expanded. Ideally, you'd expand around the time the original batteries would need to be replaced anyway, but replace them with a much larger, all-new bank (750 ah in this example).

    If nothing broke down in the meantime and everything was planned perfectly, nothing would be wasted or replaced except the original batteries, which in my idealized scenario would be fully used up anyway. In practice it won't be perfect, but with careful planning you could get close, I think.
  • kylewkylew Registered Users Posts: 15
    Re: How does one expand a system and make it work together

    hello, I know this is an older thread, but the questions I have are in line, IE adding on to an exisiting off-grid system. I understand the problems of mixing newer batteries with older (and different types etc). The suggestions often given in this forum and elsewhere is to just wait until the origional set dies, and set it up bigger/more at that point. Obviously the real world calls for other options sometimes. I once had a boat with a shore plugin battery charger that could handle 2 sets of batteries, 1 for the house bank, one for the starter bank. there were 2 sets of wires, and 2 sets of charge settings, and they handled both at once. is there no solar charge controller available with a similar feature? it seems this would have been introduced to the market by popular customer demand. has anyone ever heard of such a thing?

    Assuming the answer is big ole goose egg, is the only option then to run 2 separate systems? I saw a suggestion about an A-B-AB switch (which I had on my boat..) which i guess would work, but with obvious problems.

    thanks
    Kyle in utah

    thanks,
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: How does one expand a system and make it work together

    Kyle;

    There are charge controllers that can handle two battery banks, but they have to be the same in terms of Voltage and capacity (as far as I know).

    Example: http://www.solar-electric.com/modubachco251.html
  • kylewkylew Registered Users Posts: 15
    Re: How does one expand a system and make it work together

    Ok, this is better news. thanks I was hoping for an MPPT controller to handle 24 V panels into a 12V battery bank, but good to know options. Do you know of any such animals?

    I also saw comments on the forum about adding more than 1 controller to a single battery bank. Can you help me understand the pros, cons, and warnings of doing that?

    thanks
    kyle
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: How does one expand a system and make it work together
    kylew wrote: »
    Ok, this is better news. thanks I was hoping for an MPPT controller to handle 24 V panels into a 12V battery bank, but good to know options. Do you know of any such animals?

    I also saw comments on the forum about adding more than 1 controller to a single battery bank. Can you help me understand the pros, cons, and warnings of doing that?

    thanks
    kyle

    There is no problem using an MPPT controller to run 24 volt panels into a 12 volt battery bank. What you cannot do is use that set of 24 volt panels with one controller to charge BOTH a 12 volt battery bank and a 24 volt battery bank at the same time, even with a two-output CC.
    SMA SB 3000, old BP panels.
  • kylewkylew Registered Users Posts: 15
    Re: How does one expand a system and make it work together

    sure. what I meant was I am hoping to find an MPPT controller to charge 2 separate 12 V battery banks. Like the sunsaver you mentioned, just MPPT and higher voltage.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: How does one expand a system and make it work together
    kylew wrote: »
    sure. what I meant was I am hoping to find an MPPT controller to charge 2 separate 12 V battery banks. Like the sunsaver you mentioned, just MPPT and higher voltage.

    I have a vague recollection of Blue Sky making such a controller but don't remember the model number.

    If the battery banks are identical, you can use the AUX function on one of the better MPPT controllers to switch output to the second bank once the first is done charging. But this gets to be a balancing act, as there are only so many hours of sun in a day that you can make use of. If you have enough array to charge both battery banks from 25% DOD then you may as well simply have two separate controllers and let each take whatever it needs.

    Although off-grid systems nearly always have a bit of extra sun power to spare (if well designed) they usually do not have 2X the requirements.

    Which lead to the question of why exactly you need two separate 12 Volt battery banks?
  • kylewkylew Registered Users Posts: 15
    Re: How does one expand a system and make it work together

    i tend to be an opportunistic scrounger, and try not to have to buy everything (nothing) new if I can help it. I am always on the lookout for a deal on what i see myself needing in the next year ot 2, and I am sure i will land on a few deals on batteries even though I dont need them at the momnet, so i would want to work them in to system rather than let then sit. I was hoping to find a single controller that could support that sort of thing, rather than having to wait til the bank dies and then run to buy them new, since a 'deal" is unlikely to come along right when i need them. With unlimited money it is easier to plan big and buy everything new when you beed it, but as a scrounger I try to be a bit more flexible.

    So back to a question about mixing 2 charge controllers into the same bank. I have seen that mentioned in this forum as being possible, but I did not see any elaboration. can you direct me to some discussions about the pros, cons and warnings for doing that? it seems that the 2 controllers would be amways reading the output of the other, and not really reading the battery. Can it work, and how?

    thanks so much for your help.
    kyle
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: How does one expand a system and make it work together

    I have to say that buying bargain equipment then trying to fit it together to meet your power needs is a sure-fire formula for headache and may end up costing more than just buying the right equipment once, even if it does appear to be more expensive.

    As for mixing charge controllers, there's no problem. They will not "read each other" and get confused. They're attached to a great big mass of electrical inertia called a battery. As either brings the battery up, the other also sees the increase in Voltage and adjust output accordingly.

    Pros: cheap way to add charge power when expanding a battery bank. Can be used (necessary) for "stationary tracking" set-ups.
    Cons: you have to be sure the controllers are all programmed with the same charge parameters. Sometimes the less-expensive controllers do not have ideal set points, and so you have to designate one as the 'main' controller and accept the other as just contributing to Bulk charge.
    Warnings: works best with two (or more) identical controllers. Some of the older MPPT types got errors from PWM output during sweeps.

    There must be several threads about this on the forum somewhere as I know I personally have answered questions about it a few dozen times. :D
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: How does one expand a system and make it work together

    If the current is fairly low (1% of AH capacity), this is a float charging and you can use any reasonable wiring to put the batteries in series/parallel, and then attach your charge controllers. They should each be set to the proper voltages/time/etc. for your battery type.

    If you are in the 5%-13%+ rate of charge, you should use the SmartGuage wiring suggestions to ensure that all batteries share the current properly (not a bad idea even for the 1% rate of charge system above). Battery charging current will be "steered" by the resistance of your wiring to each parallel string. The more parallel connections and the higher the current (especially if the batteries are being cycled), the batteries with the the lowest resistance path will supply/take the most current. Batteries with higher resistance paths will get less current/less charging/less discharging.

    If you are connecting "random" charge controllers to a properly wired battery bank--Each will make its own Bulk/Absorb/Float charging decissions based on the battery voltage and current flow/timer settings. They will not always be in sync--And the controller with the "highest" voltage setpoint will eventually "win"... But if every thing is connected correctly, you will be fine.

    For a flooded cell bank, they need to be recharged for ~24 hours once per month (depending on lots of variables; solar, grid power, amount of current, battery capacity, etc.).

    If don't have a float charger--the batteries will use a fair amount of water and should be check once per month until you figure out how often they do need refilling.

    Personally, I am "cheap", so what I have done is get a "standard" battery charger (wall plug/cube in my case for floating a car battery with ~1% rate of charge) and set a heavy duty lamp timer for 1-3 hours a day of charging from the AC mains. This really reduced water usage but kept the batteries charged.

    In general, worked great--But on my inlaws' car, they sometimes left the trunk life on--which then drained/ruined the battery. So I eventually got an 8 amp "Battery Minder" charger so it floated the battery correctly, and would keep up with the trunk light if left on.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kylewkylew Registered Users Posts: 15
    Re: How does one expand a system and make it work together

    thanks, everyone, for the good direction. I hope someday i will be experienced enough to offer help to some other new guy.

    cheers
    kyle
  • PhotowhitPhotowhit Solar Expert Posts: 5,650 ✭✭✭✭✭
    Re: How does one expand a system and make it work together

    Most 'deals' on batteries tend to be mistakes, I'd read through the forum. There is a current thread about gel cells...

    Used batteries tend to be no bargain, even the large telecomunication batteries are often not made for repeated discharge, and others tend to be what people are replacing. One industry that regularly rebuilds batteries is the larger forklift traction batteries, I think there is at least one person here who has had good results with rebuilt forklift batteries and another who has stripped out bad cells from a forklift battery making a smaller battery (lake taking cells from a 36V and making a 24V) this isn't for the timid (or weak!) these single cells can weigh 140lbs or more.

    One place I have sent people looking for small system batteries is the golf course! They often swap out a percent of their golf cart batteries each year. If they buy at Sams club (and I've heard Costco) they just need a battery to exchange and a car battery is fine. So if you ask nice and get a chance to look through their batteries before they exchange them you can likely put together a small 12 or 24V bank for the cost of some dead car batteries, I keep my eyes open for them and pick up 4-5 a year. You might also ask at Sams club or costco(cheap places for golf cart batteries) if you might swap out some dead car batteries for a select few GC batteries, this is typically done at the end of the day with beer in hand for the guys...

    I mention golf cart batteries, since they are used in sets of 36 or 48V so typically one goes bad first, also 'fleets' or golf courses will replace a bunch at once so they have about the same age. Anytime you buy an unknown flooded battery you should equalize it and see how high the specific gravity gets to estimate the health of the battery.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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