Frequent Questions: Solar Panels

What kind of solar panels do you sell?
We currently sell 50W (polycrystalline), 90W, and 170W monocrystalline solar panels.  These panels were selected because of their voltage characteristics (at least 17.7 volts at maximum power point) and their relatively narrow dimensions which make them a better fit on RV roofs. 

What is better mono or poly? 
Monocrystalline solar panels can produce about 5% more power than polycrystalline solar panels of equal size.  Polycrystalline cells are square in shape with a blue color.  Monocrystalline cells are black and more octagonal (squares with beveled corners).  Both types of panels will work fine but we mainly sell the more efficient monocrystalline panels.    

Are higher wattage panels better? 
The largest panel we have sold is about 58” x 26” and rated at 180 watts.  Larger panels are easy to find, but bigger isn’t better.  In RV applications, the larger residential panels have several disadvantages.

-For the most part, panel wattage is proportional to panel size.  If you have a higher wattage panel it is most likely a larger panel.  Because the roofs of RVs are much smaller than the roofs of homes or commercial buildings, it may be very difficult to position larger solar panels on an RV roof in a way that they won’t be shaded by air conditioners, satellite dishes, etc.

-A 180W panel uses thirty-six 6” cells connected in series to produce an operating voltage of about 19 volts.  A 300W residential panel would use sixty of those 6” cells and have an operative voltage around 32 volts.  The higher voltage of a residential panel is ideal for grid-tied inverters but not so good for charging 12V battery systems.

-The larger surface area of residential panels can also act like a sail, and put more strain on your mounts and your RV roof when you drive at highway speeds.

-Larger residential panels are designed for stationary mounting on buildings or ground mounted arrays.  They may not be able to handle the vibrations of an RV driving down the road.  Sometimes conventional solar panels can develop micro fractures in their cells when they are transported by railway.

-Multiple smaller panels fit on the roof better, mount easier and have an output more suited to charging 12 volt batteries.

How many panels do I need? 
You may be thinking “I have average use, how many panels do I need?”  In our experience, there really is no average.  When people install a couple solar panels, they usually end up wanting to install more.  Everyone has different power consumption habits, roof sizes and budgets.  RV solar power systems can range in size from 100 watts to 2500 watts.  Some easy ways to determine what system size will work best are detailed on our System Sizing by Actual Use and System Sizing by “Rules of Thumb” webpages.

What if I short-circuit the solar panels?
Solar panels are very different from batteries in regard to what happens when you short-circuit them.  Batteries rely on a chemical process to produce a constant voltage, whereas the voltage of a solar panel changes depending on the load.  

When you short-circuit a battery, the chemical reaction will try to maintain that constant voltage by driving the current to an extremely high level.  This high current will be more than your battery terminals, or whatever is causing the short-circuit, can handle, and sparks will fly as metal melts.  Your battery could be ruined depending on how long the short-circuit lasts.

When you short-circuit a solar panel, nothing happens.  There is nothing driving a constant voltage and the panel behaves as if it were inert.  The solar panel will not be damaged.

How efficient are your solar panels? 
Efficiency is commonly measured as the ratio of solar panel output wattage to the 1000 watts per square meter input solar irradiance.  In other words, how much energy do solar panels produce per square foot.  Our monocrystalline panels have a module efficiency of around 16.4% and produce 14.4 rated watts per square foot.  

When you look at a solar panel data sheet you may see two efficiency ratings, cell efficiency and module efficiency.  Nobody is trying to be deceptive, they are really two different ratings.  The calculation for cell efficiency takes into account the surface area of just the cell.  Module efficiency includes the surface area of the white space between the cells and the frames.  Module efficiency is the more useful number in the context of RV solar because cells by themselves are never used, just modules.

Keep in mind that economic efficiency should also be considered.  NASA uses solar panels that are around 30% efficient but if they were commercially available their price would be about ten times what our solar panels can be bought for. 

How durable are solar panels? 
There is very little that can go wrong with a solar panel short of physical damage. In fact, all panels pass Jet Propulsion Labs Block V tests, which are: withstanding 125 m.p.h. wind loading, surviving one inch hail at terminal velocity (52 mph), and thermal cycling at temperatures beyond what you will experience here on Earth.

How should I clean my solar panels? 
You can clean solar panels like you would any piece of glass.  Use a non-abrasive cleaning agent to avoid scratching the surface or removing the panel’s anti-reflective coating.  If birds leave their mark on your panels it will be very important for you to remove the mess as the shaded portion can temporarily shut down the solar panel.

How long will my solar panels last? 
Crystalline panels usually come with a 25 year warranty but there is no reason to assume that they wouldn’t continue operating for many years after the warranty expires.  If properly taken care of, your solar panels will easily outlast your vehicle.

Are your solar panels made in China? 
As of 2014, an importer of Chinese solar panels in the United States would have to pay a 250% duty.  This makes Chinese solar panels price prohibitive.  So no, our panels are not made in China.  Unfortunately, the worldwide demand for solar panels far exceeds the non-Chinese supply; and as a result, prices are increasing.