This is a continuation of the Living in a Small RV series. It will be a bit boring for anyone who isn't interested in solar power, but I wanted to write it like this because I had a tough time finding all of this information tied together.
There are two classes of devices in an RV that need electricity, AC and DC. The DC ones run off the battery and these include things like lights, the water pump, the vent fan(s), and anything you can plug into a 12v socket.
The AC ones are primarily the air conditioner and the microwave. They get their power from either plugging the RV in to a campsite or 120v socket at a house or by running the generator.
The generator uses gas (somewhere between half and a full gallon per hour) from the main tank. Because the generator is too loud and costly to run all the time, I almost never use mine. As a result I never use the air conditioner, favoring a vent fan that pulls air through the windows and uses very little electricity.
A quick primer on electricity which will be focused more on practical application that scientific accuracy:
Think of Watt-hours as a bucket of electricity, and Watts as a hole in the bucket.
For example, my batteries store roughly 2400 watt-hours. That means that I can run a 24 watt light bulb for 100 hours. Or I could run a 200 watt TV for 12 hours.
Amps are just Watts divided by volts. So on a 12v system like all RV DC systems (as opposed to the 120v AC system), 1 amp is equal to 12w.
The best way to work with these numbers is to just multiply amps by volts and work in watts.
You can only store DC power in the battery, not AC power, so if you want to power on of your AC appliances, you need to get an inverter, which just converts DC to AC.
The problem, though, is that devices designed for AC power tend to use a lot of watts since AC power is usually so plentiful. For example, I could only run my air conditioner for about an hour and a half on a full charge IF I had a really expensive high wattage inverter.
Here's a rough breakdown of wattage:
So, just for fun (and because we'll need it in the next section), let's see how much electricity I use in a day.
I usually have one light on usually from 10pm to 3am. That's five hours times 20w. 100 watt-hours.
I have my laptop on for that same amount of time, which is another 100Wh.
The fan is on for 11 hours a day on low and 13 on medium. 130+285 = 415Wh.
Half an hour for the water pump. 25Wh.
The laptop is plugged in for about 6 hours, so that's another 120Wh.
If we add that all up, I use about 760Wh per day.
How do I get that power? Hmm....
I could run my generator for a short period of time every day. Or if I drove a lot the batteries would just charge from the inverter on the car (the same system that powers your headlights).
But... I prefer to not have to use gas and to have my electricity just magically regenerate itself.
And that's where the miracle of solar comes in. In an average day in Texas we get an average of 5 hours of full sunlight. That means maybe we get 1 full hour, two half hours, four quarter hours, etc, since the sun is only directly above us for a short period of time. If you live much farther north, you can count on 3.5-4 hours of sunlight.
You can get all sorts of solar panels, ranging from 1 watt to about 225 watts, which is the amount of watt-hours they generate in one hour. Anything more than that and you start having to get two panels and chain them together (which is very easy to do if you need that much power).
So in a five hour day a 1 watt panel can make 5 watt-hours of electricity, which is totally useless. A 225 watt panel can make 1125 watt-hours of electricity.
I need 760 watt-hours of electricity per day, so I need at least a 156 watt panel.
But... 156 watts isn't going to cut it. It's important to have excess capacity so that you can save electricity for cloudy days or for days where you use more than expected. There are also a bunch of sensors and stuff that run from the battery and some inefficiency in charging the battery which increase the actual daily requirement.
I went with a 200 watt panel. Maybe a 180 watt panel would have been enough, but I'd rather overdo it than find myself running out of power.
You can't just hook a solar panel directly up to a battery, though. A 12v panel can actually put out up to 17v in sunlight, which is way too much for a battery. Instead you buy a charge controller which regulates the charge.
There are a few different kinds of solar controllers, but the best ones to buy are the ones that have MPPT technology. The regular kind are fairly inefficient, especially during the winter, so you get up to 30% more power for using MPPT. For a more detailed and technical explanation, read about MPPT here
Of course, unless you're only going to use power while it's sunny out, then you'll need a battery (or two) to store the charge. You generally want to buy a battery that has twice the capacity of your daily solar output. This is for two reasons.
Batteries are rated in amp-hours, which are basically just watt-hours divided by 12. In my case I generate 1000 watt-hours per day, so I need approximately 2000 watt-hours of capacity. Divided by twelve to make amp-hours, that's 166Ah. Luckily my RV came with two batteries that total 180Ah, so I was all set. Since I also use my RV as my car, I can actually use that extra capacity because the batteries charge as I drive.
That's a useful how-to. You make the math comprehensible, and I like the DIY ethic. I'm guessing, from a few minutes of googling, that you paid around $1000 for a 200W panel, or maybe $500 for used? That's very reasonable in terms of payback time and being something most of us could swing.
Thanks for sharing your experiences. My boyfiend and I recently started living in a 1878 Ford Midas RV so he could pursue his dream of being a comedian, so my brother sent me your article. I love living in an RV, and I like the idea of adding solar power to it. What did it cost you to get your solar panels system set up? Thanks! Angela
Hello, Jill here: A new to the RV world gal, in a 1995 Roadtrek with a very small trickle charge solar battery installed about 10 years ago by previous owners. Love the tried and tested- well written blog here- Mr. Tynan. We are planning a trip from Seattle to LA to see friends and museums this fall. We may update our ability to use sunshine via better Solar equipment, to boondock- ish- with a Burbank permit for non-commercial vehicles. We've just come back from a glorious week going up the inside passage of Vancouver Island.
Advice we were given? If you are a friendly person and a "joiner, " think about becoming a member of the Elks. They offer boondocking to members and friendly interested faces in many places you might want to go. We (hubby & myself) are active Fraternal Order of Eagles members ourselves, and find this to be true but to a lesser degree (the boondocking opportunities- NOT the friendliness which is full-on amazing, everywhere we went in Canada, WA state and Oregon.)
This is actually too difficult for me to follow. I think it's broken down too much. I need more information with a noticeable flow rather than separate chunks sitting in linear order. Words are words math is math, compromises and hybrids of the two just confuse me. Rubrics instead of essays confuse me when I'm expecting an essay form. Don't underestimate the intelligence of your reader and just throw it all out there please, if it doesn't require any explanation, it doesn't need to be broken apart! #myopinions
Thank you for sharing, my husband and I recently starting living in our RV it's great so far.. the electric bill i know will be high so i'm considering getting the panels installed since they will pay for them selves, can anyone recommend a brand? or can anyone recommed a place to buy them ? and can this be a DIY project? i'm pretty savvy so i think I can do it my self some solar panels are like diy however I'm def not an electrician..
From the info i have gathered that we will need a lil more than 200 watts..
Any advice help would be great.
My last post on living in an RV has generated a bunch of questions by comment and by email. Instead of responding to them individually, I'm going to answer them all here.
How long did it take you to outfit the RV with solar power?
Putting solar power into an RV is a simple job, primarily because most things in an RV (everything that I use) runs of 12V DC power instead of standard household 120V AC power.
Last Thursday, I attended a seminar on residential solar organized the MIT club of Northen California. Thanks Victor Huang for getting me in ! Among the guest speakers was Paul Nahi, CEO of Enphase, a forward thinking company specialized in micro inverters for PV systems.
An inverter has two role in a solar PV system:
1. Convert the direct current generated by panels into alternative current 2. Optimize the power produced by the system through Maximum Power Point Tracking.
If there is shading or any other issue with a single panel on the array, the inverter in a conventional setting will adjust the MPPT for the whole array, leading to a large diminution of the power production. Micro inverters adjust their MPPT independently at the panel level, significantly improving the efficiency of the system. Here is a technical study on the difference by Mr. Lee and Mr. Raichle from the Appalachian State University
An other big advantage of micro inverters is that they eliminate the high voltage part of the system, making it not only safer, but also cheaper to install and repair. Any electrician can install systems with micro inverters, while conventional systems require a high voltage operating license.