Using Both Panels and Generator to Charge Batteries?

JRMJRM Registered Users Posts: 17 ✭✭
I am a solar system beginner and am trying to figure out an off-grid electric system using both a solar panel controller and a generator to charge batteries that send DC power to an inverter.  My hope is to use a generator that automatically starts at about 12.0 volts then stops automatically at about 12.5 volts to charge batteries at night and on short and/or cloudy days.  I am assuming that this would save generator fuel by storing power in batteries compared to continuous generator use for AC power.  But I have seen mixed messages about how this will or will not work with the solar panel controller?  Can reverse feed problems be handled by battery isolators that allow current flow in only one direction, or would this make matters worse?  The thoughts of people with more experience would be greatly appreciated.  I can provide more information about system components if needed, but this post is already getting too long.

JRM
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Comments

  • wellbuiltwellbuilt Solar Expert Posts: 635 ✭✭✭✭
    There is no mention of the size of your system. 
     My system runs on solar and generator 
      I use 15% to 20% of my battery power over night . 
      
     In the morning I check the system , look at the weather and decide if I’m going to run the generator or not  .(  I don’t want my system to start my genarator )
     if it’s looking like good clear sky’s the solar just charges the system . 
       If it’s looking cloudy I’ll run the generator , the charger will charge at 1900 watts , if the sun pops out the solar will add to the charging , as the sun starts adding charging power the generator starts backing off so I don’t go over my 50 amp max . 
     When I enter absorb charge my solar stops adding charging power and the genarator backs the power from the 1900watts to 400ish watts for 21/2 hours of absorb charge . 
     Then go’s to float .
     The system Just works by it self with little help from me .
       Since Christmas’s my panels have been snow covered  so I just run the generator every morning for 1or 2 hours depending on how low the battery’s get .
    it takes a lot more run time to bring my battery up to full from 40% then 30% so I run most days.
     If I’m not snow covered I get enough power every day . 
     In April I start  turning off solar strings to slow the charging 
     it’s better to charge all day and just get close to full charge  at sun down then to charge the system to full before lunch and float for the rest of the day . I use out back equipment 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • JRMJRM Registered Users Posts: 17 ✭✭

    Wellbuilt - Thank you for the comments.  It sounds like you have the generator/controller situation well under control.

    As admitted at the outset, I am a novice at solar systems.  I am starting small to find out what works.  You obviously are familiar with solar equipment and are very hands-on with its use.  My future needs are probably different.  I am looking for something that can be scaled up to a house that will take care of itself at times I am away.so my wife doesn't need to, and probably wouldn't, care for it.  This is why I want to figure out how to employ use of a self starting and stopping generator.

    I am starting with an equipment shed (nearly finished), three 300 watt panels to sit on the south facing, 34 deg. shed roof connected to a Midnite Classic 150 Solar Only controller (that has capacity for expansion) charging four 12 volt, deep cycle lead-acid batteries.  These batteries will be connected in series, providing 48 volts to a 3500 watt inverter sending AC power to a travel trailer and booster pump.  As I said, I am starting small to see what works and can be scaled up to eventually provide electricity to a house with propane used for large BTU appliances.  Three panels are probably not enough to keep up with demand when the trailer is in use, especially in the winter, so I expect to need another, backup method to charge batteries, which in this case would be the propane fueled generator, probably in the 3500 watt range so that it could power charging additional batteries in the future.

    I also have an Ames 48 volt converter/battery charger that can be connected to the positive and negative end-points of the battery bank.  (I realize that this is a “smart charger” that reduces current as voltage rises, but am assuming that the battery bank could still provide needed power for starting motors.)  The generator would start automatically to power the charger when the battery voltage drops to about 12.0 volts, to prevent battery discharge damage, and then automatically shut off when the voltage reaches about 12.5 volts, with solar energy relied on to fully charge the batteries.  While on, this converter/charger can provide up to 14 amps for battery charging and trailer power.  While the trailer is not being used (more than half the days) solar power should maintain the batteries without the generator.  This is the best combination of solar and generator use that I have come up with to provide continuous AC power.  As best I can tell, it should work okay after dark when panels are not sending power to the controller, but might (?) lead to problems if the generator comes on in the daytime when panels are sending power to the controller, which would probably happen if the trailer’s air conditioner is running.

    You have much more experience with and knowledge about solar electric equipment than I do.  My questions at this point are:  (1) Is there already somewhere (perhaps in this forum) that describes optimized use of solar panels and a backup generator for an off-grid system relying on battery power?  (2) Could directly charging batteries with power from a generator, as described, conflict with the solar controller during daylight hours? If so, is there a way to isolate the controller and generator from each other?  And (3) is there a better way to connect a generator to automatically recharge batteries? Any suggestions at this point will be greatly appreciated.

     I should add that the travel trailer has an additional two deep cycle batteries connected in parallel and charged by a 115 volt AC converter in the trailer (that has “add-on” smart charging circuitry).  These “trailer batteries” provide enough DC power for lights, fans, and a diaphragm water pump to last at least three days; but the TV, microwave, air conditioner, and plug-in appliances still require AC power.

    JRM

  • wellbuiltwellbuilt Solar Expert Posts: 635 ✭✭✭✭
    Don’t buy any thing yet . 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • wellbuiltwellbuilt Solar Expert Posts: 635 ✭✭✭✭
    Ok , first there is really no way to start small and grow a system .
      The best way to automate a system is to buy a Quality inverter/ charger I have out back equipment 
      If I was buying to day I mite go with Schneider.
        I don’t auto start my generator  it runs once a day in the morning for a hour or 2 this time of year 
      My panel have been covered with snow since Christmas . 
     It’s easy to walk out and push a button on a generator   You wife will love it 🥰 
       I would use 6v golf cart battery’s 8 215ah battery’s from sams club .
        I would use 6 300 watt panels,   my panels are at 42o I’m in ny.
         Your inverter and charge controller can work together the midnite 150 is a good unit but it would be better 
        If your equipment was all the same brand .
        Last  year I used 20 gallons of fuel  , this year It’s looking like 60 gallons .
        I run on solar for nine months and the generator gets stored . 
            The ac mite run in full sun but will drain the battery fast . 
                                                          Where are you located . 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • mike95490mike95490 Solar Expert Posts: 9,274 ✭✭✭✭✭
    Power companies have engineers and techs that inspect and maintain the gear daily.    I check and log voltages daily and inspect at least every other day.   And only use manual start generators.

    You can configure a system and get it dialed in.  I have gone on a 3 week vacation a couple times. In the summer when I don't worry about having to run the generator.  I check everything intensely for a couple days before I leave, and make sure the batteries are topped off with distilled water before I go.  

    But someone has to know the systems and be able to detect a problem like a battery that randomly develops a bad cell.  There is only autopilot for a short time, and then someone has to watch the system or be prepared for it to all fall apart.   

    Users MUST be educated to take advantage of the sun, and shift loads to daytime, no running the washer at night when you go out to the movies.
    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 ,

  • Dave AngeliniDave Angelini Solar Expert Posts: 5,910 ✭✭✭✭✭
    Wow out to the movies sounds so pre covid  ;)  Our town is still too small for a theater,  that is one business that did not fail.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • JRMJRM Registered Users Posts: 17 ✭✭
    Wellbuilt and Mike - Thanks again for taking time to provide helpful comments.  I have no disagreements, but do have a different perspective.

    First, I can address specifics - My system is located east and a little south of Sacramento, California, near the small town of Sutter Creek.  This is in the oak/grassland part of the Sierra Foothills.  I was told that the best, overall panel slope for this area is 33 degrees, but I agree that steeper would be better because the winter sun dips lower.  However, I can't stand on the 34 degree shed roof that is finally covered with tar paper while I figure out how to get shingles on it - my guess is with a rope to hold on to.

    I agree with Wellbuilt about the trailer air conditioner battery drain.  The trailer, like most, is not well insulated, so it is uncomfortably hot on a summer evening.  I am planning to install a "soft start" on the ac unit to reduce power needed to start its motor, and hope that the generator is able to pick up the slack on power use.

    My difference in perspective is that I am caught in an off-grid situation by distance from power lines and the current high cost of bringing in electricity and natural gas service.  So I am thinking off-grid for electricity, but will still be dependent on propane delivery.  My hope is to keep monthly energy costs about the same as I am now paying in town for electricity and natural gas, with up-front equipment costs that I am sure will be lower than getting utility service.

    I am trying to put together a system that doesn't require a lot of looking after.  The trailer, and if there is a house, is on a ranch where there is always more to do than time to do it.  So unless there is obvious equipment failure or a natural disaster (fire or wind), I want "maintenance" to consist mainly of periodic voltage testing or, in the case of open lead-acid cells, water level checking.  And my wife and I have reached an age where we would like to travel more, so the system would need to be on its own (relying on solar to maintain batteries with the generator turned off).

    For electricity storage, good old-fashioned open lead-acid batteries still seem to be the most cost effective, but they require checking and maintenance, as pointed out by Mike, to maintain length of service and capacity.  Now that I know more, AGM seems to be the best tradeoff between cost, maintenance, and technology at the moment.  Having been around cars and ag equipment most of my life, I know about problems created by lack of maintenance and dead cells in lead-acid type batteries.  One of the reasons I am looking into automatic generator start/stop is to minimize lead-acid battery drawdown damage while still leaving "room" for solar electric storage.  Lithium sounds good, but is costly and the technology still seems to be improving.

    About starting small, I am referring mainly to the number of panels and batteries and the size of the inverter and DC breakers.  If I get to add a house, its roof would be sloping (but probably not 34 degrees) and have a south exposure for more panels that will charge more batteries.  I am hoping that the current controller will handle a larger system, want to get a propane generator that will both start reliably and have the power to charge more batteries, and increase battery charging capacity by adding more 48 volt converter/chargers.  I also want to figure out what works before buying more or different parts to make the system bigger.  I did make the typical beginner mistake of buying parts before knowing what they were needed for.  But at least I went to a dealer who designs and installs systems so that the pieces (panels, combiner box, controller, breaker boxes, and breakers - DC and AC, etc.) will fit and work together.

    I think this covers most questions and concerns about what I am proposing to do, and I seem to have an answer to my most critical question, that feedback from panels to an active charger will not damage the system.  At this point, my most immediate problem is putting panels on the shed roof.  I have posts, rails, and clamps; but have yet to put it all together, and wonder why the panels won't slip.  Thanks again for taking time to help a beginner.

    JRM


  • 706jim706jim Solar Expert Posts: 423 ✭✭✭✭
    If you have the room consider putting your panels on the ground. On the roof sounds great until you have either access problems ir rain leakage. When my roof needed re shingling (partly caused by concentrated runoff from the glass panels), I moved everything to the ground and have never been happier.
    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 28th year.
  • mike95490mike95490 Solar Expert Posts: 9,274 ✭✭✭✭✭
    And I forgot to add, that you have to be a weatherman - or at least read the forecasts.
    While I can go 3 days without sun, I will still ( when it's convenient for me ) run the generator (which I checked oil and fuel yesterday, in prep for the weather)  and then sleep easily, knowing I'm good for 3 more days.

    There are few 48V chargers.  However. the better 48V inverters have a generator connection, and when the generator is running, the Inverter runs backwards and can charge the batteries at a pre-programmed rate, often up to 100A @ 48V.  You program the rate to be within range of the generator so you don't overload it.  I have a 3Kw generators, and with my house loads, only charge at 30A, larger generators can charge at higher rates.



    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 ,

  • mike95490mike95490 Solar Expert Posts: 9,274 ✭✭✭✭✭
    And don't forget about a pole mount for panels, they don't have to go on a roof.   I have mine at a steep angle for winter harvest, summer days are so long, the angle is of little importance

    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 ,

  • wellbuiltwellbuilt Solar Expert Posts: 635 ✭✭✭✭
    You just kinda stand on the roof and work , junior uses a Piece of foam couch cushion To Neil on and it stops you from sliding off into the dirt .👍
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • JRMJRM Registered Users Posts: 17 ✭✭
    Wellbuilt - I have been on some steep tin roofs over mountain cabins and barns and fallen off my share of ladders, but am getting a little old for this.  Besides, coming off the shed I am building would put me into a barbed wire fence that keeps the cows out.  So I am sad to say that caution is becoming more common.

    JRM
  • wellbuiltwellbuilt Solar Expert Posts: 635 ✭✭✭✭
    I have rugged ridge 1000 mounting track 
      There is a fancy bolt that go’s thru the top that holds the panel down and stops them from sliding and allso grounds  the panel to the frame ,  so you only need to ground one rail with a ground lug and copper ground wire . 
      You are in the land of sun shine , off grid is easy there , my system runs 9 months a year with little maintenance , 
       I check battery’s every month or so . 
       Add water when the battery’s get down to 3/4s or so full about every 6weeks +- 
        I check the SG of every battery 3/4 times a year . 
            This system makes things easy , I just screwed it to the wall and hooked up the wires .
         I
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • JRMJRM Registered Users Posts: 17 ✭✭
    I'll probably monitor more often at start then taper off.  It's just human nature.  Every month or two sounds about right for checking water in  batteries.  It is good to know that people still use specific gravity.  I remember old, dripping hydrometers and the holes they left in pants.

    JRM
  • jtdiesel65jtdiesel65 Solar Expert Posts: 223 ✭✭✭
    I check battery levels every week.  If I went a month, it would be below the plates.

    IMO, don't ruin a good roof by putting holes in it.

    I use a conext AGS to start the generator on voltage set points. It's rare that I manually start it.  I think you will find some people are more hands-on in terms of their system and others who take advantage of the automation and don't do much of anything except battery maintenance.

    IMO bigger generator is better. One reason is you can charge at lower load which is easier on the equipment.  If you are using a generator past ~70% capacity all the time, you are going to be buying parts. The second reason is that if you have to run a generator, you might as well as power loads (laundry, dishwasher, etc, etc, etc) while it is running. So you need a bigger generator to power both sets of loads. Here we can get 3 week stretches of minimal sun. It's not a matter of just waiting for some sun to run loads. The sun isn't coming out before the next generator run. This year was brutal. In your location, you may have weather that is more forgiving.

    One conflict with charging with generator and solar at the same time is that you can get strange behavior if your charge parameters are not set the same. That's avoidable. Another is the possibility of charging the battery at a higher current than it's rated for. The whizbangjr with the midnite controller can avoid this.   

    Also IMO, don't buy any equipment that isn't networked. You should be able to see your energy profile which will help you identify problems.
  • JRMJRM Registered Users Posts: 17 ✭✭
    This is probably experience speaking to a novice getting information from reading.  I have gathered from several discussions that solar charging can cause a lot of water loss from lead-acid batteries.  Is this because solar charging voltage or current is high and continues after batteries are full?  Wouldn't this be especially hard to manage with AGM batteries that are not supposed to "lose" water?  My experience with batteries is from the more mundane world of automobiles and farm equipment where voltage regulators are used to limit charging and there is less water loss.

    This following question probably solidifies my novice status, but I'll ask anyway.  What are the charge parameters that can be different between solar and generator charging, and how can they be set?  I am guessing that this is the voltage and current provided by solar controllers and battery chargers at different battery charge levels.

    Since I already have a Midnite controller, I will look into whether the whizbangjr can help my setup - whatever that turns out to be.

    JRM
  • JRMJRM Registered Users Posts: 17 ✭✭
    jtdiesel65 - First, thank you for comments that are getting at the heart of my concern.  I have been thinking more about your comments and realize that even if both the solar controller and generator charger behave the same at a given voltage, their current can add up to more than the battery wants.  This makes me even more interested in learning about the Wizbangjr.  I was also wondering how your generator is set up.  Are you using a transfer switch so that generator power goes directly to household loads?  Finally, the idea of networked equipment sounds great, but is another thing to learn.  I suppose I'll understand more as I gain experience, but for now I would be happy to be able to monitor battery voltage.

    JRM
  • mcgivormcgivor Solar Expert Posts: 3,815 ✭✭✭✭✭✭
    edited March 9 #19
    The controller regulates the voltage, the battery regulates the current, when partially discharged the batteries will accept all the current available  (bulk stage), as the battery approaches around 80% SOC the voltage is limited to prevent overcharging and the current begins to drop (absorption stage), when the current drops to somewhere in the 1-2% region the controller transitions to (float stage), where it is neither charging nor dischargeing. Note, cheaper controllers without float operate differently,  I'm using your Midnight's operating sequence without consideration for any connected loads.

    Unregulated the array would keep increasing the battery voltage, ultimately resulting in thermal runaway as the electrolyte is consumed and the battery is destroyed, so the controller is the voltage regulator. All well designed systems will be able to supply more energy than consumed, sounds wasteful perhaps but the excess potential will compensate when required, after an overcast day for example, without having to rely on auxillary charging like a generator.

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    More or less, water usage is a combination of charging voltage and time.

    Use the factory voltage(s) for charging and monitor water usage (this is for flooded cell lead acid batteries only). A typical deep cycle storage battery will need to be refilled about every 1-6 months. If you have to refill more often, then drop charging voltage a 1/10 or so volts. If you are not using water, increase voltage by a 1/10 or so volt at a time.

    Not all batteries are the same... Some have a large water reservoir (typically made for solar), others have a smaller reservoir (made for forklifts?). And some batteries are "low water usage" construction...

    Don't ever let the water level level fall and expose the plates. Typically add enough to well cover the plates, then charge/EQ--Once the battery is charged, you can add more water to "near" the top. You do not want to fill to the top/when cold, or the battery will spit electrolyte out the cell caps as the battery heat up and gas.

    There are automatic watering systems... A few folks here have had the watering system fail and dump the distilled water supply into one or two cells--Leaving a mess to clean up and a battery to service (dump "water" from cell, add electrolyte to cell to bring back into service--usually a hit or miss proposition to figure out how to get the SG's to "match" the rest of the cells)...

    Always use distilled or deionized water... Although, some folks use clean/filtered rainwater pretty successfully (no organics or minerals in the water).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wellbuiltwellbuilt Solar Expert Posts: 635 ✭✭✭✭
    JRM .  I was also wondering how your generator is set up.  Are you using a transfer switch so that generator power goes directly to household loads?  Finally, the idea of networked equipment sounds great, but is another thing to learn
            The inverter/  charger have a built in transfer switch  , when I turn on the ac power from the generator 
             The charger starts charging and the generator powers the loads . 
                You need to have equipment that can be networked that is the first step. 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • JRMJRM Registered Users Posts: 17 ✭✭
    Wellbuilt - I have an inexpensive (and perhaps unreliable) inverter that is not a charger.  If I scale up, it sounds like an inverter/charger should be on my system expansion list.  In the meantime, I'll find out if the Aims charger works for me.  It turns out to be less smart than I thought with voltage adjusted, but not current (unless this is buried in specs I can't find), while it is charging.  This shouldn't affect my use since the voltage range where I want to use it is all in the bulk charge stage.  Network capable will be a factor for any new equipment, and might already be included without my knowing.

    JRM

  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    JRM,

    I have not really heard much in the way of your planned energy usage... I always suggest (in rough order):
    1. Find the most energy efficient loads you can (LED lamps, laptop vs desktop computer, "solar friendly" well pump, most efficient frdige/freezer you can find, etc.).
    2. Insulation--Shade to keep sun off roof/south/west facing walls (for summer). Lots of roof/wall insulation, double pane windows, etc.
    3. Measure/accurate estimates of your loads. Rougly 1,000 WH per day system small (lights, LED TV, laptop, RV water pup). 3,300 WH per day (or 100 kWH per month--looking at yoru power bill)--A medium system. 10,000 WH per day (300 kWH per month)--Add more loads such as fans, larger well pump, more electric cooking devices, possible a mini-split A/C system, etc..
    4. Run the math. Loads=>Battery bank; Battery bank+Loads=>solar array. Weather/winter power needs=>backup genset needs...
    5. Design several systems that support the needed loads and look at batteries, hardware, software, networking etc. that supports you needs--And look at the options for cost/maintenance. Ask quetions/look reviews/talk to users of such systems.
    6. Once you have done the "paper sizing and design", then start buying hardware.
    More or less, solar runs around $1-$2 per kWH--Or 5-10x the cost of utility power. A genset runs around $1 to $2 per kWH for fuel (oversized gensets with smaller loads can waste fuel--Perhaps even a couple gensets--One to power heavy battery charging+shop loads and a smaller one for light battery charger/loads/possibly an inverter-generator that can run in evenings/nights and be quiet (depending on how close your neighbors are).

    And remember with solar--You are paying something like 5-10 years of your electric bills "up front". Batteries are expensive and need replacement (roughly) every 5-7 years, and the electronics every 10+ years.

    Sizing the system will give you a better idea of what "class of solar hardware" is out there... Small systems--limited networking/options. Bigger systems, more networking/other options. Bigger systems--You worry less about individual loads. A 3.3 kWH per day system, a refrigerator at 1.5 kWH per day is almost 1/2 your loads--And a small system may need a genset to "ride through" bad weather. A larger system--"your base loads" (loads that you need all the time, with a larger array and battery bank, you can conserve and "ride through" bad weather easier by cutting back on loads (i.e., no A/C needed during winter storms, no/much less irrigation in winter, etc.).

    It is very difficult to "scale up" (or scale down) a system by much more than a factor of 2x... More than that, you need larger batteries, higher voltage battery bank, new inverter with new battery bank voltage, etc. Even "mixing and matching" solar panels can be a pain (seems like "old model panels" go away in a few years, and hard to find "matching Vmp/Imp panels" to add to old array or replace a couple broken panels).

    Sacramento is relatively sunny in winter. In summer lots of sun so more loads (A/C and Water Pumping) are pretty well covered by more sun. If you have the room, "over sizing" the solar array, pointing 1/2 the panels South East, and the other 1/2 pointing South West gives you a little less harvest, but gives you more hours "on charge". For lead acid batteries, more hours on charge is a very good thing--Especially during winter.

    You could always do things like running your place on a geset with the "new loads" for a few days (afternoon mini-split A/C system, etc.) and see how many WH/kWH per day you need--Then design the system to support your actual needs.

    With off grid solar--You design to support your loads to avoid a too large/too expensive system. However, oversizing the solar array is usually a good thing. Solar panels last 20+ years, no maintenance. and will keep your battery bank "happier" and reduce (or possibly eliminate) generator runtime.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jtdiesel65jtdiesel65 Solar Expert Posts: 223 ✭✭✭
    BB. said:


    Not all batteries are the same... Some have a large water reservoir (typically made for solar), others have a smaller reservoir (made for forklifts?). And some batteries are "low water usage" construction...



    -Bill
    My forklift cells are 30.5" tall. The directions say the correct water level is 1/4" to 1/2" above the mat and the mat rests on top of the plates. There is very little reservoir. You have to be careful because if the water level is low when battery temp is high and then the battery cools off, you risk exposing the plates. So now I have a weekly strategy, sometimes only adding water every two weeks. I generally fill them 1/2" to 1" above the mat. I can vouch for minimal reservoir.


  • JRMJRM Registered Users Posts: 17 ✭✭
    Bill - I don't have much time to reply right now.  I think you have summarized what I have been doing, but my efforts have been less organized .  Being in California, you know that construction here requires energy efficiency.  I have been making energy need calculations and planned on propane for most high energy appliances.  I tried to explain my idea about scaling up in an earlier post, and I think it matches much of what you recommend.  What I find difficult is figuring out how the parts (solar panels, generators, batteries, chargers, controllers,, inverters, etc. work together and can be connected without creating conflicts or other problems.  This is new to me, which is why I'm lucky to be starting with something small, like the travel trailer, to make mistakes on a smaller scale before taking on trying to power a larger structure.
  • JRMJRM Registered Users Posts: 17 ✭✭
    jtdiesel65 - Thanks for explaining need for checking battery water - large battery w/ small reserve.  Something more to think about.

    JRM
  • wellbuiltwellbuilt Solar Expert Posts: 635 ✭✭✭✭
    Really my batterys don’t use any where near that much water . 
     I add about a pint of water per battery , or 2 gallons twice a year . 
     I fill them up , and have about 11/2 “ to my 
     plates , when I get down 1/2” I fill it with about a pint of water . 
     I’ve never really thought about the water being filled to the top keeping the battery’s cooler .
     Heemmmm  my battery’s never get hot 🥵  they stay cool most of the year . 
     50s in the winter when being charged every day .60/65 o in the spring and fall .
     July / August 70/ 75  
     I do leave my lid open a crack and I never see battery temps over 77 . Any thoughts 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    JRM,

    Are you planning on mounting the panels to the trailer (you want to go on the road when needed/desired)? Or the trailer a fixed installation, and you can/will ground mount a larger fixed array (home base until you build a house on site)?

    For an RV, you may end up with a smaller 12v or 24v system (good voltage choice to by/use DC native appliances/lights/etc.). For a home system (fixed array, battery and genset sheds--Keeping things separate and "not in home" can help reduce risks from electrical and gasoline/diesel fires).

    Just to give you a real quick "sizing" for a "cabin/very efficient" home system (nearly a "normal" electrical existence, LED lights, full size refrigerator/freezer, solar friendly well pump, washing machine during sunny weather, LED TV & Laptop & cell charging, propane for cooking/hot water/heating/dryer). Call it 3.3 kWH per day or 100 kWH per month (normal north American home is typically somewhere around 500 to 1,000 kWH per month).

    RV's typically have severe limitations... Not much space/weight capacity for batteries, not much roof space for panels, flat to roof or tiltable array for better harvest...

    Cabin system with "typical cost/performance system", no A/C... You can check the pricing to get an idea of the damage to your wallet.

    Load=>Battery bank. 24 or 48 VDC, 2 days of storage and 50% maximum discharge:
    • 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1 /0.50 max discharge * 1/24 volt battery bank = 647 AH @ 24 volt
    • 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1 /0.50 max discharge * 1/48 volt battery bank = 324 AH @ 48 volt
    Note: Suggest if battery bank is >~800 AH, go to next higher voltage (keep wire sizes "reasonable", and get "more harvest/amperage" from 80 amp charge controller running on 48 volts vs 24 volts (48 volt battery bank, 2x larger array wattage support with 2x higher voltage controller). Note that the battery bank is roughly the same price--Just more batteries in series and fewer parallel strings at higher voltage (same amount energy storage). Power=Voltage*Current. 2x Voltage and 1/2x Current = same power/energy storage.

    Next to size the solar array... Two calculations. First is based on battery bank size and rate of charge. Larger bank, larger "base" solar array. 5% rate of charge for weekend/sunny weather system. 10%-13%+ typical for full time off grid system:
    • 324 AH * 48 Volts * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 1,010 Watt array minimum
    • 324 AH * 48 Volts * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 2,020 Watt array nominal
    • 324 AH * 48 Volts * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 2,626 Watt array "typical" cost effective maximum
    And sizing based on loads and hours of sun per day for your location. Fixed array, Sacramento Ca, 3.3kWH per day:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Sacramento
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 51° angle from vertical (39 degrees from horizontal :
    (For best year-round performance)

    JanFebMarAprMayJun
    3.52
     
    4.36
     
    5.72
     
    6.32
     
    6.64
     
    6.91
     
    JulAugSepOctNovDec
    6.95
     
    6.95
     
    6.64
     
    5.86
     
    4.23
     
    3.41
     
    Any harvest >~3.0 hours of sun per day is a good sunny weather location. Assume that you want to run through December without a genset--And need more power in summer for possible mini-split AC system:
    • 3,300 WH per day * 1/0.52 off grid AC system efficiency * 1/3.41 hours of sun (December) = 1,861 Watt array "December break even"
    Now--In reality, you should only plan on using around 50% to 65% of your predicted harvest... Base loads are things you must run every day (LED Lighting, refrigerator, small water pump, etc.). If you have a business (need computer/networking/computer/Internet/etc.--Then add those as base loads). For example, say you want Lights, Fridge, and laptop as base loads:
    • 1,200 WH per day Fridge (Energy Star model)
    • 5 lights * 13 Watts per light * 5 hours per night = 325 WH per night
    • 10 hour * 30 Watts energy eff laptop = 300 WH per day
    • 1,825 WH per day "base loads"
    • 1,825 WH per day * 1/0.50 base load fudge factor = 3,650 WH per day base load fudge factor
    • 3,650 WH per day * 1/0.52 off grid AC system eff * 1/3.41 hours per day sun (Dec) = 2,058 Watt array "base load" oversizing
    In this guesstimate/SWAG, your "optimum" array would be around 2,058 to 2,626 Watt array.

    A 324 AH @ 48 volt battery bank can support a maximum AC inverter & Solar array of 1,000 Watts per 100 AH battery capacity (@48 volt).
    • 324 AH * 1,000 Watts * 1/100 AH = 3,240 Watt AC suggested "max" AC inverter and solar array.
    So, the "optimum" AC inverter would be around 1/2 to 1.0x the above or around 1,620 Watts to 3,240 Watts (with support for ~2x surge rating to start refrigerator compressor, well pump, etc.).

    I used x,xxx accuracy numbers so you could follow the math (and not build up rounding errors). In solar, anything withing ~10% is pretty much "dead on".

    Starting with a relatively cheap set of deep cycle batteries makes for a "good training system". Many people "murder" their first battery bank--And if you need to "up size" the battery bank (as your loads grow)--You don't feel too bad about leaving the old set behind (keep for smaller second system, give/sell to friends, etc.).

    Anyway--How the whole back of the envelope set of calculations--After the above, then start looking at hardware that will support those needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • wellbuiltwellbuilt Solar Expert Posts: 635 ✭✭✭✭

    JRM said:
    What I find difficult is figuring out how the parts (solar panels, generators, batteries, chargers, controllers,, inverters, etc. work together and can be connected without creating conflicts or other problems.  
         You problem is your equipment  is not design  to work together , it’s not that what you have won’t work . 
     But it is not a balanced system 900watts of solar is kinda small 4 12 volt battery’s is kinda small unless you have a large RE battery .
     And the amis inverters draw a lot of power all most as much as a full size frig. 
     There is no clear path to go down when running your system . 
      The biggest problem is plugging in your ac to you trailer your  converter will want to charge your battery’s and run the ac to cool the place off the solar will be on at the same time . 
     A work around is to pull the fuse out of the converter to stop it from charging the battery’s 
       Or put a on off switch in line .
      
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • BB.BB. Super Moderators, Administrators Posts: 31,684 admin
    Regarding "understanding" the solar power system... I suggest looking at the Battery Bank as the "heart" of your system. Chargers "charge" the battery bank based on Battery Voltage (and sensors). The AC inverter takes its power from the Battery bank regardless of what the "chargers" are doing.

    The "secondary stuff" such as the charger charging the battery bank and the AC inverter taking current from the battery bank--Effectively the charger is supplying current to the AC inverter is what actually happens. But from the "black box" point of view, each is just interacting with the battery bus/bank. 

    Design the charger(s) to keep the battery bank "happy" (monitor voltage, current, sometimes state of charge estimates/measurements) and get the bank recharged to 90-100% full once or a few times a week--The battery is happy.

    For the AC inverter, as long as the battery is large enough to support the current demands (don't draw too large of current) and the battery has enough capacity (Amp*Hours) to run the AC inverter overnight/cloudy days--That is what is needed.

    The other stuff... Such as starting the genset if the battery needs recharging--That is another voltage/capacity monitoring setup to start/stop the genset. How the battery got discharged (a lot of AC/DC loads, not enough sun, etc.)... The remote start system "does not care".

    Just look at the "black boxes" and how they each relate to the battery bank. For a first pass, you don't care about what is inside the black box.

    The details of what is inside the black box (such as AC Neutral to Chassis ground, or not... MSW or PSW/TSW inverter grounding issues, etc.) do matter... But don't let them confuse your 30,000 foot view of the system (high level understanding of battery bank to XYZ black boxes functions).e

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • JRMJRM Registered Users Posts: 17 ✭✭
    I have been out of town and came back to many good points that will help in the future.  Repeating earlier comments is probably not good in a forum, but the discussion is starting to drift.  My present system is to provide ac electricity to a trailer site.  The major components are three 300 watt at 40 volt solar panels going through a Midnite solar only controller to charge four 12 volt, deep cycle batteries connected in series to create a 48 volt battery bank that supplies dc power to an inexpensive 3500 watt inverter providing ac current to a pedestal outlet for the trailer.  Backup battery charging is provided by an Aims 48 volt controller charger powered by a generator.  These components I already have, plus breakers, boxes, and other parts to put it together.  My initial question is whether the charger and solar controller could both be connected to the battery bank without creating a conflict if both came on at the same time.  I am hoping that knowledge gained from using this relatively small system will help me in trying to provide an off-grid system for building a house nearby.  I realize that the number of panels is small for battery bank, that my inexpensive inverter may not have long life, automatic control of the generator might not work the way I hope, and the solar controller might not play well with the charger.  Experience and comments about this are of immediate benefit to me.  Comments about scaling up will help in the future.  And I hope to benefit from both your comments and my eventual experience with solar systems.  And thank you for the time you have spent in trying to help out a beginner!
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