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Old 06-12-2019, 04:32 AM   #1
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How much solar ?

I have a vista 36y , on the roof are 3 - 160 watt panels (480 watts or 40 amps) Battery bank Is 450 AH 12v dc. Just purchased a Vic Tron 50 amp solar charger. First time heading out west from Florida, Will this be enough power for Boondocking along the way ? We never boondocked befor. We plain to occasionally take a full hook up rv sight to dump and fill water tank. Thanks for any help.
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Old 06-12-2019, 05:52 AM   #2
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The only way to know is for you to prepare a "load chart". You need to know your energy budget, how many watts you use every 24 hours in a normal day inside the rig. There are several ways to do this, your BMS can tell you an approximation, measurement etc.



It certainly sounds good but it all depends on how many watts or AH you plan to use. The nice thing about touring is the alternator is working to recharge the battery bank. If your use at night time is reasonable you should be good with a battery bank that large. In the touring mode it really doesn't matter about the solar panels - they come into play when you are parked during the day. Driving the rig the alternator is charging much more than those panels. Think about how many hours you plan to drive each day vs how many days you will stay parked with no hooks or power.



You didn't mention a BMS, Victron makes several like the 712. That's the best way to keep up with watts, AmpHours, in and out of your battery bank.
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Old 06-12-2019, 06:32 AM   #3
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As Kayak 73 mentioned, a load chart will give you a better idea of need vs capability. We boondock long-term with 1400W solar / 660A batteries running RR, fans, lights, TV, sat and recorder, and short duration MW. Our coach also has a fairly robust parasitic load. For anything else we use the generator.

I think you're in decent shape and should 'try it out.' The generator is available if you need A/C, encounter cloudy conditions or need a battery charge boost. And your balance between solar production and battery storage is decent. You may be in a situation where you'd spend a fair bit of cash for a diminishing return.

Check out AM Solar's website for more info, and there are certainly others.

http://amsolar.com
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Old 06-12-2019, 07:22 AM   #4
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With so little info no one can answer your question.
1. What kind/size inverter do you have?
2. Residential fridge or RV fridge?
3. How much power do you use in a day?
4. How many days will you be dry camping and not driving?

Even if we knew all these things the only answer to your question is to get out there and see for yourself. After your trip youíll learn so much and then youíll know the answer.

A Battery Monitor Kit is a mandatory first step to install if you havenít already.
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Old 06-13-2019, 01:57 PM   #5
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Originally Posted by Franksteer View Post
I have a vista 36y , on the roof are 3 - 160 watt panels (480 watts or 40 amps) Battery bank Is 450 AH 12v dc. Just purchased a Vic Tron 50 amp solar charger. First time heading out west from Florida, Will this be enough power for Boondocking along the way ? We never boondocked befor. We plain to occasionally take a full hook up rv sight to dump and fill water tank. Thanks for any help.
While a load chart would be great, as long as you are careful about what power you use and for how long, 480 watts and 450AH of battery should work just fine.
Here is a link to some info about what different devices in an RV will use: The 12volt Side of Life (Part 1)
Scroll down to the bottom and click on the link "continue to part 2" for the load info.

By the way, what batteries do you have that add up to 450AH. Kind of an unusual AH total.

BTW, 480 watts of solar, at noon sun time (1pm to 1:30pm clock time) on a very clear summer day in the southern USA is more likely to give you at the most about 30amps of 12V. Very seldom do you get a really clear (read that absolutely no haze) day in the summer.
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Old 06-19-2019, 04:33 PM   #6
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I agree with everything said above in principle. One element I did not see is where and what range the solar will be used. If you are in AZ in full sun and panels are flat on the roof you may get 80% of the full power. If your in AK in the winter then you get 0% power. OK, you get the idea.



I designed many hundreds of solar stand alone sites in Michigan and Florida as a consultant. So, as you can see there is no really simple 100% answer. However, I would recommend that 70%+ boon-dockers use Lithium batteries if you can afford it. Whatever AH of the Lithium AH of the batteries are then, considering flat on the roof looking upwards with good sun, use solar panels that add up to 50% of the Lithium battery AH capacity but if you are above the 30 degree latitude and 100% boon-docking above that latitude and if you live in this area during the winter us3 100% of daily usage.


Please do not consider using A/C on solar unless you have 4X AH capacity Lithium batteries and the same sized solar panels in full sun from morning to night. Trust the sailors who only rely on solar power for everything.
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Old 06-19-2019, 07:25 PM   #7
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I agree with everything said above in principle. One element I did not see is where and what range the solar will be used. If you are in AZ in full sun and panels are flat on the roof you may get 80% of the full power. If your in AK in the winter then you get 0% power. OK, you get the idea.

I designed many hundreds of solar stand alone sites in Michigan and Florida as a consultant. So, as you can see there is no really simple 100% answer. However, I would recommend that 70%+ boon-dockers use Lithium batteries if you can afford it. Whatever AH of the Lithium AH of the batteries are then, considering flat on the roof looking upwards with good sun, use solar panels that add up to 50% of the Lithium battery AH capacity but if you are above the 30 degree latitude and 100% boon-docking above that latitude and if you live in this area during the winter us3 100% of daily usage.

Please do not consider using A/C on solar unless you have 4X AH capacity Lithium batteries and the same sized solar panels in full sun from morning to night. Trust the sailors who only rely on solar power for everything.
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Whatever AH of the Lithium AH of the batteries are then, considering flat on the roof looking upwards with good sun, use solar panels that add up to 50% of the Lithium battery AH capacity but if you are above the 30 degree latitude and 100% boon-docking above that latitude and if you live in this area during the winter us3 100% of daily usage.
What solar panel measurement do you use to have "50% of the Lithium battery AH capacity"?

I have always consider 1 watt of solar to 1 AH of battery as a minimum. I guess you could go lower solar panel wattage with lithium but I would be reluctant to design my system with less that one to one.

My system is 650watts of solar to 400AH of lithium. If I was to move to a residential fridge I would want to go to 600AH and 975 watts of panels.
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Old 06-19-2019, 10:32 PM   #8
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We have a 36Y with residential refrig. AGM batteries for a little over 400 AH, 165w panels. We have added a shunt to read our SOC. We have traveled from AZ to AK with this setup. We try to start with 90% SOC before we go to sleep. The SOC is down to 70-75% in the morning. We are comfortable with this setup. In AK our SOC gets lower during the day but we haven't fallen below 58% yet, we are normally away during morning generator hours and have no idea what it does on automatic, we do know it adds something to the battery but not very much, something is cutting it off early and we haven't figured it out yet. During evening generator hours we get ourselves up to about 95% SOC.
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Old 06-20-2019, 08:14 AM   #9
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First off, I really doubt that you will get 40 amps from the 480 watts of panels. I just installed the most efficient panels available, 400 watts worth, and get 22.5 amps at full sun perpendicular (New England). The specs state 22.8 amps for the array.

You will need a battery monitor (ex. Victron BMV-712 or similar) to monitor power consumption of your DC electric devices. Also very useful in monitoring your entire power system when done. I used a spreadsheet to calculate the power consumption as the devices only run for a percentage of the 24 hour day. You may need to estimate this at first. Add up all of your power losses for the day (xx.x amp hours) then calculate what your panels will provide, not optimally but realistically. I used a 50% factor to be conservative because of clouds, angle, partial shade etc. In the desert southwest you may get closer to 80% and you only get about 6 hours of good sun each day, again, not optimal. All is not lost though, you always have a generator or alternator to charge while driving.

Lastly, lead-acid batteries are VERY inefficient, can only be discharged to 50% and take about 24 hours to get back to full. Short of full charge will cause damage and over time will badly deteriorate the battery capacity.
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Old 06-20-2019, 08:25 AM   #10
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Solar Insolation values

A key tool for the designer is solar insolation and that can be found at Solar Insolation Chart, Solar Insolation Data | Average USA Sunlight | Solar Energy Radiation Map Of course if a RV is moving North to South and back North the amount of charge per day varies with the season. For example:



Here is a good article on solar pv tilt vs latitude: https://www.solarpaneltilt.com/
I will end this comment here bus say that the optimum tilt angle is calculated by adding 15 degrees to your latitude during winter, and subtracting 15 degrees from your latitude during summer.
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Old 06-20-2019, 08:36 AM   #11
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Lithium batteries can be discharged down to 20% remaining capacity (80% of rated AH). The also charge faster by solar, generator or shore power and last longer. The downside is that they are much more expensive than lead acid but are becoming less so as electric cars gain popularity.



I agree that everyone who boondocks for long periods should have a way of monitoring in-going and out-going amperes.
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Old 06-20-2019, 08:51 AM   #12
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We try to start with 90% SOC before we go to sleep. The SOC is down to 70-75% in the morning. During evening generator hours we get ourselves up to about 95% SOC.
We have the exact same experience. One suggestion if you keep your MH cold at night for sleeping (we keep ours at 63 degrees or less) try turning off the inverter at bed time. When we do this we wake with nearly 90% SOC and the fridge stays perfectly cold.

Then in the morning we use the genset to use the microwave and to make coffee and that's about all. Usually around 30 to 40 mins of generator time at most. Then we turn the inverter on, which turns on the fridge, and we're usually around 95% SOC already and set for the day.

However, like you, in the evening we run the gen about 2 hours to get the batteries up to 98% or so before bed.

When my 4-100ah AGMs reach their demise I plan on getting 3-LiPo4 batteries. The cost difference to replace 4 AGMs with 3 LiPos is about $1,500. But 300aH of LiPo batteries gives me more usable amp hours than 400aH of AGMs at 1/4 the weight.
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Old 06-20-2019, 01:21 PM   #13
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Charging the AGMs or other lead-acid batteries to 90-95-98% isn't doing them any favors and reduces their capacity over time shortening their life expectancy AND reducing their storage capacity i.e. not having the 400 ah (200 usable) you may think you have. This is where the true beauty of lithium comes through. They can be fully charged from 20% to full, without damage, in 4-5 hours, if you have a 50+ amp charger.

Without solar to help keep the batteries up to charge, lead-acid battery banks are a loosing proposition for boondocking. You will have to spend hundreds, even thousands of dollars in gasoline to keep them charged using a generator over their shortened life expectancy. I built a spreadsheet to model the battery systems under all sorts of scenarios and lead-acid, without solar, are not a viable option for a serious boondocker. You can get away with any kind of setup though, if you only dabble in boondocking a few short times per year and buy a new set of batteries every few years. Therefore the old adage: Pay me now or pay me later.
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