Seekin Suggestion for MPPT charge controller inverter, 24 V, 2400W, all in one would be nice

rocket999rocket999 Registered Users Posts: 9 ✭✭
edited February 5 in Solar Beginners Corner #1
Want to use it in powerwall for small RV and also move into home during Public service power shutoff in CA neighborhood with modest fire danger but no scary dangerous winds.

Have 2 BigBattert 24V 100Ah batteries

Had a MPP PIP2424 LV-MSD brand new right ouy of the box had defective LCD so returned it. The seller wanted me to repair it

Any suggestions,  all in one is nice,  seperate components also possible

Thanks in advance


  • BB.BB. Super Moderators, Administrators Posts: 31,425 admin
    Welcome to the forum Rocket999!

    Stop before you purchase any more parts... I am a big believer in a "balanced" system design. Loads => Battery bank. Loads+Battery bank capacity+Hours of sun per day => solar array...

    Once you have the basic math done and the components sized on paper, then you can start looking for the components that will support your needs (and hopefully your pocket book).

    Since I do not know your loads--I can start with your battery bank. I will start with the "conservative" lead acid type battery assumptions. If you have Li Ion of some sort, then we can tweak the math. Knowing the details for your battery (chemistry, size, any BMS, etc.) and it specifications (min/max voltage, etc.) and operating within those constraints--Then you will have good battery life and expectations for your system.

    Basic system design... For full time off grid, assume use 25% of battery capacity for 2 days (of bad sun) and 50% planned max discharge (for longer battery life). For an RV (weekend/sunny weather) can assume 50% discharge per day (1/2 size battery bank).

    For your battery bank of 24 volts @ 200 AH capacity, the average daily 120 VAC load would be (charge during day, discharge in evening/quiet times):
    • 24 volts * 200 AH * 0.85 AC inverter eff * 1/2 days storage * 0.50 max planned discharge = 1,020 Watt*Hours per day (2x evening)
    • 24 volts * 200 AH * 0.85 AC inverter eff * 1/1 day storage * 0.50 max planned discharge = 2,040 Watt*Hours per day (1x evening)
    I will just stick with the 2 day storage for now...

    Sizing the AC inverter--Normally, roughly 500 Watts per 100 AH @ 24 volts max inverter... Or 200 AH => 1,000 Watt max AC inverter (even a 300-500 Watt inverter would be a good fit too). A 2.4 kWatt AC inverter is just really large for such a small battery bank. As an example, if you use 5 hours of battery per day (evening) at 1,020 WH per day:
    • 1,020 WH per day / 5 hours of usage = 204 Watt average load for those 5 hours
    And why a "smaller" inverter is usually a better fit (and smaller AC inverters typically use/waste less energy).

    Then there is sizing the solar array based on your energy usage... Two calculations. 1) based on loads and hours of sun per day/seasonal usage; and 2) based on battery bank capacity--Larger battery bank, more solar array to properly charge.

    Sizing for your location... Example Fresno California... And you can have a "flat to roof" mount (typical for RV) or a tilted array (better for winter camping, especially the farther north you go):

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a horizontal surface:


    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 53° angle from verical:
    (For best year-round performance)


    So you can get another 1.5 hours of sun per day in December with a tilted array... Anyway, lets pick 3 hours of sun per day and 1,020 WH per day:
    • 1,020 WH per day * 1/0.52 off grid average AC system eff * 1/3.0 hours of sun per day = 654 Watt array "3 hours of sun break even"
    And there is sizing the array based on the battery bank capacity... 5% rate of charge used for backup systems, weekend/summer usage. 10%+ rate of charge for full time off grid... 13% or so is typical max cost effective array.
    • 200 AH * 29.0 volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 377 Watt array minimum
    • 200 AH * 29.0 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 753 Watt array nominal
    • 200 AH * 29.0 volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 979 Watt array "typical" cost effective maximum
    So even with a "conservative" 2 days of "no sun" and 50% max discharge--You are looking at a suggested array of 654 to 753 to 979 Watts... And for RVs with Air vents and an A/C unit mounted on the roof--Getting much more than 300 Watts of so of solar array can be difficult to fit (any partial shade on a panel pretty much "kills" the output for that panel at that time of day).

    I will stop here... I have made a bunch of guesses and assumptions. And while something like a Lithium Ion battery bank is really nice--The basic math is not much different (useful stored energy per AH @ XX Volts).

    Your thoughts?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rocket999rocket999 Registered Users Posts: 9 ✭✭
    Thank you bill
    i will digest you generous offering and respond when i can

  • rocket999rocket999 Registered Users Posts: 9 ✭✭
    I had to get some rest and start first thing in the morning to begin to digest your message. Prior electrical knowledge solely from working on houses as contractor eons ago.

    My intent is to have a system in a small RV with the two 24V 100Ah big battery boxes (maybe more later as necessary). to simulate “shore” power for a few weeks a year in short segments.  Loads will be tiny during those times, warm the coffee have nice interior lighting when not outdoors, shut the system off when not in use during sleep.

    Then move it into a cottage residence in the forest (Los Altos Hills, CA) to cover basic power needs in case of PSPShutdown by City of Palo Alto, they supply grid.  We do not get the dangerous wind so no shutdows yet.

    It will never be grid tied i hear neighbors here spent years getting permits for rooftop systems presumably grid tied.  I do not own here,  that takes $5 to 10 million.

    Just bought Phocos PSW-H 3kW 120vac/24V. I suspect its a much better than comparable MPP.

    Read and tried to digest your writing about grounding.  I can carry a copper grounding rod  drive it down 30in. Or so at locations if permitted while at sites in the RV and can easily tie into the ground rod in the cottage.  

    Sounds like fundamental design principles are:  Battery banks always large for the loads so they are not deeply discharged.  One person says. Keep them betwee 25% ans 75%.  In this case solar array could be just enough to recharge modest consumption until, and if, boondock trips get longer. Currently the solar array is homemade suit case 2 X. 100W. 5.7 A. Renogy monocrystaline.

    I have a lot to learn and it should be fun
    Thanks again
    So great to se a highly reliable source,   Forms tend to be sketchy 


  • BB.BB. Super Moderators, Administrators Posts: 31,425 admin
    I live just 20 miles to the north of Los Altos (San Mateo). So I know the costs of living here.

    The copper grounding rod is not a big issue to worry about. The solar power system does not need a ground rod to operate--Mostly just for lightning safety--And we don't get much lightning here (unless you are on the top of a hill in an open area). And you could bury a "copper ground plate" a couple feet down in the ground if you need a "temporary" ground vs the 8-9 foot ground rod driven into the ground (30 inches is not really enough).

    I have looked at the choice of an off grid solar power system vs just storing 10-20 gallons of fuel and a Honda eu2200i genset--And the genset has won for me. The longest power outage has been a week or so--And that was 60+ years ago on the coast after a major storm. Otherwise, the longest was a power safety shutdown for a couple days (windy, dry, brush fire possibilities from poorly maintained utility equipment and poor forest/grass land management making for higher fire risks). Just used an extended runtime fuel kit for the Honda (replacement fuel cap with fuel line to 5 gallon gas can) and 2. gallons of gas per day for power (running some lights and a couple refrigerator/freezers) was way more cost effective than batteries + solar (and I already have a 3.5 kWatt GT array on my home).

    At this point, the genset + fuel (fuel preservative, recycle to car once a year) was just more cost effective. Batteries age and the typical lead acid batteries (such as 6 volt @ 200 AH "golf cart" batteries) only last something like 3-5 years typically--Even if only float charged and never or slightly used). You can get "better batteries" (good quality lead acid or Li Ion) that can last 15+ years--But those are not cheap either.

    And if you are in a forest, do you have clear access to the sun for, at least, ~9am to 3pm... Solar electric panels just do not work in the shade.

    A smallish battery bank + array + inverter-charger could still be a nice solution for "overnight" power (quiet time--Although the Honda eu family of gensets, and other equivalent inverter-generators are also very quiet--Ran the eu2000i for a couple days at my in-laws and nobody could hear the genset inside the home, and could not hear it at the street or next door neighbors) could still work--Especially if you want the solar for RV use anyway...

    I would suggest that you figure out how large of solar array you can support on your RV (typically 200-500 Watts or so--again clear of A/C and vents) and then size the battery bank for that array. And get a small/quiet genset and 20 gallons of gasoline (last you almost 10 days of 24 hours per day of running) and go that route. If you have good sun at the home for the RV--Then use the RV for lights, radio, cell phone/pad computer charging. And use the genset to run the fridge/freezer, vacuum cleaner, washer, etc. as needed during the day.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rocket999rocket999 Registered Users Posts: 9 ✭✭
    Thank you Bill.
  • 706jim706jim Solar Expert Posts: 410 ✭✭✭✭
    Bill makes many good points. Another is to size the generator modestly. The Honda is quiet and fuel efficient. A larger generator, say 6500 watts, would actually cost less but is so much noisier and thirstier. How much fuel can you store when one of these burns a gallon an hour 24/7? Better to just keep your fridge and furnace going rather than trying to keep your whole house running as if nothing happened to the grid.
    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 27th year.
  • rocket999rocket999 Registered Users Posts: 9 ✭✭
    Thx for comments folks.   I'm sooo green (pun intended)  but on a steep gradient  learning.

    I thought of gas generator,  shopped shopped never pulled that trigger.    I like the "toy" aspect of solar battery generator and doubt we will have prolonged shut down.  Around here rich people get taken care of .....   Heat with wood  .... hot shower in RV sitting there,  TV over the air.    I just hope the local internet provider which uses microwave antenna communication with local repeater station,   does not get shut down.  They did last year a mile or so north,  the Page Mill rd corridor  did not.  Verizon hot spots hideoud bad.     Palo Alto Ca has no coax internet feed in this neighborhood,  even landline phone is flaky.  Amazing.
    This Phocos PSW-H 3kW 120vac/24V.  120VAC output is rated 40A yet if I put 20A breaker on it I can use 20A or less loads and be safe .... with a 20A GFI breaker,  found one that mounts of DIN rail.  Safe??

    Bill from my rookie calculation,  this phocos wants minimum 90V of solar feed for recharge the lithium batterys,     I have Renergy  100W,  5.7A,  18 or so V,   (X2),   so I think you nailed it I need 3 more to reach the 90V minimum for PV to recharge.  German engineering.


  • rocket999rocket999 Registered Users Posts: 9 ✭✭
    This location is not full forest,  its on a south exposed ridge with ability to catch some of he sweep of the sun.  An array the follows the sun would make sense here
  • BB.BB. Super Moderators, Administrators Posts: 31,425 admin
    Just remember that solar panels' Vmp and Voc change with temperature... Vmp and Voc rise with cold temperatures and fall when hot.

    You want Vmp-array-hot > 90 VDC, and Voc-array-cold to be under 230 VDC... For example, if you choose somewhere around 140 Vmp-array, then:
    • 140 Vmp-array / 17.5 volts Vmp panel = 8 panels in series nominally.
    We do not get large temperature swings here--But you always want to check the Min/Max temperature effects on the Voc / Vmp of the array.

    Many companies have web (or downloadable software) to help folks size their solar arrays... Here is one from Midnite and works pretty well for a quick check of array design voltages for other controllers:

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rocket999rocket999 Registered Users Posts: 9 ✭✭

    BB thanks for the comment about de rating,  I learn a ton by following up on your information

    Just watched a youtube super cool sun tracking array mechanism where small solar panels exposed to sunlight behind the main array energize small electric motors to change position of the array to face the sun ....   until the small panels are in full shade and main array is looking direct at the sun.  Someone should furnish plans and information about resources for us DIY folk.    

    From a quick look at climate / weather records for this area the average temps during summer are just a bit above the temps the Renogy panels are rated at (25C  ie 77F) making derating current one could expect from those panels insignificant.   Unless I misunderstand something

  • BB.BB. Super Moderators, Administrators Posts: 31,425 admin
    Just to be clear... Both Voc/Vmp and Isc/Imp change with temperature... Voc/Vmp fall (relatively fast) with increase in temperature. And Isc/Imp actually rises with increased temperature--But the change for Vxx is something like 5-10x the rate for Ixx changes--So we typically ignore temperature effects on solar panel current.

    There are several issues we look at when sizing a solar array to a MPPT type charge controller... When the panels are very cold, Voc (voltage open circuit) rises--So we need to look at the historically low temperatures of the installation to make sure that Voc-array in very cold weather does not over voltage the input to the MPPT charge controller.

    And we also need to look at the historically high temperatures to make sure that Vmp-array in summer does not fall below the input voltage needed by the charge controller to efficiently move current to the battery bank (Vmp-array-hot needs to be at least a few volts higher than the wiring+controller voltage drop to the battery bank (in "high input voltage" solar charge controllers and GT inverters with MPPT--The Vmp-array needs to be way higher than battery bank voltage because of the internal design).

    Then there is the Derating of solar panels to set our expectations of the solar panel performance. For a first approximation, the MPPT type charge controller operates as:
    • Power into battery bank = Vmp-array * Imp-array * 0.95 controller efficiency = Watts into battery bank
    Imip-array is (mostly) based on available sunlight. Imp-std (standard test conditions)--Full noon-time sun on clear day, panel pointed at sun around 1,000 Watts per square meter--And that gives ~100% of Imp rating for solar panel. Any haze/clouds/etc. will reduce Imp-array (based on actual sunlight hitting panels). Also, as the batteries get closer to full charge, the charge controller will draw less and less current from the array.

    Vmp-array is rated on "standard test conditions" which is "room temperature" under "full sun" (solar simulator light box) for a few seconds--So the solar cells stay very near room temperature during the test.

    HOWEVER, in real life, solar cells get hot from the heat of the sun (and other electrical effects). More or less, a solar panel in 77F/25C in full sun reaches about 45C (113F)... And add being on a roof/hot summer day, no wind, you have 20C/36F rise in hot summer day. Causing the Vmp-array to fall. One a worst case day, the Vmp-array falls almost 20%, add a few percent drop due to dust on panel, controller/wiring loses, hazy day--And why we use something like 77% or so losses vs the "ideal sun/ideal temperatures/etc." from the solar power system.

    The reality of all the "issues" ends up being we only see ~77% of a panels rated power output a few hours a year at solar noon on cool/clear autumn/spring days. You can see more power (and even more than panel ratings) if you are in an area with very cold (sub freezing) weather and/or water/snow/white sands reflecting light into the array along with direct sun... But it does not happen for most people in average conditions.

    Here is a relatively short discussion that goes a bit more into details about solar panels--And their deratings/issues:

    PVWatts uses this list for their deratings: (link to website program)
    System Losses
    The system losses account for performance losses you would expect in a real system that are not explicitly calculated by the PVWatts® model equations.
    The default value for the system losses of 14% is based on the categories in the table below, and calculated as follows:
    100% × [ 1- ( 1 - 0.02 ) × ( 1 - 0.03 ) ×
    ( 1 - 0.02 ) × ( 1 - 0.02 ) ×
    ( 1 - 0.005 ) × ( 1 - 0.015) ×
    ( 1- 0.01 ) × ( 1 - 0.03) ] = 14%
    The Inverter's DC-to-AC Conversion Efficiency is a separate input under Advanced Parameters with a default value of 96%. Do not include inverter conversion losses in the system loss percentage.
    PVWatts® calculates temperature-related losses as a function of the cell temperature, so you should not include temperature loss in the system loss percentage. See the Technical Reference for details.
    If you want to use a value other than the default, you can either type a new value, or use the calculator specify values for the categories listed in the table below. For a description of the categories, see System Losses Categories.
    Default values for the system loss categories
    CategoryDefault Value (%)
    Light-Induced Degradation1.5
    Nameplate Rating1
    They take temperature into account elsewhere in their software (it appears).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rocket999rocket999 Registered Users Posts: 9 ✭✭
    edited February 26 #13
    Hello BB
    1. Any comment of what a smart non combustable surface to mount inverter/MMP charger which would reside in an RV part time ie portable.  Hardy board ( concrete fiberglass mesh used under ceramic tile in bathrooms ect.)  over plywood is the "best" suggestion I've heard so far.

    Lots of folks seem to be nonchalant about fire danger.     One person said engineer it well with conductors and connections generously specifications to prevent anything happening.   Sounds good.

    thx for your abundant "energy" you must be connected.


  • BB.BB. Super Moderators, Administrators Posts: 31,425 admin

    Hardy board, some sort of sheet metal, etc. is a good non-flammable surface. Using metal conduit for electrical cables (or cable raceways, etc.). Also, the floor directly under the installation should be non-flammable too.

    For solar battery charging, the cables should be "uprated" by the NEC continuous derating factor of 1.25x (i.e., 14 amps max current * 1.25 = 17.5 amp minimum branch circuit/breaker rating or round up to 20 amps).

    The NEC cable rating is relatively conservative (compared with marine wire ratings)... Here is a simplified chart that works well (youles can use the real NEC tables and deratings which take conduit fill/ambient temperatures/into account too):

    For most wiring, use "house" wiring that is either solid or "thick stranded" cable. The very fine cables (such as welding cables) tend to "squirm out" of standard wiring/solar/etc. binding posts/screws... If you need very flexible cable (like welding cable), then crimp connectors are better (but whole issue of getting the right connectors and tools to crimp).

    I agree with you that you want a "fire resistant" installation. Solar has lots of current (i.e., 10 amps at 120 VAC is 100 amps at 12 VDC for "same power") and it can take hours to recharge the battery bank (constant maximum current for 2-5+ hours. Adding cable/wiring clamps, making sure plastic/rubber bushings/fittings are used through metal to prevent cuts in wire insulation. And using the proper rated fuses/circuit breaker to protect against short circuits/over current (fuses and breakers are there to protect the wiring, not the "device" at the end of the wire). The battery bank is the source of "high current" in most installations--And fuses/breakers should be used for every wire that leaves the battery bank (i.e., on positive cables if negative ground DC power system).

    Here is a discussion on how to pick the correct fuses/breakers for your installation:

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