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RVing message boards => Tech Talk => Solar => Topic started by: BigSkyTrailerGuy on August 29, 2017, 05:23:44 PM

Title: Drowning in a sea of solar power information!
Post by: BigSkyTrailerGuy on August 29, 2017, 05:23:44 PM
Sorry -- no idea there was a new "Solar Topics" section!

The first thing I did in our new/used Cardinal 5'er.... two new matching 6V batts.

First long trip out, I'm quickly down to "weak" 11.8v output reading, and I'm freaked out because I know I'm killing my batts.  So I run my old gennie into the charger/converter for a few annoying hours each day.

Some Amazon Solar "kits" seem to come with a (cheesy?) power converter with tiny output cables.

>> Then I started following HandyBob Solar Off-grid writings...
Am I better off going with a couple of 100W panels and a decent Bogart or Morningstar

I don't want to mount it; I'd like a portable panel, so I can chase the sun as I need to, and keep the power, and i want to mount the power converter near the batts with some 4-6 AWG battery Wire.

 :-\so,  Am I now obsessing?

Title: Re: Drowning in a sea of solar power information!
Post by: QZ on August 29, 2017, 08:30:05 PM
Oh man this sometimes turns into a book. :)
Yes, 11.8 is low, many will often try to stay above 12.2 volts. A rule of thumb is 100 to 150 watts of solar per 100 amp hours of battery capacity. Your batteries are about 215 amp hour rating.  This is not one size fits all so there are a variety of ways for people to accomplish things. 

Your battery is your bank account.
Your solar or converter are your source of income.
Your energy use is your spending but you also have to support the banker and associated costs.

You said you were quickly down on the batteries so we need to start there.  Do you mean overnight or over a period of days?
Title: Re: Drowning in a sea of solar power information!
Post by: John From Detroit on August 30, 2017, 06:23:22 AM
There is only one thing I will add.. Generally when looking at panels de-rate 50%.. That is if the panel says 200 watts. count on 100..    And make sure you have a good charge controller between the panels and the battery.... 

Finally. Solar controllers are known sources of Television and Radio interference.. In case it bothers your TV.
Title: Re: Drowning in a sea of solar power information!
Post by: QZ on August 30, 2017, 09:17:09 AM
Lets assume your battery died in one night. You should only use about half of your batteries capacity so you probably used 80 amp hours or more. When you try to replace those AH the battery will accept more amps when it is very low. As the amperage tapers off going in and the voltage goes up the final part of the charge cycle takes a good deal of time. A 50 amp converter may start out putting 40 +- amps in and gradually taper. If you need 80 AH it doesn't mean that it will only take 4 hours. To reach full charge it will probably take 6 to 8 hours IF your converter will do 14.4 volts. If your converter is only putting out 13.6 volts it could take longer. A good upgrade is to go to a 3 or 4 stage converter that does 14.4 and some will do even better with 14.8 v.

To put heavy amps back in takes a lot of solar so some people will use a program of morning generator time while cooking breakfast etc and let the solar take over to finish as the sun is higher in the sky and the panels are maxing out.  A 100 watt panel will put out about 5 amps so you can see what you are up against when trying to put 80 AH but in as there are not enough hours in the day.  I first ran 520 watts on a Bogart SC2030 attached to a Bogart Trimetric and would often see 28 amps going into my four GC2 batteries.  With 520 W and usually down 60 to 80 AH I would usually be charged each day.

You cant go by the monitor panel as it's very crude. For the battery to be fully charged you would need the converter or the solar controller to go into 13.2 volt float mode.  If you charged for a few hours and look at a volt meter reading it may say 12.6 or 12.7 but if you let the battery sit a few hours with no charging or draw you will see a more accurate resting voltage and it could well be lower. the reason is that the battery isn't actually fully charged. When you use a device like a Trimetric or Victron they are counting all the AH that go out and count them as they go back in. They can and do need to be  programed to actually replace more AH then removed so as to account for internal battery resistance and wiring losses. My Trimetric is set to return 112%.

So...if you use a generator you need a good converter that does 14.4 v or more. If your two GC2 batteries cant carry you over night to need to add two more.  You can do about a week or so of incomplete charges where you may only return 80 % or so of the AH each day and then return to shore power where the converter can fully charge and sit at float so the specific gravity is topped off. Your battery could show 12.6 yet if the SG is checked you might see that it's too low. If it's left in this condition the plates will become sulfated. The sulfate can only be driven back off the plate by completely charging.  You need a charge source that can charge with a high enough voltage that the battery will slightly gas. If you were to remove a cap you should see that it has a tiny bubble break the surface every second or so. This action keeps the acid mixed so that stratification doesn't occur. The acid will form into stronger and weaker layers if not mixed.

It's difficult to recommend some things when knowing little about your rig or lifestyle etc. If I was dead set on ground use only and keeping the cost down and having any chance of putting a good amount of those AH back in I'd probably suitcase hinge two sets of 100 or so panels together. That would give you 400 watts. Grape solar sells what I understand to be a good full feature controller that has temperature compensation and adjustable voltage for $60. The Bogart when used without the Trimetric will work as a basic controller and put out 14.4 v. Morningstar is also a good choice.  Those last two wot give you the ability to equalize without monitors  though where iirc the grape will.

The problem with ground based panels is that they may become a real pita to deal with. When people dont want to go on the roof to tilt and because panel prices are so low they will just add more panels on the roof. Without looking at the grape specs I'd guess it could handle 600 watts.

Another issue that comes up for new solar shoppers is the argument over PWM Pulse Width Modulation vs MPPT Maximum Power Point Tracking controllers. For what you are contemplating go with an PWM.  You wont get 30% more out of MPPT and more realistic is 10% which can easily be beat by adding one more panel.

No frills bare bones= Grape ($60), two 100 watt panels ($200), Anderson quick connect plug ($10), manual reset breaker between battery and controller ($15), wires etc ($40) = $325

No frills more power = four 100 watt made into two suitcases = $525

From there you would move up to roof mount and the move into something like Trimetric for complete system monitoring and adjustment.

Roof mount example basic = Four 160 watts (appox $ 550), grape ($60), combiner box cable 2 breakers tilts (not z brackets) strain reliefs terminals etc ($500) = $1110

Other points: There is no bad amount of solar, you could very well want more, no one ever says they bought too much,  most batteries die of under charging not over charging,  solar set ups often dont fully charge (not solar fault, under sized for job given), everyone doesn't need a professional, not all professionals are good.

13.6 will charge a battery if given enough time. Giving a lot of time is exactly what you dont want when running a genny and especially a loud genny.  When using solar in winter you will see a trickle of amps at daylight and a peak window of about 4 to 5 hours and a tapering into dusk.  Tilting a panel will give about 30% more.  The good thing about ground panels is that you can keep it pointed at the sun if you are there to do it. Bad about ground panels is that they can grow legs.
Title: Re: Drowning in a sea of solar power information!
Post by: Gary RV_Wizard on August 30, 2017, 10:07:45 AM
The bank account analogy is apt - you can only take out what you put in ahead of time. You need to evaluate your daily power consumption to determine how much battery capacity (amp-hours) you need, and then you need to assess how much solar (or other charging source) you need to replace that  amount of AH.

You also need to consider that solar power is highly variable with the amount of sunlight that reaches the panel as well as the duration of that sunlight. Odds are that even the best solar panel & charge controller will only produce peak output a few hours per day.  If you only have a brief period to get full solar charging, you may need more panel wattage to maximize what you can get in a short time. Conversely, if you have good sun several hours per day, a modest size panel may be entirely adequate.
Title: Re: Drowning in a sea of solar power information!
Post by: Kevin Means on August 30, 2017, 11:23:53 AM
If you want to be happy with solar, it's important to determine what your goal is - and that takes a bit of research. Assumming a sunny day... Do you want your solar to be able to completely replenish all the power you typically use, or just part of it?

Having a system that's large enough to replenish all the power you use would, of course, be ideal, but depending on your consumption, that can get expensive. If your goal is to replenish only a portion of the power you consume, you'll have to determine how much power that is.

RV solar is a balancing act - between consumption, storage capacity and solar power. Unfortunately, there is no "one size fits all" solution to everyone's needs, because there are so many variables - even with identical installations. My suggestion is: tell us what your goal is; tell us what your battery-bank's AH capacity is; tell us how much power you typically use in 24 hours (if you don't know, tell us what appliances you have and how much you use them in a 24 hour period) and tell us in what part of the country you'll typically be camping. We can go from there.

Title: Re: Drowning in a sea of solar power information!
Post by: QZ on October 16, 2017, 09:45:47 PM
X2 on what Kevin said, it's best if you can give us as much info as possible.

Do you want to run the house furnace?
What size television? Led?
Laptops, phones?
Led bulbs or incandescent?
Do you have a generator? What kind?
How many batteries and what kind?