New system

Pippin65Pippin65 Registered Users Posts: 6 ✭✭
Hi I have a Rover 40amp mppt, and two 100 watt 12 v Renogy panels.  Have two Duracell agm batteries in series/24 volt.  What’s a panel that will “fit” with the two 100 watt panels


  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    When you put solar panels in series, they need to "match" Imp (rated current) within 10% or better...

    When you put panels (or strings of panels) in series, the Vmp (rated voltage of the string) needs to match within 10% or better.

    With MPPT charge controllers, the mix and match does become a bit more complicated... For example, charging a 24 volt battery bank, you really want 3 or more of your "100 watt" panels in series for optimum operation.

    However, you also have to look at the maximum voltage the MPPT charge controller accepts. You do not want Voc-cold (panel voltages rise in very cold temperatures) to be exceeded.

    Can you tell us more about exactly which controller you have (Link to data sheet is fine), and how much more wattage to the array you want to add? AH rating of your battery bank?

    Mix and match for solar panels on an MPPT controller always gets a bit "fun".

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Pippin65Pippin65 Registered Users Posts: 6 ✭✭
  • Pippin65Pippin65 Registered Users Posts: 6 ✭✭
  • Pippin65Pippin65 Registered Users Posts: 6 ✭✭
    edited June 2020 #5
    So there’s my system.  So far.  Have another 100w renogy compact coming.  

    Live in Florida. May lose power for up to 6-8 hrs tops.  Unless out for days with hurricane.  

    Would like to be able to run a refrigerator for 6-8 per day if poor outage.  Maybe also run a window ac for 6-8 hours a day.  
    Will want to regularly charge my Ego battery packs for mower and blower. And all my Ryobi + battery packs.  
    And maybe provide 12 v led lighting throughout the yard.  

    So have : 2 100 w renogy panels    
    Rover 40amp scc 
    2 105ah agm batteries are 12 v.  

    Was running them in series at 24 volts but one 100 watt panel wouldn’t charge. So a switched to parallel and 12 v. 

    I would like to have more than 400 w panels (12v limit) as my array faces east to west with best light from morning til 2pm

    Am looking at a Samlex pst 3000 24v.  

    Am I best with 12 or 24 v  for my needs.  Will add two more batteries within 2 months.  Same brand make. 

    Would like to use the two 100 watt 12v with a 24 volt panel (or pair) at like 300-ish watts or 1kw total.  

    Please help.  
  • mike95490mike95490 Solar Expert Posts: 9,581 ✭✭✭✭✭
    Fridge and AirCon, you are in 24 or 48V system territory.  And you will need more than 400w of panels to reliably one of those appliances, for 2, you are looking over 1200w
    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

    gen: ,

  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    I know that this is a solar power forum, but a genset is usually a better solution for a short term outage that happens once or twice a year, or less...

    A Honda eu2200i (new version of the eu2000i), or eu3000 something with (for me) about 2 gallons of gasoline per day of runtime works very well. And the generators are pretty quiet. 20 feet from the house, and you probably will not even hear it.

    Building a solar power system that can run your loads for a week or so, and larger loads like fridge and A/C, are not cheap. And the "consumables" (aka batteries that last 3-5 years for "golf cart type" FLA) need to be replaced, even if they are hardly ever used (large battery bank, replaced every 5 years, not cheap).

    Generators, only consume fuel when running. And if you use fuel stabilizer (if you want to store 20 gallons for 1 year at a time), and take care when putting away (run for a while, get hot to drive moisture out of oil, dump fuel, run till empty, drain carb, maybe a squirt of oil in the spark plug hole, pull cord to compression stroke to close valves)--I have stored a couple of hondas for upwards of a decade or more between uses--Put in fresh fuel, and they start right up.

    If you have natural gas or propane on the property, that can be a nice fuel source vs gasoline (storage, recycle to car once a year, etc.).

    There is always the idea of keeping a backup or two as spares if this is "critical equipment"...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Pippin65Pippin65 Registered Users Posts: 6 ✭✭
    edited June 2020 #8
    I hate gas powered stuff but you make a good point. Here’s what I want to do?  Just have like 10 hours of a/c window unit or refrigerator or freezer in garage or some combination.  
    My idea:
    I am getting my main service panel replaced in a few weeks,  would like to have them rough out the electric at my panel for a transfer switch/ solar panel.  That I can then proceed to do an install over time ( so wife doesn’t freak out) “box” then panels etc.  
    that way this off grid will be an expensive battery charger for all my tools. And mower.  And run low voltage lighting on my property.  
    What do I tell the electrician I need??
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Be careful... You really want to plan this all out, vs just telling the guy you want a sub panel with 60 amp (or whatever) service (120 or 120/240 VAC?). And all of your "protected loads" on the sub panel (fridge, some lighting, A/C, whatever).

    Leave room for the "magic box" that will include one or two transfer switches, AC inverter interface (which may have a transfer switch), a genset interface (which may have its own transfer switch, or an AC inverter with AC1 and AC2 inputs, etc.).

    If you do not pre-plan this stuff--You can get yourself in an expensive or non-functional box.

    A lot of the (very nice) mini-split A/C systems these days are 240 VAC--There are some smaller ones that may be 120 VAC only with limited models available.

    And if you design a 120 VAC sub panel, and need 120/240 VAC for your A/C--Then you did it all for not...

    For a genset, if you use a manual AC transfer switch, this can be done pretty easily:

    You can even do something like a cord from the manual transfer switch to the genset, and use the same cord set (or a "simple" single circuit transfer switch) to do A-Genset and B-Inverter as input the the manual transfer switch.

    This stuff gets non-trivial pretty quickly.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Pippin65Pippin65 Registered Users Posts: 6 ✭✭
    edited June 2020 #10
    Appreciate you scaring the crap outta me BB!  :)    I figure while they are changing the panel it would be reasonable to lay the groungwork for future upgrades.  Funny you mention mini-splits because when my central goes, its 15 + years old now, I plan on mini splits  here in Florida
    My plan now is to get this BBQ Smoker cover/off grid system going..  have a LRA question: have a portable window up and it's 8500 btu, states 1200 watts cooling power and has a LRA/RLA of 60.5 A/ 10.  also states: FLA of fan motor  up /down as 0.58a/1.20a

    would , say a samlex pst 2000 make it run?
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin

    You can get some very nice inverters (inverters, inverter-chargers, hybrid inverter-chargers that have GT Mode too, etc.). You can get 120 VAC only, you can get 120 in/120/240 VAC out, you can get 120/1240 in and 120/240 out, etc....

    I will try a simple one first here... On the left you have a main panel (120/240 VAC). On the right you have a sub panel rated for 60 amps 120/240 VAC (60 amps * 120 VAC = 7,200 Watts, or 240 VAC * 60 Amps = 14,40 Watts). That should be enough to start.

    And you use a simple transfer switch. Two input ports (typically A:L1&L2, B:L1&L2) and one output port (L1&L2).

    And the neutral is assumed to be ground bonded in the main panel (North American Standard). And you have a common Neutral through the system (main panel, transfer switch, sub panel, and to input power ports A and B).

    For the sub panel, a 60 amp panel does not support many circuits (4x 240 VAC, or maybe 8x 120 VAC). You may choose more--Such as one to each major load (Fridge, A/C, Well pump, Freezer) and more to individual outlets and uses (change lights to LED based, a couple to hall way, major rooms, kitchen, master bedroom, etc.) and perhaps a switch to specific outlets (at least 1-2 outlets in kitchen, outlet in master bedroom for cell phone/laptop charging), a pair in the garage for home router/modem interface, alarm, perhaps one for your home printer somewhere, etc.

    The more switches in the sub panel, the more "control" you have over your loads (obviously, you will not be able to draw 15 amps from 10x circuits at the same time--150 Amps). You may have, for example, your A/C wired to a 240 VAC circuit--Your existing A/C system, and if you have a 120 VAC, it will not run from your 2 kWatt Samlex inverter... But if you have a 4-8+ kWatt 120/240 VAC genset--You can fire up the 120/240 VAC and plug the Port B cord from Samlex to genset to run your A/C, more loads when needed.... And later, if/when you decide to upgrade your AC invert to a 4 kWatt+ 120/240 VAC, you can just plug into that. (Utility is always to Port A, and alternate power source is plugged into Port B).

    The transfer switch can be automatic (basically a relay that is on Port A when there is utility power, and on Port B when utility power has failed OR when you have fired up the inverter or genset). You setup some mains power relay(s) that can auto start the inverter or genset (I am not a big fan off auto-start gensets). Or you can use a manual transfer switch... (simple relay transfer switch) (manual transfer switch)

    There are other ways of doing transfer switches too... You can have a main panel with sheet metal interlocks. Either Main Power on, or AC Genset output "on" to power house power...

    Or you can get a multi-port manual transfer switch from Home Depot/et. al. (wires to/from main panel, so you do not have to re-wire some home circuits from main panel to sub panel:

    Or a whole house transfer switch:

    Or a utility meter socket that can plug genset directly into:

    I am certainly no expert on this stuff... There are lots of options out there... And, many times, it is difficult to do "slow upgrades" to your main/backup power systems. The above show how things can be done with "dumb" backup power devices. You can also get (obviously) "smart" Hybrid AC inverters that have AC1 and AC2 inputs (auto transfer switches), generator auto start, can back feed AC power from solar to your utility (assuming you have approvals and permits). Etc.

    And you can buy pre-wired "E-Panels" that can manage your DC and AC power for various systems (Schneider, Outback, etc.).

    I showed the above because you will get a better idea of what options are out there... And you have to decide what road(s) you want to go down ($$$ vs functions). The "simple" manual transfer switch (A:B input transfer switch), or the multi-circuit "retrofit" that connects to your existing main panel are probably the easiest to install/understand. And you simply connect your alternate power source to Port B (you can have plug to AC inverter and AC Genset, or you could even have a second transfer switch that is hard wired to AC inverter and AC genset).

    But you have to follow Code (different cities/counties can have different codes they follow--and I am not a code guy). And your backup power system generally only powers a subset of your AC power usage (perhaps not central Heat/AC, Electric Water Heater, Electric Range)--So you have to decide the $$$ vs Capability.

    And, if you are looking at a sophisticated system... You may want to hire somebody to plan or even possibly go full turnkey install... There is a reason that "Dave Angelini" (his real name) has made a good living doing off grid / full solar powered homes for decades.

    Even if you do not do this yourself (or choose DIY and keep it small and simple), it does not hurt to at least have a glimpse of the universe of options out there (and a bit of drooling too).

    Regarding the A/C system... You really probably do not want/cannot run a "small" conventional A/C window shaker with a 2 kWatt inverter (locked rotor amp ~60.5 amps @ 120 VAC = 7,260 VA -- Much more than the ~4,000 VA that a 2 kWatt Samlex can output). And running 10 amps @ 120 vAC (1,200 Watts) for many hours per day--Very large array and battery bank just to keep running (10 amps * 120 VAC * 1 hour = 1,200 WH for 1 hour--Vs running an efficient full size fridge on ~1,000-1,500 WH for 24 hours).

    There are starting to be some Inverter based Window AC units... The inverter makes the A/C "soft start"--And depending on the design/programming of the A/C system, some can then run at ~350 Watts for hours on end (no cycling between 1,200 Watts + surge every 20 minutes). For example:

    Should have very little (or no) surge requirements... Still uses 1,240 Watts / 11.3 amps @ 120 VAC on full power...

    Since I am not in the business, or use A/C at my home, I cannot speak to the details of the various products and how they run... But hopefully others here can help...

    In the end, LED lights, laptop, LED TV, cell phone charging, smaller system (say 1,000 WH per day)... Add fridge, washer, well pump, medium size system (say 3,300 WH per day). Add A/C, electric range, etc. and big $y$tem (can be 10,000 WH per day).

    Here is a long discussion on Mini-split Inverter based A/C and heat pump systems:

    Your thoughts?

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