Grid Backup Question

Please help me decide:

I have a crude backup system, for which i want the best controller possible-- But only for optimum charging feature.

I don't need multiple, higher voltage, PV input options.

Over the years, i have neglected previous batteries, as they no longer charge to the full... Yet i never sufficiently monitored or really used them-- The 4KW inverter size was mainly for emergency water pumping needs, in worst case outage. I do plan on the supplemental DC lighting, to get some regular benefit.

I might try a desulphurator but read doubtful comments here.
I want new batteries, if need be, but back to charge controller:

Is there a better, plainer charge-contoller than my original
C40 Trace Controller, very old unit? (now Xantree, branding change)

My Back UpSystem:
4 T105 Trojan batteries
4 x Kyocera PV panels 135W 12V
1 Magnum MS4024

Thanks for insights.

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Grid Backup Question

    Welcome to the forum.

    The question is: what's wrong with the C40? Has it failed?
    Most PWM charge controllers work pretty much the same, and there's certainly nothing wrong with the C40's design. Your panels probably put out a maximum of 15 Amps on a 24 Volt system so you could use a smaller controller but there's nothing wrong with using the C40. Your T105's are 250 Amp hours max @ 24 Volts so you should have enough charge current, about 6% rate which is fine for a back-up system.

    Maybe I'm missing something, but I don't see a problem here.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Grid Backup Question

    Rogue has a new controller coming out around the end of December (last I read)--His other two previous models had good pricing, support, lots of features, and seem to be reliable and efficient MPPT controllers from posts here (30 amps 12/24 volt MPPT charge controllers). If you could wait, would probably be a very nice upgrade for you (mostly data logging, computer connection, etc.).

    Otherwise, the MorningStar 15 and 45 amp TSW charge controllers are good units to look at too.

    The 4kW inverter--Pretty much overkill on that small of bank--Trying to find a smaller inverter for your day to day loads would also be a good idea.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bo atkinson
    bo atkinson Registered Users Posts: 4
    Re: Grid Backup Question

    Thanks for both replies. Yes, there are a number of other factors here... In the earlier days, the batteries (when new) had only60 watts of PV panels, which i had hoped would keep them happy and idled. The oversized inverter was for my deep well pump, which, in a worse case might become a priority-- Even if only to run it briefly.... We actually went gridless for 15 days in the ice storm of 1998, here in Maine, (with a low sun angle in winter). In some ways that seemed better than wild windy forest fires, (in case we get droughts).

    My backwards approach into PVs was spurred into action, by the many rumors of pending calamities. (Some fairly persuasive voices and events still increase). I figured i could build and upgrade my system gradually. Maybe ad micro hydro, since we get a few months of that. I'm a well equipped tinkerer, but it all takes time, which comes gradually, especially as economic opportunities dry up. There's no wind here in the woods though.

    A quick look at the Rogue looks interesting... Although i still need to study a lot about keeping an 'idled' system healthier than in past...I wonder if there is an article to study on that? I'm much closer to wiring in my collection of LEDs for lighting.. Start getting some regular uses. Perhaps get a tiny-efficient inverter for my Macs... To bad the Rouge doesn't seem to support Mac OSX. I love the idea of getting a snap shot of system condition, every day. I do already have a good read out of the voltage, maybe enough? I think i need to learn, if and how to adjust charging, if that is the point of PC connections to controller.

    Bo
  • bo atkinson
    bo atkinson Registered Users Posts: 4
    Re: Grid Backup Question
    Thanks for both replies. Yes, there are a number of other factors here...

    I also have a small UPS for efficient computer-modem uses and an older, modest pulse-shaped inverter for mid range use... In case of dire outages, when it will be worth wiring these up for less loss. A hackers collection of options, to use as events unfold.

    My efforts in posing here is to see what new procedures i can learn to preserve batteries... Preferably just to float on the 60 watt panel set, for now. I don't get why that failed with the C40. My bigger PVs are not quite installed yet as i'm still trying to discern the the trade-offs between higher DC voltage controllers, (like the Classic Lite). I just don't understand how these units can convert DC to DC efficiently ... In my case where i might have enough copper on hand to input the PVs to battery space, with low resistence-losses. If i install a micro hydro, it will be a 120v AC and i have some recycled copper wiring, good for that. I'd still need to build a frost roof turbine though. (I've collected builder-wastes for decades).

    The idea of investing in new batteries sooner than later pivots on the possibility of immanent dollar devaluation [??]

    The tardiness of completing installations is due to other priorities-- Calamity always jump starts upgrade-installations.

    An unusual predicament, which IMHO might become more popular, actually, as people wake up to global events transpiring.


    Another question-- Re the leading controller tech, coming to market.... Are any them going to address mixing together disparate source voltages and currents, all at the same time? It would seem that wind and PV combos might present this aspect. While the hackers might want to add in still other odd sources as well. I've studied older electronic tech and mostly ask for key words or terms, to google, (to learn more).

    Thanks.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Grid Backup Question
    I figured i could build and upgrade my system gradually.

    This is nearly impossible, depending on your definition of "upgrade". The larger the power demands on the system, the more the system has to change. You end up with little that can be adapted to the larger system. If you can plan "what I have now" and weigh it against "what I'll need later" it can work, but usually you end up putting in a whole new system. This can be in parallel with the old one or a complete exchange. This explains one of the main reasons: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    Batteries don't really care how they're charged, so long as they're charged. In that respect one controller works pretty much the same as another, regardless of type. But there is absolutely no way to keep batteries from declining over time. You can slow the rate, but you can not stop it: they steadily lose capacity and die. You should read through this battery FAQ to begin with: http://www.solar-electric.com/decybafaq1.html

    As for MPPT controllers, the big advantage is in flexibility of array design. If there's quite a distance needed between the array and controller then running the power as higher Voltage/lower current reduces over-all power loss. Yes, there is some trade-off in controller efficiency the greater the difference between array and battery Voltages. This is why it is recommended to not go any higher that 2X on the nominal (24 Volt system with 48 Volt array for example). But sometimes it is necessary and sometimes it is a trade-off of efficiencies (loss in wiring vs. loss in controller). These losses are greatest at maximum power (during the Bulk stage) of course. Even so, the difference in controller efficiency over its input range is not great (nearly always less than 10%, depending on which controller).

    The other design advantage of MPPT is in the ability to use just about any panel on any system Voltage. These days the "grid tie" panels are the cheapest per Watt, but they tend to have a Vmp around 30 which is too high for a 12 Volt system and too low for either 24 or 48. The MPPT controller doesn't care; put some in series and it will handle the Voltage conversion.
    Are any them going to address mixing together disparate source voltages and currents, all at the same time?

    Boy oh boy is that ever a topic of discussion around here! :D The latest: http://forum.solar-electric.com/showthread.php?17716-Outback-Lack-of-Bulk-Charge-integration-anniversary-rant

    BTW, I've been around this tired old world more than half a century and there is nothing going on now that hasn't been going on in all that time and before. The major change is that we now live in an era of instant communication which lets us hear about everything as it happens. Unfortunately we also live in an era of instant hyperbole and what we hear is exaggerated sensationalism geared to attract attention rather than inform. As a result, no matter what the news story says you can be sure it isn't accurate. Sad, but true.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Grid Backup Question

    For "floating" a battery bank, you probably only need 1% rate of charge, for an operational system, you should be looking at 5% to 13% rate of charge (just a starting rule of thumb):
    • 29 volts charging * 225 AH bank * 1/0.77 * 0.01 Rate of charge = 85 watts array minimum array for float
    • 29 volts charging * 225 AH bank * 1/0.77 * 0.05 Rate of charge = 424 Watt array minimum for battery bank (operational off grid)
    • 29 volts charging * 225 AH bank * 1/0.77 * 0.10 Rate of charge = 847 Watt array nominal
    • 29 volts charging * 225 AH bank * 1/0.77 * 0.13 Rate of charge = 1,102 Watt array "cost effective maximum"

    With a 85 watt array, you would still need an AC battery charger (AC Mains, Backup generator powered) of 5% to 25% (maximum recommended). If possible, get a charge controller with remote battery temperature sensor for charge rates over ~13% rate of charge:
    • 225 AH bank * 0.05 Rate of charge = 11.25 amp minimum charger
    • 225 AH bank * 0.10 Rate of charge = 22.5 amp nominal
    • 225 AH bank * 0.13 Rate of charge = 29.25 amp max nominal
    • 225 AH bank * 0.25 Rate of charge = 56.25 amp max recommended/not to exceed

    Besides the usual of checking water levels once a month (never expose plates, do not over fill, use distilled/deionized water). Cycle the battery bank a few times a year to ~75% SOC or a bit lower, and recharge. Check SG between cells and equalize if Specific Gravity readings between low and high cells are over ~0.015 to 0.030 difference or more (equalize is fully recharge bank, then with ~5% rate of charge, continue to charge and check SG every 30 minutes--stop when SG stop rising--log temperature corrected SG and this will be "new full charge" SG). Some vendors recommend equalization 2-6x a year.

    Note: Equalization is "hard" on a battery bank and should be done per mfg. recommendations--Do not do "often" for "just because" reason.

    Regarding your battery bank--A good maximum continuous discharge rate is C/8 (we use 20 Hour discharge capacity of battery bank for all of our "rule of thumb" calculations). And C/2.5 maximum to support starting surges. For a 225 AH @ 24 volt battery bank:
    • 24 volts * 225 AH capacity * 1/8 rate of discharge * 0.85 inverter efficiency = 574 watt continuous output (drain battery in 8 hours or less)
    • 24 volts * 225 AH capacity * 1/2.5 rate of discharge * 0.85 inverter efficiency = 1,836 watt maximum surge output

    So--If you really need the 4kW surge (inverter is probably capable of 8 kW surge)--You should be looking at doubling the battery bank capacity (at least).

    If you choose a larger battery bank (say 2x), then the above calculations need to be doubled too (solar array, chargers, etc.).

    And, I really do not like to parallel connect battery strings--If possible/practicable for your usage--I would suggest getting larger AH batteries. For example, a Trojan 375 AH @ 6 volt "RE" model battery, or Trojan 445 AH @ 6 volt, etc. battery bank... Larger AH cells weigh more--so you may have to drop down to 4 or 2 volt cells to keep weight manageable (if you cannot use hoist, pallet jack, etc. to move cells around).

    Here are a couple FAQs to read about battery banks:

    Battery FAQ
    www.batteryfaq.org

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bo atkinson
    bo atkinson Registered Users Posts: 4
    Re: Grid Backup Question

    Thanks for the replies.

    Your comments and links are much appreciated. Yes, battery maintenance has been my weak point. I also do appreciate that my piecemeal approach is lacking and it is not to be advised. I just happen to think the world is in a triage phase and that preferable backup systems are out of my reach.

    I collect various kinds of deals, as they pass by. Like the 4KW inverter. I had assumed a 4KW inverter could run long enough to get some water or alternately, minimally, run freezers or misc short uses... I had figured this might compare to using the large utility transformer on the pole outside, to run just one night-light. Where AC transformer-losses are said to be insignificant. Yet it sounds as though you imply that the 4KW inverter will consume considerable power, just to convert power--Does the sine wave smoothing, specifically, eat up notable power? Do the older pulse-type inverters waste considerably less power? Is considerable power wasted when running a 1-to-2KW well pump on a 4KW inverter?

    If you don't mind one more related subject:

    Can you recommend a discussion or key-words to learn more about why the openly-watered batteries are still dominant over the closed-sealed battery types? Maybe this read would inspire me more, to get on my knees to maintain batteries more often. It just seems likely that open systems will get contaminated or loose more than water vapor, in the long run. Sealed batteries seem very time saving and cleaner.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Grid Backup Question
    Can you recommend a discussion or key-words to learn more about why the openly-watered batteries are still dominant over the closed-sealed battery types? Maybe this read would inspire me more, to get on my knees to maintain batteries more often. It just seems likely that open systems will get contaminated or loose more than water vapor, in the long run. Sealed batteries seem very time saving and cleaner.

    We call the 'openly-watered' batteries 'flooded lead acid' batteries (FLA).

    They offer the best bang for the buck (most capacity for less dollars).

    They are MUCH more forgiving of your indiscretions, i.e. overcharging and undercharging.

    The single most important advantage, in my opinion, is that you can measure their state of charge (SOC) with a hydrometer or refractometer. By this means you may adjust your charging profile to get the best life out of your batteries.
    If you have sealed lead acid batteries (such as AGM), you really don't know whether you are taking good care of them until it's too late.

    btw, have you read our host's battery FAQ?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    Re: Grid Backup Question

    "Maybe this read would inspire me more, to get on my knees to maintain batteries more often."

    My life before I found little Kindergarten type chairs somewhere. Instead of subjecting knees to nasty concrete I now can sit on a tiny chair and do the battery maintenance in relative comfort. Check yard sales.

    Ralph
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Grid Backup Question

    Flooded cell batteries tend also to last longer than AGM batteries... Not to ignore the fact that other than AGM's being 2x the price, they are very nice (clean, more efficient, less gassing/acid mist in the area, higher surge capacity, no distilled water needed, etc.).

    In general, conservation will be your friend. Generating power is almost always more expensive than to conserve it.

    With refrigerators being the #1 load for most people, well pumps are probably #2 in terms of "difficulty". There are several options for well pumps (pumps with electronic controllers--VFD (variable frequency drive)--which can reduce starting surge and even very pump speed for optimal water pumping. To pumps with internal electronics that can take power from multiple sources (solar panels, AC power, AC generator, battery bank, etc.)--But these can be as much as $2,000 or more.

    You could also use a generator to run a large pump--and pump directly to a cistern... And use a small DC (or AC) pump from the tank to pressurize your home. Or mix/match various solutions for your needs.

    A "small" off grid power system may provide 1,000 WH (1kWH) per day with a 500 watt array and a few golf cart sized batteries.

    A larger system may supply 3.3 kWH per day (100 kWH per month) on a ~1,500 watt array and give you a home that, more or less, gives you a near normal electric lifestyle (fridge, lights, power for laptop computer/modem, TV/Radio, washer, well pump). Still relatively small and not a huge hit to the bank account (say $10,000-$25,000 or so).

    Before purchasing components, it is best to measure/define your loads, then use that to define the battery bank. The rest pretty much is plug in the numbers to define solar array and backup genset power.

    We can do it sideways--Have battery bank, what needed to support XYZ AH @ YY volts. Or have $a,bcd money--how to get the best bank for buck.

    But, beware that "growing" a system over time is not usually very cost effective. You can about double capacity (battery bank + solar panels)--but beyond that, many times major components have to change (higher voltage battery bank needs higher voltage inverter--Many times mixing an old and new array has issues to find compatible panels at a good price, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset