Solar panels come in outputs...
Solar panels come in outputs ranging from 1 watt to 275 watts and more and are made by quite a few manufacturers worldwide. They have no moving parts and only need to be kept clean as maintenance. Many companies make kits specifically for RV use that include wiring and a charge controller to regulate the electricity as it moves into your batteries for storage, and if your RV does not already have one, a power inverter.
For more power, larger Mitsubishi 175 solar modules priced at $720 apiece can generate current up to 7.32 amps. A 12-watt solar module that generates 1.28 amps, roughly 12x13 inches, would cost about $130. A one-watt module would cost as little as $25.
There are even easy-to-store 12-volt flexible solar arrays that can be unrolled in the sun for recharging RV batteries when access to AC power is unavailable. Originally designed for military use, flexible panels are now available to consumers. Power outputs range from 6 watts to 60 watts, and less than half an amp to 2.5 amps.
On the other hand, permanently mounting large panels attached to a bank of batteries is the custom way to go. For example, there might be room to mount six or more 200-watt solar panels on a 30-foot RV. Such an array could provide up to 1.2 kilowatts each hour, or 6 kilowatt-hours in a 5-hour day. We found 205-watt panels for sale at retailer Affordable Solar for $570 each, so they are not inexpensive, but they do generate a considerable amount of current. Those particular panels measure 65x37.5 inches and are almost 2 inches thick.
One of the more recent developments...
One of the more recent developments are small, portable solar panels like the 6.5-watt GSE charger shown here powering an iPod. Batteries for appliances like laptops, cameras, and iPods can be charged directly from solar panels of any wattage without first storing the electricity into a battery. Photography Courtesy of Global Solar Energy
Many RV owners are intrigued by the idea of using solar power for 100 percent of their needs. In some sunny locations, using a robust system of solar panels and batteries might be possible depending on how appliance-heavy your lifestyle is.
Certain high-amp draw appliances, such as air conditioning, generally suck too much power to run on the average solar system, but things like lights, computers, TVs, and game systems for a family are well within the realm of possibility. To figure out what's feasible, estimate your power needs.
We checked with Tyler Brown at Affordable Solar in Albuquerque, New Mexico, who explained how to figure how much wattage you actually use.
"Every appliance has a wattage rating," he told us. "The easiest to understand is to take a 50-watt light bulb. If you run that light bulb for 1 hour, you will have used 50 watt-hours of energy, or 50Wh. Run that same light bulb for 2 hours and you'll have used 100Wh of power. Add up all of the light bulbs in your house, plus the wattage rating on other appliances, and that's how much energy you'd use in an hour. If you can't find a wattage rating, volts times amps equals wattage."
"Once you've figured that out, the next step is to add up the hourly usage and find out how many watt-hours (Wh) you use in a day."
Kilowatt hours are the units your power company uses on your bill, expressed as "kWh used" (1,000 watts= 1 kW/1 kilowatt).
Even a small solar panel on...
Even a small solar panel on a camper or compact RV can help extend the time you can draw electricity without running a generator. By adding more panels and more batteries, more electricity can be captured and stored.
Brown told us, solar panels are rated in instantaneous wattage. So if a solar panel carries a 220w rating, it is capable of making 220wA in one hour. So let's say you are going to use 1kWh a day. Then you'd need a 200w panel getting full sun for 5 hours. Or, you could have 5 panels running for 1 hour to achieve the same.
There is usually an efficiency loss you should account for when sizing a system. So if you need 220Wh, a 220-watt panel isn't going to cut it. 220w is achieved on that panel at the perfect sun angle, perfect temperature, and at the panel output. You will have a loss factor of about .8 through your inverter as well, so take your needed usage and divide it by 0.8. In this case, 220 divided by 0.8 gives you 275w. This means you're going to need to find a panel/system rated at 275 watts.
Battery Backup
Your RV probably already has at least one auxiliary battery, which you'll be drawing on most of the time. Solar panels can help keep that fully charged during the day, but more panels and more batteries will allow you to store more energy.
To estimate how much juice a single battery can hold in watt-hours, multiply the voltage times the amp hour rating on the battery. If you have a 42-amp, 12-volt battery, you get 504 watt-hours. That means you could run a 100-watt light bulb for 5 hours before the battery would be totally dead or five light bubs for an hour apiece. It would be possible to run a 1,000-watt appliance on the same battery, but only for about half an hour.