Need opinion on my 48 volt panel to battery setup and efficiency

I'm new to this board and got connected to this posting board having recently purchased the solar panels from your company. I just learned everything I know about solar in the last 2 months mostly reading on line and the rest talking to sales. I do not quite understanding all the ratings on pdf. spec sheets and the balance to make the system below work. Could you help me to evaluate the below system plan.

Location:
Sierra Nevada mountains, Kern County, California with winter nights lows in the low 40's for 2 months and sometimes in the high 30's---and summer highs average 80's- 90's with medium breeze blowing most of the year. No shadows with mostly full sun.

My shell/outback roof top mounted system:
Situated on roof mounts 40 degrees south/west getting full sun from 9-3 winter and 9-7 summer.
18 shell SQ-175 solar panels (2 panels in series) wired to nine 9 volt breakers split into 2 separate circuits to run from pspv combiner box to 2 mx60 charge controllers.

Questions:
Since these are 35 volt panels, will 2 wired in series provide enough charge to the below 48 volt battery bank? I was told by shell that they do not advise wiring more than 2 in series.

Is this efficient enough to charge the proposed battery bank efficiently? Will this work with 2 splits(power from combiner) feeding into separate mx 60's?

Battery bank:
16 surrette 6CS-21PS batteries wired for 48 volt output (2 groups of 8 batteries in series).  

Other system components to be gotten will be "outback" brand to connect to 220 volt system panel on my stand-alone mountain home:
2-mx60's
2-gvx3648

thanks for any help :?


Comments

  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    is there utility power there or do you see it in the near future? i ask cause i noticed you had grid tie inverters and if this is a tru stand alone system you will not want grid tie inverters as they are super fussy on witch generators can be tied into them.
  • System2System2 Posts: 6,290 admin
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    Thank-you. I should have written 2-VFX3648 inverters to output power to the existing 220 power house main panel. :-D See I told you I was new to this.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    i don't know the current rating of those particular batteries, but the current outputted by the pvs would be about 5amps give or take. now the proper percentage of charge on most batteries is between 5 and 10% of battery capacity. that means the battery capacity would be between 50 and 100amps. most batteries are 100amps and up so i'm guessing you need more pvs. these would be 2 in series, but these 2 will be paralleled with the other 2. this gives you the range of charging batteries with 100 to 200amps capacity. now you have 9 pairs so this is 9x5=45amps. the range on this is 450 to 900amps battery capacity.  does this answer that question?
    i think it will work be it is 2 in series to charge 48v batteries. one of these is good for charging 24v batteries so i see no problem.
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    i have the sq165's and i have a 24 volt system and on a 40 degree F day i get like 33-33.5 in so i question if two would put you above a good charge voltage let alone equilize voltage in that warm a climate. i would lean towards 3 in series but crewzer or one of the others that are real good at the math will chime in and answer for shure
  • System2System2 Posts: 6,290 admin
    Re: battery capacity

    The Rolls/Surrette battery 6CS-21PS specs:
    683 amp hours @20 hour rate
    current rating is 34.2 @ 20 hour rate

    My understanding is that 2 groups of 8 batteries in series @ 6 volts & 683 AH will produce a 48 volt battery bank @ about 1200 Amp Hours capacity

    The above battery information is from the battery company spec sheet and the system balance or sizing of panels to batteries was suggested by sales according to my estimated needs. What I'm trying to get is a second opinion on this outlined system balance so thanks for any suggestions.  
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    ok the percentage is <3.3%. less batteries or more pvs it would seem is needed if you wish to be in the 5-10% charge range. the capacity of the batteries will be 1366amphrs. now 5% of that is 68.3amps and for 10% you'd double that and it's 136.6amps. to produce 70amps you need 14 pairs of the pvs and that puts you at about >5%. it's harder to lose batteries because the capacity would have to be cut in half to reduce that and that's got to be out of the question for you. know that we consider 3% to be a minimum figure for charging batteries. this takes much longer to reach and is without any loads carrying off any battery power while charging. if this is acceptable and workable to you it will suffice as proposed and it can be expanded upon later with more pvs if you wish to get to the 5% charging mark. btw, if you get any good mppt action going this adds to the figures above. if you get 10% more current by mppt(which is typical) then this is another 4.5amps for a total of about 49amps from the pvs and puts you roughly at 3.6%. still abit low percentwise, but it may be good with no loads like i said. they may have figured 30% for mppt in their design, but this isn't something you can count on all of the time.
    my opinion is go for it and expand on it later if it's too little current. if you've got the extra $ to spare then go for 4 more pairs of the sq175 pvs and that'll be closer to the ball park with 10% mppt putting you just into the 5% range. 13(series groups of pvs)x4.95amps=64.35amps x 1.1(for mppt action)=70.785amps and this is 5.18%.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    I think that both halfcrazy and niel have made good points.

    Rolls / Surrette’s recommended BULK / ABSORB charging voltage for a 48 V battery bank is between 56.9 V and 58.8 V at 77 F (25 C). The EQ recommendation is between 61.9 V and 64.1 V. I think a series pair of hot 35 V modules will have difficulty supplying the MX-60 with a high enough voltage to meet this requirement. For example, the SQ175’s NOCT Vmp spec is just 32.4 V (that’s at 68 F / 20 C ambient), and I’d expect it to drop to ~30 V on a hot and sunny day, or ~60 V for two modules wired in series. Allowing for voltage drops in the [*]cabling, connectors, fuses and/or breakers, the two-modules-in-series configuration may turn out to be fairly finicky in your location.

    Since it seems that you’ve already bought 18 of these modules, I think you have two configuration solutions to consider. One would be to wire strings of three modules in series (it’s OK to do, BTW. Shell’s UL-approved max system V spec for these modules is 600 V) . The total Voc spec would be 133.8 V, and, allowing for an NEC temperature correction factor of 1.10 for ambient temps down to 32 F (0 C), the design Voc would be 147.2 V. This value exceeds the MX-60 safe operating limit (~140 V), which would cause it to briefly shut down for a while on very cold mornings, and it's close to Outback’s absolute maximum input rating of 150 V. (Note that the MX-60 permanently stores the highest Voc that it sees.)

    This configuration would probably work in your warm environment, but I wouldn’t recommend it, as ambient temps lower than 32 F are possible in your area. For example, the record low in nearby Kernville is 10 F.

    An alternative configuration would be to wire two and a half modules in series, assuming that each module actually consists of two “12 V” modules connected in series inside the junction box (halfcrazy: can you confirm this from your 165’s?). Assuming it can be done, it would create an array rated at ~87 V and would operate at ~75 V or so in BULK/MPPT mode – high enough for the MX-60 and your “48 V” battery bank. You’d be able to use 17-1/2 modules from your present inventory, or buy two more and configure from 20, which, at ~3500 W STC, is about the MX-60’s limit for a 48 V battery bank.

    Which brings us to niel’s point. You’re probably going to need more modules and/or smaller batteries. If you haven’t bought your batteries yet, you might want to consider the smaller Rolls/Surrette 6CS-17PS, rated at 546 Ah x 6 V, to make a 1,092 Ah battery bank. I’d estimate typical mid-day summer charging current from the 17-1/2 array bank to be ~45 A, or 4.1% of the bank’s capacity, and ~51 A, or ~4.7% of the bank’s capacity from a 20 module array.

    So, in summary, my evaluation is as follows:

    1. Try to confirm that the SQ175 “24 V” module can be electrically split into two “12 V modules”. If not, you may have a problem, and we may need to discuss a solution involving 24 V inverters and a 24 V battery bank.
    2. If #1 is OK, wire your PV array up in a “60 V” configuration (strings of 2-1/2 series modules per string)
    3. Buy two more modules to increase count to 20 (easily divisible by 2-1/2) and increase charging current.
    4. Buy a smaller battery bank (48 v x ~1,000 Ah to ~ 1,100 Ah) to match your array to your battery bank (charge current = ~5% of battery bank capacity)

    HTH,
    Jim / crewzer
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    The working (Vmp) voltage on those panels is 35.4 volts. Two in series will give you about 71 volts - but that is at standard test conditions. It could drop below 33 volts on very hot days, but also on very hot days your battery voltage needed for charging and equalization is lower, so it should work out.

    I am curious about who from Shell said not to wire more than two in series? Since these are mainly intended for grid tie inverters, and those can run up to 600 volts.

    It is remotely possible that with 3 in series on a very cold day that you could exceed the 140 volts max rating on the MX60, but even at 32 degrees Vmp will be around 46 volts per panel max, x 3 = 132 volts.
  • System2System2 Posts: 6,290 admin
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    Crewzer,
    My SQ175'S are conected in series in the juncion box. Although they dont have the 4 terminals for a simple 2-12volts conection they could be connected like that at the diode side of the junction box. Excellent idea.


  • System2System2 Posts: 6,290 admin
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    Thanks for all the great technical/practical advice. Some of it is beyond me at this stage, and if it makes sense I tend to follow the path of least resitance (like elctricity) :-).

    Our location is actually about 50 miles south of "Kernville", but be aware that "Kernville" weather is much colder in winter and hotter in summer. They are in a much higher altitude and are surrounded by very high mountains where cold/hot air lingers longer.  Our house with the 18 roof-top panels is situated at 3500' altitude daily lows in winter are always mid-high 40's or low 50's.  When the "cold air on a sunny day" situation might cause the extra MPPT power to exceed recommended level is a random 2 or 5 day possibility(during the day) in my location--and only in the early morning hours. And that includes all the days in the entire winter season(Dec.-Jan.)! Now nights are much colder- low to high 30's as I wrote before, but that doesn't concern the MPPT, as it is sleeping.

    And Yes the 18 batteries were ordered/paid for in Early December as the Surrette factory builds these type(larger capacity) when they are ordered. So I must make this system work with the original 48 volt configuration. I chose that quantity as they allow free shipping (when ordering over 2 tons) anywhere(commercial drop off location) in the U>S>!

    So reading all your responses to my concern for a well balanced 48 volt system makes me lean towards coupling 3 of the SQ-175 panels in series. If all it does is shut down the MPPT for a couple hours on those very very rare days then I feel it is the easiest/least expensive way in my situation to ensure complete battery charge for winter or summer. As long as I don't cause any damage to the controller is my concern and it sounds like it won't.

    Can I use my existing 9 amp breakers in the PSPVcombiner box or will the new 3-panel in series configuration require an increase in amps? Should I still keep the 2 separate circuits in this combiner box running to each MX-60 charge controller? If so, as I see it now, I will have a balance as there will be 6 groups of wire from panels to run into the combiner box knockouts. Also please explain what am I losing (power storage) by grouping 3 in series instead of 2 in series?  

    The tech support guy at "shell" Solar customer info. in Camarillo,Ca: (805)482-6800 told me that series connecting more than 2 of the SQ-175 panels is based on, (what some of you advised) MPPT suggested maximum. But he may have thought of extreme winter day temperatures with full sun as it relates to my mountain location! Again we have a very mild winter (zone 7) and that's a big reason why my wife and I bought this land. I will talk to him again next week.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    OK. Wiring three SQ-175 modules in series will create a string Voc of 44.6 V x 3 = 133.8 V at 77 F (25 C) cell temperature. Based on the manufacturer’s specs, the string’s Voc will increase by 5.8 V during early morning ambient temperatures that “are always mid-high 40's or low 50's.” That’ll put the Voc at 139.6 V, not including the modules +/- 5% tolerance spec. The MX-60 disconnects at ~140 V, but will reconnect once the array warms and the Voc falls.

    Fifty miles south of Kernville in Kern County, CA puts you near Tehachapi, where average overnight/early morning lows in Dec., Jan. and Feb. are 31-, 32- and 33 F respectively. The record low is -4 F. The NEC correction factors for temps in these ranges are 1.13 (for 31 F) and 1.17 (for -4 F). Applying these correction factors places the design Voc values at 151.2 V and 156.5 V. Outback warns to never exceed the MX-60’s input limit of 150 V. The MX-60 records the high Voc, data which can’t be user reset, and it might become an issue if your controller ever needs warranty service.

    So, I still think the three-module series solution is a potential problem. And, as noted previously, the PV array (3150 W) may be too small for the proposed battery bank (1366 Ah x 48 V), so you may have trouble “(ensuring a) complete battery charge for winter or summer”.

    I don’t understand your question about “what am I losing (power storage) by grouping 3 in series instead of 2 in series?”.

    Finally, note that with the exception of “Wind-S2”, none of the rest of us here is affiliated with Northern Arizona Wind & Sun (NAWS). We just like learning about this technology and its applications, and we enjoy helping others when we can. You get to take or leave our suggestions as you see fit, but NAWS is not responsible for the content of our posts.

    Good luck with your system!

    Regards,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    Hi Crewzer,
    Again I appreciate the calculation you gave for the MPPT charge controller eficiency/maximum manufacturers specs. You helped me to understand it better. Now I can talk more intelligently to "Shell" again and perhaps later to "Outback" about weighing the odds of 3 in series SQ-175 panels in my situation and the MX60 warranty. Everyone on this board has a great deal of knowledge and I learn more from this exchange of words.

    As always I blame myself for any decision I make. I just want to evaluate the odds and find out the consequences. And you gave me the MPPT limit detail numbers and your reason to exercise caution which I understand. I was aware of the MPPT limit as it regards the outback warranty. Everyone I talked to from day one used it as a limit when discussing with me what would work best in my proposed consumption and budget plan.

    When I asked in above recent reply:
    “what am I losing (power storage) by grouping 3 in series instead of 2 in series?”.
    I just wondered if other than the MPPT temperature potential problem -Was there enough power from 18 panels to fully charge the battery bank I outlined above?

    More detailed weather facts:
    We are actually at a lower elevation well north/west of Tehachapi which is situated at a much higher altitude, but like many mountain zones you can expect 5-10 degrees variation based on the wind chill factor and actual altitude. Our region does not exist on most weather services as it is not very populated but we are often times grouped under Lake Isabella or Tehachapi weather even though we are not experiencing the same.

    Panel angle and direction:
    139.6 V at 77 F (25 C) cell temperature not including the modules +/- 5% tolerance spec at early morning temperatures in mid-high 40's or low 50's is cutting it to the max. as it regards the MPPT and the 3-wired in series panels.

    But I also don't have an ideal direction or angle to the sun. The panels are on a 30 degree tilt stationary roof mount with an a south west direction. The sun is visible at 8 in the morning but the panels are not hit directly by sun until 9 o'clock. They are on the opposite side of the roof. So the air temperature warms them up for about an hour before they get hit with full sunlight and then the MPPT would activate.

    Over the last month I took readings (early morning) of the combined open voltage circuit from the output of the 2 in series SQ-175 panels. I got 62 - 64 amps. Is that reading in my favor to use 3-in series? Shell lists 44.6voc as an open voltage for the SQ-175 in their specs within 10%at 25 degrees cell temperature.
  • System2System2 Posts: 6,290 admin
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    CORRECTION FROM ABOVE POST:
    Over the last month I took readings (early morning) of the combined open voltage circuit from the output of the 2 in series SQ-175 panels. I got 82- 84 amps. Is that reading in my favor to use 3-in series? Shell lists 44.6voc as an open voltage for the SQ-175 in their specs within 10%at 25 degrees cell temperature.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    PV modules are considered “constant voltage” devices. A module’s output current varies with insolation, but the output voltage is fairly constant, generally only varying inversely with cell temperature. The time to measure the Voc is early in the morning between dawn and when sunlight is first hitting the front side of a module. Just take several voltage readings at the terminals (otherwise not connected to anything) with an accurate DVM, and the highest value will be your Voc of concern.

    An open-circuit (Voc) reading of 82 – 84 Volts (not Amps) from two modules wired in series corresponds to ~41- 42 V per module, vs. Shell’s 44.6 Voc spec. The lower reading works in your favor. If a series string of three modules consistently reads under 139 V on even the coldest mornings, you may well be OK in your location and environment with a three-module-per-string configuration. Ultimately, you’ll have to make that call in consultation with your local weather gods. :wink:

    With respect to the two-modules-in-series vs. three-modules-in series questiom, it's probably a wash, everything else considered. Assuming two-modules-in-series will even work with the MX-60 and a "48 V" battery bank, the MX-60 would operate quite efficiently but there would be a power loss in the array wiring due to the higher current. The MX-60 would operate less efficiently with the higher voltage from a three-module-per series configuration, but there'd be less power loss in the array wiring due to the reduced current.

    The orientation of your array will likely aggravate the imbalance between the array size and the battery bank. Running your array’s orientation specs in the Bakersfield location of the NREL’s PV Watts model, I estimate that average energy production in December will be only ~40% of expected June production. :-o You may wish to use this model to find a tilt angle that offers a better balance between summer and winter energy production.

    While I still think that fully charging the bank will be difficult in the summer, I’m even more concerned about it in the winter due to the substantial reduction in mid-day charging current. One solution might be to separate the battery bank into two sub-banks isolated by two parallel switches or breakers (rated for ~75 VDC). This would allow you to charge one bank while operating from the other.

    I hope you’ll keep us posted on your progress. Please give my regards to the Tehachapi Loop!

    Regards,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    I really appreciated all the help/responses to my questions)dating back to January of this year) as I was putting together/awaiting delivery of my "standalone" 48 volt system. I'm writing to report my results for the record for those interested and maybe ask a few final questions.  I just want to remind you all that prior to December of 05 I had no I had very little knowledge on, what solar was and am still learning, but have gained much confidence by doing a lot of the installation on my particular set-up and reading advice from you all on the various boards.

    I finished the assembly of all the components and turned on the breakers to the power center easter weekend(late April). I had been taking readings monthly of the output from the panels 18-SQ 175 shell(2 in series) 2 banks composed of 10 & 8 in 2 groups) from January, after I had bolted them to the mounts on the roof and wired them into the combiner box. I then waited for the power center to be assembled.

    We had a very rainy and fairly cold Winter season this year in the california muntains, which ran way into Spring and showed me that these panels during the coldest mornings with full sun were capable of exceeding Shell’s 44.6 Voc spec two-modules-in-series and on occasion briefly surpassed this! This made me revert to trying out the 2-in-series or 9 pairs of panels. I figured if later on I would need to change this-to accomodate full charge of the battery bank if necessary, it would not cost me much except time, as I did all the work myself.

    Battery bank:
    16 surrette 6CS-21PS batteries wired for 48 volt output (2 groups of 8 batteries in series). These were shipped to a local truck depot in town(free shipping from surrette) and I picked them up with a 10 ton capacity stake truck with the very necessary liftgate. I also bought 2-5 gallon containers of spg 165 battery acid to top them off as they were slightly under filled to make their journey from eastern Canada safer. I learned to drive the shift gear truck in the rental yard that very cold morning in February and brought them safely to my home location.

    Outback charge controllers/inverters
    2-mx60's-these I configured to 48 volt and chose the higher absorb/float numbers per Surrette's handbook. I also added the "water miser" caps to help reduce evaporation.
    2-vfx3648's-these were already programmed per my selection as master/slave 120 & or 240 outback stacking.

    The power center was pre-wired, shipped in a crate with all components assembled to a wall mount per my specifications to allow 120 or 240 power on call as needed or "Outback stacking". The only problem was that they wired up the electric panel with the plan that I would be setting the solar panels up on my detached garage roof. Well I needed to situate them on the roof of my 2 story home so I had to install a new breaker(per code) and rewire the connections to the PV & Battery breakers and add the necessary OBDCGFP2.

    I finished up by wiring the power center to my main house panel. And this I also did with much needed advice and coaching from arizona wind-sun and the outback forum. I guess the same people more or less :-) helped me out and made my installation a success.

    Here is the good news as it regards my system if I read everything correctly. Since April of this year I have been able to maintain a 52V reading on the power center monitor all night and into the next morning as I observed almost daily. This was maintained even during the rare 2 weeks(july) of 100 plus degrees here near Tehachapi,Ca. I also took a hydrometer reading many times in the past 3 months and most recently performed an equalization a week ago. The temperature outside read in the high 80's to low 90's with a continuous breeze and allowed the full equalization process which I monitored closely to continue the charge for 2 full hours at 64.0V. I manually had set it up to do this after the batteries had reached full charge by noon. For the record I always kept the batteries topped off to within 1/4-1/2" below neck since they arrived. After the equalization stopped having reached the 2 hour preset charge time the voltage reading dropped back fairly quickly to the high 50's. Is this a typical reading just after equalization? All the cells bubbled like boiling water as I observed during the equalization-so it must have done it!

    I have another question at this point and time: All my batteries have a 12.65 spg except 3 or 4 which have an above or close to 13+spg. Even after this equalization they showed this higher level. Is this something that needs further correction or attention? The battery fluid temperature I took(thermometer) showed a 90F degrees max towards the end of equalization. I expected much higher. I hope I didn't write a novel here but It has been 7 months and I just wanted to reply with my results and perhaps help someone else who may be where I was a the beginning. Again I want to again thank you all very much.
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    Sounds like you found the sweet spot for your particular combination of components and environment -- congratulations!

    "Slightly underfilled"? You may have just needed to add water and not more battery acid. You may need to contact Rolls on this matter. Remember to remove the hydrocaps and reinstall the original battery caps when equalizing. See Rolls Bulletin #605.

    Regards,
    Jim / crewzer
  • System2System2 Posts: 6,290 admin
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    Hi Jim,
    Prior to putting these brand new batteries into service Rolls/Surrette advised me to top off with spg(specific gravity 165 battery acid). After initial charge and from then on use water to top off. I bought the acid from a local battery store for $20 per 5 gal. I estimated 2 boxes of 5 gallon each in my situation. Still have 2 gallons left. These are large batteries weighing in filled at over 300 lbs.

    The caps I described and bought are water "miser caps" not the "hydro-caps. I was advised that they can be left on during the equalization. The hydrocaps or more expensive should be revoved for the gassing to properly escape.

    Yes I think the system will work out very well for us, and although at this time it appears oversized I think that will guarantee long battery life as I plan to keep them at 80%- 90% charge for longest life. Maybe even the 20 year max :-).

    What I see as being a big help on hot sunny days is the constant wind or breeze we have at our location. It must help cool down the panels. On one day when we experience a stillness(no wind for several hours) the charge controllers dropped their charge level dramatically. Also the MPPT is producing its share as well. It was a lot of money upfront but with energy prices rising, at this point and time my wife and I feel we made a good investment.

    thank you for your help in the past



  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency
    What I see as being a big help on hot sunny days is the constant wind or breeze we have at our location. It must help cool down the panels. On one day when we experience a stillness(no wind for several hours) the charge controllers dropped their charge level dramatically.

    Aha! Good to hear that your system is working well and meeting your needs. I hope you'll keep us posted on long-term performance.

    Thanks,
    Jim / crewzer
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency
    freepower wrote:

    Yes I think the system will work out very well for us, and although at this time it appears oversized I think that will guarantee long battery life as I plan to keep them at  80%- 90% charge for longest life.  Maybe even the 20 year max :-).


    i do hope you meant you won't be discharging the batteries down past that point meaning you'd maximumly discharge them by 20% or 20% dod. if you keep the batteries discharged to 80-90% soc as your comment implies your batteries will sulphate and die an early death.
  • System2System2 Posts: 6,290 admin
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    Hi Niel,
    Yes, I meant the "almost fully charged" state of charge. I still have to get more familiar with the correct verbal terminology. But you know what? From the moment I put them into use they've(The Rolls/Surrette batteries 6CS-21PS) stayed at close to a 100% fully charged state when checking early morning stored power level.

    Typically the batteries get fully charged by noon or close to that time, and then one MX-60 sleeps the rest to the day while the other one "floats" or maintains charge as needed till sundown. One day in our mountain location of very, very rare haze(no sun-grey sky) the batteries took an hour or 2 longer to reach full charge.

    We are now in the fortunate position of trying to use up some of this excess stored power. I plan to disconnect the propane frig and see how much the electric version will consume. Also this winter I still have yet to see how much electricity my central heating system(propane) will draw from this now seemingly endless storage supply.

    I will post back later on in the year with the results on this system. Thank-you also for your past or early analysis of my 48v panel to 48 volt battery system set-up. You seemed confident at that time that it would work out and it did! I appreciate both the pros & cons replies on this set-up. At that time I did not know what to expect. So the only thing to do was to go forward and see what happens according to tested guidelines and practical advice.

    I should also add that I used a #4 wire(2-wires & ground) no more than a 50 foot distance from combiner box on roof to the power center. Also the same gauge or #4 wire(3 wires & ground) from AC power center 100 feet to the main house panel. So my power loss is minimal.

    Well, that's all for now. I would have replied sooner but my modem failed last week and I could not connect on line from that location.

    thanks again
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Need opinion on my 48 volt panel to battery setup and efficiency

    fp,
    it's good that they get the full charge for as i said long periods of 80-90% soc(state of charge) which is the same as 10-20% dod(depth of discharge) will lead to sulphation and kill batteries earlier than need be. do periodically check on your batteries at least once a month for water levels, general cleaning if needed, checking specific gravity(recommend a couple times per year, but can be skipped), proper balance or equalization(per battery manufacturer recommendations), checking connections, etc. observe your system and get to know the feel of it in general as for if something goes wrong you will be more apt to catch it. this could save a part of your system from being damaged or damaged more. you get the general drift here that i'm saying and i'm glad it worked out for you. try to keep up on things too if you can as knowledge is always good.
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