minimum amount of solar

I have a 100w suitcase solar kit and I have had good luck with it

If the goal is to not run the generator as often, it works well. If the goal is to rarely run the generator, it is not enough.

In an unshaded site with sunny days, I rarely need to run the generator. If there are cloudy days, 100w doesn’t provide catch up ability.

Since I live in Michigan, with lots of clouds and lots of trees, I can’t really rely on solar, so I prefer to not put holes in my roof. With the portable panel I can put the panel where the sun is, away from trees. I changed the wire from the panel with a longer, thicker one.

pinesman wrote:
I do not plan to mount them on the roof at this time but just sit them out on the ground.

You'll tire of that pretty quickly. The wind will get them too.

pinesman,

The bare minimum is 60 watts for every 100 amp-hours of storage. Since you have flooded batteries the maximum is about 150 watts per 100 amp-hours of storage.

For a flat fixed installation (no tilt) I'd go with 100 watts per 100 amp-hours of storage. I'd go with the Grape 40 amp charge controller from Home Depot.

I have 150 watts mounted on the roof, and two 6v GC batteries, and camp in a similar fashion. My batteries remain very close to topped off all the time. We can be wasteful for a night or two with little issue.

BFL13 wrote:


I agree with others that 200 is way more useful than 100. BTDT.
Some of those folding 200w "kits" are very expensive. You can make your own with two regular panels and a couple of hinges. That way, you can start off now and get an idea what it all can do, and then use it or expand it later as needed. Get a bigger amp controller with that in mind so you don't have to buy another one later.

Way more bang for the buck if you can aim your panel(s) during the day when you happen by. Can sit them on a swivel chair or just a low dolly with castors. High enough to keep the bottom of the panel(s) out of any taller grass. You will need a long enough wire to move the array out of the shadow of the rig itself for part of the day in some locations.

On my last class C I had 400W on the roof. It was more than I ever needed (2 grp 31's charged in less than 2 hours in the AM). I am now using two homemade hinged 100W panels as a start. This allows me to also run them in series and provide 36V or so to my controller. I would suggest, as others have said, to purchase a controller with capacity to grow, and also one that accepts different voltages in case you want to run panels in series. I also noticed the ability to "aim" the panels greatly increased my throughput.

babock wrote:
For every 100W, you will get 5A with a PWM controller if you tilt. If you figure 5 hours of equivalent sun per day, that is 25AH. With a 100AH battery at 50% SOC, you will need 200W of solar to bring it back. If you flat mount your panels, figure on a 30% loss.

This is a useful first approach, but could be misleading if not careful.

Actually, a typical 100w panel has an Isc of 6.2 amps, which is what you get to the battery bank with PWM when the panel is aimed at a high sun. Most of the day either side of noon, you will get less of course, even when aimed. AH haul will vary widely depending on time of year and location.

The difference between flat and aimed or just tilted to South will vary a lot too depending on your latitude and time of year.

You can get closer to the right answer for your own situation if you can specify your likely locations and times of year, and then check the on-line solar tables for that.

Randomly saying X watts, is unlikely to give you an accurate answer.

Look at your use case...what will you run and how long will you run it?

Multiply the watts times the time that it's drawing those watts...add it up and that will give you the total watt-hours you need to replace.

Typically you can assume the watt-hr produced will be about 4 times the rating...ie: 100w panel will generate around 400watt-hr per day.

If you are willing to crank up a generator or provide an alternate charging source, this is probably good enough for the solar panels...if you want to be able to go say 3 days without another source, figure a bit less than 3 times the wattage to allow for cloudy days with minimal output.

Then you need to assess the battery bank...Divide the watt-hr by 12 to get amp-hr needed, then size the battery bank accordingly. Note: For traditional lead acid batteries, you can only use around 30-50% of the rating without causing damage and short life, so you need a rating of 2 to 3 times what you calculated (lithium are a different ballgame and more complicated).

For every 100W, you will get 5A with a PWM controller if you tilt. If you figure 5 hours of equivalent sun per day, that is 25AH. With a 100AH battery at 50% SOC, you will need 200W of solar to bring it back. If you flat mount your panels, figure on a 30% loss.

pinesman wrote:

BFL13 wrote:
What do you want to do more than now off-grid? You say no problem with how it is.

With our current work life, weekends are about all we can do now. As retirement is quickly approaching and longer trips to our favorite dry campgrounds are in the future, I want to be able to stay longer before we go home or to a campground with electric to recharge. We have one generator and might get a smaller one just for running the converter but I think I could like the silence of solar. I am just basically asking what is the minimum to be worthwhile. I do not plan to mount them on the roof at this time but just sit them out on the ground.

I agree with others that 200 is way more useful than 100. BTDT.
Some of those folding 200w "kits" are very expensive. You can make your own with two regular panels and a couple of hinges. That way, you can start off now and get an idea what it all can do, and then use it or expand it later as needed. Get a bigger amp controller with that in mind so you don't have to buy another one later.

Way more bang for the buck if you can aim your panel(s) during the day when you happen by. Can sit them on a swivel chair or just a low dolly with castors. High enough to keep the bottom of the panel(s) out of any taller grass. You will need a long enough wire to move the array out of the shadow of the rig itself for part of the day in some locations.

1 Panel, 200 Watts And you can use a PWM controller if you wish.