Thanks to solar power, we have lived completely off the grid in two trailers and a sailboat full-time since May 2007. Without doubt, our solar power installations have given us more independence and freedom as full-time RVers and sailors than anything else in these lifestyles. It has allowed us to go anywhere at anytime, and has revolutionized our lives.
On this page I describe the two systems we have had on our trailers. These were installed in 2007 and 2008 respectively. Prices for solar power equipment have dropped every year since then, however the prices listed throughout this page are from August 2014:
- A Small (minimal) RV Solar installation for ~$700 that we used full-time for a year of boondocking in 2007
- A Full-timer (all you need) RV Solar installation for ~$2,500 that we have used for full-time boondocking since 2008
I also offer a little theory and reveal some of the discoveries we have made along the way. For more info, please see our Solar Power Tutorial pages and our Sailboat Solar Power Installation page.
Links to all of our articles about solar power can be found on our Solar Power For RVs and Boats page.
You can navigate to different parts of this article by using these links:
WHY BOTHER WITH A SOLAR POWER INSTALLATION ON AN RV?
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The biggest advantage of a solar power system in an RV is that the system works from dawn to dusk, silently, odor free and without requiring any fuel or maintenance, no matter where you are or what you are doing. Towing, parked at the grocery store, or camped, the batteries are being charged. They start getting charged before you finish breakfast, keep charging while you hike or go sightseeing, and continue all day, rain or shine. They don’t quit charging until nightfall. You never have to think about the batteries getting charged. It just happens. In our current rig, I feel like we have electrical hookups all the time — and we never get hookups any more!
Traveling full-time since 2007, we have connected to electrical hookups for a total of about 25 days, and that was during our first 18 months on the road. The last time we got electrical hookups was in October, 2008. Since we began our full-time travels in 2007, as of November 2018, we have boondocked in our RV nearly 3,000 nights. We also lived on solar power on our sailboat for over 900 nights during our sailing cruise of Mexico.
We do carry a Yamaha 2400i generator, but use it only a few days each year, either after a long period of winter storms to give the batteries a boost, or on hot summer days to run our 15,000 BTU air conditioner. We have used it a total of about 20 times since we purchased it in December 2007. We run it every six months or so to flush the gas through the lines. Little as we have used it, we have found the Yamaha to be a fabulous generator. It has always started on the first pull, even after it sat in storage for 20 months when we first moved onto our sailboat!
Our first solar power installation that we used for a year in 2007 was a “small” system that allowed us to use almost every appliance we owned, that is, laptop, TV, hair dryer, vacuum, two-way radio charger, power drill, etc. However, we had to be very conservative with our electrical use during the winter months. A similar “small” RV solar power kit can be found here.
Our second “full-timer” solar power system that we have been using since 2008 is like having full electrical hookups wherever we go. Very little conservation is necessary! On our biggest electrical use day to date, we watched our 26″ LCD TV with its huge surround-sound system and sub-woofer for 15 hours (it was the Olympics!) and ran two 13″ laptops for 7 hours, made popcorn in the microwave and ran several lights for 4 hours in the evening. It was July, and the next day was very sunny and the batteries were fully charged by mid-afternoon. A similar “full-time” RV solar power kit can be found here.
Here are some sample kits, smaller and bigger in size, and their prices. The only trouble with buying a component kit is that if one component fails the whole kit has to be returned. The third item, however, is a portable suitcase kit that does make a lot of sense for someone who doesn’t want to hassle with the installation just yet (you can always sell the portable kit later).
BASIC ELEMENTS OF A SOLAR POWER INSTALLATION
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BATTERY CHARGING and AC POWER
The basic components of all solar power installations is the same, and is comprised of two major subsystems: BATTERY CHARGING to get the batteries charged up and AC (120v) POWER for appliances that can’t be run on DC (12v) power (i.e., TV, computer, vacuum, hair dryer, etc.).
The BATTERY CHARGING subsystem includes these components:
- Solar panel(s)
- Charge controller to protect the batteries from getting overcharged
The AC POWER subsystem includes this component:
- Inverter(s) to convert the batteries’ 12 volt DC power to 120v AC power
GET YOUR HANDS DIRTY!
A 350 watt portable inverter
Plug it into a cigarette lighter
It is hard to “play with” the battery charging subsystem of a solar power installation to get a feel for how it works until you actually take the leap and buy a solar panel, charge controller and cables and hook it all up to the batteries. One great option if you don’t want to do any wiring but want some hands on experience is to get a portable solar panel kit. You can sell it later if you want to upgrade to a rooftop system.
You can get the hang of how the AC power subsystem works very easily. Simply run down to Walmart or any auto parts store and pick up a $15-$20 inverter that plugs into a cigarette lighter DC outlet. Plug it into the lighter in your car, turn it on, and then plug your laptop into it or your electric razor or any other small appliance. Now your 12 volt car battery is operating your 120 volt appliance.
Big inverters that can run the microwave, toaster, blender and vacuum cleaner work on exactly the same principal, the difference is just the amount of power the inverter can produce. Big inverters are also wired directly to the batteries rather than plugging into a cigarette lighter.
IS SOLAR POWER EXPENSIVE? SMALL SYSTEMS VERSUS BIG SYSTEMS
The difference between the “small” system we used for one year on our little Lynx travel trailer and our “full-timer” system we have now on our big Hitchhiker fifth wheel is simply the overall capacity of each of the components. That is, the capacity of the battery charging system (solar panels, batteries and charge controller) and of the AC power system (the inverter).
In functional terms this means that the difference between the “small” and “full-timer” systems is threefold:
1) the ability to run more appliances at once (i.e., have two laptops running while the TV and blender are going)
2) the ability to run larger appliances (i.e., using a VitaMix versus a small blender)
3) the ability to run more appliances for a longer time at night without discharging the batteries too much.
So, in a nutshell, the two subsystems — battery charging (batteries + panels + charge controller) and AC power (inverter(s)) — combine to do the same job as plugging a generator into the shore power connector on the side of the rig. The panels and charge controller charge the batteries. The inverter makes it possible to use AC appliances.
The cost of the parts for these installations is:
Small: $700 – Comparable to having a Yamaha 1000i generator
Full-timer: $2,500 – Comparable to having a built-in Cummins Onan 2.5KW generator
With solar power there is no noise, no fuel cost, no maintenance and no smell, unlike a generator. However, it is not possible to run the air conditioning in the summertime on solar power, unless you have a massive system with several hundred pounds of batteries and a roof absolutely loaded with panels. As mentioned before, we use our Yamaha 2400i generator to run our 15,000 BTU air conditioner.
OUR “SMALL” RV SOLAR POWER SYSTEM (~$700 in parts)
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This setup is a fully functional, inexpensive solar power installation, and is what we used for a 350 nights in our first year in our Lynx travel trailer. It could power a 19″ LCD TV and DVD player, radio, laptop and vacuum as well as charge camera batteries, razor, toothbrush, cordless drill, cell phone, etc.
- Two 6-volt batteries (wired in series) giving 220 amp-hours of capacity $250
Ours were Energizers from Sam’s Club
- 140 watts of solar power $175
Ours was a Kyocera 130 watt DC panel. Today Kyocera sells the 140 watt panel instead.
- A charge controller that can support at least 10 amps $90
Ours was a Morningstar Sunsaver 10 amp charge controller (consider a Sunsaver 20)
- A portable inverter that can supply 1000 watts of AC power $80
Ours was a Pro One 800 watt inverter
- Cables, connectors and mounting brackets $100
Here are the parts for the system (except for batteries and cables) — solar panel, solar charge controller and inverter:
This system is the smallest size system I would consider for an RV if you want to drycamp or boondock for more than a night or two and be comfortable. This setup worked great in the spring, summer and fall when the sun was high in the sky and the days were long. We never thought too much about our power use until the wintertime when the days got short and the nights got long and cold. Then we began to wish for a bigger system.
Mark installs our first solar panel on the roof.
He chose a nice spot by the ocean to do it!
On those long cold winter nights we had to conserve our use of lights and the TV to make sure our furnace (which used a lot of battery power) could still run. We used oil lamps a lot in the evenings. If we had stayed in that trailer longer, we would have installed a vent-free propane heater that did not use any battery power (we eventually did that in our bigger trailer the following winter: see our Vent-Free Propane Heater Installation page).
I think every RV should have this kind of a charging system installed as standard equipment, as it is useful even for the most short-term camping, like weekends and week-long vacations during the summer months.
When we installed this “small” system in our little Lynx trailer in June 2007, we were quoted $135-$350 for installation. Mark is very handy (although he is not a Master Electrician), and he found the installation was not difficult at all and completed it in one day.
SOME THEORY – SIZING THE SYSTEM
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CHARGING & CONSUMPTION
Here is some theory to explain why the above system is “sufficient” but is not great for “full-time” use. When it comes to a solar battery charging system, the concept of power charging and consumption is very simple. The amount of power you can use, or take out of the batteries, is essentially only as much as the amount you can put into the batteries. If you use (or take out) more power than you replace (or charge them with), sooner or later your batteries will be discharged and dead. The batteries are just a temporary storage place for electricity. They act as a flow-through area for the power you are going to use.
The most important part of any solar setup is the amount of charging going on (i.e., the total size, or capacity, of the solar panels), and you want that to be greater than the amount of electricity you use. More must go into the batteries than comes out. You can have an infinite number of batteries and eventually discharge them all completely if you repeatedly use more electricity than your solar panels put in.
We often find people want to add batteries to address their power shortages when what they really need to do is add more solar panels. As a rule of thumb, don’t use more than 1/3 to 1/2 of the total capacity of the batteries in one night. More important, though, is that the bigger the solar power panel array, the better. And lastly, Keep the size and age of all the batteries in the system fairly similar so the strong ones don’t waste their energy helping the weak ones keep up.
AMPS and AMP-HOURS
Appliances use amps to run. Another unit, the amp-hour (abbreviated as “Ah“), refers to the number of amps an appliance uses when it is run for an hour. For instance, an appliance that uses three amps to run will use up three amp-hours when it runs for an hour. These amp-hours will be drawn from the batteries, and the batteries, in turn, will look to the solar panels to recharge the amp-hours they have forked over to the appliance. It is for this reason that you need to know how many amp-hours you will use in a typical day. Ultimately those amp-hours must be replaced by the solar panels, so the size and number of panels you purchase will be determined by how many amp-hours you use in a day.
To estimate how many amp-hours you might use in a day, estimate how many hours each appliance will run and multiply that by the number of amps the appliance uses. We have measured some of the appliances in our trailer, and this is how many amps they use:
Single bulb DC light — 1.5 amps
Dual bulb DC light — 3.0 amps
Dual bulb fluorescent light — 1.5 amps
19″ LCD TV — 5.5 amps
DVD / CD Player — 0.5 amps
13″ MacBook laptop, on & running — 6-8 amps
13″ MacBook, off and charging — 1.6 amps
Sonicare toothbrush charging — 0.1 amps
FM Radio w/ surround-sound — 3.0 amps
12′ string of rope lights — 3.3 amps
We find that we typically use anywhere from 50 to 150 amp-hours per day, most commonly in the 70-90 range.
HOW MANY AMP-HOURS DOES MY FAVORITE GIZMO USE?
Since RV solar power systems are DC battery based, it is helpful to know how many amps (in DC) various appliances use. Multiplying that value by the number of hours the appliance is used each day then reveals how many amp-hours the appliance will require from the battery in the course of a day.
Most DC appliances list their amp usage in the user manual or spec sheet. In contrast, most AC appliances list their wattage in the user manual instead of amperage. So, for AC appliances that are run on an inverter you have to do some math to get their equivalent DC amperage rating.
You can get a rough estimate of the number of amps that an AC device will use on an inverter simply by dividing the wattage by 10.
Why is that?
Here’s one way to look at it: Technically, Watts = Volts x Amps. AC circuits run at ~120 volts. DC circuits run at 12 volts. An AC appliance will use the same number of watts whether running on a DC or AC. On a DC circuit (using an inverter so it can run), that AC appliance will use 10 times as many amps as it will on an AC circuit (that is, 120/12 = 10).
Here’s another way to look at it: Watts / Volts = Amps. So, to determine most precisely how many DC amps an AC appliance will use when running on an inverter, start by dividing the number of watts it uses by 12 volts to get its Amps DC. HOWEVER, keep in mind that inverters are not 100% efficient. Typically they are only about 85% efficient. That is, an inverter loses a bunch of watts to heat as it runs — about 15% of the watts it needs to run get dissipated into heat. So, it takes more watts to get the required amps out of the inverter, the exact figure being 1 / 85%. This means that after you divide the appliance’s Watts by its Volts (Watts / 12, as I mentioned above), then you have to divide that result by 0.85. This is messy.
Rather than dividing watts first by 12 and then again by 0.85, you can simply divide the watts by 10 and get a pretty close estimate. (That is, (1/12)/0.85 = 0.1)
Our AC 19″ LCD TV is rated at 65 watts. How many amps is that DC? 65/10 = 6.5 amps DC. We measured the TV at the volume we like to hear it and it was using 5.5 amps. If we cranked up the volume, the meter went up to 6.5 amps.
Likewise, our old white MacBook Pro laptop was rated for 65 watts. As we opened and closed files and started and stopped various programs, the meter zoomed all over the place between 3 amps and 8 amps. When we ran Adobe Lightroom, which is very disk and memory intensive, the readings hovered in the 7-8 amp range. So on average you could say it uses about 6.5 amps DC.
When we shut down the laptop and left it plugged in and charging, the meter dropped to 1.6 amps. This is important if you are trying to conserve electricity! Run your laptop on its own battery until the battery is depleted. Then turn it off and let it charge from the inverter while you do something else!
HOW DO YOU MEASURE THE POWER USAGE OF A DEVICE?
If you have nothing running in the rig (no computers running, no TV, no vacuum or toaster, etc.), you can measure the current a device is drawing from the batteries using a clamp-on meter around one of the battery cables. To measure the AC current of a small device, you can use a Kill-a-Watt meter. Simply plug it into an AC outlet and plug your device into it.
WHERE DO THE BATTERIES FIT IN?
Battery storage capacity is measured in amp-hours (Ah), and more is better. As a starting point, most new RVs come equipped with one 12-volt Group 24 battery which will give you about 70-85 Ah of capacity. Assuming the sun has charged the batteries completely by nightfall, and sticking to the rule of using only 1/3 of your total battery capacity each night, you will have only 25 Ah available each evening. That isn’t very much!
What is the best upgrade strategy?
Upgrading to two 12-volt Group 24 batteries (wired in parallel) will give you 140-170 Ah of capacity.
However, a 6-volt golf cart style battery has the same footprint as a Group 24 12-volt battery (although it is about 3″ taller), and a pair of them wired in series will give you about 210-240 Ah of capacity.
So, rather than buying a second 12-volt Group 24 batteries and getting just 140-170 Ah of capacity out of the pair, why not sell the 12 volt battery and buy to two 6-volt golf cart style batteries for 210-240 Ah of capacity? That’s what we did on our first trailer. Just make sure that you have enough height in the battery compartment for the taller golf cart batteries.
WHAT ABOUT BATTERY MAINTENANCE?
So far I’ve been talking about wet cell batteries, and these kinds of batteries need to be maintained. Wet cell batteries are made with thick metal plates and liquid between them. Over time the liquid evaporates and needs to be replaced with distilled water. Also, over time, sulphite builds up on the plates and needs to be removed by “equalizing” the batteries.
Use a hydrometer to check each battery cell.
Before we upgraded to AGM batteries, Once a month Mark would check the liquid levels in each cell of each battery and pours in a little distilled water wherever needed. He also checked the condition of each battery cell using a hydrometer. This little device indicates whether a cell is functioning at full capacity. Then he equalizes the batteries by programming our charge controller to raise the voltage on them to one volt higher than their normal charging voltage for five hours. Last of all, he re-checks the liquid level in each battery cell and adds distilled water as needed and re-checks each cell with the hydrometer. Usually any cells that had a poor reading before equalizing now give a good reading.
This maintenance stuff can be avoided by buying AGM batteries which are maintenance free. However, AGM batteries are really expensive. One big advantage of AGM batteries for sailors and for people with tight battery compartments is that they operate fine in any position, that is, they can be installed on their sides and will operate when a sailboat is heeling. We had them on our sailboat.
On our trailers, we initially opted for wet cell batteries. We had Trojan 105 wet cell batteries for the first five years on our fifth wheel. Then we replaced them with cheaper Costco batteries from Interstate (Johnson Controls).
The Trojans worked very well, but replacing them with cheapo batteries was a mistake. The cheap batteries failed completely within 14 months.
We now have four Trojan T-105 Reliant AGM batteries which are truly awesome. They are a little more money than the T-105 wet cell batteries, but they are superior and, in our minds, worth the extra little bit of cash.
For price comparisons: Trojan Reliant AGM (single), VMaxTanks AGM (set of 4 & free shipping), Trojan T105 Wet Cell (single):
AND HOW ABOUT THE SOLAR PANELS?
Battery capacity is only part of the story. The ultimate limiting factor is how many amp-hours the solar panels can put into the batteries during the day. If the solar panels are sized too small to charge the batteries sufficiently each day, you will eventually discharge the batteries over a series of days and they will be dead.
Solar panels are rated in terms of Watts. The relationship between the amp-hours that the panel can store in a battery and the panel’s watts rating is not straight forward. Suffice it to say that a 130 Watt panel produces 7.5 amps in maximum sunlight when the panel is exactly perpendicular to the sun, and both of those numbers are available in the specs for the panel. What isn’t stated, however, is how many amp-hours a panel will produce in a given day. That is because it varies by what latitude you are at, what angle the sun is to the panel (which changes all day long), how brightly the sun shines, how many clouds go by, etc.
We have found that each of our 120 watt and 130 watt panels typically produces between about 8 Ah and 40 Ah per day depending on the season, weather, latitude, battery demands, etc. Most commonly, they produce around 25-30 Ah per day each.
If you have the time and inclination (who’s got that stuff?), you can figure out how many amp-hours you use each night. Make sure that that number is less than 1/3 of your total battery capacity AND make sure your panels can provide that many amp-hours of charging each day.
But all that sounds very difficult.
Solar panels also come in a variety of flavors, including rigid or flexible and monocrystalline or polycrystalline as seen below:
NEVERMIND THE THEORY – JUST TELL ME WHAT SIZE STUFF I NEED!
As I have mentioned before, we changed how we lived when we had a small solar power installation and again when we got a big one. You can opt to live with very little electricity or not.
We met a couple living on their 27′ sailboat on its trailer in the desert in Quartzsite, Arizona (they were on their way to launch it in the Sea of Cortez). They were using just 6 amp-hours per day because they had a tiny solar panel. Lord knows, I never saw their lights on at night!
In our little Lynx travel trailer we used about 25-35 amp-hours per day. We relied on kerosene lamps for much of our lighting at night in the winter.
In our Hitchhiker fifth wheel we use an average of 60-120 amp-hours per day and we do not conserve electricity.
So as a rule of thumb, here is the number of amp-hours you might consume per day:
• 6 Ah = living ultra-conservatively
• 35 Ah = living very modestly
• 120 Ah = living much the way you do in your house
The amp-hour capacity of your battery bank should be three (to four) times your typical daily amp-hour usage.
A popular rule of thumb is to match (roughly) the amp-hour capacity of the batteries to the watts capacity of the solar panels. So, 140 Ah of battery capacity “goes with” 140 watts of solar power. 440 Ah of batteries “goes with” 440 watts of solar power.
However, having more solar capacity than that is not a problem, as it gives you much more flexibility in case you have cloudy days, the panels aren’t oriented well towards the sun, or you have periodic shading during the day from buildings or trees.
Side note: The average American house uses about 30 kilowatt-hours (kWh) of electricity per day (see here), whereas we use anywhere from 0.6 to 1.2 kWh per day in our RV. This is because houses are much bigger and more complex and have much larger appliances and systems that run on electricity (refrigerator(s), stove/oven, hot water heater, heat and air conditioning, etc.).
It is also interesting to note that the ~1 kWh of power that our fifth wheel requires to recharge its batteries every day is approximately the same amount of energy that is required to recharge the batteries of a Tesla Model S after it is driven three miles (see here). Charging a frequently driven Tesla’s batteries exclusively with solar power would require an immense solar panel array.
OUR “FULL-TIMER” RV SOLAR POWER SYSTEM (~$2,500 in parts)
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In a nutshell, in order to run your RV with the same level of comfort as a house, using all of your appliances whenever you feel like it without thinking about conserving at all, you will need at least the following:
- Four or more 6-volt batteries giving you at least 440 amp-hours of capacity
We have four 6-volt batteries (2 pairs of batteries in series to make two 12-volt equivalent batteries, and then those 2 twelve volt equivalent batteries placed in parallel with each other). We had Trojan 105’s for the first five years, and after that we’ve had batteries from Costco, ~$480, which we soon replaced with Trojan T-105 AGM Reliant batteries, $1,200 (see note below).
- 500 or more watts of solar power (preferably 600-800 watts)
We have three 120-watt Mitsubishi panels and one 130-watt Kyocera panel, for a total of 490 watts of solar power, `$1,140
- A charge controller that can support 40 amps or more (preferably 60 or 80 amps)
We have an Outback FlexMax 60 60 amp charge controller (consider the FlexMax 80) $565
For more info see our page: Solar Charge Controllers – Optimizing RV Battery Charging
- A true sine wave inverter that can supply at least 1000 watts of AC power (preferably 2000 or 3000 watts)
For 7 years we had an Exceltech XP 1100 watt true sine wave inverter $600.
PLEASE NOTE: In April, 2015, we upgraded to Trojan 105 Reliant AGM batteries ($1,200) and an Exeltech XP 2000 watt true sine wave inverter ($1,700). See our post RV Electrical Power System Overhaul to learn more.
This system will power everything except the air conditioner, regardless of weather or season. My notes indicating “preferably” larger sizes for everything reflects the fact that our installation is now quite old and component parts costs are half what they were when we were buying. More is definitely better.
I’ve never heard anyone say they wished they had less solar power!
Mark did the installation of this solar power system on our Hitchhiker fifth wheel. My rough guess is that the installation might have cost $700-$1,500 if done by an experienced installer. It took him three partial days, largely because we were boondocked in the woods about 15 miles from Home Depot, and I had to keep running back and forth to get little things for him!
NOTES and LESSONS LEARNED
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More and more solar power equipment manufacturers are selling complete kits for RVs, boats and cabins. Here is an example full-timer kit from Go Power, and a slightly smaller full-timer system from Renogy. Here is a small solar power kit from Go Power for “weekender/vacation” use and another small solar kit using Renogy panels.
Also, if you don’t want the hassle of doing an installation, here’s a nifty portable solar panel kit that folds into an easy-to-carry suitcase!!
INVERTER and CONVERTER CONFUSION
If you are like me, the terms “inverter” and “converter” are confusing. They sound so similar it seems they must be one and the same thing. They are actually two very different components with very different missions in an RV.
A converter takes the AC power coming in from the shore power cord (via electrical hookups or a generator) and gives power to all the DC appliances in the rig so the batteries can take a break. It essentially does what the batteries do, but does it only when there is shore power.
The DC converter in an RV also charges the batteries while connected to shore power. Some converters have sophisticated multi-stage charging mechanisms, and others simply provide a trickle charge.
For more about single-stage versus multi-stage charging, click here.
The DC converter is not involved in the solar power system. In our “full-time” solar setup, the DC converter is actually unplugged because our inverter powers all the AC outlets in the rig. Because of our converter’s design, when it is plugged in it senses when there is AC power available and automatically turns on. This would impose a huge demand on our batteries whenever we turned on the inverter.
Once in a while, when the skies have been overcast or stormy for a few days, we fire up our trusty Yamaha 2400i generator to bring the batteries up to full charge. We plug our shore power cord into the generator, unplug the inverter and plug in the converter. Now the converter is charging the batteries.
The converter that came with our rig was a single-stage trickle charge Atwood 55 amp converter. This was very inefficient for use with the generator because it charges at such a slow rate that we had to run the generator for hours and hours to get the batteries charged up.
In April, 2015, we replaced that converter with a slick new Iota DLS-90 / IQ4 converter. This converter can put as much as 90 amps into the batteries and has a true multi-stage charging algorithm. To see our introductory post about our big electrical system upgrade, see this post: RV Electrical Power System Overhaul
For more about converters, visit: RV Converters, Inverter/Chargers & Engine Alternator Battery Charging Systems
Almost all trailers and many smaller motorhomes have a converter installed at the factory.
An inverter takes the DC power from the batteries and converts it to AC power so you can run things like TVs, computers, vacuum cleaners, hair dryers, toasters, etc., and also charge things like your phone and camera batteries. Turn on the inverter, plug an AC appliance like an electric razor or TV into it, and poof, the razor or TV works.
Inverters come in two flavors:
True Sine Wave (or Pure Sine Wave) which means the AC power signal coming out of the inverter is identical to the power signal of a wall outlet in a house (a smooth sine wave).
Modified Sine Wave which means the waveform is clipped at the top and bottom and is stair-stepped in between rather than being a smooth sine wave.
It is easier to convert DC power to a square-type wave than a smooth sine wave, so modified sine wave inverters are much cheaper. However, some sensitive AC appliances don’t work with a modified sine wave inverter.
We purchased a high-end true sine wave inverter for our “full-time” solar setup, because it matched the quality of the system and our particular unit was noted for its ruggedness (we run it 15 hours a day, sometimes 24). Our Exeltech true sine-wave inverter is designed to operate medical equipment, so it provides exceptionally clean and stable AC power.
See our story “How Much Inverter Is Enough?” to learn about what happened to us when we accidentally “blew up” our fancy Exeltech true sine wave inverter and had to live on a tiny cheapo 350 watt modified sine wave inverter while waiting for the parts to fix it!
Ironically, some RV parks have unstable AC power that can damage AC appliances in an RV. Our inverter power from our Exeltech is cleaner and more reliable (Exeltech inverters are designed to power sensitive medical equipment)! Desktop computers, laser printers, TV and stereo equipment and Sonicare toothbrushes are the most likely appliances to have trouble with modified sine wave inverters. However, when we used modified sine wave inverters exclusively with our small solar power setup on our Lynx travel trailer, we never had a problem with any of our appliances. Modified sine wave inverters often have loud fans, and Mark did have to put some WD40 on our Radio Shack inverter twice when the fan quit working unexpectedly.
To add to the confusion about inverters and converters, some inverters combine a little of the functionality of both an inverter and a converter. These are called inverter/chargers and have two independent functions: (1) convert the batteries’ DC power to AC (inverter), and (2) use the AC power from the shore power cord (connected to electrical hookups or generator) and charge the batteries.
These are pricey pieces of equipment and many higher end motorhomes come with them. Our sailboat came with both a 600 watt pure sine wave inverter (which we used for everything on the boat except the microwave) and a 2500 watt modified sine wave inverter/charger (which powered the microwave and charged the batteries when we plugged into shore power).
NOW THAT IT’S ALL CLEAR, THE MANUFACTURERS MESS US UP!
The distinction between inverters and converters is pretty easy, isn’t it? However, recently when I was in an auto parts store I noticed a box labeled “POWER CONVERTER” and the picture and description were very clearly that of an INVERTER! So, maybe the distinction is going to get all muddied up after all.
For more about inverter/chargers, visit: RV Converters, Inverter/Chargers & Engine Alternator Battery Charging Systems
AN IMPORTANT NOTE ON RV REFRIGERATORS
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Because conventional propane RV refrigerators are inefficient and are (shockingly) expected to fail within ten years of service (see our blog post about that here), the current trend in full-time RVs is to manufacture them with residential AC refrigerators. These RVs are built with an inverter large enough to power the refrigerator while the RV is in transit. This is great for folks that are going to plug into electrical hookups 100% of the time. However, the electricity required to run a refrigerator, whether AC or DC, and no matter how Energy Star Efficient it is rated to be, is astronomical.
A typical 10 to 12 cubic foot Energy Star refrigerator will use over 300 kilowatts per year, or 822 watts per day. There is some energy lost when running on an inverter, so this will be roughly 822 Watts / 10 Volts = 82 amp-hours per day. To keep this fridge operating during the short days of winter when the sun is low in the sky, you will need 400+ watts of solar panels and 200+ amp-hours of battery capacity in addition to whatever you will need to run the rest of the household.
If you plan to boondock a lot, and you don’t want to run your generator 24/7, be prepared to outfit your rig with over 1,000 watts of solar panels and close to 1,000 amp-hours of battery capacity to power a residential refrigerator.
Non-Energy Star compliant DC electric refrigerators are even worse. Our sailboat had a 3.5 cubic foot DC refrigerator (“counter height” or “dorm size”) that was built for RV use. It did not have a freezer compartment. We had 710 amp-hours of AGM batteries and 555 watts of solar power. Granted, we were living in the tropics and the ambient cabin temperature was generally 85 degrees. The refrigerator compressor ran about 50% of the time and our solar power system was pushed to the max to keep the batteries topped off every day.
We had a separate standalone 2.5 cubic foot DC freezer on our sailboat. If we turned the freezer on, the solar panels could not keep the batteries charged without supplemental charging from the engine alternator every third or fourth day.
Residential refrigerators have vastly improved in recent years, running on a mere 25% of the electricity they used to use in 1986, and they are only getting better. For more information about refrigerator energy use and energy saving tips, see this resource: How Much Electricity Does My Refrigerator Use?
I have corresponded at length with a reader who has been boondocking 95% of the time for 6 months in a 40′ Tiffin Phaeton motorhome. He has a Whirlpool 22 cubic foot residential refrigerator, 1,140 watts of solar panels on his roof and 940 amp-hours of battery capacity in his basement. His fridge is powered with a dedicated Xantrex pure sine wave 2,000 watt inverter that is wired through a transfer switch to both his shorepower line and his generator, just in case the inverter fails (he had a 1,500 watt modified sine wave inverter that literally burnt up and started smoking).
So it can be done, but it will be easier in a motorhome that has a big payload capacity than in a fifth wheel or travel trailer that has a smaller payload capacity due to the weight of the batteries required. Even though we had to replace our RV refrigerator in its 8th year of service, we do not want double our battery bank and solar panel array just to power a residential fridge. I would rather put that extra 275 lbs into other things we need in our mobile lifestyle.
PHEW! THAT WAS A LOT OF INFO. WHAT NOW?
Still confused about the components and operation of an RV solar power system? See our four part RV SOLAR POWER TUTORIAL series where these concepts are re-introduced and discussed in greater detail:
Learn more about the different kinds of solar panels on the market:
Solar Panel Selection – Flexible vs. Rigid, 12 volt vs. 24 volt, Monocrystalline vs. Polycrystalline – PLUS Wiring Tips!!
Get the quick-and-dirty shopping list of things to buy for your solar power installation:
Three RV Solar Power Solutions: Small, Portable, and Big!
Want to learn more about BATTERIES and understand how battery charging works at a deeper level? Our Intro to Battery Types and our four-part tutorial series covers all the details involved in charging RV and marine batteries and takes a close look at a variety of specific charging systems, from converters to inverter/chargers to engine alternators to solar charge controllers. It also reveals how these systems work together:
Curious about the solar power installation we did on our sailboat? See our page: SAILBOAT SOLAR POWER INSTALLATION.
In April, 2015, we overhauled our electrical power plant on our trailer. See the introductory post about this upgrade here:
RV ELECTRIC POWER SYSTEM OVERHAUL
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