RV Starter System

System · May 2010

I have placed a deposit on a used Class C 24' RV that I have not seen in the 'flesh' but have started thinking about a solar system. I have been told that it currently has 2 Les Schwab Group 24 deep Cycle batteries.

I know VERY little about a solar system and want your comments on the following as a starter system. It is my intent to add a second 215 Watt Panel and replace the Group 24s with 4 T-105s, or something equal in AH later, but will live with this beginning system until I have the additional money. It is my best guess that I will be using less than 50 AH per day with this system and then will go to about 100 AH.

(1) Kyocera KD215GX-LPU 215 Watt Solar Panel
(1) Xantrex C60 60 Amp Solar Charge Controller
(1) A Battery Monitor but don't know which one (?)
(1) Xantrex Truecharge2 12-Volt, 20-Amp Battery Charger to replace existing converter

I have devoted some time to the Forum and thank all that have contributed to what little I know about a solar system - it is the student not the teachers that have limited that knowledge.

ED

BB. · May 2010

Re: RV Starter System

Some of your questions:

Battery Monitors (NAWS) Trimetric has some users here that like it (for lower price)
Victron Battery Monitors (others here have said nice things too)

I am not quite sure what your other questions are... If you want to predict / estimate how much energy per day you can get from your solar panel(s), let us know where the unit will be, if the the panels are flat or can tilt. Also, when do you plan on camping (summer/4 seasons/etc.). Is dry camping your plan, or a mix of dry and shore power?

Also, some folks have put a second panel on an "extension cord" to allow the panels to be placed in better sun (if RV is parked in shade, can place panel in sun). Of course, you have to secure the panel against wind and thief. Also, smaller panels (like 135 watt) may be easier to use as "portable panels".

In the end, how you treat your batteries will determine much of their life... You can read up on a couple battery FAQs (and get more confused

):

Deep Cycle Battery FAQ
www.batteryfaq.org

Also, you might look at the eventual size of your AC battery charger. 4x T105 batteries will be around 450 AH capacity. At a 5-13% rate:

450 AH * 0.05 = 22.5 Amps
450 AH * 0.13 =58.5 Amps

You might want to look at the TC 2 x 40 amp charge controller (get the remote battery temperature sensor too). The TC-2 x 20 amp might be a bit on the small size if you install the larger set of batteries. It would be nice to know if you plan on using a genset with the AC battery charger---A large genset with small battery charger is not very fuel efficient. Ideally, it would be nice to have the battery charger at around 50% +/- of the genset capacity (or charger+other AC loads on genset).

Also, a remote battery temperature sensor option would be nice for the C60 solar charge controller too (batteries are temperature sensitive).

-Bill

icarus · May 2010

Re: RV Starter System

Not much time tonight, but a couple of quick questions. Why a 60 amp charge controller with only 210 watts of panel, capable of putting out ~10 amps at best? 4 t-105s are a lot of battery. Ideally they would like at least 25 amps of charge current.

A balance between PV, batteries and loads are quite important. This starts with knowing your loads well.

FYI, we use ~600 wh per day, with ~400 watts of panel, 450 ah of battery. (12 vdc system)

System2 · May 2010

Re: RV Starter System

BB,
Thanks for the information, some of it I think I understand. You said:

"I am not quite sure what your other questions are... If you want to predict / estimate how much energy per day you can get from your solar panel(s), let us know where the unit will be, if the the panels are flat or can tilt. Also, when do you plan on camping (summer/4 seasons/etc.). Is dry camping your plan, or a mix of dry and shore power?"

Yes, I'm trying to predict/estimate if I can replace 50 AH with the one panel and 100 AH with two. I plan on fulltiming in the RV and will follow the sun during the seasons; perhaps Mexico in the winter months. I did not intend on having tilt panels and it will be a mix of dry camping and shore power with more dry camping after I add the second panel and bigger battery bank.

icarus,

Thank you also, you said:

"Why a 60 amp charge controller with only 210 watts of panel, capable of putting out ~10 amps at best? 4 t-105s are a lot of battery. Ideally they would like at least 25 amps of charge current. ....This starts with knowing your loads well."

I was thinking that I would get a controller that could manage both panels to begin the system rather than buy a second controller when I add the second panel and go to the bigger battery bank. Is this not a good idea, what would you suggest?

I am only guessing that my daily usage will be 50 AH to start and the move up to 100 AH per day. I won't know what it is for sure until I live in the RV on the road for some time. I'm trying to set up a system that will allow me that ability to grow without replacing everything that I start with.

Thanks again to both of you!
ED

Cariboocoot · May 2010

Re: RV Starter System

Some "simplified math" that might help you with this set-up:

430 Watts (two of those panels together) / 14.2 Volts (charging for a 12V system) = 30 Amps. That's why Tony was wondering about your choice of a 60 Amp charge controller.

4 T105's would be 12V @ 450 Amp/hrs (they're 225 each). Ideally that would want at least 22.5 Amps charge current (5% of 450) and 45 Amps would be better. So, "yes" on another panel or "no" on the parallel battery bank.

With one set of T105's you could manage 100 Amp/hrs @ 50% DOD. That would yield approximately 1000 Watt hours per day. That's about right for a 12V system. Your panel yield probably won't be as good as with a fixed installation; always a problem with RV's unless you use the "portable panel" method so you can get good aiming no matter what the site. One 215 Watt panel at best would harvest 688 Watt hours. Rather less than the maximum intended usage.

So you can see, lots of panels and less battery. The #1 mistake made in solar installs is too much battery for the panel. You can also see how important it is to get control of the loads.

Like I say, this is simplified math; no compensation for system losses (other than averaging panel output). You're already pretty close to a well working system.

icarus · May 2010

Re: RV Starter System

Pv systems don't always grow well, but there are some things to do to mitigate that. Batteries of different ages and sizes should not be mixed, and it is important to have enough charge capacity for any given battery bank.

I would start with a controller big enough to grow into, but 60 amps would handle ~ 800-900 watts of PV (12vdc) which is probably way more than the RV is going to be able to hold. I would consider the Rogue MPPT 30 amp, or the new Morningstar MPPT, or maybe some of the smaller Morningstar pwm controllers.

PV can grow as long as the batteries are big enough (charge currents ~5-15% for flooded batteries)

A couple of things to realize. Loads always grow with time. People always overestimate their solar potential net/net. Finally, people usually destroy one set of starter batteries as they learn how to use them.

As Marc and Bill suggest,, "do the math" figure the loads as carefully as you can, build in a fudge factor. This will give you a optimal battery size, then you can figure out what PV/CC to use with that battery.

Tony

BB. · May 2010

Re: RV Starter System

To play some numbers games, you can use the PV Watts website. It gives monthly power estimates for solar systems based on location... You could do winter in Arizona and Summer in Idaho (examples).

If you ever do plan on going dry camping into the snow/north during winter, tilting panels may help quite a bit (as could an MPPT type charge controller).

To use the PV Watts program, use 1 kW (1,000 watts) of panels (sorry, minimum size program will support). Use derating of 0.52 for an off grid system using AC inverter and flooded cell battery bank. Set the array to fixed, 0 degree tilt (flat)--then run the numbers for the location(s) of interest--Say Tucson for this example:

"Station Identification"
"City:","Tucson"
"State:","Arizona"
"Lat (deg N):", 32.12
"Long (deg W):", 110.93
"Elev (m): ", 779
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 0.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 8.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.57, 50, 4.25
2, 4.41, 57, 4.84
3, 5.85, 85, 7.23
4, 7.21, 100, 8.50
5, 7.91, 109, 9.27
6, 8.16, 108, 9.18
7, 7.04, 95, 8.07
8, 6.87, 94, 7.99
9, 6.16, 83, 7.05
10, 5.02, 70, 5.95
11, 3.89, 53, 4.50
12, 3.23, 45, 3.83
"Year", 5.78, 951, 80.84

So, 1,000 watts of panels will produced ~100 kWatt*Hours per month in spring and as low as 45 kWHr in December:

100,000 Watt*Hours * 210 watts / 1,000 watts of panels * 1/30 days * 1/12 volt battery bank = 58 AH per day in spring
48,000 WH * 0.210 panels * 1/30 days * 1/12 volts = 28 AH in winter

Take the same single panel and tilt it to 47 degrees in December for Tucson:

"Station Identification"
"City:","Tucson"
"State:","Arizona"
"Lat (deg N):", 32.12
"Long (deg W):", 110.93
"Elev (m): ", 779
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 47.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 8.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 6.18, 93, 7.91
2, 6.37, 84, 7.14
3, 6.95, 102, 8.67
4, 6.96, 96, 8.16
5, 6.38, 87, 7.40
6, 6.11, 79, 6.71
7, 5.64, 75, 6.38
8, 6.25, 84, 7.14
9, 6.84, 92, 7.82
10, 6.91, 99, 8.42
11, 6.43, 92, 7.82
12, 5.76, 87, 7.40
"Year", 6.40, 1070, 90.95

Went to ~87 kWH per month per 1,000 watts of panels, or almost double the 45 kWH output of a flat mounted panel...

So--depending on season and location, tilting of panel(s) may have significant improvement in winter.

Of course, you have to have the room and ability to get on roof to tilt the panels....

-Bill

System2 · May 2010

Re: RV Starter System

icarus, you said"

"Batteries of different ages and sizes should not be mixed, and it is important to have enough charge capacity for any given battery bank....Loads always grow with time. People always overestimate their solar potential net/net. Finally, people usually destroy one set of starter batteries as they learn how to use them."

I know about the different ages, sizes and not mixing issue. It is my intent to destroy the existing Group 24 batteries, if I do any destruction, then replace them with 2 T-105s with one 215W panel. I hope that system will then give me the experience to know what to do as my load grows to what I'm now estimating to be 100 AH.

Note: Some of my history includes 6 road trips with a Teardrop Travel Trailer with virtually no load. I powered the lights and a very small 12v fan from an emergency jump start battery. The 12 AH battery was recharged each travel day by plugging into the tow vehicle cigarette lighter. I used this set up for as long as 7 days between charging and never had a full discharge. I' sure that my conservative power use practices will decline as more power become available but I do have a conservative mind set. The RV also has a gas/AC refrig so at the beginning of my learning process the only dc loads will be lights, fan and 150W inverter for my laptop.

Thanks very much for your recommendations for the controller.

ED

RV Starter System

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