I have (x3) 150W panels, and need 1600Wh a day. Suggestions for battery banks?

[Fractalcathedral]

So I didn't get much of a response from my last thread, and after some research I realize probably why, (a couple of dumb mistakes and general ignorance).

So let's try this more specifically. I have (x3) Renogy 150Watt panels, and a 40Amp Renogy MPPT charge controller, along with a 12v Microsolar 2000 Watt Pure Sine Wave Inverter. I am looking to produce 1600 Watt hours a day in an RV, and be completely off the grid. If it is very cloudy for a couple days I can scale back usage to about 600-800Wh per day so I don't dig too deep into my batteries.

I can return both the charge controller and the Inverter if necessary, (if 24v or 48v inverter turn out to be better). What would you do for battery bank? Brands? I was thinking of x4 Rolls Surrette S-550, in parallel/series. Good choice or not?

[Fractalcathedral]

Okay, scouring these forums, and seeing 2500w inverter at 12v is a big no-no. It's in its box and will be sent back via Fedex first thing tomorrow. I was wondering about putting all those panels in 36v series, feeding into a 24v battery bank? Or do I get another panel, make it 2/2 in series/parallel, feeding to a 12v battery bank and keeping a more humble sized inverter? Please folks, any suggestions at all? I am totally down to learn. There is alot of misinformation on the web and I just need a lead.

[Sunking]

You panel wattage determines maximum Inverter size. 1 watt panel = 1 watt inverter. You have 450 watts of panel which means it can only support up to about a 500 watt inverter. Panel Wattage, Charge Controller, Battery, and Inverter all have to be matched up to work with each other.

For a 12 volt system maximum Inverter size is 1000 watts. That means

Panel Wattage = 1000 watts
MPPT Charge Controller = 80 Amps
12 volt battery capacity = 800 to 1200 AH or 550 to 850 pounds of lead.

You want a 2000 watt inverter?

Panel wattage = 2000 watts
MPPT Charge Controller = 80 amp
24 volt battery = 800 to 1200 AH or 1000 to 1500 pounds of lead.

Do you have a 1000 pound battery? I did not think so.

[Fractalcathedral]

Sunking, I am considering buying another 150w to bring my inverter up to 6,000watts, (and just generally increase that beautiful, clean energy).

Based on your experience, what products would you personally to meet my ends? My high-estimate daily usage came out to 1600 watt-hours a day, and I'll be travelling between Washington, Oregon, and California, (3 to 5 peak sun hours a day), and it would be nice to be completely off-grid in Washington during Winter, if possible. My surface area is basically 16.5' x 7' feet shuttle bus, and I'm down for returning panels if it would be more advantageous to have the higher voltage GT panels feeding into the CC.

Safety is priority number 1, but a balance between cost and efficiency, (and weight of batteries) is obviously ideal. I can make do with 600watt inverter. There's alot of crap out there and I'm afraid I just don't have the experience to discern between it without deferring to the opinion of experts.

[Wy_White_Wolf]

Normally to get 1600WH usable you need to produce 2400WH from your array. For 3 hours that would be 800W array. But your panels are mounted flat on an RV roof. You'll be lucky to get 70% production from that angle and with no set location you'll also get quite a bit of shading. So you're looking at 1200 watts minimum for your array.

Battery you're looking at 1600WH x 5(20%daily) x System voltage

so 12v = 667AH minimum
24V = 334AH minimum

You're also looking at 2 60amp MPPT controllers for 12v or 1 80amp controller for 24v system.

WWW

[Sunking]

Sunking, I am considering buying another 150w to bring my inverter up to 6,000watts,

Huh! How does 600 panel watts = 6000 inverter watts? You got a shocker coming your way. I wil let other people break the news to you and let them be the Bad Guy for a change.

Everything is based on daily usage which you stated is 1.6 Kwh per day. I will give you just one answer. 1600 wh or 1.6 Kwh requires:

12 volt 650 AH Battery
24 volt 325 AH battery
48 volt 162 AH battery

Take your pick.

[Fractalcathedral]

Huh! How does 600 panel watts = 6000 inverter watts? You got a shocker coming your way. I wil let other people break the news to you and let them be the Bad Guy for a change.

Everything is based on daily usage which you stated is 1.6 Kwh per day. I will give you just one answer. 1600 wh or 1.6 Kwh requires:

12 volt 650 AH Battery
24 volt 325 AH battery
48 volt 162 AH battery

Take your pick.

Sorry, that was a typo. Hence the "I can make do with a 600 watt inverter." comment in the same post. I just would like the ability to run Zbrush and Photoshop on 2 monitors for 6-8 hours a day, if need be, and keep my fridge plugged in and running, (471 watts a day Igloo 5.1 chest freezer).

[Fractalcathedral]

Normally to get 1600WH usable you need to produce 2400WH from your array. For 3 hours that would be 800W array. But your panels are mounted flat on an RV roof. You'll be lucky to get 70% production from that angle and with no set location you'll also get quite a bit of shading. So you're looking at 1200 watts minimum for your array.

Battery you're looking at 1600WH x 5(20%daily) x System voltage

so 12v = 667AH minimum
24V = 334AH minimum

You're also looking at 2 60amp MPPT controllers for 12v or 1 80amp controller for 24v system.

WWW

I've currently got 3 heavy duty adjustable tilt mounts for my Renogy 150w panels. 3 at the moment, but there's room up there for a 4th. Since its a shuttle bus conversion, I have an "escape hatch" leading to the roof, so I can go up there and adjust as required, (or flatten then if I'm going to be moving). If I get another panel, and wire them in strings of 2 parallel strings, I am thinking they would be closer to the Vmp of 22.5V and be better on the issue of partial shading than if I put 3 or 4 panels in series. And since Vmp being too close to the batteries voltage would make getting a full charge problematic, keeping the battery bank 12v.

The Imp per panel is 8.38A, and the Short-circuit current is up to 9.05 A. The Max Series Fuse Rating is 15A. Why would I need 2 60amp charge controllers? I'm not saying I don't, I just hope you can explain why. I'm eager to learn anything to make this setup as efficient as possible.

My estimate of 1600Watt-hours is probably higher than it needs to be, and during cloudy days I can cut it back to 600 watt-hours a day. Just leave my laptop on the shelf and open a book. Not a big deal.

[LETitROLL]

Sorry, that was a typo. Hence the "I can make do with a 600 watt inverter." comment in the same post. I just would like the ability to run Zbrush and Photoshop on 2 monitors for 6-8 hours a day, if need be, and keep my fridge plugged in and running, (471 watts a day Igloo 5.1 chest freezer).

So is that Igloo freezer a 120v AC model and the main item you need the inverter for?, or is it 12v RV style?

[Fractalcathedral]

So is that Igloo freezer a 120v AC model and the main item you need the inverter for?, or is it 12v RV style?

Its 120vac, and pretty much my main load besides laptop and Tv. I got a great deal on it, and its very energy efficient due to being a chest freezer. I've noticed most charge controllers have an input for DC loads, which led me to wonder- besides being able to bring DC power from module to battery, can it extract some of the DC energy back out from the batteries to maintain the freezer? Do you have any suggestions? Freezer is within returnable 30 day period.

[LETitROLL]

Its 120vac, and pretty much my main load besides laptop and Tv. I got a great deal on it, and its very energy efficient due to being a chest freezer. I've noticed most charge controllers have an input for DC loads, which led me to wonder- besides being able to bring DC power from module to battery, can it extract some of the DC energy back out from the batteries to maintain the freezer? Do you have any suggestions? Freezer is within returnable 30 day period.

It takes a bigger solar system than most think, with a good inverter (read not cheap) to run a AC freezer on 12v (even at just 471wh/day). It helps alot to step up to 24v system, the start up surge that your freezer causes every time the compressor kick on will probably be between 70 and 100 amps @ the 12v battery (the starting point of safety concerns) of course only 1/2 that at 24v. It can be done easily both at 12v and 24, 48, etc. but not cheap to do it right. The losses are worse at lower voltages and likelyhood of early battery failure, inverter problems, controller problems all increase at the higher amperages, normally the up front cost for a 24v system should be about the same, but quite a bit better in the long run. The only way to do it on the cheap is mixing in some conservation, are you needing the chest freezer to keep things frozen, or just using it for a converted refrige?

PS, If I understand your question correctly about the DC loads from you controller, most of those are only for running conservative loads, and they do pull from the battery and/or energy coming in from the panels, but most are not designed to run a large variable load like a fridge/freezer from those outputs, that usually goes direct to the battery bank/inverter.

[Fractalcathedral]

The only way to do it on the cheap is mixing in some conservation, are you needing the chest freezer to keep things frozen, or just using it for a converted refrige?

PS, If I understand your question correctly about the DC loads from you controller, most of those are only for running conservative loads, and they do pull from the battery and/or energy coming in from the panels, but most are not designed to run a large variable load like a fridge/freezer from those outputs, that usually goes direct to the battery bank/inverter.

Thanks alot, quite a lot of helpful information. I forgot to mention we intend to use it as a converted fridge, bought a Johnson Control device that you can adjust the temperature with. I assume we'll be keeping it around 40' degrees and opening it sparingly and for seconds at a time. The 471w/h a day estimate is its listed energy usage as a freezer. How much does that change the equation? Will the start up surge still require as much Amperage, but basically not be activated as frequently? Or will the amperage be reduced, with the run cycles remaining consistent?

[LETitROLL]

Thanks alot, quite a lot of helpful information. I forgot to mention we intend to use it as a converted fridge, bought a Johnson Control device that you can adjust the temperature with. I assume we'll be keeping it around 43' degrees and opening it sparingly and for seconds at a time. The 471w/h a day estimate is its listed energy usage as a freezer. How much does that change the equation? Will the start up surge still require as much Amperage, but basically not be activated as frequently? Or will the amperage be reduced, with the run cycles remaining consistent?

Start up surge will be the same, just the compressor wont come on quite as often, or run for as long when it does. A lot of variables, but in general at 40 degrees and keeping trips to the frige to a minimum should drop kwh a fair amount (if it is in a room under 75 degrees). A few people out there say they are down as low as 125 -200 w/h per day on similar setups, 250 - 300 would probably be safer to assume. The difference in the size and cost of system between 471 w/h vs 300 w/h per day is pretty big, that is what I meant by conservation, every watt you save is bigger than most realize to your long term cost. The buffer for multiple cloudy days and the batteries it takes to get you through that is by far the most costly (short and long term) issue. The only big short cut there would be either go propane refrige and a smaller solar system for other electronics, etc. or size your system for 2 or 3 day buffer instead of 4 or 5, also try and run the fridge mostly during daytime production and have it off more at nite to reduce battery needs. Lastly when the bad weather comes buy a block of Ice and put in there, in cooler weather the ice would last a few days, and unit could still come on a little bit to help. 6 dollar worth of Ice per month could save you 15 to 30 dollars a month in system cost.

[Fractalcathedral]

A few people out there say they are down as low as 125 -200 w/h per day on similar setups, 250 - 300 would probably be safer to assume. The difference in the size and cost of system between 471 w/h vs 300 w/h per day

Awesome, thanks. So, then my high-estimate for Daily watt/hours becomes 175-200 less, taking it down to around 1500. Probably closer to 1000-1200 on most days.

x3 150 Watt Panels in Series.

450Watts per peak sunlight hour. More like 400, realistically, (before inverter losses.)
3 Peak Hours= 1200 W/h. (1080 after inverter losses, fine with considerable conservation.)
4 Peak Hours (average)= 1600 W/h. (Becomes 1440 after inverter, totally fine.)
5 Peak Hours= 2000 W/h. (Plenty)

Advantage = Safety of having 24v inverter delivering low-amperage surge to fridge compressor. Less likely to cause problems with early battery failure, inverter, or controller.
Advantage = Cheaper wires.
Advantage = MPPT controllers work better with higher voltages.
Advantage = Inverter wattage capability doubles to 1000w(?)

Downside = If any of the panels is partially obscured, the entire input is reduced to basically nothing.
Downside= 36v for panel string is higher than Vmp of 22.5V. (Does this really matter, or will the MPPT controller convert that extra voltage to amperage?)

2 Strings of 2 Panels.

600 Watts per peak sunlight hour. More like 500-525, realistically (before inverter losses)
3 Peak Hours= 1500-1575 w/h (Plenty)
4 Peak Hours= 2000-2100 w/h (Plenty)
5 Peak Hours= 2500-2625 (Plenty)


Advantage= Panels operating closer to 22.5V Optimum Operating Voltage.
Advantage= If either string is partially obscured, power can be drawn from other string.

Downside= Need fuses and combiner box? Or will a Y-branch MC4 connector be adequate?
Downside= Need to keep the battery bank at 12v, or risk being unable to completely charge 24v battery bank, which leads to…
Downside= Safety concerns regarding fridges start-up surge (Is there a work-around for this?)
Downside= Bigger, more expensive cables needed for 12v battery bank.

x4 150W Panels in Series.

600 Watts per peak sunlight hour. More like 500-525 realistically, (before inverter losses.)
3 Peak Hours= 1500-1575 w/h (Fine, even with inverter losses taking it down to 1350.)
4 Peak Hours= 2000-2100 w/h (Overkill)
5 Peak Hours= 2500-2625 (Overkill)

48 volt 162 AH battery

Advantage = Safety of having 24v inverter delivering low-amperage surge to fridge compressor. Less likely to cause problems with early battery failure, inverter, or controller.
Advantage = Cheapest, smallest wires.
Advantage = MPPT controllers work better with higher voltages.
Advantage = Inverter wattage capability moves up to 1800 (?) (Also, overkill)

Downside = If any of the panels is partially obscured, the entire input is reduced to basically nothing.
Downside= 46v for panel string is higher than Vmp of 22.5V. (Again, not sure if really matters or if MPPT controller convert that extra voltage to amperage.)

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Do I have all that right? Any mistakes or oversights?

[LETitROLL]

Advantage = Safety of having 24v inverter delivering low-amperage surge to fridge compressor. Less likely to cause problems with early battery failure, inverter, or controller.
Advantage = Inverter wattage capability doubles to 1000w(?)

Downside= 36v for panel string is higher than Vmp of 22.5V. (Does this really matter, or will the MPPT controller convert that extra voltage to amperage?)

The advantage of the 24v inverter is that it will draw only 1/2 the amps from the battery. The frige compressor will get the same from the inverter in any of the systems because they all eventually convert it to your 120v AC.

A watt is a watt, so you are not really doubling your inverter capacity, but the higher voltage inverters are more efficient because it is less of a step up from 24v to 120v then from 12v to 120v, and also again only drawing 1/2 the amps from your battery so less problems with wires, connections, etc.


Yes, Mppt charge controllers will convert the overvoltage to amperage, to match whatever battery system you run.