I know this subject has probably been beaten to death, but I'm contemplating s9lar. Is 100 watt panel enough? Flexible or rigid panel? Don't want to do a lot of off grid, but want to keep my 2 6volt golf cart batteries charged. Have a 1973 Sequoia

thigh19 wrote on Fri, 01 November 2019 14:13

I know this subject has probably been beaten to death, but I'm contemplating s9lar. Is 100 watt panel enough? Flexible or rigid panel? Don't want to do a lot of off grid, but want to keep my 2 6volt golf cart batteries charged. Have a 1973 Sequoia

First Questions.......
What are you planning to power?
- If you only plan to keep the battery alive while the coach is parked, a 50 watt panel will take care of that.
- If you plan to use the solar for power, we have MORE questions.
- Are you supplying only 12v dc power appliances? This should be easier for you. To get the Amp rating of a panel, you divide the panel (100 watt) by the voltage (12v dc) which would be 8 AMPs.
Most 12v appliances are low amp ratings, or low watt ratings.
More Understanding ---- Your best solar charge is at Sun hours. This generally is related to static homes, and can vary from 3 to 5 hours per day.
A 100 watt solar panel in a 4 sun hour day will charge up to 400 watts, or 32 amps.
Another thought, If you have a 100AH battery, that 100 watt solar panel will take over 3 days to restore a battery that has been discharged.

If you are planning on using an inverter, prepare to be shocked.
In order for a inverter to create 5 amps of 120v ac power, your battery needs to supply 50 amps of 12v dc power.

A fast rough idea of time.... a 12v dc 100 AH lead acid battery will supply 5 amps for 20 hours. The above example would not last long.

Another fast thought......... Batteries, either Lead Acid or Lithium, do not like to supply high amps for extended periods. If you can keep the draw down around 5 amps, occasional spikes to 10 amps is ok, the battery will have a longer life.
So if you planned to run 15 amps often from your batteries, You may want to supply two batteries. 15 AMPs would be supplied by two 100 AH batteries at 7.5 amp per battery. Checking the rough guide above, you'd have about 15 hours.

Panel depend on how you will be supplying power.
FIRST ----- Flexible are not highly recommended. The flexible panels tend to fail in 4 years. No matter how you care for them, the inner circuitry seems to break down. The flexible panels have no good cooling method and heat is detrimental to flex panels.
In the case where you have a space problem and the flex panels seem to be the only choice, look for a TOP BRAND panel with a warrentee, but be warned, the flex panels tend to go away as fast as they show up. most are made in China and no matter how long your warrantee is, they most likely will not exist by the time yours fails.

In framed panels there are two types, Poly and mono. One is suppose to be better than the other but according to tests, they both perform pretty much the same in sun/shade. Do some research on this if you want to be picky about which you go after but the test results concluded that there are not large differences.

The space you have on your RV will most likely be the determining factor of how many panels you can have.
300 watts is a good number but again, what are you going to use it for.
If you want to run TV lights and computer at night, you have to figure your loads, play with the battery numbers, figure sun hours (yes it is important even in an RV) and then go with it.

Here is a quick list

Coffee makr 950 watts
Toaster oven 1200 watts
MicrWave 750 watts
Sm Floor htr 750 watts
Lg floor htr 1500 watts
Sm Tv 90 watts
DVD player 60 watts
16 cu ft frost free frig 725 watts
Xbox 360 106 watts
rv frig 343 watts
Stereo Recvr 75 watts
Computer 120 watts
Telephone 100 watts
Florescent lamp 20 watts
fan 100 watts

Figure these figures as ONE HOUR USE. If using the tv for 3 hours, multiply the 90 watts by 3 for one days use.

So if you are using the tv for 3 hours at 90 watts total is 270 watts

in a 4 hour sun day area, a 300 watt set of panels can produce 1200 watts, that is enough to cover the 270 watts for the
tv and to charge the batteries.

Play with the numbers and see where you might end up.
Also look in to the mppt controllers. They are supposed to charged even when not in direct sunlight.

[ PANEL ] = [ roof fuse ] = [ Regulator ] = [ ckt breaker ] = [BATTERY]

I mention the roof fuse because recently the rv community has had a bad installer install solar to unsuspecting users. He
made the hole through the roof too small and scraped the insulation from the power wires. Several Rvs have burnt down
recently because of this installer.
Besides, you need to protect your sources both from the panel and from the battery.

good luck.

As I am fully in play mode with solar now, ALL my figures are created in hourly segments unless otherwise stated.
I created many Ecell worksheets to play with the numbers, and I will admit I am not perfect but I am getting some
pretty good numbers that compare to working systems.

My original comment was an attempt to help the user understand that SOLAR is a balancing act between the panels, batteries and the load.
One scenario is where you may have a high count of solar watts which allows you to run some appliances during the sun hours
while the batteries maintain charge.
Another scenario is where you charge the batteries during the day and use the battery storage in the evening, requiring more batteries.
The scenarios go on and on, it is all a customizing game to the use you have for the system.
No one system is the same.

My only comments on the batteries is they need something charging them, solar, vehicle alternator, generator or all of the above.
Recent reads have come up with information that says that even though you CAN use the power in a battery and run its level down, IDEALLY, you want
your battery levels high, near full.
We had lead acid batteries in battery banks that would last 25 years.
the Lithiums, and i am not going to get into an argument over these new batteries, but they have concerns that no one seems to
consider. All that is heard is they can last longer and discharge further. I will say that is true, but, they don't like
that deep of a discharge and every deep discharge is taking some life away from the battery.
Also, NO BATTERY likes High loads for extended periods. Besides shortening the life of the battery, extreme high loads will find your
system weak spots, usually connections, and they will get hot or burn. That is why I mentioned that time measure formula some kind
person offered here at GMC net at one time, it is a loose figure to work with,
but it is close enough to get an idea of what you are working with.

IDEALLY, the batteries like low loads of 5 to 10 amps. You start to get high loads from the batteries, you need more batteries
to share the load.

Running the inverter is expensive on your battery power. at 12v dc, its a factor of 10. 20 amps of 12v dc into the inverter
will supply 2 amps of 120v AC. The normal roof top AC is plus or minus about 9 amps, which would be 90 amps from the battery/hr.
So that is not likely to happen as physically, the GMC does not have enough roof for panels or space for batteries to support that.

The RV Nomads have taken to home windows units which run at about 3-4 amps/hr to run. This translates to 30 to 40 amps/hr of 12v dc into
the inverter, still requires an extra panel or two and one or two more batteries, but it can be done.

One important thing to keep in mind is if you draw high amps from the Lithium batteries, they start to get hot. That should be a warning
but most don't understand. The article I read said that if those components, and that chemical mix begins to ignite, that battery
fire is very difficult to put out, and you cannot use water on a lithium battery fire. If the fire department finds out there are
lithium batteries involved in a fire, they become much more cautious about attacking that fire. So much so you may lose your rig.

This is the main reason that batteries, including Lithium batteries, should be planned to supply low current loads, within reason, to the system
including the inverter.
Keeping the current loads down extends the battery life and runs at a much safer operating margin.