Solar panel battery charge

[Steve_911]

For those of you who use solar for charging your batteries when dry camping, how many watt panel/s do you use, and are you satisfied with the results?
I want to use solar to charge my two 6volt deep cycle setup, but not quite certain of how many watts I should be looking at.
Thanks in advance for any replies.
Steve

[TurnThePage]

I can go almost indefinitely with my two 6v charged by 150w of solar, rain or shine. I'm usually parked where I get the least direct sun as possible. We typically watch a movie or two at night in addition to the regular lights, pump, fridge. Maybe I'm a miser.

[webwrangler]

pianotuna wrote:
Hi webwringler,

Going MPPT is similar to any other decision made about a solar system.

If you want every last watt and have no more room on the roof, MPPT may get you there. If you don't then a good quality PWM controller with adjustable voltage set points and a battery temperature sensor, may be a better choice.

Handy is/was a Morningstar fan and the controller he loved was twice the price of the Xantrex c-35.

So his advice needs to be taken with a LARGE grain of salt, for it is not terribly useful. You need to be quite knowledgeable about what to accept from him and what is chaff. So it is no place for a beginner.

In 2005 going MPPT with 200 watts of solar was a no brainer because cost per watt for panels was $5.50. That is why I have MPPT with 256 watts.

webwrangler wrote:
But he does debunk the belief that you need an MPPT controller for 250 watts in an RV.

Fair enough.

[time2roll]

One of the advantages to MPPT is using low cost 24v panels.
And please do not compare a low-end $25 PWM controller to a full featured MPPT.

[Dirtpig]

I have 300 watts on my roof. 2x 140watt panels, and a 20 watt panel. They are located front, mid, and rear of the roof. This allows me to get some sunlight on at least one of the bigger panels in most areas where i camp. On the island here where i live there are many tall trees or high mountains and having full sun such as an open field does not really happen. This way I usually can get ~150watts of charging for 5hrs or so, sometimes even more if im in a bit more sunny spot. My power usage is considered very light, my solar panel wattage would be way overkill but i factored in only 1/2 of it ever working at one time. I am extremely happy with solar and so is my friend who i helped install his system. Neither of us ever use a generator during spring/summer even on 10+ day trips. Our families are outdoor campers, there is no tv watching/indoor shenanigans eating power up other then a radio, sensors, fridge and charging kids electric quad batteries. I also have 2 6v batteries (trojan)

[pianotuna]

Hi webwringler,

Going MPPT is similar to any other decision made about a solar system.

If you want every last watt and have no more room on the roof, MPPT may get you there. If you don't then a good quality PWM controller with adjustable voltage set points and a battery temperature sensor, may be a better choice.

Handy is/was a Morningstar fan and the controller he loved was twice the price of the Xantrex c-35.

So his advice needs to be taken with a LARGE grain of salt, for it is not terribly useful. You need to be quite knowledgeable about what to accept from him and what is chaff. So it is no place for a beginner.

In 2005 going MPPT with 200 watts of solar was a no brainer because cost per watt for panels was $5.50. That is why I have MPPT with 256 watts.

webwrangler wrote:
But he does debunk the belief that you need an MPPT controller for 250 watts in an RV.

[time2roll]

About 100 watts per battery. More for heavy use, less for misers.
But then with heavy use you may need more batteries.

> Members Solar Installations With Pics

[webwrangler]

pianotuna wrote:
Handy's information is, at best, dated. It is not a site for a beginner.

Hooterville wrote:
To really understand solar for rv's Google handybobsolar and read his words of advise. I followed his advise for a reasonably priced system that actually works.

But he does debunk the belief that you need an MPPT controller for 250 watts in an RV.

[webwrangler]

2oldman said it: a couple hundred should do it. I have 170, due to starting out too small and adding on. I wish I had 200 or 250. In the spring, summer or fall in a sunny location, I can go indefinitely. In February in the Olympic rain forest, I'm good for about a week. YMMV depending on your power use. I use the water pump, lights (have put LEDs in the most-used fixtures), satellite radio, phone charging and in February, occasionally the furnace. The furnace fan will run your batteries down fast.

[qtla9111]

One 240W panel, two deep cycle 6V batteries and a 600W inverter. I also use a smaller inverter in the bedroom. Works great.

A four month trip to Canada and back w/o the generator and this summer five weeks with no hookups or generator.

Laptops, lamps, television, etc.

[pianotuna]

Handy's information is, at best, dated. It is not a site for a beginner.

Hooterville wrote:
To really understand solar for rv's Google handybobsolar and read his words of advise. I followed his advise for a reasonably priced system that actually works.

[Hooterville]

To really understand solar for rv's Google handybobsolar and read his words of advise. I followed his advise for a reasonably priced system that actually works.

[KD4UPL]

It all depends on how much power you actually use. More is always better. As an example: If you drain your batteries half way that's about 100 Ah. It will take close to 500 watts of solar to do that in one day.
I hope you won't be draining them that far in one day. If you are you need a bigger battery bank.
100 watts is about the smallest panel that makes any sense to buy. The best deal on panels on a dollar/watt basis is usually in the 225 to 280 watt range. These will require an MPPT charge controller.

[RoyB]

The charging rules are the same... If you batteries are down to 50% charge state then it will take 17-20AMPS DC charge for each battery from your solar panels if you want them to be back up to their 90% charge state in a three hour time frame. This will happen in around three hours time if you have that much DC Current going into them...

But since you only get 5-6 amps out of each 120WATT panel then you are not going to get them recharged in three hours and can only hope the high sun is there for several more hours during the day...

Where everyone gets saved is their panels start charging good probably around 9-10AM each morning and go all day to 6-7PM in the evening. this will top off your batteries BIG TIME...

My case is going to be different however as I know I will draining 20-22AMPS DC current from my batteries starting at 6PM to 10PM everyday running all my Ham Radio and momabears toys... I know I can get them recharged to 90% using the generator so that what I am going to do...

It could be for me that I may only have to run the generator for the first hour of my recharge cycle each morning until I get past the very high 52-55AMPS of DC Current demand when I first start my charging cycle. It starts tapering down after 15-20 minutes - then perhaps switching over to solar panel after the first hour I can get my batteries going to the full 90% charge state while still in the high sun all day...

As you can see if different for everybody haha...

Roy Ken

[pianotuna]

Here is a simple flow chart.

Budget-->Energy Audit-->Battery bank size-->number of watts-->PWM or MPPT. What ever type of controller is chosen, make sure it has adjustable set points and a temperature probe that is on the battery.

If you use solar as a battery charger, one rule of thumb is between 60 and 150 watts of panels per 100 amp-hours of storage. The smaller the battery bank the higher the wattage needed (per 100 amp-hours). Here is a link to the rather special spreadsheet which includes an energy audit, that N8GS has created to help size solar battery charging systems!

solar spreadsheet by N8GS

If you full time or use an inverter lots, then populate the entire unshaded area of the roof with panels. I'm considering replacing my awning with solar panels.

For a nice explanation of solar, try this link:

Golden rules of solar