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Mod #14: Solar Panel

Posted By Mark Corgan On June 18, 2008 @ 6:46 am In electrical, green | 25 Comments

A solar panel converts sunlight into electricity. There. Now you know what a solar panel does. But it’s not that simple. Solar panel performance is just as dependent on sunlight as it is on the type and size you choose. So installing one (or more) on an RV takes careful consideration of your options if you want to get the best bang for the buck.

Mod Difficulty:

This mod starts by assessing your needs. Do you want to have a way to keep your batteries topped up while the RV is in storage without shore power? Do you “boondock” a lot and need a way to re-charge your batteries after heavy usage over a few days? Maybe you just don’t want to run your generator for hours on end just to get that last 10% of charge in to your batteries. Your total power requirements will determine what type of solar panel configuration and sizing you should install. You can be as simple or as elaborate as your pocket book can handle. But it’s all about managing your expectations in terms of power as a solar electric system can get very expensive if you want (or need) a lot of power.

An example of a simple configuration is one that just keeps the batteries topped up. There are many companies that will gladly sell you a small panel and state that it will recharge your batteries in no time and give you lots of extra power to run devices. Don’t be fooled by these claims. At a minimum, you will need at least a 15 watt panel just to keep up with the idle power consumption of the RV without any appliances or lights being used. The LP gas detector and the refrigerator circuit board normally draw a small amount of current and this is what runs the batteries down over time when not on shore power. A small panel can just keep up with this small power demand, but no more, and that’s in direct sunlight!

A more common configuration is to use a single 100 to 125 watt panel with a charge controller. A charge controller provides a way to ensure the solar panel cannot overcharge your batteries. It does this by switching the higher charging voltage from the panel to a lower float voltage when the batteries are fully charged. This ensures your batteries won’t be damaged by excessive voltage from the solar panel over time. Some charge controllers, like the MPPT (Maximum Power Point Tracking) type, can actually boost charging current as much as 20%. Get one of these if you are in a high latitude area or if you expect to have mostly less than sunny conditions.

100 watts of power can provide about 6 to 7 amps of DC power in direct sunlight. This is enough to provide some charge to the batteries while running a few lights, or the water pump occasionally. Anything more and you will have to add another panel. If your power consumption is higher than what the solar panel can produce, you will need an alternative way to recharge your batteries as they will eventually become discharged. Or, add another panel. Did I already mention that? You can see where going solar can add up in a hurry if you have higher power demands.

Larger power requirements need an array of solar panels and high-current charge controllers to keep up with demand. Many high-end class A and class C motorhomes have options for high power solar systems from the factory. These systems are typically sized for total power self-containment, meaning all demands on the DC RV electrical system can be met on solar power. These systems are very expensive and should be carefully considered against using a generator instead. If you just have to have the best, then go for it. The choice is yours.

TipWith any solar panel, maximum output is only achieved if the solar panel gets sunlight directly from overhead. Even partial shade or sunlight from an angle on any part of the panel or panels can diminish the power output greatly. Keep this in mind when looking for that shady spot to keep the RV cool. No sunlight, no solar power.

TipTo get the most out of your solar panel, position the panel (or RV) to face the south and tilt it perpendicular to the sun in the afternoon. This will ensure you get the most sunlight throughout the day and thus the most power output from your panel. Tilting mount kits are available to help with this.

ModMyRV recommends these parts for this mod:
SunForce 60 Watt Monocrystalline Solar Panel with 7 Amp Charge Controller (Pack of 3)
Go Power! 80 Watt Solar RV Kit
85 Watt 12 Volt Solar Panel - Ul Approved - Tl(rv)
Go Power! ARM-UNI Tilt Mount Kit

General Reference
RV Solar Electric Power Article
The Ultimate RV Electrical System


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