12 or 24 volt sytem help please

Hi, what are the benefits of a 24volt system compared to 12volt? I realize there is less current drawn in a 24volt system allowing reduced wire size but does the reduced current draw also equate to longer battery capacity?

I'm looking at building an off grid system that would be able to power a 37 inch lcd tv rated at 180 watts along with a dvd player, a desktop computer with satellite internet eqpt. and a small indoor dc water pump and a dc freezer (SunDanzer) that draws 40-80 watts and a small microwave, I think you can get them dc powered also.
Could I get by with a 1800 watt inverter?

Any equipment recommendations?

MPPT charge controller?

Inverter? I'm leaning towards a Xantrex Prosine 1800.

Solar panels?

Batteries? This is really hard for me to choose. Flooded, Gel, AGM. Cost/benefit!

Any help would be greatly appreciated, thanks!

Comments

  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: 12 or 24 volt sytem help please

    welcome,
    there is another advantage in that the batteries may be kept in series rather than parallel. a series arrangement helps to keep the charging/discharging on the batteries more even and is more forgiving. once one goes into parallel there is a better chance of an imbalance that could affect battery life. don't get me wrong here as parallel can be done, but most everyone here agrees that 2 in parallel be it strings or single batteries is fine and that more than that is pushing one's luck on the odds of something going amiss.

    anyway, it is nice that you want to power these things, but you need to know for how long for each item.

    the rest is kind of up in the air until more info can be given, but i will say that many do go with golf cart batteries to start with so a mistake could be less costly.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 or 24 volt sytem help please

    Welcome to the forum.

    This is probably the first thing you should look at: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    Beyond that, it is vital to get some numbers on how much power you need. The more power you need to store up, the more beneficial the higher system Voltage will be.

    A Prosine 1800 is a 12 Volt inverter, and perfectly capable of running the equipment you list. But depending on the total Watt hours you need to have on hand a 24 Volt system may make more sense. It usually does, btw.

    The DC water pump and freezer may not necessarily be a good choice either. If you're going to have an inverter running anyway, making the most use of it is to your advantage.

    Once you do get the maximum Watts and total daily Watt hours figured out you can size the battery bank and inverter. The panels and controller is determined by how much battery you need to recharge. For a first set of batteries flooded cells are usually the best choice; they are inexpensive for the power they produce and are more forgiving of mistakes. Gel batteries are definitely not a good choice for RE.

    If you've got any of the equipment you want to run (or even similar), get yourself a Kill-A-Watt meter and start measuring how much power the stuff uses under real operating conditions. It is essential information for planning an off-grid system.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: 12 or 24 volt sytem help please
    DaveHaze wrote: »
    Hi, what are the benefits of a 24volt system compared to 12volt? I realize there is less current drawn in a 24volt system allowing reduced wire size but does the reduced current draw also equate to longer battery capacity?

    It will not directly change battery capacity in that the total watt-hours will always be the sum of the watt-hours of the individual batteries. But there is a critical difference:
    With a higher voltage you can get the total energy capacity you need by putting high AmpHour low voltage batteries in series instead of putting lower AmpHour (and maybe higher voltage) batteries in parallel.
    Any way you can avoid having to put batteries in parallel will make it much easier to maintain your batteries in good health.
    Putting batteries in parallel can lead to unequal drain from the batteries under load and unequal charing rates during recharge. Those inequalities can be made worse in a self-feeding way by differences in battery temperature.
    With a series string, all batteries are forced to deliver exactly the same current, regardless of temperature and other differences. It is still important to keep the capacity of batteries in the series string well matched. This means do not mix different battery types of same Amp and Volt ratings and do not mix new batteries with older ones.
    SMA SB 3000, old BP panels.
  • bill von novakbill von novak Solar Expert Posts: 864 ✭✭✭✭
    Re: 12 or 24 volt sytem help please
    DaveHaze wrote: »
    Hi, what are the benefits of a 24volt system compared to 12volt? I realize there is less current drawn in a 24volt system allowing reduced wire size but does the reduced current draw also equate to longer battery capacity?

    Not in and of itself. 2kwhr of battery storage is still 2kwhr.

    However it will tend to reduce losses overall - and that will lead to longer battery runtimes.
    I'm looking at building an off grid system that would be able to power a 37 inch lcd tv rated at 180 watts along with a dvd player, a desktop computer with satellite internet eqpt. and a small indoor dc water pump and a dc freezer (SunDanzer) that draws 40-80 watts and a small microwave, I think you can get them dc powered also.
    Could I get by with a 1800 watt inverter?

    Get a kill-a-watt meter and measure the microwave. They are typically around 1000 watts. If your loads are together less than 1800 watts then you're good.
    Inverter? I'm leaning towards a Xantrex Prosine 1800.

    I've used one and it worked well for me. Go with 24 volts unless you have a good reason not to (like 12V appliances you want to run.)
    Batteries? This is really hard for me to choose. Flooded, Gel, AGM. Cost/benefit!

    Flooded - cheaper. AGM - longer lasting, easier to keep indoors, less tolerant of abuse.
  • icarusicarus Solar Expert Posts: 5,313 ✭✭✭✭
    Re: 12 or 24 volt sytem help please

    You could probably get by with a sure sine 300 inverter if hitch the micro wave. Micro waves are notorious high current draw items, so that even thgh they may say "500 watts" they tend to draw very much more at least while starting. Another suggestion is to turn the desk machine into a good lap top, which will drop the power to -~100 watts or less. SAT ISP will draw ~30 watts.

    Tony
  • PhotowhitPhotowhit Solar Expert Posts: 5,011 ✭✭✭✭
    Re: 12 or 24 volt sytem help please
    A Prosine 1800 is a 12 Volt inverter, and perfectly capable of running the equipment you list. But depending on the total Watt hours you need to have on hand a 24 Volt system may make more sense. It usually does, btw.

    Prosine can be 12 or 24 volt, Mine is 24 volt. ...adding to the confusion there is a Prowatt 2000, also a 1800 watt inverter though called a 2000( I think, only made in a 12 volt version) which is made by the same parent company, Xantrex/Schnieder. It is very inexpensive starting around $350, Prosine 1800 likely start around $1000-1200, come in 12 and 24 volt models and assorted outputs as well.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • DaveHazeDaveHaze Registered Users Posts: 4
    Re: 12 or 24 volt sytem help please

    Thanks for the replies, is it better to run dc appliances directly rather than go through an inverter. I thought there were losses converting dc to ac so that is why I looked at the dc freezer specifically. I added up the wattage of everything I need to run and it is 1185 watts total, most of it coming from the dc powered microwave (660 watts) which will be off mostly. The only device that will be on all the time is the freezer at 40-80 watts draw. Not sure what the daily watts will be, my best estimate is 3680 watts. I will have a generator to charge the batteries if the solar panels can't during winter periods. Can the battery bank, charge controller and solar panels needed be determined from this? Thanks!
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 12 or 24 volt sytem help please
    DaveHaze wrote: »
    Not sure what the daily watts will be, my best estimate is 3680 watts.

    I think (hope) you mean 3680 wattHours. I think you should ditch the DC only idea. Modern sine wave inverters are pretty efficient. You can buy one that includes a high quality battery charger and a transfer switch (for the generator input). DC wiring is inefficient and DC switches are hard to find and expensive. AC appliances are more efficient than ever and are much less expensive than comparable DC appliances. The money you save on an AC freezer will buy enough panels to more than make up the lesser efficiency (if it is less efficient) of the AC freezer.
    DaveHaze wrote: »
    Can the battery bank, charge controller and solar panels needed be determined from this?

    Yes! By understanding your loads you are way ahead of most new forum participants. (btw, welcome to the forum). One more thing we need to know is your location so we can determine your solar insolation.

    After determining your loads, the next step is to decide on battery voltage and capacity. That can be a difficult decision. The rest is easy... just buy enough panels and electronics to keep your batteries happy. Living off grid is all about keeping your batteries happy.

    If your daily load is 3700 watthours, you want a battery with a capacity of about 10-15 kilowatthours. You never want to discharge your batteries below 50% SOC (state of charge), and it is much better to cycle them on a regular basis to about 80% SOC.

    At 24 volts you would want a battery capacity of 400 - 600 amphours. Now which battery? The most important thing is to have just one series string of batteries. There are a number of choices. My personal preference (others will differ) is to use cheap mass produced batteries. That means golf cart batteries or L16 batteries. These batteries are 6 volt and you would need 4 in series. Unfortunately, to get the capacity you need, you would need 8 of these batteries (two parallel strings). Something to consider is going with a 48 volt system. Then you could have those same 8 cheap batteries in series. Of course you could stick with 24 volts and use higher capacity, more expensive batteries. One advantage of 24 volts (over 48 volts) is that you have only 12 (rather than 24) pools of sulfuric acid to maintain.

    Anyway, the ball's in your court now... since you know your loads its time to pick your battery. Then we can talk about balance of system.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • bill von novakbill von novak Solar Expert Posts: 864 ✭✭✭✭
    Re: 12 or 24 volt sytem help please
    DaveHaze wrote: »
    Thanks for the replies, is it better to run dc appliances directly rather than go through an inverter. I thought there were losses converting dc to ac so that is why I looked at the dc freezer specifically.

    There are. However DC wiring is more lossy in general because currents are higher and voltages are lower. If you have to make long runs with medium to high power devices you may end up with less loss overall by using an inverter. (Not because it's AC, because it's 120V instead of 12 or 24V.)
    I added up the wattage of everything I need to run and it is 1185 watts total, most of it coming from the dc powered microwave (660 watts) which will be off mostly. The only device that will be on all the time is the freezer at 40-80 watts draw. Not sure what the daily watts will be, my best estimate is 3680 watts. I will have a generator to charge the batteries if the solar panels can't during winter periods. Can the battery bank, charge controller and solar panels needed be determined from this? Thanks!

    Yes. (Vtmaps answered that pretty well.) Note that your generator will give you a bit more flexibility since you'll be able to do full charges of a larger battery bank (if, for example, you're going to wait on building out your array to 100%.)
  • DaveHazeDaveHaze Registered Users Posts: 4
    Re: 12 or 24 volt sytem help please

    Yes, I meant 3680 watt hours. And I see what you mean about giving up on the dc appliances and going with ac. My location is Colorado and looking at the gps it indicates I'm at N40 50.342 if that helps to determine solar insolation. So I should go with a 24 volt system as everyone recommends and what wattage solar panels do you guys advise I get? Would four L16 type batteries in series with 370 ah each work out well or do I need eight (less ah rating) batteries in a series parallel arrangement? Any recommendations on the other eqpt. like mppt charge controller and what size inverter and brand? Thanks!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 or 24 volt sytem help please

    Let me throw some fun generalized math at you.

    3680 Watt hours AC. Inverter about 90% efficient, so that's roughly 4kW hours on the DC side. Plus the inverter consumption (say 480 Watt hours). So you need 4.5kW hours of storage in your batteries. At 24 Volts that's about 187 Amp hours. That's a minimum 375 Amp hour battery bank. For 25% DOD it would be twice that: 750 Amp hours.

    Now using that as an example, you'd want a 10% peak charge current or 75 Amps @ 24 Volts. That's 1800 Watts, less typical panel & controller derating: 2337 Watt array.

    With me so far?

    So the L16's at 370 Amp hours would work, but you'd be better off with eight (two parallel strings of four) or going up to a 48 Volt system. On a 48 Volt system you'd only need 37 Amps peak charge current, and that's the difference between an FM80 or Classic 150 running full out and just about any 60 Amp MPPT controller leisurely doing its job.
  • DaveHazeDaveHaze Registered Users Posts: 4
    Re: 12 or 24 volt sytem help please

    I see what you mean. I'm looking how I came up with the 3680 watt hours and I need to get some more accurate info on that. It is the watts consumed by a device times the hours it is drawing that power?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 12 or 24 volt sytem help please
    DaveHaze wrote: »
    I see what you mean. I'm looking how I came up with the 3680 watt hours and I need to get some more accurate info on that. It is the watts consumed by a device times the hours it is drawing that power?

    Yes. A 100 Watt load running for 1 hour is 100 Watt hours. So is a 50 Watt load running for 2 hours.
    The biggest problem with determining loads is trying to go by the power ratings on the device. In another recent thread this was pointed out quite nicely by the tag reading "5.3 Amps @ 120 VAC" which would indicate 636 Watts. The flaws are that it is a maximum 5.3 Amps and the refrigerator does not run constantly.

    This is why Kill-A-Watt meters are such an invaluable aide.
  • PhotowhitPhotowhit Solar Expert Posts: 5,011 ✭✭✭✭
    Re: 12 or 24 volt sytem help please

    Something else to consider... at 8 - L16 Your spending a pretty good chunk of change, and you might go back to a 24V forklift battery (I paid @$2550 delievered for a 24V 800Ah battery), there are reports of forklift batteries lasting as long as 20 years. L16's would average 5-7 maybe 7-10 for Trojans.

    ...but, for your first setup, I might well go with 4 L16 or 8 smaller golf cart sized batteries(In a 48 volt configuration) as the first time out often people misjudge usage or configuration of their system, or don't pay enough attention to their system(or understand what is happening) and end up killing off the batteries....
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 12 or 24 volt sytem help please
    DaveHaze wrote: »
    I see what you mean. I'm looking how I came up with the 3680 watt hours and I need to get some more accurate info on that. It is the watts consumed by a device times the hours it is drawing that power?

    Yes, the watts times the hours is the watthours. By the way, you usually cannot figure out the watts that an appliance consumes by looking at the nameplate... you need a kill-a-watt meter. Many appliances specify the amps and volts that they use, but you cannot calculate the watts (or watthours) from that info.

    As far as the balance of the system, take a look at the midnite prewired E-panels:
    http://www.solar-electric.com/ouinsy.html
    They come complete with inverter/charger, charge controller, shunt for a battery monitor, all circuit breakers and disconnects, DC ground fault, lightning arresters, and inverter bypass switch. All safe and meets code.

    Just screw them to the wall, connect the battery, the generator, the ground rod, connect the cable from your combiner box, and connect the AC output to your main circuit breaker panel.

    When you start the generator, the inverter will automatically become a battery charger and the generator output will be fed through to the house.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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