12v, 24v, 48v or a combination?

Was all set up and ready to order my inverters then started to question my plans...Help me out here.

My plan was to go with a full 48v system (two 3048 Outbacks) with 3 strings of 4 12v 100Ah batteries and 4 Kyocera 170's as one.

Shading on the panels is not really an issue. I have time limitations with trees in the AM and PM (I do get 5-6 hours a day during the middle of the day, just that the sun runs behind trees long before it approches the horizon).

We are setting the system up primarily for backup right now. Cost is keeping us from adding 16 panels. We are starting with the 4 just to get the system rolling, getting NC's tax credits, and to hopefully augment the grid charging a little bit (should be enough to do the float charge).

The run from the panels to the inverters and batteries is about 60 feet. I've not purchased cable yet and have no problems going with large cables to lessen the voltage drop.

Question is, would it be better to stick with the full 48v system, or should I do some combinations, like 48v the panels, use the MX60 to drop the voltage to say 24 and run two 3024's and rearange the battery strings? Would a 24v panel set up dropped to a 12v inverter/battery set up be wiser?

Comments

  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?

    this is like saying 6 of one and a half dozen of the other. 12v from 48v i would say no to, but 24v from 48v is workable though unnecessary. there may be a slight loss in downconveting, but this could be offset greatly in having earlier/later charging ability and greater cloudy day benefits. you could change your mind on the battery arrangement, but not the inverter voltage input rquirement so you do have to decide now for the future as even a 48v to 48v system is more pv expandability compliant than the 48v in to 24v out system due to the controller's abilities so there's nothing wrong in deciding to go 48v to 48v either. do watch that the voltages are high enough for straight through conversions to take place. if it is the same voltage area as that found on the kc175 go with the 48v to 24v as it would not be an actual 48v pv arrangement to allow 48v to 48v. do remember that the battery system will not be expandable in the future so designing now with more battery capacity to allow the percentages to be around 5% does allow a doubling of the pvs in the future.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?

    Powerless,

    I recommend you consider your complete objective system and then work back from there. The KC175 has replaced the KC170, so let’s use that module as the basic building block for your system.

    Here’s an example of a large PV array and a 48 V nominal system that I believe will be NEC compliant and (just) fall within OutBack’s MX 60 specs.

    Key module specs (STC) of the KC175GT:

    Pmax: 175 W
    Vmp: 23.6 V
    Imp: 7.42 A
    Voc: 29.2 V
    Isc: 8.09 A

    Array specs (STC) (4 modules per series string, five parallel strings):

    Pmax: 20 x 175 W = 3,500 W
    Vmp: 23.6 V x 4 = 94.4 V (note: Very good high ambient temperature compatibility with a 48 V battery system)
    Imp: 7.42 A x 5 = 37.1 A
    Voc: 29.2 V x 4 = 116.8 V (note: Very good low ambient temperature compatibility, but not excellent.)
    Isc: 8.09 A x 5 = 40.45 A

    NEC Calculations vs. Outback specs:

    Temperature Correction Factor (ref NEC 690.7): The NEC temperature correction factor for Chapel Hill’s record low temperature (-8 F; Jaan., 1985) is 1.25. 1.25 x 116.8 Voc STC = 146 V. This is just over the MX’s 140.5 V “suspend operation” spec, but within the 150 Voc absolute maximum.

    As a practical matter, -8 F is in the shallow end of the NEC’s 1.25 correction factor range (the correction factor for -4 F is 1.17), and such low temperatures are very, very rare in your area. The average January low is 27 F. Should the Voc exceed ~140.5 V, the MX will suspend operation until the array warms up and the Voc drops. Little energy will be forfeited due to the very low sun angle.

    Maximum Current (ref NEC 690.8 ): Maximum current = total Isc x 125%; 40.45 A Isc x 125% = 50.6 A -- well under the MX-60’s 60 A input limit including the NEC’s 125% multiplier.

    Performance:

    Assuming cold, clear and sunny mid-day charging of a 48 V battery bank at 50% SOC and 99.5% controller efficiency (a ver rare but possible “alignment of the stars”), the output voltage would be ~52 V and the charging current would be 3,500 W x 99.5% / 52 V = ~ 67 A – just within the MX-60’s user-selectable 70 A output current limit.

    Recommendation:

    Wire the four KC170GT modules in series and go for the 48 V battery bank. Add your new 175 modules in strings of four as you can until you achieve your objective system (there's little difference between the 170 and the 175). If you're planning on having an inspection, you might want to first go over the design with your local inspector. The main problems with choosing a 24 V battery system is that you’ll need two MX controllers (one couldn’t handle the possible ~ 135 A output current, and you’d need larger cables between the controller, batteries and inverters.

    HTH,
    Jim / crewzer
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?

    crewzer,
    recheck your math as there will only be 4 pvs. you added voltages and currents. the currents should not have been added for a series arrangement.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: 12v, 24v, 48v or a combination?

    I would back up and reconsider the entire system from the ground up, especially the batteries.

    What you have for inverters is way oversized for both the panel and the battery capacity - and 12 volt 100 ah batteries are not the best choice for such heavy inverters.

    Think about what you really want to accomplish and consider that the weak link in all battery systems.. is the batteries. Don't really recommend using them for grid tie unless you need the backup power.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?
    Cost is keeping us from adding 16 panels. We are starting with the 4 just to get the system rolling,

    Looks to me like powerless is planning on a 20 module system (~3,500 W). My math is fine.

    Jim / crewzer
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?

    Wind-s2 makes a good point about the batteries. For your planned ~3,500 W array, an appropriate 48 V battery bank would be something ~1,000 Ah. You’ll need 40 12 V x 100 Ah batteries to build this, and the resulting wiring- and maintenance challenges will be daunting.

    Banks this size could be built using big batteries from Rolls, L-16’s (16 of ‘em, in two series strings of eight per string = 16 batteries, good for 48 V x ~800 Ah), or perhaps some big AGM 8A8D batteries (16 batteries, 4 per series string, good for 48 V x ~1,000 Ah). The AGM’s would cost more, but they’d require virtually zero maintenance, and they’re much more recharge-efficient than regular ol’ flooded-cell batteries.

    A twist to all of this is that the initial 740 W sub-array would struggle to charge a bank this size, and it’s usually not a good idea to start with a “small” battery bank and add to it later. However, if you’re planning to start with the “small” 300 Ah battery bank now and then replace it with a full-sized bank later, then that would work.

    So, tell us more about your overall strategy.

    HTH,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: 12v, 24v, 48v or a combination?

    Sorry to take so long to get back to this topic.

    As for my batteries. I get these used telecom batteries for about $12 each. They are 2 years old when I get them and have been "performance tested" by the folks I buy them from. I currently have 16 of them, but one is not charging to capacity so I figured on using 12. I can get more (or less) of them. I can buy them new (to me) once a year and I am offered a pallet of them, last year was 24 batteries, this year was 16, I have to take what is offered if I take any. So their longevity is not real important. If this source ever dries up, I'll switch to "real" solar batteries.

    I ordered the panels before I was ready to do the inverters because I'd heard of shortages and backorders, I figured that it would take weeks or months to get them here, so we called W&S and ordered them up. But instead of waiting weeks (or months), 5 days later I was picking them up from FedEx...I ordered the 170gt's because of all the panels I could find they had the best $/W ratio.

    Our house averages 45KW per day in use. We've gone with as much conservation as we can think of for our day to day. Our big draws (beyond A/C in the summer) is my Koi ponds, 4 big pumps running 24/7. We also have tropical birds so special lighting is necessary and heat a major concern (house heat is natural gas with 110v fan). Wife insists on showering when we are without power, so the 220v well and 110v septic pump must also be available. We also have a hot tub that sucks power all the time. We have constant power drops that last from minutes to days. We have had 6 power outages that have lasted more than 7 days in the last 10 years. Our longest was 14 days after hurricane Fran. We were without power after an ice storm for 11 days 3 years ago.

    So back up is our primary concern with this system, we would like to expand it over time to move us further and further from the grid. I have in been using a 5kw gas generator to provide light, heat and water. But would like to get away from using it for 10-15 hours a day during outages. So we have learned to live on very little power, and can. when necessary, do with very little. When we have outages, I rotate which pond is running (each pond can go 6-8 hours off and 4-6 on and be fine for several days). We concentrate the heat to one or two parts of the house and put the birds in those rooms. We cook on the grill more (electric range). I spend less time reading the boards on the computer...

    I'm still trying to learn the solar stuff. I'm not an engineer, I'm a carpenter. And all this math comes hard. I've called 11 Solar installers from 4 states, only one has come out to the house, when I explained what I had in mind, he said "sounds like a great plan, good luck" and we never heard from him again. He has not returned phone calls or emails. Several installers told me right up front, that if I could not "guarantee" 6 hours of sun a day, they would not come out (with our early and late shading, I can only get 5 hours at the middle of winter). So I'm having to design and build it myself.

    I'm wanting to buy stuff once, and use it "forever". That's why I'm thinking the big inverters, giving me the chance to keep them as my system grows. I'm willing to have my mind changed on my system with good sound advice to back it up.

    So Jim, that's the closest I've got to a strategy...Thoughts, comments and advice accepted and wanted.
  • System2System2 Posts: 6,290 admin
    Re: 12v, 24v, 48v or a combination?

    I'm guessing that you really didn't read everything I wrote in either of the posts. I'm starting this system as back up it will primarily be charged from the grid, we started with the 4 panels simply to get the federal and NC state tax breaks (otherwise I would have held off on the panels for a while longer). We don't even work the 5kw generator hard when we are in back up mode.
  • BB.BB. Super Moderators, Administrators Posts: 29,634 admin
    Re: 12v, 24v, 48v or a combination?

    Powerless,

    If you needs are to have backup power from a few hours to a few days--and you have natural gas. Getting a quiet emergency generator (that runs off of natural gas) with an automatic transfer switch is probably your best bet (money wise). If you must have some electricity in any condition, then keeping the 5kW generator that runs off of gasoline, diesel, or propane as a second backup is wise too.

    Installing lots of solar panels--just for standby use--is not cost effective. If, you install a big solar system with battery backup, with inverters that can be Grid-Tied to the main grid help to supports both your emergency needs, plus for the other 360 days per year, you are helping to reduce your power costs.

    If you still want a, primarily solar powered backup system, then you need to decide how much of that power you will want to supply with solar. The birds, fish ponds, some lights, and water pumping may be all you will want to spend money on. The A/C may need to run from a generator.

    Once you have decided the solar electric load... Say 10 kWhrs/day, then how may days of battery support do you want. Pick 3 days. And you will only want to run the batteries to 50% discharge (because drawing more than 50% from a battery bank will usually ruin them very quickly). Now:

    10kWhrs/day * 3 days * 1/50% = 60 kWhr battery bank.

    Near San Francisco (just out of the fog belt), a 3kW peak Grid Tied system will give you about 5-10 kWhr per day (winter some days much less in poor weather like we had this year) or 10-20 kWhrs/day (summer). Using new parts, that is probably a $20-$30,000 system (installed--no batteries, no power fail backup). My system was to reduce my power bills. I have a small (and quiet) gasoline generator to use during a power failure (those have been few and far between--waiting for the next big earthquake).

    A 18kW Onan standby generator with Natural Gas connection and a 100 amp automatic power transfer switch may cost you $10,000 (plus shipping and tax). And you only pay the fuel bill when the power is out. It seems a standby generator system would be more of a cost-effective solution for your particular needs.

    You could design a system such that the batteries charge from the grid (or generator if the power is out) (wind-s2 or other here can give you help and model numbers to look at)--but without knowing how much power you really need from the batteries during an outage--it is not really possible to give you size/costs/design help... Anything is just a guess.

    A grid tied solar system may be a good way for you to reduce your electric bill. My local power bill for 48kWhrs/day--the top billing tier would peak at between $0.30/kWhr (flat rate) or round $0.47 to $0.52 per kWhr during the afternoon (summer, Time of Use billing)... So, I would not need to be 100% solar, but if I just covered a 1/3 or 1/2 my bill, I could shave off those very high peak rates (and pay closer to $0.11 to $0.30 per kWhr for the part I don't generate with solar). My solar panel system probably costs me around $0.14 to $0.17 per kWhr (after California Sate and Federal rebates/credits).

    The people here really want to help you--but the way you are stating the problem right now--it just does not make a lot of sense (at least to me) to build the system the way you are suggesting right now.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: 12v, 24v, 48v or a combination?

    Bill, Unfortunately in NC with Progress Energy or Duke Power, NO system will ever be "cost effective". When we built our house 18 years ago, we were put on a rate plan...it now works out to about $0.12/Kw. Electricity is cheap. I'll never "pay back" on any system.

    Natural gas here has risen over 220% in the last 4 years, and is only going to continue it's rise. Generators make noise, panels don't. Generators require the uninterrupted delivery of natural gas, or me driving around trying to find a gas station that has both fuel and electricity (been there, done that), batteries require neither.

    I'm not sure why I'm feeling so much resistance to my using solar. I feel as though my needs are simple; I want uninterrupted electricity. I want to minimize running my generator and the need to find/store gas for it. I want to use less electricity from the grid. I want to be able to expand my system, in the future, to use less and less. I want to build a system that is expandable, not just upgradeable.

    I have a starter set of panels here, now. I've built the rack for them and they are ready to go on the roof. I have an electric supply house that has miles of whatever cable I want/need. I have batteries, and access to more. All I need is the chunk that goes in the middle and makes the power available from the panels and batteries usefull for more than jump starting my truck. I have not said that I need to do this cheap, though I don't want to spend uselessly. I just sent out a good sized chunk to NAWS for the panels, and I'm ready to pull the trigger on an Outback PS2 with 2 3048's. This might hint to some of you that I'm willing to spend what is needed to build a system. Just because I'm not willing to spend $40K on enough panels to supply ALL my A/C needs, does not mean that I'm not able to pay for the system I want/need.

    What I need:

    -battery back up for 10 to 15 kw/day for 3 days
    -ability to use 220v
    -expandability/growability

    What I want:
    -easy to use system
    -system that does not require "babysitting"

    I'm a carpenter/woodworker, I spend all day running power tools, I have the ponds, and we have the birds. I realize that my power consumption is huge...but it's the way I live. If I can offset some of that down the road with more panels, more power to me. But my main concern now is to have a system that will kick on when the grid goes down and supplies the electricity that I have to have to keep my birds warm, my fish breathing, and my wife showered and clean...Ding, we are done.
  • BB.BB. Super Moderators, Administrators Posts: 29,634 admin
    Re: 12v, 24v, 48v or a combination?

    OK Powerless,

    What you have asked for is pretty clear (at least to me...). I am not the expert in which model or brand to purchase--but you can start with a block diagram by:

    You saw my numbers for a 10kWhr per day battery storage for 3 days. If you want 15kW/day, then use 90 kWhrs worth of batteries. With batteries, it is hard to make it "expandable" because batteries want to be grouped with other batteries of the same age/history... Example, 3 old batteries and one new battery... The new battery will tend to supply more of the load than the other three batteries (if in parallel)--so the "new" battery will age very quickly and may not last much longer then the older batteries in the string (I think I have my analogy correct). So--it is good that a set of batteries all of the same age and history and therefor you start with the capacity that you need (if you have a second charging/inverter system--you create a second system with new batteries and, of course, that won't affect the old system/set).

    Next, charging... If I recall correctly, I read the specs for one unit here on Wind-Sun that was a really cool grid tied charger/inverter systems that you can program to do almost anything you wish (I will look through the threads here after dinner--if somebody does not find it first). Connect the charger/inverter to a battery bank, a generator, the power grid, and your load(s). You can program the system to charge the batteries from the grid only at night--or during the day if the batteries are low--and/or from the generator (again, day/night options)... And, you can program the inverter to supply power to the grid depending on battery voltage and other conditions). The charger/inverter also had a generator exercise function too.

    I don't remember, but you either connect a separate solar (or wind) charger directly to the battery bus (or it may have been through the charger/inverter) and you can add solar power that way.

    That unit would meet many (if not all) of your requirements listed below... However, that does come at a price. 90 kWhr of battery storage is not small--you will have to replace the batteries, roughly, every 7-15 years. If you get normal storage batteries, you will have to check the electrolite every few months or so and check your cables/wiring.

    The electronics are not that expensive... Wiring, labor, permits will cost something. Batteries, if you get the AGM (sealed) batteries are really nice--last longer but cost more. And, of course the Solar Panels will probably be the single largest cost of your system (if not the batteries).

    So, if you build the basic system out (charger/inverter/batteries) you have the basics. You can add a generator (or use your current one). And, add the solar panels as funding permits (with the caveat that you will probably want the same brand/model panels--or at least figure out which panel units you can intermix--or add a panel/control set at a time... I.E., add 4 panels with a small charge controller. Then get size panels of a different model/manufacturer with a different charge controller, etc.).

    At least, from my limited understanding, I believe the system described above gives you much of what you need at the start (three days of battery power) and the ability to add generator and solar panels when you wish. The major maintenance will be the batteries and generator in any power system. At the begining, the charging will be done from your power line... Eventually you can add a larger generator (probably needed to charge a large battery bank quickly), and eventually, you will be able to sell excess solar back to the grid (assuming that your power company allows).

    Powerless, Is this the kind system block diagram/function(s) you were looking for?

    If yes, I am sure that the others here can give you the exact components that will meet your needs.

    Good Luck,
    -Bill

    PS... One note on the amount of fuel a generator uses... 10 kWhrs is probably less than 2 gallons of fuel in a properly sized generator... So, for even 11 days of off-line fuel storage--that is only 22 gallons (or probably 130 1bs of propane--SWAG--guess) fuel at 10kWhr/day. This is the engineer talking in me--just looking at the price/performance issues. Propane will obviously keep forever. Diesel and gasoline only a year +/-... If you can find a dual/tri fuel generator for your home--that would be ideal. Solar is great--but it is expensive if you are not selling your surplus power back to the utility. -BB
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?

    powerless,
    as far as expandability goes the mx60 is a good controller and you can parallel more as needed, but you may as well compliment it with a set of outback inverters. the ac quality is there and they expand very well if you need them to. grid tie is available as are the entire panels for all of the breakers, controllers, combiners, etc. that you may want or need. see www.outbackpower.com or check on naws for some and their pricing.
    on the point of the batteries i do have to agree get the batteries you will need now for the final system you have in mind. until you are able to have them maintained and charged with as large of a pv system as you designed for, know that the outback inverters do have builtin ac chargers in case you had to use some of the battery power for an outage before you reach your pv goals. you do have to put the power back in and the 4 pvs you will start with will not charge up the full bank you have in mind. i have heard the xantrex are overly rated on their chargers. the 4 pvs you should use to maintain the battery bank until you have the ability to come up with more pvs. if you elect you can go with better batteries like the agms, but you could start off with any other lead acid battery type and i'm sure that after the 7-10 yrs or so, or sooner if something should go wrong, that you should be able to have the full pvs you want and any other adjustments and expansions by that time.
    seeing as you are a carpenter either get a solar installer/electrician to help or take the time to learn about it all and do the install yourself. i'm very sure naws and/or outback could advise you further, even possibly on an installer too. i do know where you are coming from with your outages and i empathize with you on this, but it should be thought out and planned well without hurrying through it. i know the season approaches and you'll be able to get something going before then. if you run into any problems with outback or aren't getting your questions answered to your liking ask here for boB to help you out with those questions concerning the outback systems, inverters, controllers, etc.
    btw it's not that we don't want you to have a system, but we hessitate somewhat in saying for you to get this this and this. we can do that, but we have to be 100% sure of your total wants and needs with any other parameters like costs involved. it will be your system, paid for by your money, and to be within your wants and needs or it comes back on us for giving this kind of advise. we don't get paid to do this, but we try to help anybody out that we can. if you want the best opinion on a system call upon naws again, but even they want to sell you what it is you need and are looking for. therefore, have some patience with all of us and i'm sure it will come together.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?
    What I need:

    -battery back up for 10 to 15 kw/day for 3 days
    -ability to use 220v
    -expandability/growability

    What I want:
    -easy to use system
    -system that does not require "babysitting"

    Powerless,

    OK. Let’s start with a requirement for a battery back up of 10 kWh for 3 days. Assuming a maximum discharge of 50% (down to 50% SOC), you’ll need a battery bank rated at 10 kWh / day x 3 days / 50% = 60 kWh. Assuming a nominal 48 V battery bank, that’s 60 kWh / 50 V = 1,200 Ah.

    Using the 12 V x 100 Ah batteries you have available, you’ll need 48 of these batteries to build the bank. You’ll need to wire four batteries in a series string to create a sub-bank rated at 48 V x 100 Ah,  and you’ll need to wire 12 sub-banks in parallel to create a bank rated at 48 V (nominal) x 1,200 Ah. The bank will need to be physically protected.

    Whether this bank of used batteries of unknown type will be easy to use or will not require babysitting is hard to say at this point. Flooded-cell lead acid batteries (the ones with caps) require venting (to avoid build up of hazardous hydrogen gas) and a fair amount of preventive maintenance (checking water levels and specific gravity in each battery cell, checking connections and for leaks, plus periodic equalization charging).

    Since these are used telecom batteries, it’s likely that they are VRLA (sealed) lead-acid batteries. If so, they’re either gel or AGM technology, and they will require virtually no electrolyte maintenance. They’ll still need protection and periodic mechanical checks for leaks and wiring connection torque.

    At 15 kWh /day, this bank should last about 2 days before dropping to the 50% SOC level, assuming they’re fully charged and healthy. VRLA batteries are more tolerant of deep discharges than are regular ol’ flooded-cell types, so you may be good for ~2-1/2 days.

    Wiring so many battery strings in parallel may create problems. It’s likely that some strings will discharge and charge differently from the other strings, especially when using batteries of different ages, and this will likely lead to reduced overall performance. Temperature variations between “inside” and “outside” batteries within a bank like this may also lead to further performance problems, as the charging voltage for relatively warm batteries is lower than that for relatively cool batteries, and the capacity of cool batteries is less than that of warm batteries.

    The preferred battery solution is to use few strings (one or two, maybe three or four) of big batteries from the same brand, model number and date of manufacture. Accordingly, what you may perceive to be “resistance” from the forum participants is that in this particular case (many strings, small batteries, different manufacture dates), you’re asking for help in deploying a system that most, if not all, of us would not recommend.

    It may also be a reason why your suppliers are balking, as I suspect they aren’t interested in the likelihood of responding to (warranty?) service calls for a system containing a probable major weakness. Frankly I wouldn’t want my name associated with such a system either.

    The issue with the installer’s insistence on “6 hours” probably translates form the design guideline of clear sun from 9 AM to 3 PM (local solar time). Fewer hours of sun resulting from shade means costly service calls (“Why isn’t my $35,000 solar system working right?”) and/or a bigger PV array.

    However, in your defense, that guideline applies primarily to off-grid systems or to consumers looking to ”net-zero” their annual consumption. If your intent is to have a back up, reduce grid consumption and perhaps sell back to the grid a bit, then you can get by with fewer hours of sun and/or a smaller system, as the inverters described below will use their internal chargers to keep the batteries topped off.

    The objective PV system I described above (~3,500 W) is an appropriate match for a battery bank of this size. The calulated charge current (~67 A) is about 5.6% of the battery capacity (1,200 Ah), and that’s a good match. Should you decide to incrementally build your system, and assuming that the batteries are indeed VRLA, then you can probably get by with charge rates as low as ~ 2% while mixing-and-matching the sizes of your battery bank and array.

    Note that a 3,500 W system will likely not allow you to endlessly consume 10 -15 kWh / day with the grid down. Assuming the equivalent of 4 hours of full sun per day and an overall system efficiency of ~67%, your average net energy production will be ~ 3,500 W x 4 hours x 67% = 9.4 kWh. You’ll likely have to find a way to cut back on non-essential loads (i.e., hair dryers  :wink: ) in the event of a prolonged outage

    Since you’re looking for a system using Outback inverters that will be used for both back-up (power your home when the grid fails) and grid-intertie (aka grid-interactive; sell excess energy to the grid), you’ll need to look at their grid-tie (GTFX or GVFX) models. The FX- and VFX models connect to the grid but are not grid-interactive. However, Outback’s grid-intertie models don’t work well (if at all) when using a generator as an AC input source, so, if you also want to use your generator for additional back up, it’ll need to be connected down-stream from the Outback inverters and it therefore won’t charge the batteries without an separate external 120 VAC battery charger. (I hope I got all of that right…  :roll: )

    Since you’ll also need AC and DC breakers and a bunch of other hardware and wiring, you may wish to consider a pre-wired PS 2 system (240 VAC two-phase) that includes two 120 VAC inverters. See:

    http://www.outbackpower.com/pdfs_brochures/PS2%20System-Final.pdf
    http://www.outbackpower.com/pdfs_wiring_diagrams/PS2AC-DCSYSTEM.pdf

    You’ll also need a Hub and a Mate from Outback in order to program the inverters and for the MX controller and inverters to be able to communicate as a system.

    Finally, it may be useful to look for a few more ways to cut energy use, as it can be cheaper to invest in energy conservation that in energy generation.  New fridges use about ½ the energy of old models, and a solar water heater is much more efficient than primarily heating water with solar generated electricity. Both qualify for 2006 and 2007 federal tax incentives. Front-loading wash machines use much less energy and water than do top-loaders, and a solar dryer (a clothes line  :wink: ) uses no utility energy. Compact fluorescent lights are much more energy efficient than are regular ol’ incandescent bu’bs, and they’re now pretty cheap ($10 / six-pak at Home Depot). A big ol’ outdoor propane grill is an alternate to an electric range/stove, and a gas water heater may work as a back up to a solar model.

    I’m tired…

    HTH, and Good Luck!
    Jim / crewzer
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: 12v, 24v, 48v or a combination?

    Your situation sounds very similar to mine. I have grown my system from a single SW4048 with two parallel strings made from class 27 ,105 AH marine battery to present system of two SW4048's, two SW5548+'s and 8 parallel strings (32 batteries, 900 A-H).

    I have gone through three hurricanes in last few years and primary purpose is backup power.

    I prefer 48 v system for anything above 2KW.

    I will probably get jumped on for using marine batteries but you can not ignore the logistics/cost attributes. If I was using system as primary off-grid power source all the time I would go for a better deep discharge batteries. Also will probably get jumped on for eight parallel strings.

    I watch the recharge current and they have stayed pretty will matched. I never let the highest recharge current string draw more then 25% of A-H capacity (in amps). During power outage I recharge batteries when they discharge 40% (60% rated capacity remaining) Can not complain as my original batteries are going strong and reaching over 7 years on them.

    If you are targeting backup/UPS only you should think about float charge power consumption. The lead-calcium batteries have lower leakage then lead-antimony. The difference can amount to a few bucks a month extra on your electric bill for float charging a 1000 A-H plus array.

    The primary attribute of having the battery based system is you can yield about half the gas consumption over just a backup generator because the generator is run at near rated output power just to recharge batteries.

    Last year I had a 15 KW generator and about hour and half in morning and hour and half in evening recharge from generator kept me going. I recently bought a Yamaha EF3000sei and plan to use it as a more or less, continuous run "trickle charger" The attribute is it is lower noise (about 56dbA SPL) then my outside central AC compressor. The only down side is the inverter generators in this size class are only 120 vac and generally do not like to have their neutal side of plug connected to ground. I have two 55 lbs, 2KW isolation transformers to isolate the inverter generator and produce 240 vac, groundable neutral to feed into the two series stacked SW4048's. I limit AC2 inputs to 11 amps max.

    The two SW5548plus's are primarily only for the central AC. Their AC2 inputs go to the 15KW generator inlet.

    I have been looking at adding 5kW worth of PV's to the system. You can not justify based on $ but looking down the road a few years I would not be surprised if the energy situation similar to what happened in California several years back becomes more wide spread. If gas gets to $5-$7 a gallon and you are being subjected to several hours a day of rotating blackouts you will wish you bought the PV panels.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?

    it's always good to hear what some people do and especially in areas known for electrical outages due to mother nature. it does look as though gasoline prices are going to continue rising into the summer so there's a possibility of it hitting $5/gal. the rolling blackouts are happening in texas as it has been unexpectantly hot there sooner than normal. that says something very strongly that we do not have reliable electrical supplies as it would seem anything abnormal or unexpected throws it all for a loop. i imagine in some places it is normal for outages happening routinely without weather or geological causes. this isn't normal for a good electrical utility just to inform you. i also seem to think it would be a good idea for many of you that have survived hurricanes to post your stories in energy use and conservation. go into what worked for you and what didn't work. what was done about everything from lighting to food preservation. the season is nearly here so your experience could be valuable to others and i look forward to hearing some of these. island boy, i know you have experience with it so would you like the honors of starting your story there as we haven't one dedicated to such a thing so that would be the most appropriate section to put it into? i don't want to put you on the spot if you or anybody else doesn't want to do this, but if you do please list out your equipment as a kind of preface to your experience(s).
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?

    i'm not sure what your point is ba as you confirmed that they didn't EXPECT the ABNORMALLY hot weather and that our electrical systems can't always be relied upon. agree or disagree?
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 12v, 24v, 48v or a combination?

    i didn't wish to imply panic, but we are in agreement.
  • System2System2 Posts: 6,290 admin
    Re: 12v, 24v, 48v or a combination?

    What batteries are you using? I just added more today for a total of 4 strings of 48 volt @ 100 AH @ the C8 rate. Hawker 6VF11 and 1 48 volt string of Lucent 4VR125E (115 AH @ c8). There is also a flooded string of 48 volts GNB (500 AH @ C8) The goal is to put this on a buss bar through a Square D QO (Which is rated for up to 48 volts DC) and that way I could turn on or off any string and feed the inverters that way. Like you powerless, I am looking for backup power. You get your batteries for lots less than I do (I am paying $.40 per pound) but I can trade them back in and get more for the same weight @ no charge plus buying the guy lunch. Just wondered if you had thought of a buss system using a breaker panel for the different strings.

    Good luck, and Lacy the 31 year old goffin cockatoo likes to stay warm too. What kind of birds are you keeping warm?

    Skip
  • System2System2 Posts: 6,290 admin
    Re: 12v, 24v, 48v or a combination?

    :-o "Our house averages 45KW per day in use"
    It staggers my mind. With conservation, my use is now in the range of 4 KW per day. I realize not everyone can cut their use to this level, but I do question if any of us has the right to squander such huge amounts of energy, especially from non-renewable sources.
    I have no desire to offend, I just can't control my shock. Sorry.
    Wayne
  • System2System2 Posts: 6,290 admin
    Re: 12v, 24v, 48v or a combination?

    Heh...

    I guess you don't want to hear that I use about 90 KW a day in the summer...
  • nigtomdawnigtomdaw Solar Expert Posts: 705 ✭✭
    Re: 12v, 24v, 48v or a combination?

    Powerless Ive read this thread and Ill keep my reply simple and offer a slightly dirrerent route which may let you have your cake and eat it.

    Take a look at the new Xantrex Xw6048 system soon ? to be launched. It is worth speaking to Solarguppy who has an installed working unit . Check him out at his own forum although he is a regular participant here.

    Stay 48v more efficient and cost effective on charge controllers and wiring. Fact!
    You can wire your PVs to a higher voltage later according to the additional PV you buy at zero cost a bonus feature of the MX60 or XW60 MPPT CC.

    The XW will offer grid tie ability (very high efficency rating) and battery backup with 240/120 vac all in one box. + bonus of more efficient power corrected charging of your batteries from your genset. You can then sell your excess pv power to the grid. Which will be most of the year ! I know this is new yet to be available stuff, but I think were talking days not weeks for public release and it would seem foolhardy not to have a close look at the next generation of stuff be 4 you make your choice !

    Use and abuse what 2nd user batteries you can accumalate from your supplier over the next couple of years your basically getting them free anyway. to provide for grid outages and have a backup genny to support when your early solar/ batteries package cant cut it. Over time when you have built up say a 3/4kw of PV (very modular stuff PVs) and want to polish your system off spend the dosh on a new set of a high capacity batteries in an efficient single string via 24 x 2v mono block cells.

    But b4 any of that . As mentioned on this thread several times b4 consider firstly how to reduce your energy consumption for when when the grid goes down
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