# Sizing a 12v Solar system for an RV

Registered Users Posts: 13✭✭
I have been reading posts and trying to understand the sizing equations people like Bill and others use to appropriately size a solar array. Most of the discussion on this forum I have read uses these equations to size a battery bank from an existing solar array so I've had to invert the equations. I'm not certain when to use charging volts vs discharge volts and what those voltages should be for these calculations.

The RV currently has a 105AH battery.
So an ideal minimum size would be
105AH * 0.13 (rate of charge) / 0.77 efficiency * 12.9v (charging?) = 229Watt panel size

My Use
(amp draw of items were found online, and are reliable as such. So I have a low current DC clamp ammeter on its way from that place in the Amazon, which will help once it arrives)
Refridgerator running on LP 0.25A *24H = 6AH
LED and Fluorescent Lights 3.5AH use per day
Furnace
Draws 2.8A while running (theoretically)
If it runs 25% of the time (2.8A*0.25*24H) =16.8AH
Total is 26.3AH
Multiply by 4 =105AH the battery should be sufficient

I am considering replacing the battery or buying a second to double the battery size which should allow for 75% use on the furnace necessary for wintertime use (may prove to be difficult . Which would equate to 59.9 AH of battery use per day.

To size the solar array from Amp Hours used, your equation is:
59.9AH * 13.5volts (charging, again I have no idea) / 0.52 (inefficiency) / 5 hrs of sunlight (an appropriate underestimated average for Colorado use) = 311 Watt solar panel

Also:
210AH battery * 0.1 (rate of charge) / 0.77 (inefficiency) * 12.9v (charging?) = 352 Watts solar array.

Do I have these equations correct?
Would I need a 30 amp MPPT solar charge controller to achieve 13% charge rate on a larger battery.
And a 300 Watt solar panel to power it.

Would someone advise me of the correct voltages to be used in these calculations, please?
Thank you for the vast wealth of knowledge contained in this forum.

-Reid
1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.

Re: Sizing a 12v Solar system for an RV
The RV currently has a 105AH battery.
So an ideal minimum size would be
105AH * 0.13 (rate of charge) / 0.77 efficiency * 12.9v (charging?) = 229Watt panel size

105 AH * 12.0 volts battery * 0.13 rate of charge * 1/0.77 panel+controller derate = 213 Watt array
105 AH * 14.5 volts charging * 0.13 rate of charge * 1/0.77 panel+controller derate = 257 Watt array

Marc (Cariboocoot) uses the first equation, I use the second. Not a huge difference--I tend to be a bit more conservative. But--It also depends on where you put your fudge factors... I put mine in charging. Others may put them in their loads (i.e., * 1.33 loads for "buffer" for growing loads, bad weather).

The thing to avoid is doing to many fudge factors and making the system 2-3x larger than you need.
My Use
(amp draw of items were found online, and are reliable as such. So I have a low current DC clamp ammeter on its way from that place in the Amazon, which will help once it arrives)
Refridgerator running on LP 0.25A *24H = 6AH
LED and Fluorescent Lights 3.5AH use per day
Furnace
Draws 2.8A while running (theoretically)
If it runs 25% of the time (2.8A*0.25*24H) =16.8AH
Total is 26.3AH
Multiply by 4 =105AH the battery should be sufficient

Your numbers are consistent... But they do seem a bit low for others (a couple people measured their forced air RV furnance running closer to ~8 amps--But if your number is "right", then that is great).
I am considering replacing the battery or buying a second to double the battery size which should allow for 75% use on the furnace necessary for wintertime use (may prove to be difficult . Which would equate to 59.9 AH of battery use per day.

A pair of 6 volt @ ~200 AH each--Are hard to beat the price (12 volt @ ~200 AH battery bank).
To size the solar array from Amp Hours used, your equation is:
59.9AH * 13.5volts (charging, again I have no idea) / 0.52 (inefficiency) / 5 hrs of sunlight (an appropriate underestimated average for Colorado use) = 311 Watt solar panel

13.5 volts is OK... Again--I tend towards "worst case" of 14.5 volts volts charging--But the differences are not huge, and you can always add another panel (if you have room).

The "5 hours of sun" is quite a bit unless you are looking at summer camping. using PV Watts, array mounted flat to roof for Eagle Colorado:

Month
(kWh/m2/day)

1
2.42

2
3.22

3
4.30

4
5.70

5
6.57

6
7.31

7
6.81

8
6.20

9
5.13

10
3.89

11
2.58

12
2.07

Year
4.69

If you are going to be using the heater a lot--December is (on long term average) 2.07 hours of sun per day.
Also:
210AH battery * 0.1 (rate of charge) / 0.77 (inefficiency) * 12.9v (charging?) = 352 Watts solar array.

You are changing Battery AH numbers around a bit... So--Assuming a pair of 6 volt ~210 AH batteries in series with 5% to 13% rate of charge (using my 14.5 volt charging--Remember, very cold batteries need higher charging voltages anyway). Note, this is based on the recommended battery charging current:

210 AH * 14.5 volts charging * 1/0.77 panel+controller derate * 0.05 rate of charge = 198 Watt minimum array
210 AH * 14.5 volts charging * 1/0.77 panel+controller derate * 0.10 rate of charge = 395 Watt nominal array
210 AH * 14.5 volts charging * 1/0.77 panel+controller derate * 0.13 rate of charge = 514 Watt "cost effective" array

If you ware weekend dry camping, the 5% rate of charge is sort of OK.

If you are seriously dry camping for weeks at a time (and/or many months of the year), the 10-13% rate of charge will be better (and less genset run time).

But--We still need to figure out your array size based on actual power usage and when you will be camping. Winter time is difficult to be pure solar--Generally, you will need some sort of backup genset.

My estimating rule of thumb is to dump the bottom 3 months (you will be using the genset at times). And make the 4th month "break even"... Using the above numbers, that would be February at 3.22 hours of average sun per day--

26.3 AH * 14.5 volts charging * 1/0.52 system eff * 1/3.22 hours of sun = 228 Watt array (Feb Break even)
Do I have these equations correct?
Would I need a 30 amp MPPT solar charge controller to achieve 13% charge rate on a larger battery.
And a 300 Watt solar panel to power it.

You are close--Need to understand your load numbers a bit better, and how much sun you really want to plan for.

14.5 volts vs 12/13.5/3 etc. is more conservative and will "give you" a larger array.

Many RV installations are limited by roof space for solar panels, and by space/weight limitations for battery banks. So--You are pretty much stuck with what you can fit (and afford). The above equations (usually) give a "balanced" system design. Having a huge battery bank OR a huge solar array OR a huge AC inverter--Usually is a waste of money/space/weight. The battery bank is really the heart of your system, and your loads/charging current/etc. should match the abilities of the battery bank itself.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Banned Posts: 17,615✭✭✭
Re: Sizing a 12v Solar system for an RV

Labels help.

105 Amp hour 12 Volt battery.
Peak charge current of 13 Amps.
On PWM controller: 13 Amps * 17.5 (average Vmp for '12 Volt' panel) = 227.5 Watts.
On MPPT controller: 13 Amps * 12 (minimum system Voltage where maximum current is required) / 0.77 (typical efficiency) = 203 Watts.

In the case of using maximum 13 Amps (high side) you could round down to the nearest available panel size and check it for 10% minimum current.
• Solar Expert Posts: 61✭✭
Re: Sizing a 12v Solar system for an RV

To use the KISS formula, 400-600 watts, min 4 6volt batteries, that is the way most RV's are set up.
• Banned Posts: 17,615✭✭✭
Re: Sizing a 12v Solar system for an RV
lipets wrote: »
To use the KISS formula, 400-600 watts, min 4 6volt batteries, that is the way most RV's are set up.

Which if they are 220 Amp hour 6 Volt batteries means the array is slightly inadequate for full solar charging. 440 Amp hours @ 12 Volts would want 770 Watts on a PWM controller. Fortunately most RV's have a generator on board which solves the problem nicely.

Quite often the PV on a motorhome or camper is a matter of how many Watts you can fit, and deal with the shortfall if necessary.
• Solar Expert Posts: 61✭✭
Re: Sizing a 12v Solar system for an RV

agree space is a premium, I use 3 195W with a Voc of 66V, Mppt controller, works well, but Kerocera stop making those panels.
• Banned Posts: 17,615✭✭✭
Re: Sizing a 12v Solar system for an RV
lipets wrote: »
agree space is a premium, I use 3 195W with a Voc of 66V, Mppt controller, works well, but Kerocera stop making those panels.

I understand completely: Sharp stopped building anything under 200 Watts, including the nice 175's I have.
• Registered Users Posts: 13✭✭
Re: Sizing a 12v Solar system for an RV

Thank you Bill and Marc for your assistance. Your clarifications have helped.

I agree I was jumping around AH numbers a lot. I’m torn between conservation and maximization of my potential. I indeed have a limited area for installation, and so am proceeding cautiously so I can realize as much potential as I’m willing to pay for.
Based on the current 105AH battery
BB. wrote: »
105 AH * 14.5 volts charging * 0.13 rate of charge * 1/0.77 panel+controller derate = 257 Watt array

The installation is on a Volkswagen Eurovan Camper, a poptop van (tilted roof). Ideally always parked with the panel facing south. Eagle appears to have the lowest solar radiation numbers in the state, good for conservative estimation. I only go weekend camping and the occasional weeklong RV trip or music festival, and can charge via the alternator (ie. driving several hours) on a second or third day if weather and use necessitates. A large majority of this camping is done from April to September, so 5hrs solar equivalent seemed an appropriate estimate living in Boulder and camping in Alamosa or Grand Junction, as I frequently do.

The DC clamp ammeter arrived and at the 4A (1mA accuracy) range on the meter and running everything in the van at the same time I can’t get it to draw more than 1A.
I have the wire sandwiched between the jaws and the meter perpendicular to the wire. How long of a straight section does the wire need to be? (Photos) Otherwise my previous assumptions are generous.

So a 250 Watt array should give me
250Watt /14.5v charging * 0.52 system eff * 5hrs = 44.8 AH from the panel on a below average day.

Will a 105AH battery not accept more than 13% of the AH of the battery 13.6A?

I was suggested to pair a 245 Watt SolarWorld Polycrystalline panel with a Midnite The Kid charge controller. Is this system overkill and permit the van to roam Arizona indefinitely during the zombie apocalypse?
Would a smaller panel and a Sunsaver 15A MPPT be the maximum my battery can accept anyway (or PWM)? Why was I suggested against using the same panel with the sunsaver and told it will only accept up to 200W solar panel?
Because 250Watt/14.5v * 0.77 panel +controller derate = 13.2 A max charge rate anyway

I suppose this situation is low risk since I'm only short term camping and can run the vehicle when necessary. I would just like to avoid what has been happening that I'll have to start the van in the middle of the night on the second night when running the furnace.

Thank you for your guidance. Very much appreciated.

-Reid
1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.
Re: Sizing a 12v Solar system for an RV
The DC clamp ammeter arrived and at the 4A (1mA accuracy) range on the meter and running everything in the van at the same time I can’t get it to draw more than 1A.
I have the wire sandwiched between the jaws and the meter perpendicular to the wire. How long of a straight section does the wire need to be? (Photos) Otherwise my previous assumptions are generous.

Just to be clear--A single wire through the hole in the middle of the jaws, you do not "clamp" the flats of the jaws on the wire itself. The jaws must close completely. And the closed jaws encircle the wire/cable. The wire can be "floppy loose" floating around in the hole in the middle. It will not change the readings a bit.

Also, you only clamp 1 wire at a time... If you clamp two wire (such as the +/- wire pair to a load), the "sum of the current" adds up to zero amps, and the meter will read zero amps.

And, for DC measurements, you need to "zero" the DC amps to zero. It is the nature of a DC current meter readings to drift over a few minutes.

Try clamping the battery positive (or negative) lead. Turn on the head lights, you should read 10-15 amps load with the meter. Start the car and you should see 10-50 amps or so from the alternator charging (depending on battery charge, engine RPM, etc.).

One wire, clamp closed, is all you need to measure the current properly. How they work:

http://www.kew-ltd.co.jp/en/support/mame_02.html
So a 250 Watt array should give me
250Watt /14.5v charging * 0.52 system eff * 5hrs = 44.8 AH from the panel on a below average day.

Will a 105AH battery not accept more than 13% of the AH of the battery 13.6A?

On average--If you have a near dead battery and recharge it at more than ~13%, it can overheat without active cooling.

In general, batteries at less than 80% state of charge will accept very large current current and not overheat (charging is very efficient).

Once a battery is over ~90% state of charge, it will accept much less current and can overheat with too high of charging current... Even a 2.5 to 5% rate of charge going into a 100% charged battery (typically "equalization" charging), can easily overheat a lead acid battery.

The 13% "upper limit" is suggested for generic lead acid "rated" charging current to keep batteries relatively cool. Also, if you drain the battery bank by ~25% per day, on average, the battery will easily reach "float" charging (fully charged) by mid-day for most people. Putting a larger solar array on will not recharge the battery any more. However, if you have other loads (say you run a well/irrigation pump and other loads in the afternoon, you may be able to "cost effectively" use a larger array).

And, if you have >13% rate of charge, you should look for charge controllers that have remote battery temperature sensors. As lead acid batteries get hot, their charging voltage falls. This can help limit the chances of thermal runaway (battery gets hot, controller sees battery voltage "drop", things needs more charging current, battery gets hotter, voltage falls more, controller pumps out more current--etc.). Practically speaking, around 20-25% is probably a good limit for maximum charging current in most situations (size of wiring, limited ability of battery to accept higher currents, etc.).

Again, just generic rules of thumbs--There can be good reasons to do something different for special situations.
I was suggested to pair a 245 Watt SolarWorld Polycrystalline panel with a Midnite The Kid charge controller. Is this system overkill and permit the van to roam Arizona indefinitely during the zombie apocalypse?
Would a smaller panel and a Sunsaver 15A MPPT be the maximum my battery can accept anyway (or PWM)? Why was I suggested against using the same panel with the sunsaver and told it will only accept up to 200W solar panel?
Because 250Watt/14.5v * 0.77 panel +controller derate = 13.2 A max charge rate anyway

In round numbers, The "cost effective" maximum solar array for a 15 amp MPPT controller on a 12 volt battery bank:

15 amps * 14.5 volts charging * 1/0.77 panel+controller deratings = ~282 Watt array (roughly) maximum cost effective array

So, 1x 250 panel is find for the controller--Two on a 15 amp @ 12 volt controller would be way over paneled, and a waste of money.

Can you fit 2x 245 watt panels on your van roof? These are pretty large panels (and can the roof support ~100lbs for two panels?):

Pmax: 245 Watts
Voc: 37.5 Volts
Vmp: 30.8 Volts
Isc: 8.49 Amps
Imp: 7.96 Amps
Weight: 46.7 Pounds
65.94" x 39.41" x 1.22"

Some people have made "awnings" so they can get more panels on their RVs. Mounting so they don't blow off on freeway is not trivial.
I suppose this situation is low risk since I'm only short term camping and can run the vehicle when necessary. I would just like to avoid what has been happening that I'll have to start the van in the middle of the night on the second night when running the furnace.

Energy usage is a set of highly personal choices... Anything I suggest as "practical" or not for your needs would be pretty much worthless. You need to measure/make estimates of your power needs.

A kill-a-watt type meter for measuring 120 VAC loads. A DC AH/WH meter for DC loads. A Battery Monitor would be very nice--But probably a bit pricy for a smaller off grid system. A DC current clamp DMM meter can help estimate loads too.

The RV heater may be one of your "worst loads"... Some seem to draw ~8 amps for 1/2 the night. You might look at alternatives for lower power space heaters (if there are any).

If you will be needing more power--A Honda eu1000i or eu2000i inverter generator (900 or 1,600 watt rated respectively) is hard to beat. They are not cheap (around \$700/\$1,000)--But they are light weight and very quiet. Also, overall, much more fuel efficient vs running your van engine--Plus you can move the genset 50' away on an extension cord to keep the noise and fumes down.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 140✭✭
Re: Sizing a 12v Solar system for an RV
BB. wrote: »
The RV heater may be one of your "worst loads"... Some seem to draw ~8 amps for 1/2 the night. You might look at alternatives for lower power space heaters (if there are any).

There are a variety of catalytic propane heaters that are suitable for RV use, such as the Olympian Wave series.

Of course, the worst thing about the forced-air furnace is that you need it most at night, precisely when your PV array isn't producing any power.
• Registered Users Posts: 13✭✭
Re: Sizing a 12v Solar system for an RV
BB. wrote: »
Just to be clear--A single wire through the hole in the middle of the jaws, you do not "clamp" the flats of the jaws on the wire itself
Aha! I incorrectly interpreted the little pictogram on the lame excuse for an instruction manual. I thought the big X through the image with both (+/-) wires was telling me not to put one wire through the middle, and the correct image looks like its clamped on the wire. That's what I get for ordering the cheapo Chinese ammeter from Amazon. Thanks for the correction.

Now, operating it correctly, I have confirmed the numbers that I used in my first post are accurate. This is only a pop-top camper van, not a class C RV. Smaller than a Sprinter. Thank you for your usage concerns. And I have nothing that runs off AC and already calculated my usage in my first post.
BB. wrote: »
Can you fit 2x 245 watt panels on your van roof? These are pretty large panels (and can the roof support ~100lbs for two panels?)
I am talking about pairing one 245W panel to a The Kid charge controller, not a pair of panels.

Why was I suggested against using a 245W panel with the sunsaver and told it will only accept up to 200W solar panel? Do they not believe in derating, since they tell me the output would be clipped at 15A?
At this point this question is only academic, since the cost difference between a 15A sunsaver and 25A MN KID is only \$60 to gain a digital readout and full utilization of a 250W panel. But I would like to understand better.

Can you help me understand why any solar panel between 130W to 300W all seem to cost the same, between 225\$ and 300\$. The cost per watt drastically increases for a panel half the size. I've been trying to come up with a lesser powered lesser cost alternative setup to the NAWS has quoted me, but the only cost savings would be >~\$100 decrease in charge controller cost. It seems as if I've hit a "constant investment" range where I can have any system from 150W to 260W and spend the same amount of money.

I think I have convinced myself of my decision.
-Reid
1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.
Re: Sizing a 12v Solar system for an RV

The Morningstar 15 amp MPPT charge controller has been a very good performer... If you are in a hot climate, derating is fine (and safe).

If you live in a very cold climate, you could get more power from sub-zero panels... However, if you have a choice (for example) of a 200 or 250 watt panel and they are virtually the same price, and the 250 watt panel fits--Go ahead and get the larger panel--It will work fine.

Regarding Morningstar products--Yea, they make a lot of money on "options" (digital meters, remote batt temp sensors, computer interface).

Midnite and Rogue (generally) give you everything you need with the controller--Not too many "options" that you have to buy to make a "nice" system.

The Midnite Kid sounds like a great product--I would not have any fear using it. Get the "optional" (:p) remote battery shunt monitor + shunt--And you will have a system that few products can touch (getting close to battery monitor functionality--I heard that it needs another software release or so to get "full" BM functionality). The Battery Shunt allows the controller to measure/control charging current/states by looking directly at the battery. A huge improvement over the "traditional" charge controllers which cannot "see" the difference between battery charging current and current going to loads.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 203✭✭✭✭✭
Re: Sizing a 12v Solar system for an RV
AuricTech wrote: »
There are a variety of catalytic propane heaters that are suitable for RV use, such as the Olympian Wave series.

Of course, the worst thing about the forced-air furnace is that you need it most at night, precisely when your PV array isn't producing any power.

An Olympian Wave 3 is my main heat source for my off-grid RV. It's good most of the time, but when it gets really cold I break out the Mr. Heater. On reflection I maybe should have gotten a larger Olympian, but the Wave 3's low setting is good for when it's a bit nippy, but not super cold.

Running an RV's forced air furnace is not an ideal use of solar/battery power. Very inefficient, not just with electricity, but also propane. They're also rather loud and obnoxious. Only benefit is that you can set the thermostat and keep a somewhat even temperature.

My RV's furnace developed a problem, I think a bad fan based on the racket it makes when it's running, plus mice decided the ducts were a good place to nest, resulting in an overwhelming smell of mouse urine whenever the furnace ran. I'm happy to use space heaters now. Far more efficient anyway.
• Solar Expert Posts: 135✭✭
Re: Sizing a 12v Solar system for an RV
At this point this question is only academic, since the cost difference between a 15A sunsaver and 25A MN KID is only \$60 to gain a digital readout and full utilization of a 250W panel. But I would like to understand better.
-Reid

The Kid is a 30 amp controller, you could safely run 2X 250 watt panels threw it.
I installed a kid on my trailer a few months ago and am very pleased with the product. Would definitely recommend the Whiz bang Jr and battery temp sensor to go with it.
• Solar Expert Posts: 203✭✭✭✭✭
Re: Sizing a 12v Solar system for an RV

EurovanCamper, here are some numbers that may help you. I'm currently living full-time in an off-grid RV.

I have two 158W Dmsolar panels wired in parallel. \$200/ea locally sourced, ~\$185/ea online if you buy a 2-pack. These are off-grid panels.

I plan on getting two more, for a total of 632W, 33.88 max amps @ 12V. These will all be wired in parallel.

I have two Trojan T-105 batteries wired in series, giving me 225 ah @ 12V.

My understanding, based in large part on info I've gleaned on this board, is that four of these panels will give me a charge rate of ~12% with the various sundry inefficiencies factored in. This is right in the sweet spot Trojan recommends (10-13%).

Charge controller is a Morningstar TriStar 45 PWM. This is a good size for 4 panels, maybe 5 if I wanted to push it, but I've seen >10 amps out of one panel despite it's rated 8.47 Imp.

Don't have their meter yet, but Morningstar will be sucking up a bit more of my paycheck soon. A good meter is a must. I'm currently using a Watts Up on the charge controller output. Adequate since I only have two panels, but won't be able to handle the current once I get four panels. I have a Kill-A-Watt on the AC end of things. Also have an Extech clamp meter.

I just use a little 150W car-type inverter plugged into a cigarette adapter. I don't need a large inverter, prefer to minimize my no-load draw since I keep it on 24/7 (no load draw of my inverter is 0.27 amps @ 12V).

Right now my batteries are staying well above 75% on a daily basis. I'm using roughly 20-30 ah @ 12V per day. When it's sunny out, my batteries are fully charged by the time I get home from work. Since I got my second panel I haven't had to run my generator to charge my batteries, but that also coincided with the onset of sunny weather. I measure state of charge with a hydrometer, lately a Hydro-Volt, which is a vast improvement over the cheap auto store hydrometers, which can be be a PITA to use on a regular basis.

In terms of RV loads, here are some measurements I've made on my RV:
-- Fridge : max of 0.3 amps, roughly 4.5 ah per day @ 12V when run on propane (this just runs the controller)
-- Lights : 1141 LED bulb draws 0.13 amps
-- Converter : no-load draw is roughly 0.24 amps, though that includes some phantom loads
-- Water pump : 4.4 amps

You can test your own electronics and appliances with a Kill-A-Watt. My biggest single load is computers (netbook, big laptop, smart phone).
• Registered Users Posts: 13✭✭
Re: Sizing a 12v Solar system for an RV
BB. wrote: »
you will have a system that few products can touch
The Battery Shunt allows the controller to measure/control charging current/states by looking directly at the battery. A huge improvement over the "traditional" charge controllers which cannot "see" the difference between battery charging current and current going to loads.

Thanks to all who provided assistance and input. After running the math I ended up with a 250W Kyocera solar panel for only \$244 and a Midnite The Kid charge controller.
I already installed Yakima tracks on the roof of the pop-top and ran the MC4 wires, circuit breakers and wired the charge controller up. Tonight I should connect the battery and solar panel and be up and running!!

I did not get the WhizBang Jr yet, but I intend to do so when NAWS has them stocked again.
I have both a battery positive and battery negative terminal 1foot away from the battery outside the battery box with loads and charge equipment hooked up to these points.
My question: Where does the WhizBang get installed?
Between the terminal and the battery on the negative side? The information on their website does not specify.

Also, I have a 105AH flooded cell "deep-cycle" marine battery from O'reilly Auto parts that I've had for 2 years. (Definitely going to upgrade to a true deep cycle battery when this one goes) But I can't find any specifications for charge conditions. The charge controller has plenty of settings that can be changed and I think it defaults to a certain amount of time in Absorb phase til it jumps to float.
What are your charge profile settings? Any suggestions for settings on charging volts (Bulk, absorb, float) and Amp cutoff for absorb/float transition?

Thanks
1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.
• Registered Users Posts: 13✭✭
Hello, I'm back again.
Thanks to everyone for their help the first time around.

My auto parts store 105AH battery is toast and is needing replacement.

I am trying to decide between two true deep cycle batteries.
One that is 150AH and another that is 130AH. Which one do I buy?

I have 250W solar panel and 30A Midnite The Kid charge controller. For when the Van is outside.
I have a 20A ProMariner battery charger for when the Van is stored inside the garage.
The van is used for camp trips boondocking without outlet or generator power from a few nights long to just a weekend. When camping the battery will only get power from the solar panel.
My use is ~ 25AH/day but could increase to 35AH/day cold winter camping.
The solar setup should be able to provide 250W / 14.4 Charging volts *0.77 battery derating * 4.5 PvWatts hours = 60 AH into battery system each day.

I want this new battery to last. Is 150AH too large for this system?

Thanks

1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.
• Solar Expert Posts: 115✭✭
Hello, I'm back again.
Thanks to everyone for their help the first time around.

My auto parts store 105AH battery is toast and is needing replacement.

I am trying to decide between two true deep cycle batteries.
One that is 150AH and another that is 130AH. Which one do I buy?

I have 250W solar panel and 30A Midnite The Kid charge controller. For when the Van is outside.
I have a 20A ProMariner battery charger for when the Van is stored inside the garage.
The van is used for camp trips boondocking without outlet or generator power from a few nights long to just a weekend. When camping the battery will only get power from the solar panel.
My use is ~ 25AH/day but could increase to 35AH/day cold winter camping.
The solar setup should be able to provide 250W / 14.4 Charging volts *0.77 battery derating * 4.5 PvWatts hours = 60 AH into battery system each day.

I want this new battery to last. Is 150AH too large for this system?

Thanks

I am just getting into the end of this thread, and have scanned it, but I must ask, do you really need solar. I ask this for two reasons:

1) Your boon-docking interval is not long. If you use 25AH per day from a fully charged 150AH battery, even at 50% discharge, that gives you three days. Even 35AH per day won't harm a good deep cycle battery. For three nights that would take your battery down to 70% and 80% would be acceptable.

2) Since I presume you are driving your van to your camping destination, an isolator from your alternator could give you much more charging capacity than a 250w panel even without considering that the panel orientation will not likely be optimal, particularly with Winter insolation.

• Solar Expert Posts: 115✭✭
edited September 2015 #19
• Solar Expert Posts: 5,183✭✭✭✭
How did you 'toast' your first set? tell us what you have learned...

KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
• Registered Users Posts: 13✭✭
edited September 2015 #21
The deep cycle/marine battery was new in spring 2012.
Solar was installed June 2014.
The 20A battery charger is new and currently being installed replacing the old magnetek converter. This OEM magnetek was not able to raise the battery voltage above 13.3V ever. This was recently determined, and was unknowingly killing my battery for a long time as it was never able to charge the battery and may have only slowed its death by maintaining the vehicle's parasitic loads when in storage.
Also the battery, due to this rotten charger, has been drawn down below 10.5V a handful of times since the capacity of the battery was so diminished due to its first 2 years of abuse.
Replacing the charger should be the solution to the batteries only lasting 4 summers. 4 summers is not a terrible lifespan for cheap auto parts "marine" battery, but with a new charger, and a real deep cycle battery I hope the battery lasts twice as long.
1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.
• Registered Users Posts: 13✭✭
edited September 2015 #22
So the larger the battery I get = a lower % DOD I would take the battery on a per day basis. So a larger battery is better for discharge cycles.

I previously stated I plan to use 26.3AH per day. (This is an assumption based on amp draw rates during discharge, and not kWH using a Watts Up, which would be helpful)
If the furnace runs more than I anticipate (its hard to estimate its duty cycle, since there are so many factors) It is possible to use 40AH (or more) in a night.
40AH (use) / 130 AH (battery) = 31 % Degree of discharge

40AH (use) / 150 AH (battery) = 27 % Degree of discharge

I'm slightly worried a lower rate of charge will reduce the new battery's life if its oversized.
Solar charging:
With my Charging voltage
250 Watt panel / 14.4 V * 0.77 derating / 150AH battery = 0.089 rate of charge

250 Watt panel / 14.4 V * 0.77 derating / 130AH battery = 0.102 rate of charge

Plug in charging:

20A * 0.77 derating / 150 AH battery = 0.102 rate of charge

20A * 0.77 derating / 130 AH battery = 0.118 rate of charge

I'm trying to split a pretty fine hair here. Which situation (130AH or 150AH battery) will be better for the life of the battery in the system I have as-built?
1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.
• Solar Expert Posts: 5,183✭✭✭✭
40AH (use) / 130 AH (battery) = 0.69 % Degree of discharge

40AH (use) / 150 AH (battery) = 0.73 % Degree of discharge

I'm trying to split a pretty fine hair here. Which situation (130AH or 150AH battery) will be better for the life of the battery in the system I have as-built?
Using your figures, that is actually 31% DoD and 27% DoD

which is a reasonable amount of daily use, either battery will do, you still have a minimum of another 40Ah of use left if needed and still be in the safe zone.

hth

KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
• Registered Users Posts: 13✭✭
Correct, I'm confusing my terms here.
100% - 31% DoD = 69% (State of Charge) remaining
I know that either battery will function, knowing I could have doubled the old battery (105AH * 2 = 210AH) and would still have a system that worked.

Which is a better situation for the battery though?
130AH: 31% DoD and 10.2% (max w/ sun) rate of charge

150AH: 27% DoD and 8.9% (max w/ sun) rate of charge

I know the rate of charge helps to mix the electrolyte and prevents stratification and sulfation of the battery
And I know drawing down the battery too far also causes irreparable damage.
Which side of this (more discharge with more mixing by charging)
or (less discharge with less mixing by charging) ?

1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.
• Solar Expert Posts: 5,183✭✭✭✭
You are right about hair splitting. It's pretty much a wash as long as you use that panels and Kid CC and mot the lousy builtin (non)charger the RV came with...

In my eye, as I am cautious about excess use , YMMV, and you have the heater variable, I would opt for the larger one... the 150Ah is 115% of the 130. Is there a +15% difference in price over the 130Ah battery?

KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
• Solar Expert Posts: 494✭✭✭
If the cost of the larger battery will not break the bank, go for bigger. Use increases oftentimes.
Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
• Registered Users Posts: 13✭✭
The price difference is less than +15%. This is also the reason why I want it.
In fact, there are plenty of reasons I want the larger battery.

I wanted to make sure it wasn't oversized for the charging systems. For example, I heard these renewable energy systems like to 'breathe' and be put through shallow charge and discharge cycles.
So I was wondering what too shallow of a discharge/charge cycle is, especially if it only does 15 cycles each year?
1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.
• Solar Expert Posts: 5,183✭✭✭✭
shallow refers to the depth of discharge and usually to < 10% DoD

KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
More or less for solar power--If the numbers are within ~10%--That is pretty much in the margin of error (measurement error, average solar production, variation in loads/usage, etc.).

For RV systems--Many times the larger battery system does not really give you much--The batteries typically die from aging/deep cycling or an "oops" (somebody left the lights on and killed the battery bank).

I would not worry too much--But I would probably tend to the smaller battery bank--That will give you a slightly better charging rate for the batteries, and hopefully lower costs (and weight).

But the differences are very small in the practical world.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 13✭✭
Wiring question :
I have an RV, 250W panel, 30A Kid charge controller, and 150AH T-1275 trojan deep cycle battery.
The RV chassis battery, trojan "coach or house" battery, and 20A Promariner sport battery charger (labelled converter on diagram) negatives are all grounded to the chassis. The PV panel positive and negative are isolated from the chassis.

I want to add a load circuit to the vehicle (from the load controller on the Kid charge controller), and connect the charger to the engine battery.

Can I ground the load circuit negative to the chassis ground?

Can I only run one wire from the positive of the battery charger to the engine
, and the battery charger 2nd bank negative to the chassis ground?

1999 VW Eurovan Camper
250W Kyocera GT PV, KID CC, 100AH Renogy 12V Lithium
Isolating solenoid to charge system from engine, 20A ProMariner ProSport charger for when plugged in storage

2008 Leopard 40 sailing catamaran - Installing a second solar array
1st array 750W of Sunpower flexible panels, 60A Renogy Charge Controller
2nd Array (planned) - 3 x 415W Trina Bifacial panels wired in parallel then 8 AWG wire to 40A breaker, 150V/100A Victron SmartSolar Charge Controller with 4AWG wire to 100A breaker to batteries, 600Ah 12V Lithium battery bank all parallel wired.
• Solar Expert Posts: 9,583✭✭✭✭✭
you can tie negatives to the chassis, but try to include an actual conductor. With rubber isolators, rust proof coatings, the chassis is a poor conductor.

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 ,