7 replies to this topic

[Jon R]

I suspect many of you more experienced folks will read this and say, "no s%#t, Sherlock," but I thought I'd post anyway.

I've been using my new system for about 6 weeks now. I have two 200 watt rigid Renogy panels with a Victron MPPT 100/30, and 200Ah of LiFePO battery. I chose the panels to maximize my use of the area between the roof vents on the Grandby, and my thought was that, while it's way more panel than I need in sunny weather, it would make a big difference the dark cloudy off season in the PNW.

After experiencing a few completely cloudy days in the Seattle area, including yesterday and today, which are among the longest days of the year, I wonder if I should have bothered with the second panel. If it's sunny or even partly sunny, my system is caught up to fully charged by mid to late morning. If it's heavy overcast (even now in July), I get about 5 to 7% of rated panel output. This helps offset the refrigerator draw so I don't fall much further behind during the middle of the day, but it doesn't get the battery ahead at all.

So my hope that doubling the panel capacity, relative to what would be needed for indefinite sunny weather use, would make a significant difference in PNW overcast does not appear to be playing out. Maybe it will make the difference in some partial sun campsite conditions in sunny weather. I can see in the gray season on longer trips I will be largely dependent on the DC to DC charger, but at least my large battery will give me 3 to 4 days before I must charge.

So if I was doing this again, I would go with the advice several of you have previously given to get one panel of the largest power rating that fits and is compatible (currently 300 or 320 watts probably), save the extra weight on the roof, and call it good.

Edited by Jon R, 01 July 2021 - 07:38 PM.

[drumwood]

I suspect many of you more experienced folks will read this and say, "no s%#t, Sherlock," but I thought I'd post anyway.

I've been using my new system for about 6 weeks now. I have two 200 watt rigid Renogy panels with a Victron MPPT 100/30, and 200Ah of LiFePO battery. I chose the panels to maximize my use of the area between the roof vents on the Grandby, and my thought was that, while it's way more panel than I need in sunny weather, it would make a big difference the dark cloudy off season in the PNW.

After experiencing a few completely cloudy days in the Seattle area, including yesterday and today, which are among the longest days of the year, I wonder if I should have bothered with the second panel. If it's sunny or even partly sunny, my system is caught up to fully charged by mid to late morning. If it's heavy overcast (even now in July), I get about 5 to 7% of rated panel output. This helps offset the refrigerator draw so I don't fall much further behind during the middle of the day, but it doesn't get the battery ahead at all.

So my hope that doubling the panel capacity relative to what would be needed for indefinite sunny weather use would make a significant difference in PNW overcast does not appear to be playing out. Maybe it will make the difference in some partial sun campsite conditions in sunny weather. I can see in the gray season on longer trips I will be largely dependent on the DC to DC charger, but at least my large battery will give me 3 to 4 days before I must charge.

So if I was doing this again, I would go with the advice several of you have previously given to get one panel of the largest power rating that fits and is compatible (currently 300 or 320 watts probably), save the extra weight on the roof, and call it good.

Take into account that the sun angle is much lower in the winter months, which greatly reduces the solar gain on panels mounted flat. That is a big reason you need extra panel watts.

Being able to tilt your panels to the sun angle would really help. In my case, I already have over 300 watts in panels so tilting would be my next improvement. It would likely be while stationary only. I have a portable panel I can tilt but it is a hassle to carry and hook up.

[Vic Harder]

Good real world data Jon R.  My setup is similar, and I use about 26AH with my 130L truckfridge overnight.  Fully charged again most sunny days before I even wake up.  That said, clouds, winter... not much solar charging happening north of the 49th parallel.  

[Wallowa]

Hmmmm...not certain...considering the sunlight angle, period [daylight hours], intermittent cloud cover, temperature...having "extra" solar watts might just beat ending up with not enough....true DC/DC is a boon to charging especially into an LiFePo4 battery; but it does need the motor to be running...just my take and of course I could be wrong.. tantamount in my mind to carrying more water than you plan on using... 

 

 

A lot depends on Latitude, "Changes in attitude",...Vic has about 17+ hours of daylight and we have about 15.5 hours [45.43N]....Fall or Winter, Vic may be lighting candles.....

Edited by Wallowa, 02 July 2021 - 03:05 AM.

[bsharp007]

I pretty much have your same setup 200 watts on the roof and I tend to camp a lot near the ocean in Northern CA or OR (lots of fog even in the summer) and find that on most days I am topped off sometime in the early afternoon but sometimes when I traveling or need an extra boost I bring a Renogy 100 watt suitcase and that tops off the 200 ah batteries quite a bit faster.  Most of the time the suitcase just stays in the truck.  Also it is nice on hot days to park in the shade and deploy the suitcase and it can be angled to the sun.

So far this system has worked all year round in a variety of climates.

[goinoregon]

i put 2 100 watt panels on roof with the thought that with more surface area, i would have better luck catching the sun's rays while camping in the woods with shade.

[Jon R]

I actually have two 200 watt panels. When they are partly shaded by trees or if it’s overcast I only get around 20 to 60 watts total from the array.

[DavidGraves]

An old farmer I know said leave the front of your roof down and point your truck downhill southward.....it is not 45 degrees but it is better than flat.

 

Or, you could drive to the equator .

 

DG