Solar Tutorial Part I – Understanding the Basics of Boat & RV Solar Power

I wrote our initial RV Solar Installation page in 2008 after we had lived on solar power in two different trailers for a year and a half.  I have received lots of email since then from people trying to sort out exactly what they will need for a solar solution on the roof of their RV.  This page is the first in a series about RV (and sailboat) solar power that will hopefully demystify the subject and make everything clearer.

We have been living almost exclusively on solar power since 2007, first in a travel trailer, then in a fifth wheel trailer and then in a sailboat.  We don’t stay in RV parks or campgrounds or marinas, and on the rare occasions that we do, we don’t hook up to shore power.  At last tally, we had spent over 1,800 nights off the grid.

A solar power installation in an RV gives you the freedom to have full electrical power anywhere and at any time: at a rest area, in a parking lot, at a National Forest campground.  Likewise on a boat, you can anchor out for an unlimited time in bays and coves.  Solar power runs without using $4 a gallon gas, is silent, doesn’t smell, and doesn’t require any setup (those shore power cords are mighty ungainly).  Although we do have a gas generator in our trailer, we use it only when we want to run our air conditioning, not for charging the batteries.  It is a Yamaha 2400i and the air conditioner is a 15,000 BTU unit.

Wrapping your brain around solar power for a rolling or floating home can be confusing, but it is actually quite straight forward.  Here’s the whole thing in a nutshell (wherever it says “RV” you can also think “sailboat,” as the principles are the same).

RV Solar power instalation on a fifth wheel trailer

Mark finishes three days of installing our fifth wheel’s solar power system while boondocked in Flagstaff, AZ.

There are 2 functions that your rig needs to have if you want to live without electrical hookups:  

  •  A system to charge the batteries
  •  A system to create AC power for the rig so you can watch TV and surf the web

There are 3 components (or “parts”) used in an RV solar power installation to accomplish the two objectives listed above:

  •  Solar panels
  •  Charge Controller
  •  Inverter

Now put it all together…

To charge the batteries you need:  Solar Panels and a Charge Controller

To use your batteries to generate AC power for your TV, computer, etc., you need:  An Inverter

That’s it!!   Very simple.  To flush it all out a little, here it is in more depth:

Solar Power Function #1 – Charging the Batteries

When an RV comes from the dealership, it usually has either a Converter or an Inverter/Charger in it so it can charge the batteries when it is plugged into shore power (via “hookups” or gas generator).  Converters are cheaper and are factory installed on most trailers.  Inverter/Chargers are expensive (because they are dual-purpose, see below) and are factory installed on higher-end motorhomes.

These appliances take the AC power coming in from the external source (hookups/generator) and use it to charge the batteries.  They usually have a 3-stage charge cycle that charges the batteries quickly at first and then drops to a trickle charge once the batteries are close to fully charged.

morningstar sunsaver 10 charge controller

A $45 charge controller for a small solar power installation

How do you charge the batteries when you don’t have shore power?  That is where solar power comes in.

When you install a solar power system in an RV, you add two things:  Solar Panels and a Charge Controller.  The solar panels are installed on the roof and they gather energy from the sun and pump it down to the charge controller.  The charge controller keeps an eye on the batteries and takes only as much power coming from the solar panels as the batteries can handle.

Outback Flex 60 MPPT Charge Controller

A $500 charge controller for a big solar power installation

Early in the day, the batteries are hungry and the charge controller passes everything it can to the batteries.  As the day wears on, the batteries become more fully charged and require less and less power.  By afternoon, if the system is sized right for the way the RV is being used, the batteries throw up their hands and say, “No More!!” and the charge controller puts them into “Float” mode, a fancy term for a trickle charge.

None of this has anything to do with running your TV or computer.  It is only about charging the batteries up after they become depleted from use the night before.

The solar panels will charge the batteries no matter where your RV is parked.  If you are out hiking, or shopping at Walmart, or taking a nap inside, the batteries will be getting charged all day long.  If you are at an RV park or marina with metered electricity, save a few dollars and don’t plug in!!

If you park under a tree, and the panels are shaded, you will get dramatically less power from the sun.  A tiny bit of shade results in a huge decrease in how much the charge the batteries can get.  We always park in full sun.

Sailboats have a terrible time with unwanted shade from the mast and boom.  When at anchor, pulling the boom over with the traveler and forcing it further out with a preventer helps a lot, but the mast is always a problem when the sun comes from forward of the beam.  If you are sailing and heeled away from the sun or the panels are shaded by the sails, too bad!!  So, on a sailboat, install more solar panels (more total watts) than you think you’ll need!

100 watt portable inverter from Walmart

A 100 watt portable inverter ($15). Plugs into a cigarette lighter and has one AC outlet

Solar Power Function #2 — Generating AC Power to run the TV

When an RV comes from the dealership, it usually has a shore power cable so you can plug the rig into electrical hookups or into a gas generator.  The shore power cable takes the AC power from the source (“hookups” or generator) and passes it straight through to your AC outlets.  In other words, when the rig is plugged in like this, all the AC outlets and the microwave become “live” and you can run your AC appliances like the TV, computer, toothbrush charger, electric razor, hair dryer, vacuum, etc.

If you want to have AC power without plugging into shore power, you have to have an Inverter.  An Inverter converts the DC power that is stored in the batteries into AC power so you can run your AC appliances like the TV and computer.  However, the Inverter is not technically part of the RV solar power installation.  That is, it doesn’t connect to the solar panels in any way.  You can use an inverter and not have any solar panels installed.  However, unless you plug into shore power, your batteries will get run down by watching all that TV!  That is why Inverters are lumped into the overall notion of RV solar power installations.  They are a vital component if you want to dry camp.

You can buy small, portable inverters for $15 that will run your laptop from a cigarette lighter.  These work on the cigarette lighters inside an RV just the same as they work on the cigarette lighter in a car.  No difference.  If you are puzzled by all this, go out and get a little power inverter at Walmart and try it out.  I was totally enlightened the first time I turned on a small inverter in a car and saw the “charging” light on my laptop light up.

300 watt portable inverter

A 300 watt portable inverter ($20) with cigarette lighter plug and 2 AC outlets

Small portable Inverters can run small TVs too.  Anywhere from 150-300 watts is fine for pretty much everything in an RV except the microwave, hair dryer, vacuum and air conditioner.  You need 1000 watts or more to run a small microwave, hair dryer or vacuum.  You can’t run an air conditioning unit from an inverter, period.

Any inverter up to 1500 watts is fine for everything you might use.  You just can’t run the big appliances (microwave, vacuum and hair dryer) simultaneously.  If you are content using these appliances one at a time, don’t bother with an inverter larger than 1500 watts.  We power everything on the boat except the microwave with a 600 watt inverter.  We power everything in the fifth wheel, including the microwave, with an 1100 watt inverter.

Some higher end motorhomes come with an Inverter/Charger (see above), so they don’t need to have an Inverter installed – they already have one.  Turn on the Inverter switch on the Inverter/Charger, and shazam – all the AC outlets in the rig are “live.”

Atwood converter

A converter – this was factory installed on our fifth wheel

Most trailers do not come with an Inverter/Charger.  They come with a Converter instead.  So if you have a trailer, you will need to get an Inverter to watch TV.

This terminology is unfortunate, as “Inverter” and “Converter” sound so much the same.  However, they are almost the opposite of each other.  A Converter charges the batteries, i.e., it takes AC power from an external source — hookups or generator — and puts that energy into the DC batteries to charge them up.  In contrast, an Inverter takes the DC power from the batteries and creates AC power so you can watch TV.

Wait, what was all that, again??

So, to recap:  when you install Solar Power in your RV, you are tackling two problems:  ( 1 ) Charging the batteries, and ( 2 ) Generating AC power from your DC batteries so you can watch TV, surf the internet, and charge your camera batteries.

You need three types of components or “parts” to do all this:

  •  Solar Panels and a Charge Controller to charge your batteries all day every day.
  •  An Inverter to create AC power out of the DC power that is stored in your batteries so you can use the TV and computer.  You can use little portable ones that plug into cigarette lighter outlets and/or you can install a big one.

If your rig came with an Inverter/Charger, you are halfway there and need only to add the components for charging the batteries (Solar Panels and Charge Controller).

Most of the components for an RV or marine solar power installation can be purchased at Amazon.

Shown here is a complete "weekender/vacationer" kit (far left), a small charge controller (middle) and a small inverter (right). More comprehensive listings of each component type can be found at the following links: