In an earlier post, I covered electrical use while unplugged – how your coach batteries store electricity for use while you're parked and enjoying the scenery in your Roadtrek. There are various ways to get electricity back into them. All RVs charge the coach batteries off the van's alternator while the van engine is running. Many also have a generator which produces 110 volt alternating current (house current or shore power) that another component, usually a converter or inverter/charger, transforms into direct current in the 13-15 volt range to replenish the batteries.
Both of these methods charge the batteries, true, but they also create noise and exhaust fumes, not particularly conducive to enjoying the wilderness experience. Generators are a convenient – and valid – target of criticism from folks who don't like RVs in their vicinity. Nobody wants to be around when a group of RVs are parked somewhere and all running their generators; it sounds and smells like a bus depot or parking garage. Big rigs can close the windows and run the A/C – I've rented beach condos smaller than some Class As. Us little rigs feel like we're hiding in a closet when we try that.
What if there were another way to get electricity back into your batteries that's silent and odorless? Solar panels are the solution to the noise/fumes problem, and increasing numbers of Roadtreks and other RVs are utilizing this power source. What I would like to do is cover some of the basics of solar panels – how they work, and what they can and can't do in keeping your batteries topped up and making electricity for you to use in your Roadtrek.
First a little dreary and hopefully brief science background on how solar panels work. An amazing amount of energy falls on the earth's surface from sunlight – about a kilowatt per square meter. A kilowatt will run a microwave – that's a bunch of power. Solar panels convert some of that energy into electricity by utilizing the ability of certain materials, silicon in the case of the panels we use, to produce an electrical current when exposed to light. Skipping over a bunch of boring details like p-n junctions and electron holes, the basic mechanism is that photons from sunlight knock electrons loose, and these electrons are collected. Flowing electrons are what we call electricity. OK, the science part is over – now wake up your neighbor and we'll proceed.
What solar panels CAN do is produce electricity directly from sunlight – no moving parts, no noise, no fumes. What they CAN'T do is capture all of it. Remember that kilowatt per square meter? Because much of that energy is the wrong wavelength to knock electrons loose in the silicon, like infrared and ultraviolet, efficiency ratings for commercially available panels struggle to get up to 20%. Most are in the mid to high teens. With limited rooftop space on a Class B, you want the most efficient panels you can put up there. A solar panel's not going to produce the 2800 watts your generator produces or the 1800 watts your alternator cranks out. Try 100 to 200 watts for a typical panel. Solar panels will produce a steady flow of power, but they aren't going to fully charge your depleted batteries in an hour like shore power or a generator.
The angle of the sunlight hitting the panels is also important. Maximum solar panel power ratings are produced with direct overhead sunlight. Us folks in the temperate latitudes don't have that. Your maximum sun elevation is 90 degrees minus how far north you are from the Tropic of Cancer – 23 degrees north. The penalty isn't significant for slight deviations from directly overhead – you'll still get 90+% of available power anywhere from 64 degrees on up, but 45 degrees is 71% power, and it goes downhill fast from there. Fortunately most of our camping is in the summer, when the sun is high in our sky. For RVs, moveable panels aren't easy to engineer. You want securely attached panels that won't blow off as you drive down the road, and also won't produce wind resistance. Almost all RV solar panel installations are flat on the roof, so the lower the sun the less power you get.
Another engineering challenge is matching the solar panel output to the batteries' charging needs. There's a basic difference in temperament between the two – solar panels' voltage increases dramatically as they get more light, whereas batteries have a threshold voltage below which they won't charge at all, and can be damaged by too high a voltage. For this reason, solar installations charging batteries use a charge controller or maximum power point tracker (MPPT) to provide marriage counseling trying to reconcile and resolve differences between the mercurial solar panels and the phlegmatic batteries. MPPTs provide an increase in efficiency by boosting low panel voltages up to where they'll charge the batteries in low light conditions, with a pickup of 30% in efficiency under certain conditions.
Most people who install solar panels also increase the size of their coach battery bank. This is because your battery bank size is your electrical equivalent of a savings account balance – you want electricity available for when you want to use it. If you watch TV in the evenings after the sun's down, you need an ample reserve of power so that you won't have to turn the set off halfway through a movie. Most people also get a larger inverter/charger to utilize the increased amount of electricity available. Solar panels, inverters, and especially batteries add weight to your RV, and reduce its cargo carrying capacity, so don't get carried away with adding components without checking the weight limits, and calculating how you'll be able to carry water, fuel and supplies while staying within your vehicle's weight limit. Solar charging systems are systems – get people who know what they're doing to install it, because voltages are high, and bad wiring is the cause of many RV fires.
Properly installed, a solar panel or two (or three) will substantively increase the functionality of your Roadtrek, especially if you like to go to remote locations for extended periods of time. I spent seven months boondocking along the Pacific Coast Highway, hanging out all day watching the waves while surfing the web and watching TV, and didn't plug in once – all our power came from the sun and occasional generator use on cloudy days. If you're familiar with oceanfront campsite prices in the commercial campgrounds along the California and Oregon coast, you'll quickly realize that solar panels greatly enhance the financial functionality of your Roadtrek as well. You can escape the cycle of generator use every 2-3 hours to recharge your batteries that makes you a bad neighbor to the day trip folks at the beach – as far as they're concerned, you're just another picnicker, except you're eating hot meals from the microwave or stovetop instead of fighting ants for soggy sandwiches like they are.
Maintenance? Compared to a generator, there isn't any. No oil changes, no generator exercising every month, no Sea-Foam to keep your float bowl from varnishing. Just keep dirt from building up on them and blocking the sunlight. A ladder and a long-handled brush two or three times a year, and you're done. With a good charge controller or MPPT, you can truly install it and forget it. Another incentive is the solar energy tax credit- Federal income tax rules allow you to deduct 30% of the cost of solar systems (panels, batteries, inverter, MPPT, wiring and installation) from your tax bill. You provide 70% of the cost – the government picks up the rest of the tab.
So consider your Roadtrek's use pattern and see if solar is an attractive option for you. If you just go out a few weekends a year and to places with electricity available, it's probably not worth it. But to escape to the wilderness or a distant lake or seashore and hang out a few days you may find it will come in handy. It's also nice to know you're doing your part for the environment, and that you're a good camping neighbor.