How I am using the Grid instead of it using me.

KJ7YMKJ7YM Solar Expert Posts: 30 ✭✭
I have a 1KW panel array pushing a MorningStar MPPT 60 controller, charging four Crown CR-185 12 Volt Batteries, wired as a 24 volt system. AC is provided via a Schneider Electric SW Conext 4024-120 3500 watt inverter. I use this system solely to power my Refrigerator/Freezer. All my house lights are on a separate independent Solar Setup that has been running for a year or so now. I have had the refrigerator/freezer system active for a few weeks now and am still tweaking things. This inverter can pass AC through from an external source and simultaneously charge the battery bank, as it can be set up as a backup power device.

I am however using that feature differently, instead I trick it to use Grid Power to maintain my batteries at no less than 20% DOD after dark when needed. At first I was doing this by applying AC power to the inverter whenever the battery levels dropped below 24.8 volts, in the small hours of the morning. I soon realized though that I was probably killing my batteries much sooner. The reason is that the batteries were being subject to two charge cycles every 24 hour period. Once by the Solar Panels via the controller, and then again by the inverter systems charger at night. This I realized was synonymous with opportunity charging. So we had to rethink our strategy. I realized I needed to stop waiting until the battery had discharged, but find a way to keep the charge state up late enough into the evening to allow it to reach my 24.8 Volt lower limit just before the natural start of the Solar Recharging Cycle. I do this by using a timer with a built in Sunset Curve program I think they call them Astronomic timers. After running several logging test to determine at what precise time the sunset in my area dropped the battery terminal voltage to 27 volts, I set the timer to apply Grid AC to the inverter which then takes over maintenance of the batteries floating them at 27 volts. To the batteries it is as if the sun were staying out longer. The grid power through the inverter simultaneously carries the refrigerator freezer load until later in the night to the time I have pre-determined allows for a natural discharge to 24.8V by morning.
allowing for a once a day recharge cycle of the battery bank.

This is a backwards way to "Tie to the Grid", but this way I am able to use 100% of the power I harvest, and then use the Grid power to benefit my system instead of my system feeding them. My goal here is to get maximum life out of the Battery Farm. It did not take long to see that the batteries are the single biggest expense in the solar game. They can totally make or break you over the years. I am fortunate to have access to grid power and by using it this way, it appears I should be able to nearly double my battery life by preventing deep discharge. I am open and look forward to thoughts and recommendations.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,509 admin
    KJ7YM wrote: »
    I have a 1KW panel array pushing a MorningStar MPPT 60 controller, charging four Crown CR-185 12 Volt Batteries, wired as a 24 volt system. AC is provided via a Schneider Electric SW Conext 4024-120 3500 watt inverter. I use this system solely to power my Refrigerator/Freezer. All my house lights are on a separate independent Solar Setup that has been running for a year or so now. I have had the refrigerator/freezer system active for a few weeks now and am still tweaking things. This inverter can pass AC through from an external source and simultaneously charge the battery bank, as it can be set up as a backup power device.

    I personally like to see one larger off grid/backup solar power system vs two--I think that makes a lot more management/maintenance work for you, the owner. But I do understand why you did it this way.

    Regarding how to charge your Crown batteries--There has been a change in their recommendations in the last year or so:
    DLwindsun wrote: »
    I just wanted to clarify something. Last year Crown updated their charge voltages for the SLI (CR) line of batteries when used in a renewable energy application. This is directed towards PV/WIND mostly. Below is a link to the PDF with these changes. They increased the voltages to overcome the resistance in the batteries to prevent sulfation.

    http://www.solar-electric.com/lib/wi...fety-first.pdf

    Voltage settings for a 12 volt battery.
    Absorption - 15 volts
    Float - 13.5 volts
    Equalize - 15.6 volts
    I am however using that feature differently, instead I trick it to use Grid Power to maintain my batteries at no less than 20% DOD after dark when needed. At first I was doing this by applying AC power to the inverter whenever the battery levels dropped below 24.8 volts, in the small hours of the morning. I soon realized though that I was probably killing my batteries much sooner. The reason is that the batteries were being subject to two charge cycles every 24 hour period. Once by the Solar Panels via the controller, and then again by the inverter systems charger at night.

    From my understanding, I would suggest that 20-30% would be a good discharge level. Less than 20% could negatively impact battery life.

    I would highly suggest a good glass hydrometer (log temperature corrected specific gravity once a month of all cells) and check your discharge levels via SG readings. Measuring battery voltage is not very accurate by itself (amount of charging/discharging currents, temperature, amount of rest time to readings, etc.).

    If you want a really nice hydrometer, you might want to look at this guy--Some very good reviews here:

    mnhydrometer-web.jpg
    MidNite Solar Hydrovolt Battery Hydrometer

    Make sure you take a couple of draws/rinse of distilled water to clean out the hydrometer before you put it away. Otherwise they gunk up and get sticky insides.
    This I realized was synonymous with opportunity charging. So we had to rethink our strategy. I realized I needed to stop waiting until the battery had discharged, but find a way to keep the charge state up late enough into the evening to allow it to reach my 24.8 Volt lower limit just before the natural start of the Solar Recharging Cycle. I do this by using a timer with a built in Sunset Curve program I think they call them Astrological timers. After running several logging test to determine at what precise time the sunset in my area dropped the battery terminal voltage to 27 volts, I set the timer to apply Grid AC to the inverter which then takes over maintenance of the batteries floating them at 27 volts. To the batteries it is as if the sun were staying out longer. The grid power through the inverter simultaneously carries the refrigerator freezer load until later in the night to the time I have pre-determined allows for a natural discharge to 24.8V by morning. Allowing for a once a day recharge of the battery bank.

    You might want to look at a battery monitor. They are not perfect (still need to watch voltage/specific gravity to make sure the battery monitor is properly configured/operating and not miss-leading you). The Trimetric is not bad, and Victron makes a couple nice units. The Victrons also have programmable outputs based on state of charge (alarm, can use for automation--possibly).
    This is a backwards way to "Tie to the Grid", but this way I am able to use 100% of the power I harvest, and use the Grid power to benefit my system instead of my system feeding them. My goal here is to get maximum life out of the Battery Farm. It did not take long to see that the batteries are the single biggest expense in the solar game. They can totally make or break you over the years. I am fortunate to have access to grid power and by using it this way, it appears I should be able to nearly double my battery life by preventing deep discharge. I am open and look forward to thoughts and recommendations.

    Yea--Batteries are a necessary evil. I am not sure if cycling them daily saves you any more money overall (battery wear vs cost of utility power)--But floating them "forever" until you have an outage is probably not great for them either. Another option would be to cycle them to 25 to 33% or or so once a month--Both to exercise the battery bank (for longer life) and to "test them" to ensure they still meet your needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KJ7YMKJ7YM Solar Expert Posts: 30 ✭✭
    Thank You BB for your input. I ordered the hydrometer today. I called Crown and asked what the definitive answer for an 80% DOD was, and the little lady told me that it is 2.05 volts per cell.(24.6 for 24 volt System) That confuses me greatly because it does not seem to fall in line with the Flyers and other documentation I have from them. Fortunately the other numbers you mentioned are what I am using for Absorption, Float , and Equalization. I decided to err what I thought was on the side of caution to preserve my batteries by trying to maintain they never see a terminal voltage level below 24.8. Is this a soft discharge? AS I mentioned in my early post, I have been extending the solar charge cycle artificially by using a timer to pick up right as the Solar Panels drop of, and then maintaining power into the evening long enough that the batteries run down to 24.8 by morning. I could easily look back at my logs and determine an earlier cutoff time for the secondary charger to alow a deeper discharge. What do you feel an honest 80% DOD would be?
  • BB.BB. Super Moderators, Administrators Posts: 29,509 admin
    KJ,

    At this point, I am not sure what to tell you... There is some discussion (last I heard) between Crown and NAWS on some of these issues. The latest manual from Crown:

    https://www.crownbattery.com/en/wp-content/uploads/2013/09/Deep-Cycle-Product-Support-Broch.pdf

    But--It may be updated again.

    Just to give you an idea of how Lead Acid Batteries look during charging/discharging:

    http://forum.solar-electric.com/forum/solar-news-reviews-product-announcements/solar-information-links-sources-event-announcements/4426-working-thread-for-solar-beginner-post-faq?p=194303#post194303

    And, of course, there are temperature based voltage variations too.

    Good start is to look at the measured SG and then measure the battery bank voltage under that condition... That would be a good starting point for your desired voltage set-point.

    Probably a good starting point is around 24.0 to 23.0 volts (23.0 volts under heavy load for a few minutes) as your "maybe I should start the genset" time (or reduce loads).

    24.8 volts is probably a bit high as a set-point, especially if the bank is under load.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KJ7YMKJ7YM Solar Expert Posts: 30 ✭✭
    I should mention that the only load this system ever sees is about 300 Watts, my refrigerator freezer. But as I looked at my logs you are right, the 24.8 I am seeing is under load in the AM at the times just before the solar begins a new charge cycle. Unloaded before a chilling cycle starts on the fridge it will be setting unloaded at about 25.07V then when the fridge kicks in it drops usually to 24.8 sometimes just a tad lower. I think I will back off the night time charge to about an hour sooner and see what the low end gets to in the AM before sunrise. Again BB, thank you for working on this with me. There is so much divergent advice on the web out there. I trust NAWS, I know you guys are there to make a profit and that is what keeps America running. But I have always had the feeling that NAWS is working for an honest dollar. And that is when America really works. Thanks again.

    Larry
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    KJ7YM wrote: »
    I know you guys are there to make a profit
    FYI, all posters here, except 1, are NOT employed by nor have any affiliation with NAWS, other than to purchase needed items from NAWS..... that includes the Moderators!
    We are a kind of 'pay it forward' group...
    End Rant...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • BB.BB. Super Moderators, Administrators Posts: 29,509 admin
    Larry,

    To confirm what Westbranch typed, all of the moderators and posters here are volunteering our time to try and help (and ask) questions. NAWS started the forum years ago (and continues to pay for hosting, software, and maintenance), and has pretty much turned day to day "moderating" over to us (currently) three folks--And all of you out there that kindly provide most of the content for the forum.

    Also, as many here will attest--I am not a battery engineer/tech support person. I try to post a brief overview of the subject and (almost) always post to source documentation for the reader to do their own research when answering questions.

    Batteries are probably the most "sensitive" portion of an off grid power system. Treat them badly, and they will die long before their time. Treat them well, and they should give you good service. What the "best treatment" is--There are lots of facts and opinions floating around. And many will depend on who made the battery/battery type and your application (loads, charging, temperature, seasons, sun, etc.).

    Take what I (and others) post as a starting point in your studies. There are lots of people here with hard earned education and experience trying their best to help. But, in the end, it is your system and your choice how you run it (and all that nature throws at it with seasonal variations, weeks of cloudy weather, etc.). The decisions (reduce loads, run a genset, etc.) are yours to make.

    If something does not make sense or is not clear--Ask the question again or in a different way. We are limited (pretty much) to reading the posts--And we (or at least I) do sometimes misinterpret / go down the wrong path.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Solar Expert Posts: 1,297 ✭✭✭✭
    I see that Crown also talks about equalizing somewhere between weekly and monthly with an up to 9.5 hour charge time. And a 10-20% C charge rate.

    http://www.solar-electric.com/lib/wi...fety-first.pdf

    I am available for custom hardware/firmware development

  • KJ7YMKJ7YM Solar Expert Posts: 30 ✭✭
    Well you guys truly AWESOME! When I do call into NAWS for advice, and talk to Dave or any of the other guys, I do get the feeling that customer success takes precedence over profit. That is a real testament to them as well, that I can get that same kind of vibe from them as I get from you guys.

    I am sure it has been said to you guys so many times, but thanks for all you do.

    Larry
  • KJ7YMKJ7YM Solar Expert Posts: 30 ✭✭
    Hey Jonr,
    Holy Cow Batman! 9.5 hours of blasting the battery at 31.2 Volts every week? I wonder how I will keep water in that thing :-)
    Has anyone else fantasized about a vibrator plate under our batteries?

    Larry
  • BB.BB. Super Moderators, Administrators Posts: 29,509 admin
    Larry,

    You can read about one of our guys here that drilled holes in a battery to pump compressed air down to the bottom of the plates to stir the electrolyte.(end results, did not appear to be worth the costs/effort for an off grid solar system).

    Another who tapped the sides of batteries to "burp them". And another that took his batteries in the old truck on a rough dirt trail and found shaking them up (from charging to load--Don't quite remember the details) found the batteries worked better.

    NAWS and Crown Engineers are talking about the details (and revisiting the documentation)--But that Crown Link (dated 2007) seems to be the "more accurate for off grid" set of numbers--Hopefully, we will hear the results in days or a few weeks. The Crown batteries appear to do better (last longer) with higher voltage charging for off grid solar/RE systems.

    Solar RE is tough on Lead Acid Batteries--9.5 hours of charging is difficult in the best of times--In winter, fire up the genset.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • verdigoverdigo Solar Expert Posts: 428 ✭✭
    I just shuffled my batteries yesterday. Shook them while moving them as well. Don't know if it will help but I figure it can't hurt. 
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