How much solar

[WTSMatt]

Thinking of changing my solar setup from roof mounted hard panels to hood mounted soft panel to help with MPG. Currently running 2x100 watt panel to a 100AH AGM battery with a Redarc controller. I have a ICECO 45L dual zone fridge, led lights and that’s it. Fridge uses about 10watts per hour, or so I’ve read. Do I really need 200 watts? Hood mount woukd help with MPG but woukd only be max if 100 watts with what I’ve found so far.

 

[OTH Overland]

I was carrying (2)100 portable panels as I have a softshell RTT and a Jeep hood that is not conducive to mounting a flexible panel on, I figured out over a years time that I never needed to use the panels so now leave them at home unless going to be camping in one place for at least three days. Typically we travel each day and even in winter running an electric blanket and a diesel heater we have not used more than 60 percent of the 100ah battery and the redarc manager 30 will top off battery from 60 percent in just over an hour or so. We have an inverter but rarely use it and have found that our typical loads just do not use enough battery to justify needing solar, If I had roof space available I would go with a single 100 watt panel just to keep things topped off when parked in the driveway and perhaps take a bit of load off of the alternator.

 

[El-Dracho]

It is a good question. The question of whether a certain power of the solar panel is sufficient cannot be answered in a general way.

It depends on many factors and also on whether solar is the only source to recharge the battery or if, for example, you drive daily and it is also charged by the alternator. Then the answer depends on how high quality a solar panel is. A 100 watt panel does not deliver 100 watts, but a high quality one probably delivers more like 80 or 85 watts (this power rating is sometimes independently certified, depends on the product). Then the location and the season is quite crucial. The number of hours of sunshine and the angle of irradiation changes so massively.

Thus, we have to make many assumptions and calculating the actual sizing is not easy either. However, you made a good start by asking yourself what consumers you actually have. I would do the following:

Make a list and write down how many watts these consumers consume and how long you use them per day. This way you can determine the required watt hours. This is the energy that you need to draw from and return to your battery during one (average) day. An example:

Fridge 30 watts for 10 hours a day = 300 watt hours
Lights 5 watts (LED) for 3 hours a day = 15 watt hours
Charger Tablet/ Phone 15 watts for 2 hours a day = 30watt hours
In total 345 watt hours

Now you need to know how long on average the sun shines at your travel location. And you can calculate how big the module should be in average. Let me make an example: In Germany, the sun shines on average about 4 to 5 hours a day and in summer much more. After deductions for wiring losses and efficiency of the panel and general safety buffer, you now see that a 100 watt solar module could be sufficient in above mentioned example. In a month like November or December where we have here sometimes only 2h sunshine per day it could be not sufficient. But on the other hand it is cold then and we do not need a fridge or it runs not so often so needs less energy.

Let's look at the practical application. For me, a 100 watt module has proven itself in practice. I run a 100 watt solar module with a MPPT regulator into a 95Ah AGM aux battery since over 10 years in my rig. I run a compressor fridge, some light and charge laptop, tablet, etc. on the aux battery.

Maybe this train of thought will help you a little chosing your setup.

 

[WTSMatt]

Super helpful guys! My Redarc controller switches between using my alternator while driving then switches automatically to solar when parked. I’m in California and our travels have been/probably will remain in the West during spring/summer/fall so typically sun is not an issue, tree cover can be at times. We’re also pretty nomadic on our trips rarely staying in 1 spot more than a day or 2. Once again OB does not disappoint in help!!

 

[MOAK]

I have 2 panels for I believe 210or 225 watts, I don’t remember. I’m running a fridge and a freezer, along with charging batteries, running water pumps, etc. I’ve got two batteries with 140ah, or so. On a clean clear day in perfect conditions a 100 watt panel is perfect to charge up that batteries in a few short hours. But imperfect days is why I have two panels.

 

[smritte]

But imperfect days is why I have two panels.

same here and i have a 180 folding panel for forest trip's.

 

[JackAttack]

G'day,

I work in the industry of 4x4 and camping in Australia and I'll apply to you the simple qualification process I apply to my customers:

Based on what you've said, I'll make a couple of assumptions.

1. Your fridge's power consumption is in fact going to be closer to 1.5AH (18WH) rather than the 0.84AH (10WH) you've described.
2. You intend to run your LED lights for 4 hours per day. You haven't disclosed the quantity of lights and so I'll assume you have 2, both consuming 1AH (12WH) each.
3. The bonnet of your vehicle is a fairly flat surface
4. You will not be running your vehicle to supplement the charging of your aux battery via the Redarc. I will qualify your needs based on the scenario that you are not driving at any point during the day.

Your daily power requirements, based on what you've said and our assumptions, will be 44A (528W).

A 100W monocrystalline can generally produce up to 8.4AH. Manufacturers will base the power production of their panels on testing done in laboratory light boxes etc, not real world environments. Thus we need to apply inefficiencies to get a more accurate indication of how much power we will generate.

A panel, laying flat (eg. on your bonnet) will produce varying results based upon weather:

• Clear & Sunny - will generally produce 73% of it's rated production. Therefore, with your 100W panel, you can expect 73W (6AH). You would require 8 hours of sunlight for this panel to be sufficient
• Light cloud - will generally produce 59% of it's rated production. Therefore, with your 100W panel, you can expect 59W (4.91AH). You would require 9 hours of sunlight for this panel to be sufficient
• Cloudy - will generally produce 37% of it's rated production. Therefore, with your 100W panel, you can expect 37W (3AH). You would require 15 hours of sunlight for this panel to be sufficient
• Overcast - will generally produce 15% of it's rated production. Therefore, with your 100W panel, you can expect 15W (1.25AH). You would require 35 hours of sunlight for this panel to be sufficient

You should build your solar to sufficiently charge your system with 4-6 hours of sunlight, thus I do not recommend you rely on only 100W of solar.

Hopefully this helps!

Cheers,

 

[79bj40]

I've got a 315W LG panel mounted to crossbars on my RTT. That runs through a controller to a 100ah wheelchair battery. I also have a DC/DC charger connected to the starting battery that charges the aux. I typically run an Engel and ARB fridge for trips over a week, one as refer and one freezer. I can run all of my aux lighting consisting of led strips under the awning, interior lighting, charge phones and speakers, cell booster etc and the batter is usually charged back to 100% by 10AM.

I never have to set anything up, never have to worry about running out of juice and don't even have to park so the panel is directly into the sun.