Advice for a newby

maddymaddy Registered Users Posts: 8
Hello all, first I must say how informative this forum is and will say a big thank you in advanced, THANK YOU.

I will try and keep my request short, as i have a problem explaining my self, ok I need help with my solar install, I have an old motorhome and I want to install 6X 100W 12V panels that I've already bought, I'm thinking of 6X Trojan T105, Volt 6, AH 225 I've read lots and lots but i now have brain overload, I would like to know whats the best way to hook all these up, please? I know i need a MPPT controller, which one? i looked at a Morningstar Tristar MPPT 45 amp 12/24/48V, but its a lot of money is there a good alternative? sorry if grammar and all that looks strange (I try my best) but its due to accident with effects of carbon monoxide poisoning many years ago, ok, if any other advise it will be a great help many many thanks. I am from the UK.

Just to add I want to run a fridge freezer, lowest running cost that i can find, so i will need an inverter, and just to say that there is already a 85W solar on the roof and its got cheap charge controller, and 1 battery, also got a 24v to 12v batt charger for starter batts and going to the leisure battery, oh and aslo there is a sterling 12v 1000w propowerQ,all this is in the living part of my truck under the seat, but I really want to start afresh, and put the new lot in the garage part at the rear. Thanks.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,063 admin
    maddy wrote: »
    I have an old motorhome and I want to install 6X 100W 12V panels that I've already bought, I'm thinking of 6X Trojan T105, Volt 6, AH 225 I've read lots and lots but i now have brain overload, I would like to know whats the best way to hook all these up, please?

    The first question I always like to ask--How much power do you really need (have you measured your usage with a Watt*Hour meter)?

    Second is conservation--In general, selecting/buying appliances that use as little electric power as possible is usually less expensive (long term) vs trying to build out a larger off grid solar power system. And with an Motorhome, space for solar panels and batteries is a hard limit to how much solar power you can install.

    The one appliance that usually pushes power usage and solar power system sizing is a refrigerator--For weekend/seasonal living, a propane refrigerator is usually a more practical. If you are living off grid 9+ months a year, then an electric refrigerator can make economic sense (of course, if you are in Europe--Your fuel costs are several times that vs the United States--So propane may be quite expensive to use even for seasonal usage).

    And then there is where you live/when you will need solar power. For example, London England with panels mounted flat to the roof--The amount of (long term average) sun is terrible:

    http://solarelectricityhandbook.com/...rradiance.html
    London
    Average Solar Insolation figures


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

    Jan
    Feb
    Mar
    Apr
    May
    Jun


    0.75
    1.37
    2.31
    3.57
    4.59
    4.86


    Jul
    Aug
    Sep
    Oct
    Nov
    Dec


    4.82
    4.20
    2.81
    1.69
    0.92
    0.60


    If you mount the panels on an angle, you can increase your harvest (changing angle seasonally can help too):
    London
    Average Solar Insolation figures


    Measured in kWh/m2/day onto a solar panel set at a 38° angle from vertical:
    (For best year-round performance)

    Jan
    Feb
    Mar
    Apr
    May
    Jun


    1.27
    2.04
    2.76
    3.67
    4.17
    4.20


    Jul
    Aug
    Sep
    Oct
    Nov
    Dec


    4.25
    4.16
    3.26
    2.41
    1.53
    1.05


    Realistically, if you are under 3-4 hours of sun per day, the amount of power generated by solar is pretty low. And remember that dark/stormy days, you may get only 1% of the systems sunny day capacity.
    • 600 Watt array * 0.75 hours of sun (January, flat to roof) * 0.52 system efficiency = 234 Watt*Hours per day
    • 600 Watt array * 4.0 hours of sun (4 months of year, tilted to roof) * 0.52 system efficiency = 1,248 Watt*Hours per day
    A small/very efficient refrigerator may use 250 Watt*Hours per day. During the summer, you can, perhaps, keep up with a typical/small refrigerator.

    Power usage is highly personal, but planning ahead can save you a lot of money.

    Which sort of leads us to your battery bank... Batteries only store the energy you can collect from the solar array. We look to size the battery bank for your needs and available solar array.

    A full time off grid home, we would be suggesting 2 days of storage and 50% maximum discharge for long battery life and optimum costs/performance. For an R/V with less space and weekend/seasonal usage, you might go with a 1 days storage and 50% maximum discharge--But that leaves you either not using power or using a genset+fuel a lot more during bad weather.
    • 660 AH * 12 volt battery bank * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 1,83 Watt*Hours per day average
    Thank can be enough battery for a small/efficient refrigerator--It is close. Does not leave much power for other uses (laptop computer, fan, lighting, etc.).

    And then there is recharging the battery bank... Normally we suggest 5% to 13% rate of charge (based on the battery bank's 20 hour capacity):
    • 660 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate o charge = 621 Watt array minimum
    • 660 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate o charge = 1,243 Watt array nominal
    • 660 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate o charge = 1,616 Watt array "cost effective" maximum
    So, your 600 Watt array would be the absolute minimum I would recommend for your battery bank size. And if you where living full time off grid--I would be suggesting a 2x larger solar array.

    And, depending on when/where you will be using the R/V, during winter you do not receive very much sun anyway--And you will be needing a lot of shore power/generator hours to keep the batteries charged (lead acid batteries hate sitting at less than ~75% -- They will sulfate and be ruined fairly quickly (sulfation starts in hours, and sitting days/weeks/months unused will kill the battery bank pretty quickly).
    I know i need a MPPT controller, which one? i looked at a Morningstar Tristar MPPT 45 amp 12/24/48V, but its a lot of money is there a good alternative? sorry if grammar and all that looks strange (I try my best) but its due to accident with effects of carbon monoxide poisoning many years ago, ok, if any other advise it will be a great help many many thanks. I am from the UK.

    For a "smaller system"--If you are already committed to "12 volt 100 watt panels" (Vmp~17.5 volt rating)--A PWM controller may be just fine for you. If you are looking at 3x 200 Watt panels instead (for example Vmp~30 volt panels), then a MPPT controller would be needed, and overall, could cost less (less expensive panels, more expensive charge controller). But don't buy any hardware until you have answered the above questions.

    Your English was fine here (probably better than my US/English).
    Just to add I want to run a fridge freezer, lowest running cost that i can find, so i will need an inverter, and just to say that there is already a 85W solar on the roof and its got cheap charge controller, and 1 battery, also got a 24v to 12v batt charger for starter batts and going to the leisure battery, oh and also there is a sterling 12v 1000w propowerQ,all this is in the living part of my truck under the seat, but I really want to start afresh, and put the new lot in the garage part at the rear. Thanks.

    There are DC powered refrigerators--And there are several types. There is the "absorption cycle" -- these are the common "propane" powered refrigerator--They have an AC/DC powered option (using electric heater)--But on electricity, they are horribly inefficient.

    Then there are the pure electrical refrigeration with a mechanical refrigeration pump. These are much more efficient but either require an AC inverter, or you can get DC powered versions too. But the DC powered versions tend to be very expensive too. For a house, an AC refrigerator + AC inverter is usually less expensive overall. However, for an R/V with little space for solar array+batteries, a DC powered refrigerator may be the only possible solution--A standard AC fridge uses a pretty large AC inverter (1,200 to 1,500 watt inverter and and 600 AH @ 12 volt battery bank minimum) battery bank (high starting surge).

    You need to do a lot of research on your side of the pond to understand what is available--And how much it will cost before you start spending.

    Sorry for all the math and questions... To help you with an accurate (and cost effective) answer--We really need to discuss the details.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • petertearaipetertearai Solar Expert Posts: 446 ✭✭✭✭
    Hi look into the new inverter fridges . Here in NewZealand they are relativity cheep and are very efficient and they don't have big start up surges . Also lots better than having a propane flame running.In my opinion.
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
  • maddymaddy Registered Users Posts: 8
    Hello again, thanks for the replies. Bill thats a very detailed reply thanks, i did forget to mention i will be wild camping through in southern Spain and hopefully southern Sicily, so it will be more sun?

    peterearai i will look into them inverter fridges, but i bet they will cost a lot over here most things always do.
  • BB.BB. Super Moderators, Administrators Posts: 31,063 admin
    Oh yes... Lots more sun... I have given you one link where you can figure out your "hours of sun" per day (vs tilt on the panels/location/etc.). And there is a simple formula for figuring out Watt*Hours per day based on hours of sun (or divide by 12 volts for AH @ 12 volts per day if much of your stuff is DC).

    And, you need to estimate/measure your loads vs the array size/mounting/seasons/location to see if it works out or not (need utility connection, genset, etc.).

    There is something to be said for a propane fridge that uses a 1/2 lb of propane per day if you are weekend/summer camping (vs 9+ months per year usage where an electric compressor type fridge usually makes more sense).

    Sounds like a lot of fun.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maddymaddy Registered Users Posts: 8
    I've been thinking on connecting the solar in series to 24v and aslo the batteries in series to 24v (not with the 6 trojan) I could also charge my truck batteries from the solar as they are 24v would this set up be more efficient?
  • BB.BB. Super Moderators, Administrators Posts: 31,063 admin
    In general, a properly designed 12 volt or 24 volt solar power system does not really affect efficiency... Power = Voltage * Current -- Double the voltage and 1/2 the current -- Still get the same Power (Watts and Watt*Hours).

    The reason we go with higher voltage systems is two fold... First, simply gets expensive and difficult to wire up a >100 amp circuit to supply 1,200 Watts of power to an AC inverter:
    • P=V*I
    • P=12 volts * 100 amps = 1,200 Watts
    At best, the 12 volt battery will drop down to 11.5 volts under load, and your inverter will operate down to ~10.5 VDC... Given that the inverter will supply 2x load for starting surge (2,400 watts), and such... you need to design the wiring from the battery to the inverter for 100 Amps and ~0.5 volt maximum drop for reliable operation. That is a lot of current and a lot of expensive/heavy copper wiring.

    So, for larger power systems, we go with 24 or 48 volt battery banks... 50 amps and 1.0 volt wiring drop for a 1,200 watt @ 24 volt system is much easier to design/build (wiring is about 1/4 the amount of copper).

    Another reason to go with higher voltage is to put more batteries in series vs parallel. Battery banks really do not do great if you have lots of parallel battery strings. They do not always share charging/discharging current well, and an open or shorted cell is "hard to find".

    But if your loads are 12 VDC, then a 24 volt battery bank just does not make much sense...

    Anyway--We are talking generalities here... We need to talk specifics for your needs. And that gets back to how much energy (watt*Hours, or amp*hours at what voltage) do you need. Can you fit the battery bank to support those loads? Can you put enough solar panels on the vehicle to charge the batteries and support your daily loads? If you cannot, then you need to look at you loads again--Conservation (small/efficient laptop computer or tablet vs a desk top computer, propane fridge vs electric). Perhaps more generator run time/more fuel usage/more noise and smoke, etc during the day--And a smaller solar+battery system for night time loads.

    I don't want to talk too much in generalities--It is confusing and lots of hand waving. Your loads and your needs first. Design the system to support those needs/re-evaluate those needs if you cannot (space, money, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maddymaddy Registered Users Posts: 8
    Thanks again Bill for the detailed reply. I guess its manly the 240v fridge freezer that's going to be the main draw as i'm going to be moving around sunny Europe i want to keep food cold, the other lite draw will be the 12v water pump, and 12v led lights, there is already a small 12v/240v/gas fridge but way to small, for my use, also the TV is 240v but i dont watch that much tv just the odd movie at night, there is a small 240v 800w microwave, oh and the toilet is 12v flush, I will be getting some 12v fans to keep cool with, i think thats about it. I do have a suitcase genny that i have not long bought for backup. the fridge freezer i will turn off at night but not open the doors then back on in the morning. The thing is a am trying to find the best way to set it up, without having to spend loads of money. I've not bought the batteries yet or the charge controller, or the 24v to12v b2b charger, all these items seem to cost a lot, i know there is cheaper makes on ebay but can they be trusted? I guess i got to decide and just go for it. thanks again.
  • BB.BB. Super Moderators, Administrators Posts: 31,063 admin
    How much time do you have before you need the system up and running for the trip?

    Perhaps you can find an R/V wrecking yard and see if you can find a DC compressor type refrigerator/freezer.

    The LED lighting and a modern LED back lite LCD tv (or laptop computer w/ TV) is going to be pretty energy efficient.

    An 800 Watt microwave oven will require a larger battery bank to manage the power--But if you end up with enough battery bank + solar array to run the refrigerator, you probably can run the microwave for 20 minutes a day pretty easily.

    Anyway--You really need to measure your power usage--then design the solar power system. I still think you are better off with ~10 kG every few weeks--depending on your usage (or whatever your standard propane cylinder sizes are) vs solar+batteries. Especially if this is a once in a life time trip... If you are planning on living off grid in southern/sunny Europe for many years to come, then solar may be the way to go.

    Run the costs for a solar power system + DC compressor cooler vs the cost for using propane for fridge + oven (vs microwave). I would guess it will take many years to recover your solar power costs vs a 1 year trip with propane+propane powered fridge+cost of propane.

    If you end up spending money on petrol for the genset vs propane -- I am not sure that is the best trade off. 1,000 Watt*Hours per day of electricity for a 240 VAC refrigerator would take something like 1 liter of petrol. Plus you have to pull out the genset and run it (perhaps) several hours/times per day).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maddymaddy Registered Users Posts: 8
    Hi Bill, thanks again for the reply. My power usage will be very light, only the fridge/freezer is going to be used on this solar/battery bank with an inverter, maybe 2000w? nothing else, i forgot to mention that there is already a 85w solar panel with a pwm controller, plus a b2b 24v to12v charger, with 1x 12v 110ah battery with 1x 1000w sterling inverter that the previous owner put in, that runs the 12v lights and a tv, although he has done a crap job of it, it all seems to work.

    Getting back to my install i have now fixed all 6 solar panels to the roof of the motorhome, i am going to be using 2x 12V 25A 300W MPPT solar charge controller regulators, (I am aslo thinking of fitting one of these: CBE CB516 Caravan Motorhome Camper 16 AMP 12v Leisure Battery Charger,so if i connect my genny to the EHU it will charge the batteries aslo) i have not yet bought the batteries, so i wonder if you could help me decide, do I go for my original plan of 6X Trojan T105, Volt 6, AH 225, if yes what would be the best way to connect them? I've been reading this: http://www.smartgauge.co.uk/batt_con.html but still cannot get my head around how to best connect the 6x Trojans? or would i be best to use 4x 12v batteries, if yes whats the best way to connect them? also someone suggested that i use 4x 12v 180ah truck batteries, (as thats what they have been using for the last 5 years without problems, and he runs a fridge and freezer from them) but wont they die early, as they are not deep cycle? sorry to sound unsure of things but i like to do the best research and get the best answers, and you seem like someone who knows what you are talking about. Thank you for your time bill it is most appreciated.
  • BB.BB. Super Moderators, Administrators Posts: 31,063 admin
    maddy wrote: »
    Hi Bill, thanks again for the reply. My power usage will be very light, only the fridge/freezer is going to be used on this solar/battery bank with an inverter, maybe 2000w? nothing else,

    I hate to be repetitive--But to be clear, a 2,000 Watt AC inverter and a typical 240 VAC refrigerator/freezer is not a small system. To run a standard refrigeration compressor, you need ~1,200 to 1,500 Watt AC inverter. And to run a 2,000 Watt AC inverter on a 12 volt battery bank, you would need a minimum of 800 Amp*Hour @ 12 volt battery bank. Plus some very heavy copper cabling from the battery bank to AC inverter DC input:
    • 2,000 Watts * 1/0.85 AC inverter eff * 1/10.5 inverter DC cutoff = 224 Amps continuous (and upwards of 448 amps @ 12 volts surge current to inverter).
    That is a lot of current/power/energy. Cables have to be very short and heavy to hope to be able to drive the Inverter to full rated output power.

    Also, your cooler may average around 50 Watts (50 watts * 24 hours per day = 1,200 Watt*Hours per day)... And the AC inverter, if left running all the time draw another 20 Watts itself--Or almost 50% of the refrigerator's power consumption. So your array+battery bank needs to be ~50% larger just to support the inverter running 24x7. You can save some energy by running the inverter in "search mode" (low power standby) if it has that mode. Or run the inverter only 12 hour per day, etc.... But this is a lot of power from an off grid solar power system in a smaller RV.
    i forgot to mention that there is already a 85w solar panel with a pwm controller, plus a b2b 24v to12v charger, with 1x 12v 110ah battery with 1x 1000w sterling inverter that the previous owner put in, that runs the 12v lights and a tv, although he has done a crap job of it, it all seems to work.

    The present 85 Watt panel will only supply you around:
    • 85 Watts * 0.52 off grid system eff * 5 hours for a good summer day = 221 Watt*Hours per day
    Or about 1/5th of the energy needed for just the refrigerator Not a lot of power from that panel by itself.
    • Getting back to my install i have now fixed all 6 solar panels to the roof of the motorhome, i am going to be using 2x 12V 25A 300W MPPT solar charge controller regulators,
    What size solar array?
    (I am aslo thinking of fitting one of these: CBE CB516 Caravan Motorhome Camper 16 AMP 12v Leisure Battery Charger,so if i connect my genny to the EHU it will charge the batteries aslo) i have not yet bought the batteries, so i wonder if you could help me decide, do I go for my original plan of 6X Trojan T105, Volt 6, AH 225, if yes what would be the best way to connect them?

    Your battery bank would be a 12 volt @ (3*225=) 670 AH battery bank... A pretty large battery bank for 12 volts, and a lot of batteries/weight for an RV.

    For an AC battery charger, you probably would want a minimum of 10% rate of charge (5% is absolute minimum--13% to 20% about the maximum):
    • 670 AH * 10% rate of charge = ~67 Amp battery charger @ 12 volts
    That is a pretty good size AC battery charger. A 16 amp AC battery charger is not really big enough if you want to get significant charging:
    • 670 AH * 50% state of charge / 16 amps charging = 21 hours (really ~25 hours) to recharge the bank
    And deep cycle flooded cell batteries really like a 10% minimum rate of charge.
    I've been reading this: http://www.smartgauge.co.uk/batt_con.html but still cannot get my head around how to best connect the 6x Trojans? or would i be best to use 4x 12v batteries, if yes whats the best way to connect them? also someone suggested that i use 4x 12v 180ah truck batteries, (as thats what they have been using for the last 5 years without problems, and he runs a fridge and freezer from them) but wont they die early, as they are not deep cycle?

    You take 2x 6 volt batteries and connect them in series... That gives a 12 volt @ 225 AH battery string. Put three of those "strings" in parallel--Then you have a 12 volt @ 670 AH battery bank.

    Personally, i suggest 6 volt @ 225 AH batteries... I like the ability to measure voltage across each 6 volt battery with a digital multi meter--Very fast and easy to make sure all of the batteries are working OK. Also, a 12 volt @ 225 AH battery would be 2x heavier vs [email protected] AH battery (6 cells vs 3 cells). May be easier to move batteries around and fit them into the battery box easier. In the US, Golf Cart batteries are about the cheapest ones you can get (other battery configurations are more expensive).

    I don't know about truck batteries--If they are getting 5 years of life from them--That is really good. A typical golf cart battery is usually good for 3-5 years.
    sorry to sound unsure of things but i like to do the best research and get the best answers, and you seem like someone who knows what you are talking about. Thank you for your time bill it is most appreciated.

    I hope some other folks can help answer your questions too... A standard 120/240 VAC refrigerator is a very significant load for any off grid system--And for RV's where space and weight pose significant limits, it makes it even more difficult.

    There are some new technology refrigerator/freezers that are "inverter" or "linear compressor" types. These have much less surge current and are much more off grid system friendly... The "average" AC refrigerator may draw 60-120 Watts running, but take 600 Watts or more starting. The new inverter type refrigerator compressors may only start/run at ~120 Watts maximum--A real help to keep battery bank and AC inverter sizes smaller.

    I am very concerned that your solar power system may not keep the cooler (as designed) happy. But, I am not in the UK/Europe--So I really do not know if your compressor systems are much more efficient/low surge vs what we see with "typical" cooling systems here in US.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maddymaddy Registered Users Posts: 8
    Hi bill just a quick reply for now, the solar panels that i've put on roof are 6x 600w and in 2 sets of 3 using 2x 3 into 1 connectors but not gone through the roof yet, as this solar install will have nothing to do with the 12v stuff already in the rv, so at this point would i be better off making this new install 24v and getting a 24v inverter, then cabling can be smaller also i can use 12v batteries in serious ? It is how my truck starter batteries are connected, im not sure if any of what i'm saying is making any sense it's just that i keep reading that's it's better if you can to go 24v and as this install im doing is not going to be connected to the already 12v system on the rv maybe its the better option ? I'm not too sure though if i've enough solar panels for this? Does any of what i've just said make sense ? Sorry but i am very new to all this and wanting to learn more and more as i go on. Thanks again for your already great help.
  • maddymaddy Registered Users Posts: 8
    I'm now trying to work out if i need to fuse the solar panels as i have them joined in 2 x 3s with the 3 in to 1 mc4 connectors, i keep reading that anything over 2 strings need a fuse is this correct?
  • BB.BB. Super Moderators, Administrators Posts: 31,063 admin
    Sorry--Real life got me:
    maddy wrote: »
    Hi bill just a quick reply for now, the solar panels that i've put on roof are 6x 600w and in 2 sets of 3 using 2x 3 into 1 connectors but not gone through the roof yet, as this solar install will have nothing to do with the 12v stuff already in the rv, so at this point would i be better off making this new install 24v and getting a 24v inverter,

    Really depends on your loads... I would suggest spending your money in the most efficient cooler you can--Reducing Watts and average Watts*Hours usage per day. this may mean getting a (very expensive) 12/24 VDC cooler (native DC refrigeration pump) and insulated box. This will keep the size (and cost) of your off grid power system smaller.

    Just using rules of thumbs design (for off grid home/cabin). You have a 600 Watt array and 10% rate of charge (5-13% recommended, 10%+ if full time off grid, no utility/generator power used):
    • 600 Watts * 0.77 panel+controller derating * 1/14.5 volts charging * 1/0.10 rate of charge = 319 Amp*Hour @ 12 volt battery bank
    • 319 AH battery bank * 12 volts * C/5 max discharge rate * 0.85 AC inverter eff = 651 Watt max recommended AC inverter rating
    • 319 AH * 12 volts * 0.85 AC inverter rating * 1/2 days storage * 0.50 max discharge = 813 WH per (no sun) day of storage (2 days from bank)
    • 319 AH * 12 volts * 0.85 AC inverter rating * 1/1 days storage * 0.50 max discharge = 1,627 WH per (no sun) day of storage (1 day from bank)
    • 600 Watt array * 0.52 typical off grid eff * 4 hours minimum sun per day = 1,248 WH per relatively sunny day (outside of winter for many sunny regions)
    The above would be my "nominal" rated battery suggestion for a reliable system... You could do a 2x larger AH battery bank (5% rate of charge), but you will (probably) have to use utility power/genset/vehicle power more often to keep the battery bank properly charged.

    12 vs 24 volt battery bank (and inverter/etc.) is not going to help you at all with this size battery bank (even it you up to 638 AH @ 12 volt or 319 AH @ 24 volt battery bank--Same stored energy, just 12 or 24 volt battery bus--2x voltage and 1/2 current/capacity).
    then cabling can be smaller also i can use 12v batteries in series ? It is how my truck starter batteries are connected, im not sure if any of what i'm saying is making any sense it's just that i keep reading that's it's better if you can to go 24v and as this install im doing is not going to be connected to the already 12v system on the rv maybe its the better option ?

    I am not quite sure--Do you have a 12 volt vehicle or 24 volt vehicle (two 12 volt batteries in parallel is 12 volts at 2x AH; or two 12 volt batteries in series for a 24 volt battery bus at 1x AH battery rating).

    In either case, the present size of system (solar array and functional/recommended battery bank) does not really need a 24 volt battery bank. It is your choice at this point--Match 12 volt RV to 12 volt vehicle bank; or 24 volt RV to 24 volt vehicle bank.

    In general, 24 volt AC inverters are higher wattage rating (and waste more power--idle losses)--An efficient 12 volt AC inverter in the 300-600 Watt range is a much better match. Finding a 300-600 Watt 24 VDC input inverter may be difficult... And running an >1,000 Watt 24 VDC inverter just wastes power, and flooded cell lead acid batteries cannot supply that much surge current (AGM or LiFePO4 batteries can supply higher surge current--But pure storage of WH or AH per day--not that much difference).

    If you where going to be living off grid for a few years and really wanted to be "grid and generator/fuel independent", a LiFePO4 battery bank may be worth it (smaller physical size, lighter weight, more efficient, higher surge/charging current). But--At this point, running a standard AC Refrigerator is probably beyond a 600 Watt array (or right on the ragged edge).
    I'm not too sure though if i've enough solar panels for this? Does any of what i've just said make sense ? Sorry but i am very new to all this and wanting to learn more and more as i go on. Thanks again for your already great help.

    You are close--Typically, I would suggest that you plan your base (everyday loads) at 65-75% of planned/predicted output power from your array (1,248 WH per day * 75% = 936 WH per day "base load")... Just makes running a typical fridge/freezer off grid closer or the "wrong side" of the ragged edge.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • maddymaddy Registered Users Posts: 8
    Hello Bill hope all is well, yes that real life stuff can get you good proper.
    Thank you for your help, I've not completed my install yet, its a slow process because of my circumstances at the moment, I am reading and re-reading everything you've wrote, all of it makes sense, but I'm a bit of a stubborn mule lol I'm going to just put it all together and hope for the best (then cry later hehe) as my time is running out. One thing i'm doing is taking out the 85w panel at the front and putting in a single 12v 250w panel, with mppt controller to feed 2x 6v T105 and that will run the led lights, pump, little fridge, if needs be, as its a gas fridge too, and the1000w modified inverter, for the little TV. (I dont watch much TV) I am wondering if there is a way i can connect this to the rear batteries to help with charging, If there is any spear, maybe with a split chargers or something, i'm still investigating this option.

    Edit: This is a Annual Energy Consumption 377 Kwh of a digital inverter fridge/freezer i've been looking at, would my set up handle this?

    Anyway Bill thank you for taking the time to reply, I really do appreciate. Keep well.

    Armando.
  • BB.BB. Super Moderators, Administrators Posts: 31,063 admin
    Gas refrigerators tend to use a lot of electricity. Keep an eye on that.

    377kwh/years is about 1000wh per day. A 600 watt system is close. 4 hours of sun per day will do it with some extra power (see one of my first posts for math. On a tablet right now)

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