New Off Grid PV system guidance

mtang45
mtang45 Registered Users Posts: 8
I'm putting in my first off grid PV system at a remote location that I get to about once every 3 months. I have a growing collection of vehicles, equipment, etc that have batteries, and I'm getting tired of buying new batteries every year. So, the initial desire was to run battery maintainers and to have some lights at 115v; no appliances or anything heavy. THEN, I had an opportunity to have a well put in that I couldn't resist, so add to the maintainers and lights a .75 hp pump at 230v.

I have been studying this awhile and have gained some knowledge by perusing forum posts; however I am still very much an amateur with electrical things so all help is much appreciated.

I have gathered the following and would like to start installing in the next few weeks.

4 - Canadian Solar 250w 24v panels in parallel
1 - Midnite Solar Kid 24v Charge controller
8 - Trojan T-105 6v 232ah batteries (2 strings in parallel/ of 4 batteries in series)
1 - Cotek 1000w 115v inverter
1 - Cotek 1500w 230v inverter

Wire gauge:
I plan on running the PV panel wires to a buss bar and then 6 ga wire to the charge controller.
From the controller to the battery banks 6 ga.
Between the batteries and to the battery buss bar 4 ga.
From buss bar to both inverters 2 ga.

So bottom line, does the equipment match up reasonably well? Are the wire gauges correct? And last but not least, where do I insert fuses and how big?

Thanks much!

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: New Off Grid PV system guidance

    Whoa !

    1) I doubt the 1500 w inverter will do more than blow a fuse with a 1.5hp motor on it. (my inverter logs 1Kw on a 0.5hp pump) Starting surge is at least 5x running load.
    Power Factor of the pump motor and motor efficiency gets you here.

    2) the 1,000w inverter is way too big, and will consume a lot of power just in idle. Look for an inverter that will be 80% loaded with your normal loads.

    460ah of batteries needs about 45a of charge current to keep the electrolyte stirred up. On a good day your panels could possibly produce 30A, a bit short.

    keeping batteries on long term float - I don't know if they are all the same style, and could share a charger, but if you mix Low Maintenance, standard starter, or anything else, you will need a different charger for each battery. And, on float, they only need an hour or 2 a day, of charge, to keep them alive.
    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 ,

  • mtang45
    mtang45 Registered Users Posts: 8
    Re: New Off Grid PV system guidance
    mike95490 wrote: »
    Whoa !

    1) I doubt the 1500 w inverter will do more than blow a fuse with a 1.5hp motor on it. (my inverter logs 1Kw on a 0.5hp pump) Starting surge is at least 5x running load.
    Power Factor of the pump motor and motor efficiency gets you here.

    2) the 1,000w inverter is way too big, and will consume a lot of power just in idle. Look for an inverter that will be 80% loaded with your normal loads.

    460ah of batteries needs about 45a of charge current to keep the electrolyte stirred up. On a good day your panels could possibly produce 30A, a bit short.

    keeping batteries on long term float - I don't know if they are all the same style, and could share a charger, but if you mix Low Maintenance, standard starter, or anything else, you will need a different charger for each battery. And, on float, they only need an hour or 2 a day, of charge, to keep them alive.


    Mike,

    Thanks for the input! I need to correct my post on the pump; it is actually .75 HP. The 1500W Cotek is rated at 3000W surge, so I thought this would be sufficient. Please let me know if you think its still not enough. As far as the array size for charging, I used the bank capacity of 460 AH / the charge rate of 30A to get a C/15 charge rate, which I had interpreted as adequate, especially since I use the system for a couple of days every other month. Can you explain why 45A would be necessary? The 1000W Cotek uses .15A on standby and would only power a battery maintainer (for my vehicles) on a continuous basis; naturally when I'm not there the 1500W Cotek would be switched off. Still too much draw?

    Thanks!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: New Off Grid PV system guidance
    mtang45 wrote: »
    The 1000W Cotek uses .15A on standby and would only power a battery maintainer (for my vehicles) on a continuous basis; naturally when I'm not there the 1500W Cotek would be switched off. Still too much draw?

    But it may draw 6-20+ watts when the inverter is "on"... So when the battery maintainer is drawing 5-10 watts (typical inverter "turns on" with a >6 watt load), your load on the battery may be 11-30+ watts * 24 hours per day. That can be very significant and kill your battery bank if there are a few cloudy day in a row when you are not there.

    Other options, get small solar panel+charge controller and put one on each vehicle (or larger panel + multiple small charge controllers to charge a "group" of batteries or vehicles parked together).

    http://www.harborfreight.com/15-watt-solar-battery-charger-68692.html
    Solartech 10 Watt Multicrystalline Solar Module
    SunGuard 4.5 Amp 12 Volt Solar Charge Controller

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Off Grid PV system guidance

    You don't need the pump when you're not there, right?
    Building the system up to power that (surge demand could be well over 2kW, even over 3kW) will cause a lot of unnecessary expense. You would not only need a large inverter (do not rely on surge ratings for this) & 240 VAC but also a big battery bank to be sure there's enough power to handle the pump demand.


    My advice is: keep the batteries up with the solar, run the pump from a gen as-needed.

    As for the other equipment spec'd, the 1,000 Watts of solar will only slightly exceed the Kid's capacity so that is not a problem. But 30 Amps may not be sufficient for 464 Amp hours of battery. You probably do not need that much battery just to maintain the starting batteries in the vehicles.

    You do not want to run those panels all in parallel: the Vmp is too low for a 24 Volt system and also if you put them all in parallel you'd need a combiner box with breakers or fuses on every panel. Run two parallel strings of two in series; solves all the PV wiring and Voltage issues.

    You really need to know what the loads will be. How many maintainers? How much will each draw? How much if they are all on at once? You also could benefit from having them not on all the time; some timers could be used so that they would only be on during the daylight hours, and/or use of a Voltage controlled relay to make sure they are off if the batteries are low (do not rely on non-programmable LVD on inexpensive inverters for this).

    Frankly the batteries should last 3 months left on their own, even with today's built-in parasitic automotive loads. A battery that won't is no good and needs replacing anyway. You could just fire up a big, cheap gen when you get there and charge everything at once while you do whatever you need to do including running the pump. Investing in a lot of solar equipment that most of the time will not be fully utilized doesn't make economic sense.
  • mtang45
    mtang45 Registered Users Posts: 8
    Re: New Off Grid PV system guidance
    You don't need the pump when you're not there, right?
    Building the system up to power that (surge demand could be well over 2kW, even over 3kW) will cause a lot of unnecessary expense. You would not only need a large inverter (do not rely on surge ratings for this) & 240 VAC but also a big battery bank to be sure there's enough power to handle the pump demand.


    My advice is: keep the batteries up with the solar, run the pump from a gen as-needed.

    As for the other equipment spec'd, the 1,000 Watts of solar will only slightly exceed the Kid's capacity so that is not a problem. But 30 Amps may not be sufficient for 464 Amp hours of battery. You probably do not need that much battery just to maintain the starting batteries in the vehicles.

    You do not want to run those panels all in parallel: the Vmp is too low for a 24 Volt system and also if you put them all in parallel you'd need a combiner box with breakers or fuses on every panel. Run two parallel strings of two in series; solves all the PV wiring and Voltage issues.

    You really need to know what the loads will be. How many maintainers? How much will each draw? How much if they are all on at once? You also could benefit from having them not on all the time; some timers could be used so that they would only be on during the daylight hours, and/or use of a Voltage controlled relay to make sure they are off if the batteries are low (do not rely on non-programmable LVD on inexpensive inverters for this).

    Frankly the batteries should last 3 months left on their own, even with today's built-in parasitic automotive loads. A battery that won't is no good and needs replacing anyway. You could just fire up a big, cheap gen when you get there and charge everything at once while you do whatever you need to do including running the pump. Investing in a lot of solar equipment that most of the time will not be fully utilized doesn't make economic sense.

    Thank you for the advice. So I can see where running the panels in series/parallel to get 60v and 500w gets more quality charge time during the day; good suggestion. But that only gets 8A into the charge controller (if I understand correctly) and therefore the charge on the battery bank is very weak. Taking the well pump out of the equation, since I also want enough power to run a few lights and maybe some small power tools (in addition to the maintainers) on the days I'm there, should I still cut back on the battery bank size to get the charge rate more acceptable, OR should I go ahead and add panels to bring the charge rate up to an acceptable level.

    As far as the batteries lasting for 3 months, I know I said I get down there every 3 months or so, but in reality, there is usually a 4 or 5 month period every year that they are unattended (mostly winter). I like your idea of a timer to control the charge times rather than have the maintainer run 24/7. Could I also move the timer upstream in front of the inverter to eliminate the standby draw?
  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    Re: New Off Grid PV system guidance

    isn't 500W Kicked down to 12V by the Charge Controller 41.666666 Amps?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: New Off Grid PV system guidance
    mtang45 wrote: »
    Thank you for the advice. So I can see where running the panels in series/parallel to get 60v and 500w gets more quality charge time during the day; good suggestion. But that only gets 8A into the charge controller (if I understand correctly) and therefore the charge on the battery bank is very weak. Taking the well pump out of the equation, since I also want enough power to run a few lights and maybe some small power tools (in addition to the maintainers) on the days I'm there, should I still cut back on the battery bank size to get the charge rate more acceptable, OR should I go ahead and add panels to bring the charge rate up to an acceptable level.

    Nope. MPPT charge controller: Watts in is nearly equal to Watts out.
    1000 Watts * 0.77 efficiency / 24 Volts nominal = 32 Amps out.
    It will not give you any power advantage on cloudy days because PV is a current source; the current is not derived from Voltage differential so there is no advantage is running higher V.
    It will make certain there is enough Voltage to actually charge the batteries at 28.8 Volts or more after accounting for V-drop from hot panels and wiring losses. That's the part that's most important.

    Without determining exactly what your loads are you're playing a guessing game with battery size. In such a case you have to ask "what will happen if the system is too small or too large?" The latter is easy; you spend too much money on stuff you really didn't need. The former can be more problematic.
    As far as the batteries lasting for 3 months, I know I said I get down there every 3 months or so, but in reality, there is usually a 4 or 5 month period every year that they are unattended (mostly winter). I like your idea of a timer to control the charge times rather than have the maintainer run 24/7. Could I also move the timer upstream in front of the inverter to eliminate the standby draw?

    Well the good news there is that a battery stored in Winter has a lower self-discharge rate than in Summer. It would be best to disconnect the batteries, charge them fully, then leave them alone. A good battery should not go dead on its own even in half a year. Case in point: I let one of our cars sit all Summer this year without even a solar panel on it (really those little ones are useless, btw) and when I needed to start the van this past month when its battery had died of age I just pulled the smaller battery out of the other car and hooked up the jumper cables. Then I recharged it fully and put it back.
  • gww1
    gww1 Solar Expert Posts: 963 ✭✭
    Re: New Off Grid PV system guidance

    I had two cars parked in a garage for two years and only came home every 6 months. I only had to jump start one car one time and used the battery till the waterpump went out. Another year.
    gww
  • mtang45
    mtang45 Registered Users Posts: 8
    Re: New Off Grid PV system guidance

    Thanks for the great advice. I ordered 2 more panels today so I can run 3 parallel strings of 2 panels in series. So I will be pushing 60V 750W to the charge controller. Enough for the batteries?
  • mtang45
    mtang45 Registered Users Posts: 8
    Re: New Off Grid PV system guidance

    Added info: The 4 bank battery tender draws .2A on float for each charger so .8A if all are active. I have 7 batteries in equipment/vehicles that need maintenance, so I will need 2 - 4 bank tenders. I'm guessing that I can put those on timers and one day per week alternate tenders. Run them for 6 hours during daylight to minimize battery drain. So one day per week will have approximately 550 watt hours. When I'm there (every other month) I may run 100W of lights for 4 hours on 2 consecutive days, plus some minor use of small power tools, maybe a laptop for an hour, and a phone charger. The well pump is out of the picture for now, so my question is, am I big for my usage or too small?