To Solar or Not To Solar

[GallenH]

I'm hoping to get some advice on the practicality of installing solar on an old (1997 PW) Rv. It currently has a single size 24 house battery. Normally there isn't a problem since we are usually driving somewhere during the day even if we return to the same campground. But recently we spent 3 days without driving and the power ran low.......low enough to set off the CM alarm during the night. I ran the engine for a while and it stopped, but I'd rather not have to do this.

So...........I'm thinking about a solar panel to help keep the battery up in voltage while I'm relatively stationary.

Can anyone give me advice as to whether or not this is a good idea? If so, the size of the panel for this purpose? I think I can squeeze in a size 27 battery. Should I? Normal LA batteries ok? Gel?

Sorry about so many questions. Any help appreciated.

[Ron J. Moore]

Have you thought about replacing your battery? If the battery is weak, it will go down. You can go to AutoZone and have it checked. It is not an AGM, I would install one. Try that for starters; If it were mine, I wouldn't go near solar, enjoy that RT for now. If you want it downstream, it is available, but there are some really talented folks here that can discuss solar pros and cons. Stay safe, Ron.

[BBQ]

.

Solar is cheap these days.
And they are easy to install.
Lots of how-to video on youtube.
Lots of complete turn-key kits on amazon.

Plan on 100w of panel(s) for every 100AH of batteries.

[booster]

The first, and likely most important, question is how you camp.

If you are camping in areas that don't receive much sun, such as shady National Forest type sites, the solar will be a lot less effective. A 100 watt panel can turn into a 15 watt panel in the poor conditions, so it would take many more panels to cover even your fairly low usage, which I probably 20ah or less per day if you got near 3 days out of a group 24 battery.

You might be better off to add a second battery, if 3 days is about maximum and you camp in the shade a lot.

If you are able to get sun all, or most, of the time solar is great, but you need to have enough battery capacity to cover the poor conditions periods.

[XLent]

Fresh battery (s) with more capacity would be the way to go.

[SteveJ]

I use a folding portable 100 unit from Renogy. One of the panels broke due to my negligence and I've since added another 100watt portable folding unit. The Renogy comes with a decent PWM four stage 30 amp controller mounted behind one of the panels. I have installed the controller inside the Roadtrek, closer to the battery. This controller is adjustable for battery type and also has a direct cable to the battery for voltage readings and also has temperature compensation. All good things.

I have two 25' connecting cables so I can park under the trees and put the panels in a more favorable position and also move the panels during the day if required.

This system keeps up well for our boondocking needs even with the Fantistica fan running during the day and/or the furnace running at night. We also sometimes run a cell booster and charge various devices, and occasionally watch an LED TV with an amplifier on the antenna lead.

Our parasitic load is about 8 watts with a fan in the fridge and the newer style electronic absorption fridge running on gas with the gas engaged.

This all works for us with occasional genny usage to make up for extended cloudy weather and/or sub optimum solar conditions.

That Renogy unit is available for $259 on Amazon. The cheaper ones have cheaper controllers. The second panel I bought was an HQST which uses China panels vs. the German panels from Renogy and has a flimsier carrying case. I threw the HQST controller in the garbage as it was clearly inferior to the Renogy unit.

We really like this for extended(up to two weeks) boondocking. Genny pretty much only runs to fire up the microwave, toaster oven or run the AC for the killer attack Chihuahua if we are away for a bit and it's hot outside.

HTH and have fun. ttfn

[GallenH]

Thanks to all of you who responded. I might try adding a second battery and then see what further needs I have BUT that brings up a couple of questions.
1. The flooded type battery requires venting. Do the others? I have a dedicated compartment for the existing battery but it will only hold one.
2. I've heard that if you add batteries that you should not mix old battery with new one. That you should buy 2 new ones. True?
3. I'm assuming that the time needed to charge 2 batteries would be greater regardless of whether or not they're being charged by the engine alternator while driving or solar.
4. Is a "short" charge ( say charging up from 50% to 70%) harder on a battery than a "full" charge (50% to 100%)

Again, thanks for all the help on this..................slow learning curve on my end but with help I'll get there...............

[booster]

Originally Posted by GallenH

Thanks to all of you who responded. I might try adding a second battery and then see what further needs I have BUT that brings up a couple of questions.
1. The flooded type battery requires venting. Do the others? I have a dedicated compartment for the existing battery but it will only hold one.
2. I've heard that if you add batteries that you should not mix old battery with new one. That you should buy 2 new ones. True?
3. I'm assuming that the time needed to charge 2 batteries would be greater regardless of whether or not they're being charged by the engine alternator while driving or solar.
4. Is a "short" charge ( say charging up from 50% to 70%) harder on a battery than a "full" charge (50% to 100%)

Again, thanks for all the help on this..................slow learning curve on my end but with help I'll get there...............

1. They claim all batteries need to be vented, but in reality AGM can be inside the van, but I wouldn't put them in a sealed box.

2. True, if you go to two new ones get a matching pair, preferably 6v golf cart batteries

3. Two batteries will take longer to get up to about 70% full, but not double off the alternator, usually, but close. The time from 70% to full is going to be essentially the same for one or two, as you have enough amps as they taper.

4. Short charging will be faster, so you will recover a day or two of use faster off the alternator. Current recommendations for most lead acid, wet and AGM, batteries would be that as long as you get the batteries all the way to full every 7-10 charge cycles or every couple weeks if fewer cycles, battery life will not be significantly reduced.

[sebtown]

I have a single 12v deep cycle wet cell battery and a 100 watt Renogy solar suitcase. We have boondocked for five days with this setup on numerous occasions.

[booster]

Originally Posted by sebtown

I have a single 12v deep cycle wet cell battery and a 100 watt Renogy solar suitcase. We have boondocked for five days with this setup on numerous occasions.

I don't think anyone would argue that you can't go for days on end with one battery and 100 watts of solar. What would be of question is what the weather and site conditions are, and how much you drive. 5 days on one battery and shady conditions in the rain, would likely be completely different.

We have 300 watts of solar, but also have compressor frig, use the microwave off of the inverter, run fans, computer, tv/dvd, etc and can also go indefinitely off grid if it is sunny where we are camped. But--because we know we can't count on the sun all the time, we also have 440ah of battery capacity, that will take us for 5-7 days even in poor sun conditions with no driving. If we didn't have a lot of battery capacity, we would be done in a couple of days if not driving some.

My point is not to say folks are wrong in saying how long their solar will let them be off grid. The point is to define the conditions you do it under. I think we often mislead newbie solar adapters into thinking the maximum sun condition results we often quote, will be all the time, and this is just plain not going to happen.

Perhaps a conditions rated scale would be in order: For us":

Maximum off grid time with good sun all the time or down to 60% of the time---indefinite

Minimum off grid time with very poor sun all the time---5-7 days

Added days from driving times while camped--1 day of capacity per 15-20 minutes of engine running.

A similar list could be made for any battery/solar/alternator size system, and I think would be much more useful for the new to charging and off grid camping folks that are here to get answers.

[hbn7hj]

This is just opinion.

1. keep the battery you have or replace it if defective.

2. Install a Bogart battery monitor or something similar

3. Install at least 100 watts of solar upgradable to 200 watts

4. Provide for the solar to charge the chassis battery (Trik-L-Start)

5. Install a smart battery charger to work with the generator.

Not everything has to be done at once. When complete you will have an electrical system as flexible as possible to adapt to your changing needs. The order of purchase is the order listed. You can skip the solar but it certainly adds to utility. Long term outside storage, for example. You are looking at $500 plus solar if you do it yourself. Steps 1 and 2 you should do ASAP. The battery monitor will tell you how you are doing and if you need to go further.

Harry 2003 C190P Roadtrek

[SteveJ]

Booster:

Perhaps a conditions rated scale would be in order: For us":

Maximum off grid time with good sun all the time or down to 60% of the time---indefinite

Minimum off grid time with very poor sun all the time---5-7 days

Added days from driving times while camped--1 day of capacity per 15-20 minutes of engine running.

For us: This is based on 100 watts. With either heat or fan we are good to about 60% depending on how cold it gets overnight. Quite a bit of our camping is at elevation. This would be for an indefinite time period using a single cheapo group 24 RV/marine "deep cycle" battery. A lot of variables. If it was quite cold over night and the forecast was for a day leaning toward sub optimum solar, we would probably run the genny for a half an hour or so in the morning to throw some quick amps at the battery. We have a PD converter with Charge Wizard. There are days/overnights that we pull more than 50%, depending. I think it helps a lot to have the portable as it can be set up to best capture the angle of the sun, especially in northern latitudes.

We do not have a fancy Bogart meter. Instead, we use two of these,, one for each direction of current:



https://www.amazon.com/bayite-6-5-10...tt+solar+panel

Starting this year we will no longer have the Onan. (Hurrah!!). I will be installing a much larger battery or two 6v into that space when we get to MN this spring as my brother there has a lot of fabricating stuff in his shop. My current genny is a remote start inverter Champion 31/2800 mounted on the motorcycle trailer tongue. It can be easily moved to a draw bar luggage carrier if for some reason we would travel without a motorcycle. A lot less noise and easier to access than the unreliable, expensive to maintain, loud, previously negleted Onan.

[EsotericSnowman]

Just wanted to mention that the U.S. Government just put a 30% tariff on imported solar panels. So get'm while they're cheap.

[Saldar]

Originally Posted by booster

....We have 300 watts of solar, but also have compressor frig, use the microwave off of the inverter, run fans, computer, tv/dvd, etc and can also go indefinitely off grid if it is sunny where we are camped. But--because we know we can't count on the sun all the time, we also have 440ah of battery capacity, that will take us for 5-7 days even in poor sun conditions with no driving. If we didn't have a lot of battery capacity, we would be done in a couple of days if not driving some.
...
Perhaps a conditions rated scale would be in order: For us":

Maximum off grid time with good sun all the time or down to 60% of the time---indefinite

Minimum off grid time with very poor sun all the time---5-7 days

I not clear on how a solar charger works faced with variable or poor sunlight.
Your post made me wonder if your solar setup does 'bulk' charging, or do you never drain that far, even when out for say a week?

Is is possible to do bulk charging without a constant current level or the idealish 0.2C amps? Or does solar just do it's best to approach the kind of "bulk" mode accomplished when plugged in? I guess this would be on and off with the amps available at the moment. Would absorb mode be the same, variable amps at a fixed (boosted?) absorb voltage? Could someone explain what is going on in solar charging? Can the charger trade power for volts or amps?

Do you top off when you get home by plugging in? Do you think your system is able to keep your batteries in shape, as well as supplying nicely for you off grid?

[booster]

Originally Posted by Saldar

I not clear on how a solar charger works faced with variable or poor sunlight.
Your post made me wonder if your solar setup does 'bulk' charging, or do you never drain that far, even when out for say a week?

Is is possible to do bulk charging without a constant current level or the idealish 0.2C amps? Or does solar just do it's best to approach the kind of "bulk" mode accomplished when plugged in? I guess this would be on and off with the amps available at the moment. Would absorb mode be the same, variable amps at a fixed (boosted?) absorb voltage? Could someone explain what is going on in solar charging? Can the charger trade power for volts or amps?

Do you top off when you get home by plugging in? Do you think your system is able to keep your batteries in shape, as well as supplying nicely for you off grid?

I actually just finished a way to long couple of posts in the high voltage battery charging thread that describe better what the solar controller goes through when the sun and loads don't play well together. It can get pretty weird.

Bulk stage is called constant current, which would be what the charger can supply wide open. For solar, I would agree with you that it is a misnomer, as the solar isn't really constant current capable all the time. Maybe "pre absorption" could be used

If we have good sun and normal loads every day, our system won't stay in bulk more than a few hours as we will only be down 15-20% after overnight. Often full again by 11:00am in good conditions. If it is cloudy or shady for a few days, we will not get full until the conditions get a lot better, or we have a drive day. In those situations, we are short charging some amount every day, somewhere between 20-80% SOC or so. We will need to get full somehow every 7-10 days to preserve battery capacity.

We are able to keep the batteries in good condition while on the road, but we need to make sure we get the full charge regularly as mentioned above at 7-10 days. We can get full by getting a week of good sun, even from 20% SOC, I think, by driving for a couple of hours and then topping with good sun, or a night of shore power.

We do plug in when we get home, to keep things full, and also I have found that the AGMs will very slowly charge over about 3-5 days in float until the level off on the amps they taking.

Solar panels generate watts of power. Voltage will float up and down with sun conditions and load, and amps will follow. A PWM controller will just knock down the voltage to what you need, leaving the amps the same. A MPPT controller will reduce the volts to what you need and use that power to increase the amps above what the panels are providing so closer to watts in = watts out.

[Saldar]

Originally Posted by booster

I actually just finished a way to long couple of posts in the high voltage battery charging thread that describe better what the solar controller goes through when the sun and loads don't play well together. It can get pretty weird.

I'm still trying to sort out how solar even works in pristine situations, and hope to move on to comprehend weird interactions. Your summary of how MPPT and PWM controllers work helps, and your description of how your charging works day to day. My first batteries are "training" batteries, I'm afraid. I hope they function until I learn decent care and best (and/or easy enough DIY) mods to help the next set last.

Booster's long post starts here and it is a good one:
http://www.classbforum.com/forums/f2...ages-7280.html

[booster]

Originally Posted by Saldar

I'm still trying to sort out how solar even works in pristine situations, and hope to move on to comprehend weird interactions. Your summary of how MPPT and PWM controllers work helps, and your description of how your charging works day to day. My first batteries are "training" batteries, I'm afraid. I hope they function until I learn decent care and best (and/or easy enough DIY) mods to help the next set last.

Booster's long post starts here and it is a good one:
http://www.classbforum.com/forums/f2...ages-7280.html

Good idea on the training batteries, it is very similar to what we did. Our "intermediate" system (which I thought was going to be permanent when I put it in) was pretty good, but we also found some weaknesses with it. Luckily, I was able to rig it to work similarly to how we thought we wanted for testing (some manual input needed). We then tested using just the two Trojan GC 260ah batteries, not using the generator, standalone inverter for micro, larger single alternator, to try to see how it would go when scaled up. We certainly had some glitches, but the Trojans survived about two summers of camping and testing well, and we learned enough to be confident enough to spring for the 4 Lifelines, Magnum, second alternator.

[wincrasher]

On my Travato, I had 260 watts on the roof, but suffered some shading depending on conditions. It was hit or miss on being "enough" to keep up with my power demands (even though no inverter). I figured that most days, I only got 125-150 watts out of it due to shading, a low performance PWM controller, and mismatched panel sizes.

On the solar install I put on my Xplorer, I have 400 watts, all matched panels, no shading and a much higher performance controller (Victron MPPT). I have no issues with meeting my power demands, even with heavy use of my 2800 watt inverter.

So my thinking is that 400 watts and an MPPT controller is pretty much the floor for use on an RV if you want to do more than trickle charging battery maintenance.

All that said is applicable if you are a traveling type - you take longer trips and go unplugged for long stretches.

If you are a weekender though, or you only go from campground to campground (with services), I would argue that you would be better off putting your money in a few extra batteries and forgo the solar. If you can make it thru a weekend on 400 ah, then you can plug back in when you return home.

[Saldar]

Originally Posted by booster

Bulk stage is called constant current, which would be what the charger can supply wide open. For solar, I would agree with you that it is a misnomer, as the solar isn't really constant current capable all the time. Maybe "pre absorption" could be used

"Pre-absorption"
Booster, you are of a mind with another sharer of excellent battery knowledge, "MaineSail" at compassmarine. He argues a big degrader of marine batteries is "pre-floatulation".

[BBQ]

Originally Posted by Saldar

"Pre-absorption"
Booster, you are of a mind with another sharer of excellent battery knowledge, "MaineSail" at compassmarine. He argues a big degrader of marine batteries is "pre-floatulation".

LOL

What happens after Post-Trickle ?