Upgrade suggestions

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rrroae
rrroae Solar Expert Posts: 46 ✭✭
Looking to upgrade my current off grid system and would like advice/recommendations if anyone would be inclined.


Currently, we have:

Trace 1512 inverter
3 Kyocera 120 panels
Blue Sky 2000E MPPT charger
8 US 2200 batteries run in series parallel(abused)


Looking to upgrade with:

Magnum 2812
Midnight solar MNE250STM E-panel
Outback FM-80
6 Kyocera 130 panels(added to our current Kyocera 120 panels)
6 Concorde Sunxtender Tall Golf Battery 6 volt 305

We've used our current system since 2005 and have been pretty happy except for winter when we seem to be continuously charging with a generator and would like the capacity to add a small ac unit(5,000-7,000) to run in summer for a couple hrs a day during particularly hot, muggy days.

Our current draw is very limited with the bulk of our wattage being used for my wife who works from home with a laptop and a couple hrs of tv on a small LCD in the evenings. Also a couple of CFL lights and maybe 2 loads of laundry a week. We're pretty lucky as we have a gravity spring for water and a couple of gas wells that give us gas for our fridge, heat, cooking, hot water and back up lights.


Any changes or suggestions about our upgrades?

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,474 admin
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    Re: Upgrade suggestions

    My two cents worth of suggestion--since you are going through a complete upgrade of your system, I would look for 24 or 48 VDC battery bank. The Magnum seems to be a good inverter/charger for your use--and they do have a 24 volt and 48 volt versions available.

    Yes, they are more expensive, but for ~50% more cost, you get ~2x the power output. And reducing your current by changing from 12 volt by 1/2 or even down to 1/4 of the 12 volt load.

    This allows you to run smaller wire (if you don't need the full inverter output), less expensive switches and fuses/breakers and have more headroom for voltage drop (12 volt to 10.5 volt--1.5 volt kills inverter==48 volt to 42 volt--6 volt drop to kill inverter output).

    Also, some devices operate at 12, 24, and 48 volts... The Solar MPPT Charge controller you are looking at (the Outback) is one of those. By increasing the battery bank voltage, the one controller can "manage" more solar panels... Roughly (without bothering to read the manual right now) the maximum (useful) solar array rating for the FM-80 would be:

    80 amps * 15 volts = 1,200 watts
    80 amps * 30 volts = 2,400 watts
    80 amps * 60 volts = 4,800 watts

    At 12 volts--the FM-80 would be about max'ed out at 9-10 of your 120/130 watt solar panels. With a higher voltage battery bank--you can continue to add solar panels without adding more charge controllers (note, I am skipping some configuration issues with 9 panels and a 48 volt battery bank for simplicity right now--there is some more pencil work done to properly configure the FM-80 at 48 volts with the panels).

    And, I am a big believer in not paralleling a lot of battery strings together (I would suggest 3 strings in parallel max; others have suggested 4 strings max). You want to balance the battery bank current--and the more parallel strings you have, the more difficult it is.

    If you have a need for 12 volts (existing pumps, 12 VDC converters, etc.)--with the larger system you may be able use the Magnum Inverter instead (in search mode) and leave it on to power the random AC power use at night.

    And, if you want to add heavy loads (AC, tools, etc.)--the larger inverter and higher voltage battery bank will be a big help.

    For A/C -- Read this thread for some very nice information:

    Sanyo mini split AC (inverter/variable speed)

    Obviously, your battery choice would require a couple more to run at 48 volts.

    Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: Upgrade suggestions
    BB. wrote: »
    My two cents worth of suggestion--since you are going through a complete upgrade of your system, I would look for 24 or 48 VDC battery bank. The Magnum seems to be a good inverter/charger for your use--and they do have a 24 volt and 48 volt versions available.

    Yes, they are more expensive, but for ~50% more cost, you get ~2x the power output. And reducing your current by changing from 12 volt by 1/2 or even down to 1/4 of the 12 volt load.


    Bill, appreciate the comments.

    The part I always seem to get confused about is going up to higher voltage systems(I'm math impaired). How would going from a 12 volt to 24 volt system give me 2x the power?

    If I assume correctly, I would need to pair my current 120 12 volt Kyoceras to get 24 volt and since I have 3, one would be an odd duck unless I get a matching panel. If I did go 24 volt, any recomendation for panels?

    Also looking at the spec sheet for the Magnum inverters, I see the no load draw for the Magnum inverter is 30 watts. Maybe a different inverter would suite us better as we can go hrs a day without any load on our inverter and we would like as little power consumption as possible when we're not drawing power. We also turn our inverter off at nights as we have no electrical needs. Really like the E-panel our host sells with the Magnum inverters as it would make life so much easier for me to install but if there are better options out there, I'm all ears.


    As for the batteries and going to a 24 volt system, if running 3 batteries in parallel is the most you would recommend, what would be a good sealed battery(don't want to mess with water, equalizing, etc,.) that would give us at least 800 Amph storage capacity?

    Closest I've seen would be these and their pretty pricey.

    Sun Xtender PVX-2580L AGM Sealed Battery
    255 Amp Hour, 12 Volt Group 8D

    http://store.solar-electric.com/cosuagmba.html
  • BB.
    BB. Super Moderators, Administrators Posts: 33,474 admin
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    Re: Upgrade suggestions

    Regarding voltage and power:

    Power=Voltage*Current

    There are two ways I am using that equation... The first is the current that is flowing around through your Battery Bus to the inverter... For example your Magnum 2812 inverter is a 2,800 watt at 12 volt inverter. Assuming minimum voltage of 10.5 volts and 85% efficiency:

    P=V*I
    I=P/V= 2,800 watts * 1/0.85 eff * 1/10.5 volts = 314 amps @12v

    If you run the same power from 24 and 48 volts banks:

    I=P/V= 2,800 watts * 1/0.85 eff * 1/21 volts = 157 amps @24v
    I=P/V= 2,800 watts * 1/0.85 eff * 1/42 volts = 79 amps @48v

    So--you don't get 2x or 4x the power, you get 1/2 or 1/4 the amount of current (smaller wire, cheaper fuses/breakers, easier to wire up for the same 2,800 watt output power requirements).

    For the MPPT Charge Controller (MPPT or Maximum Power Point Charge Controllers) are "different animals"--they are, almost like a Variable AC transformer--can take high voltage/low current and "transform" it into low voltage/high current with 90+% efficiency). You can read about MPPT vs PWM controllers on NAWS charge controller section:

    All About Charge Controllers
    Read this page about power tracking controllers

    In the case of FM-80, its maximum output power is "current limited". So it will output a maximum of 80 Amps... Whether that is at 12 volts, 24 volts or 48 volts... (really, maximum charging voltage for batteries are around 15v, 30v, and 60v)... So, just like above, we use the power equation (I will leave out efficiency to make it easier to see):

    P=I*V
    P=80 amps * 15 volts = 1,200 watts maximum amount of solar array power
    P=80 amps * 30 volts = 2,400 watts max
    P=80 amps * 60 volts = 4,800 watts max

    Now--there is no energy being created or destroyed here--just a humble charge controller that is limited by its maximum output current operating at different voltages... And with higher output voltages, the total power it can manage (P=I*V) will increase as the battery bank voltage is increased.

    Regarding picking an inverter--it is tough. There are a lot of options out there and I am not a user of any of them (my system is on-grid, and I am not in the solar RE industry--and I have to be careful--we have the designers of many of the Solar RE Inverters on this forum so I don't want to got anythin rong and lok stubid :blush:).

    Many inverters (including the Magnum) have a low power search mode where they consume ~4-6 watts and only "turn on" when there is a load (some 20-30 watts of inverter operational power + whatever the load is).

    In some cases, it may make more sense to have a couple inverters--one small one to power a few lights and a radio (in search mode)... And the larger inverter to run the home appliances.

    One of the nice things with the larger 48 volt inverters (Magnum and Xantex are two I am aware of) is that some come with native support for 120/240 VAC 60 Hz split phase power (just like North American home utility service)--if you can use the 240 VAC power--it is a nice thing to have.

    Obviously--having a larger inverter with larger loads (and running more time) would require more solar panels and batteries (just jumping the voltage from 12 volts to 48 volts does not increase the power available by 1 Watt*Hour).

    Battery wise--I will leave it to others here. You may be in Pennsylvania, so you would probably do well to visit a couple of your local battery distributors (batteries are heavy, can be hazardous freight, and expensive to ship long distances). See what brands they carry and research which ones have a good reputation (you can check back here).

    Our host, stands by the batteries he sells--so those would be good brands to research (and you can check with NAWS to see if they can give you a good price for delivery to your area--again, I have no connection with NAWS other than to help control spam here).

    On occasion, people find good deals on old stock batteries (including AGMs) as they look around.

    Since you will have an expen$ive battery bank--I will humbly suggest that you also include a Battery Monitor in your system... The one tool that will help you ensure that you are treating your batteries properly. And almost a requirement with AGM battery banks (you cannot measure the charge with a hydrometer in a sealed battery).

    A battery monitor will tell you the state of charge at anytime in your battery bank and some even have external contacts that can be used to setup an alarm when the batteries are below xx% State of Charge. Very simple to use. Even guests and kids can just look at the display and see if they are near the 50% state of charge level (or whatever limit you set) and need to start the generator or cut back on their electrical usage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: Upgrade suggestions

    Bill, really appreciate the help. I can run solar for the next 20 years and I'll still have noobie questions.


    For our situation, I think we wouldn't really benefit from moving up to 24 volt since our largest draw is our washer/dryer that run about 350 watt each. Already have the thicker wire for the batteries and panel from our current configuration as well.

    Still, wouldn't be opposed to set up 24 volt for future applications depending on cost. If I gather correctly, I would have to buy about 2x the battery bank to get up to 24 volt with the same storage capacity and 1 additional 12 volt panel to bring my current 3 panel 120 watt kyoceras to 2 120 watt 24 volt panels in addition to the panels I'm adding.

    Would like to have a battery bank of at least 700 amph or 350 useable amph with no more than 3 strings(2 preferably) run in parallel. Not sure the best batteries or most cost effective way to get to that point. Any advice on configuration would be much appreciated.
  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
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    Re: Upgrade suggestions
    Currently, we have:

    Trace 1512 inverter
    3 Kyocera 120 panels
    Blue Sky 2000E MPPT charger
    8 US 2200 batteries run in series parallel(abused)

    I have a similar setup to yours but using a pair of 12 volt fork lift batteries in series for 940 amp/hours. I am running my KC125's and other similar rated panels in triplets for 36 volt nominal into an MX60 charge controller which likes the arrangement fine. I think you will find the 24 volt setup more efficient and easier to maintain. Only one series string of batteries, for less equalization problems, you could use the panels you have and add 6 or 9 more KC130's to have 3 or 4 parallel strings of 3 panels. I have 5 strings of 3 series panels in my system. Number 10 wiring should be sufficient from the panels to your combiner box as long as you don't go over about 30 ft. You can build an in expensive combiner box like I did or buy an off the shelf model. You will need 15 amp breakers on each series string in your combiner box, an 100 amp breaker on the output of your FX80 should be close to code. It sound like your battery cabling is already sufficient for your "current" use and would be more than adequate at 24 volts. Just my opinion.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,474 admin
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    Re: Upgrade suggestions
    rrroae wrote: »
    Still, wouldn't be opposed to set up 24 volt for future applications depending on cost. If I gather correctly, I would have to buy about 2x the battery bank to get up to 24 volt with the same storage capacity and 1 additional 12 volt panel to bring my current 3 panel 120 watt kyoceras to 2 120 watt 24 volt panels in addition to the panels I'm adding.
    Actually no... The energy storage capacity of a 12 volt bank vs 24 volt bank is the same (when using the same number of batteries)...

    For example... You want 700 AH of storage at 12 volts. Say you have 350 AH 6 volt batteries (just an example).

    Configuration 1. would be two strings of two batteries each (a string would be 2x 6 volt batteries, two strings in parallel). Placing the two 6 volt batteries in series gives you 12 volts at 350 AH; putting two strings in parallel gives you 12 volts at 700 AH at 12 volts.

    Configuration 2. would be placing all 4 batteries in series. That would give you 1 string at 24 volts and 350 AH of storage.

    Now, #2 sounds like it has 1/2 the storage of #1... And in Amp*Hours that is true. But energy is not Amp*Hours but Watt*Hours (Amp*Hours * voltage):

    P=V*I=Watts
    Energy or Work = Power * Time = P*T=Watts*Hours

    Work=12 volts * 700 Amp*Hours = 8,400 Watt*Hours
    Work=24 volts * 350 Amp*Hours = 8,400 Watt*Hours

    So--the two setups have exactly the same amount of energy storage. However, the maximum current of the wiring in the 24 volt battery bus will be 1/2 that in the 12 volt battery bus. Less copper, smaller fuses and switches, and better voltage drop performance/immunity.
    Would like to have a battery bank of at least 700 amph or 350 useable amph with no more than 3 strings(2 preferably) run in parallel. Not sure the best batteries or most cost effective way to get to that point. Any advice on configuration would be much appreciated.
    I am not in the solar business--so I would be doing the same thing you would. Looking on web and calling battery distributors for pricing and delivery charges.

    Some suggestions. Review what your installation looks like. Do you have access (and the tools--if this is do-it-yourself) to move heavy batteries around--or do you need to limit them to 100 lbs each because will be unloading them and moving them into a battery shed yourself.

    For example, if you can move a 320 lb/144 kg battery, here is a very nice 10 year warranty flooded cell Surrette 6 volt 820 Amp Hour battery. From NAWS (shipping from Az may not make sense), that would cost $2,746 for two or $4,640 for 4 batteries. 1 series string of 2 batteries (for 12 volts at 820 amp*hours) and you are done. You could also put 4 of these in series and have 1x 24 volt string with twice the storage capacity (there is also a 683 AH 6 volt battery at 271 lbs for a bit less money).

    In the Torjan battery family (again using NAWS as a starting point)--if you want a 118 lb battery (easier to move)--4 batteries of Trojan L16RE-A 325 AH Deep Cycle Battery -- 2 strings of 2 (12 volt at 650 AH) or 1 strings of 4 (24 volts at 325 AH) would cost you $1,175 for a 5/7 year warranty.

    You can also get "one" battery... an 850 lb fork lift battery that should last 20-25 years of heavy usage. 1,090 AH for $3,172.

    Concord SunExtenders are also available in 2 volt cells (NAWS does not list stock or price). A PVX-9150T (PDF) would be 94lbs and 915 AH at a 24 Hour Rate. Put 6 of those cells (~$380 each?) in series for 1 string of 12 volts.

    Or, get the PVX-4050HT (PDF) at 6 volts and 120 lbs. Put 4 of those (could not find price on Web) in 1 series string for 405 AH of storage at 24 volts (remembering that 12 volt bank has 2x the AH rating as the "same size" 24 volt bank).

    Since battery banks don't "live" in isolation, the rule of thumb for solar panel per battery bank... Generally about 5%-13% of the 20 Hour Rate worth of solar panels is good starting place. You want 700 AH at 12 volts:

    700 AH * 14.5 volts (battery charging voltage) * 0.05 * 1/0.92 controller eff = 552 watts of solar panel minimum

    700 AH * 14.5 volts (battery charging voltage) * 0.13 * 1/0.92 controller eff = 1,434 watts of solar panel maximum

    Your planned wattage of 600 watts fits nicely in the minimum solar array "requirements". Gives you room to add more solar panels if you ever need more power (while keeping the same sized battery bank).

    Regarding configuring your panels... With an MPPT charge controller, the Vmp (Voltage maximum power) of the solar array should be (roughly) maximum battery voltage + 2 volts (controller and wiring drop) to ~100 volts DC (at nominal temperature).

    So, you have options on how many "12 volt" (Vmp=17.6 volts STC) panels you put in a string. The maximum would be around 5-6 panels in series (depending on how cold it gets in your area).

    Assuming the 120 Watt panels have a Vmp~17.6 volts: You could easily configure one string of 3x 120 watt panels + two strings of 3x 130 watt panels (total of three parallel strings) with the array Vmp=52.8 volts -- that will nicely charge both a 12 volt and a 24 volt battery bank (MPPT controller will efficiently down covert the Vmp=53volts down to the 14.5v required by the battery bank).

    I will stop typing here--I am probaby confusing you, and risk confusing myself. :roll:

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: Upgrade suggestions
    mikeo wrote: »
    I think you will find the 24 volt setup more efficient and easier to maintain.



    The more I think about it(and the more it's explained to me), the more I'm leaning that way.
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: Upgrade suggestions
    BB. wrote: »
    Actually no... The energy storage capacity of a 12 volt bank vs 24 volt bank is the same (when using the same number of batteries)...

    For example... You want 700 AH of storage at 12 volts. Say you have 350 AH 6 volt batteries (just an example).

    Configuration 1. would be two strings of two batteries each (a string would be 2x 6 volt batteries, two strings in parallel). Placing the two 6 volt batteries in series gives you 12 volts at 350 AH; putting two strings in parallel gives you 12 volts at 700 AH at 12 volts.

    Configuration 2. would be placing all 4 batteries in series. That would give you 1 string at 24 volts and 350 AH of storage.

    Now, #2 sounds like it has 1/2 the storage of #1... And in Amp*Hours that is true. But energy is not Amp*Hours but Watt*Hours (Amp*Hours * voltage):

    P=V*I=Watts
    Energy or Work = Power * Time = P*T=Watts*Hours

    Work=12 volts * 700 Amp*Hours = 8,400 Watt*Hours
    Work=24 volts * 350 Amp*Hours = 8,400 Watt*Hours

    So--the two setups have exactly the same amount of energy storage. However, the maximum current of the wiring in the 24 volt battery bus will be 1/2 that in the 12 volt battery bus. Less copper, smaller fuses and switches, and better voltage drop performance/immunity.


    All kinds of bells and whistles just went off. That's the part that I couldn't understand. When looking at the cost of batteries, I can spend basically the same amount of money on the same batteries going to 24 volt with fewer batteries run in parallel(more in series) but have the same amount of storage capacity because I'm running at a higher voltage.

    Concord SunExtenders are also available in 2 volt cells (NAWS does not list stock or price). A PVX-9150T (PDF) would be 94lbs and 915 AH at a 24 Hour Rate. Put 6 of those cells (~$380 each?) in series for 1 string of 12 volts.

    From what I've read, it seems that many people suggest running the fewest possible strings for better battery performance. IF that's the general consensus, then wouldn't this option be one of the better choices? I like this battery option with the Concords because I basically get the same amount of storage capacity at almost the same cost but in a more efficient set up.



    Regarding configuring your panels... With an MPPT charge controller, the Vmp (Voltage maximum power) of the solar array should be (roughly) maximum battery voltage + 2 volts (controller and wiring drop) to ~100 volts DC (at nominal temperature).

    So, you have options how many "12 volt" (Vmp=17.6 volts STC). The maximum would be around 5-6 panels in series (depending on how cold it gets in your area).

    Assuming the 120 Watt panels have a Vmp~17.6 volts: You could easily configure one string of 3x 120 watt panels + two strings of 3x 130 watt panels (total of three parallel strings) with the array Vmp=52.8 volts -- that will nicely charge both a 12 volt and a 24 volt battery bank (MPPT controller will efficiently down covert the Vmp=53volts down to the 14.5v required by the battery bank).

    I will stop typing here--I am probaby confusing you, and risk confusing myself. :roll:

    -Bill

    lol, yes I'm a little confused here.


    Can I keep my current array of 12 volt 120 watt panels intact(wired at 12 volt) and just buy additional panels that run at 24 volt and the charge controller will take care of the conversion to 24 volt for the entire panel array? Or would I have to have separate battery banks for the 12 volt and 24 volt arrays? If this is the case, I would change my current configuration to run at 24 volt to match the 24 volt system.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,474 admin
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    Re: Upgrade suggestions
    rrroae wrote: »
    lol, yes I'm a little confused here.

    Can I keep my current array of 12 volt 120 watt panels intact(wired at 12 volt) and just buy additional panels that run at 24 volt and the charge controller will take care of the conversion to 24 volt for the entire panel array? Or would I have to have separate battery banks for the 12 volt and 24 volt arrays? If this is the case, I would change my current configuration to run at 24 volt to match the 24 volt system.

    To make it a bit more confusing... There are MPPT controllers (like your Blue Sky) that do down convert voltage--but they only have a maximum input voltage range of 30 volts maximum... So, you cannot run "higher" voltage strings with it.

    Then there are the newer/larger/more feature rich MPPT controllers... The FM family can run around 140 VDC maximum Array voltage--so you can put more panels in series and still run a low voltage battery bank (12, 24, 48 volts).

    So--you would need to reconnect your 3x 1 120 watt array (3 parallel) into a 1x 3 120 watt array (1 series string of 3 panels). That will bring the voltage way up to near 60 Volts DC... But with the MPPT Controller, it will efficiently down convert (an MPPT charge controller is typically a "buck mode" power supply internally--if that means anything to you) any high voltage/low current array (within specifications--of course ;) ) down to the low voltage/high current battery bank (so a 3x series panel array would work exactly the same if connected to a 12 volt bank or a 24 volt bank--is not quite high enough voltage for a 48 volt bank).

    Of course, there are more details that need to be understood--but for a 50,000' foot overview--that is how it works.

    Our Host NAWS--has some nice FAQ's regarding charge controllers on their site--worth reading. Also, the Deep Cycle battery FAQs and Inverter FAQ's are important too:

    Solar Charge Controllers
    Deep Cycle Batteries
    Off-Grid Inverters

    The FAQ's are nicely written and have about 95% of the information you will want to learn about your off-grid system.

    And, don't forget the Battery Monitor. Pretty much worth the costs when you have expensive battery banks (and almost a requirement for running AGMs). You have been off-grid for years--but I think you will really love it (Trimetrics are good, low cost units. The Xantrex are very nice high end units).

    Outback has a Battery Monitor Option for the FM controllers (I believe)--I don't know anything about it--but you should look at that one too.

    -Bill

    PS: Please note, I am not an expert on the Solar RE equipment... I am just dumping information from memory regarding the rough specifications of the controllers/items we are discussing. As always, refer back to the manuals/specifications for exact ratings and limitations...

    I am avoiding the detail parts of the discussion for the moment to try and keep things simple and straight forward. The other stuff is important--but can be confusing when trying to discuss/learn the basic concepts.

    When you get into the details, it does become complex (limitations of controllers, ratings of wiring & fuses, etc., and differing configurations with their pluses and negatives). However, once you understand the basics--the details are easier to understand in context.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nigtomdaw
    nigtomdaw Solar Expert Posts: 705 ✭✭
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    Re: Upgrade suggestions

    Also Magnum do there own battery monitor dedicated to there system, like Outbacks, both use there own digital display controller , I think the Magnum is a bit cheaper that the Outback version, which offers more monitoring senarios but the Magnum will be fine for your system.

    I concur with Bill that a battery monitor is a must in a off grid home battery based system.

    Nigel
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: Upgrade suggestions

    Updated system specs. Hopefully, this system looks better.


    - Magnum 2824 or Outback 2524 inverter
    - Midgnight solar E-panel(pre wired with all fuses and disconnects)
    - Outback FM-80 or Xantrex XW MPPT 60 Amp charge controller with monitor(currently have TM-500)
    - 4 Kyocera KD205GX-LP 205 Watt 12 volt Solar Panels ($500 cheaper than 6 130 watt Kyoceras 12 volt panels and a little more wattage). Will run in pairs for 24 volts and run my 3 current Kyocera 120 watt 12 volt panels in parallel which will be downconverted by the MPPT charge controller.
    - remote temperature sensor
    - 4 Concorde Sun Xtender PVX-2120L AGM Sealed Battery 212 Amp Hour, 12 Volt run in series parallel for 848 amp hour capacity at 24 volts.



    Suggestions/comments?



    Wanted to thank everyone for their help and patience(especially Bill). This board is a tremendous asset and helps take away some of the voodoo of solar.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,474 admin
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    Re: Upgrade suggestions
    rrroae wrote: »
    - 4 Kyocera KD205GX-LP 205 Watt 12 volt Solar Panels ($500 cheaper than 6 130 watt Kyoceras 12 volt panels and a little more wattage). Will run in pairs for 24 volts and run my 3 current Kyocera 120 watt 12 volt panels in parallel which will be downconverted by the MPPT charge controller.

    My question--I am not sure you have a working configuration with this combination... And therefore we need to look at the details.

    Yes, the larger panels are very cost effective when compared with the smaller panels.

    However, the Vmp and Imp need to match (within roughly 10%) for your application when sharing series/parallel connections for optimum output power. So--we need to do some checking.

    The Kyocera 120 watt panels are (remember, always double check the data posted by any anonymous person on the web--I cannot know for sure your model or that the website I ramdomly selected for a quick lookup is accurate):

    Max voltage: 16.9 Volts
    Max current: 7.10 Amps


    The 205 watt Kyoceras are:

    Maximum Power Voltage: 26.6 volts
    Maximum Power Current: 7.71 amps
    Open Circuit Voltage: 33.2 Voc
    Short Circuit Current: 8.36 amps
    Maximum System Voltage: 600 volts
    Series Fuse Rating: 15 amps

    2x 26.6 volts = 53.2 volts Vmp for two series connected 205 watt panels
    3x 16.9 volts = 50.7 volts Vmp for three series connected 120 watt panels

    The Vmp is not an exact match--but is within 10%--so should be OK to tie together (with appropriate series fusing) to a 2x205 + 3x120 series/parallel connection to a good quality MPPT controller.

    You will need to look up the information for the Kyocera 120 Watt panels (by model number) to make sure tha they are rated to operate above ~125 volts... The "modern" panels designed for Grid Tied and large MPPT controllers are rated to operate > 600 volts (per NEC requirements).

    Many of the older panels were only rated to operate at 70 volts maximum (or less)... Part of the "details" for system design.

    Otherwise, looks like a good starting point for your new system.

    One thing--you obviously have been off grid for a long time--so you know how everything runs in your current system (amount of sun vs the amount of power you are currently consuming). Do you have a goal with your new system (more power) that you wish it to obtain? The PV Watts Website is a great place to estimate system performance with various options (use a system derating factor of 0.52 for off-grid with flooded cell batteries and inverters; use ~0.59 if you are using AGM batteries).

    And you are very welcome--We all try our best here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: Upgrade suggestions

    Bill, I'll need to research to see if my older 120 Kyoceras are rated to run up to 125 volts. They were manufactured in 07/2005 and have a max voltage of 16.9 Volts but I forget the other specs. If they are rated for 125, I think a better fit will be getting 6 Kyocera 135 watt 12 volt panels that NWS has on sale for about $3 a watt!! Same difference in max voltage(53.2 vs 50.7) between panels but easier to handle and install.


    One other change I think I'm going to make is going with the Outback FX2524 or FX3524 instead of the Magum 2812. The Outback seem more efficient in idle and search mode but I can't seem to find if they can take a direct charge from my Honda EU2000i???



    Again, can't thank you and everyone else enough for all the help.
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: Upgrade suggestions

    Haven't ordered yet because my head is going in circles.

    Can someone please confirm my numbers and which setup would work the best?


    These are the 2 configurations from a NAWS sales representative.

    Configuration #1

    - Outback VXF2812
    - Mate and battery temp monitor
    - Outback FM80 charge controller
    - Midnight solar MNE250ST E-panel(fully setup and tested)
    - 6 Kyocera 135 watt 12 volt panels(which will be added to my 3 Kyocera 120 watt panels)
    - 6 Concorde Sunxtender 6 volt 305 amp hour batteries(run 2 in series, 2 strings)

    This should give me 1170 watts of PV with a 915 amph battery bank at 12 volt


    Configuration #2

    - Outback VFX3524
    - Mate and battery temp monitor
    - Outback FM60 charge controller
    - Midnight solar MNE250ST E-panel(fully setup and tested)
    - 6 Kyocera 135 watt 12 volt panels(which will be added to my 3 Kyocera 120 watt panels). Will wire panels 3 in parallel for 53.1 volt(new panels) and 50.3 volt(old panels) strings.
    - 8 Concorde Sunxtender 6 volt 305 amp hour batteries(run 4 in series, 2 strings)


    This should give me 1170 watts of pv with a 610 amph battery bank at 24 volt.


    Now if I go by BB's calculations below, would I be right to assume that the 24 volt system with the 610 amph battery bank would give me 14,640 watts of storage (Energy or Work = Power * Time = P*T=Watts*Hours) vs 10,980 watts of storage with the 12 volt system?


    Also, which of the 2 configurations would you prefer?

    Both of these systems give us more PV and battery storage than we need but if we're going to upgrade, we'd rather do it once, do it right and be done.






    BB. wrote: »
    Actually no... The energy storage capacity of a 12 volt bank vs 24 volt bank is the same (when using the same number of batteries)...

    For example... You want 700 AH of storage at 12 volts. Say you have 350 AH 6 volt batteries (just an example).

    Configuration 1. would be two strings of two batteries each (a string would be 2x 6 volt batteries, two strings in parallel). Placing the two 6 volt batteries in series gives you 12 volts at 350 AH; putting two strings in parallel gives you 12 volts at 700 AH at 12 volts.

    Configuration 2. would be placing all 4 batteries in series. That would give you 1 string at 24 volts and 350 AH of storage.

    Now, #2 sounds like it has 1/2 the storage of #1... And in Amp*Hours that is true. But energy is not Amp*Hours but Watt*Hours (Amp*Hours * voltage):

    P=V*I=Watts
    Energy or Work = Power * Time = P*T=Watts*Hours

    Work=12 volts * 700 Amp*Hours = 8,400 Watt*Hours
    Work=24 volts * 350 Amp*Hours = 8,400 Watt*Hours

    So--the two setups have exactly the same amount of energy storage. However, the maximum current of the wiring in the 24 volt battery bus will be 1/2 that in the 12 volt battery bus. Less copper, smaller fuses and switches, and better voltage drop performance/immunity.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Upgrade suggestions

    I would go with the higher voltage system (24V) for less copper losses in the battery wire, and there is more reserve in the larger battery bank.

    con: larger battery bank will not recharge as fast, with the same size PV, so you may have a bit more genset run time on cloudy days, to save the batteries.

    If you have 12V appliances, they don't work well on 24V.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Upgrade suggestions

    i agree with mike and my preference would be the 2nd one. the bigger battery bank and inverter will handle the higher future consumption better too. pv input is the same, but that you can add some to it if need be down the road making the 2nd one more versatile imho.
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: Upgrade suggestions

    Thanks for the replies.


    From what I've read, the less you discharge AGM's the longer their lifespan. We do run our Honda generator when we get low but we also have a bad habit of waiting until we're down in the 50-55% area before we do. I'm thinking if we stay on the high side of PV to batteries, we'd have a better chance of keeping our batteries discharging to only 70% for better lifespan(especially with AGM's). We also like the idea of the 24 volt system for efficiency and any future expansion.

    Maybe a better fit for us would be to get the 24 volt system but instead of the 8 305 amph 6 volt Concordes, get 4 255 amph 12 volt Concordes(wired 2 in series, 2 strings). This would give us a 610 amph battery bank at 24 volts to go along with 1170 watts of PV.

    Is this the correct thinking?


    For comparison, we've been running 360 watts of PV with an 880 amph battery bank at 12 volts since 2005. We know we need a better ratio of PV to battery bank but want to make sure we have a balanced system.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: Upgrade suggestions

    stay with the original 2nd system. you may charge a smaller bank faster, but it discharges faster and deeper too assuming both would also have the same loads. this would put the batteries at a lower soc than the original system so i'd go with the 8 concordes.
    of course i am still basing this on your adding the 3 120w pvs you already have as well to make the charge % over 5%, it would be about 3.75% otherwise.
  • rrroae
    rrroae Solar Expert Posts: 46 ✭✭
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    Re: Upgrade suggestions

    Thanks Niel!


    Sorry for all the questions fellas. Want everyone to know I appreciate their patience and knowledge(especially the patience part, lol).
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
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    Re: Upgrade suggestions
    rrroae wrote: »
    From what I've read, the less you discharge AGM's the longer their lifespan.

    Unless I'm mistaken, this is true for any lead-acid type of battery.