Frequent Questions: Solar Panels

What kind of solar panels do you sell?
We currently sell 100W and 160W 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 currently only 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 160 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 160W panel uses thirty-six 6” cells connected in series to produce an operating voltage of about 18 volts.  A 265W residential panel would use sixty of those 6” cells and have an operative voltage around 31 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.

Can I get solar panels that are made in America? 
As far as we know, there are no US manufacturers that produce solar panels that we consider appropriate for the RV market.  We hope this changes soon.  Solar panel manufacturing is a relatively young industry in the United States; and as a result, most of the focus has been on more lucrative and high volume grid-tied panels. 

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.

Frequent Questions: Charge Controllers

Charge Controllers
Do I have to shut off the charge controller when I connect to shore power?
You can have multiple sources charging the same battery bank at the same time.  Whether it is shore power, an alternator, a generator, solar panels, etc., it doesn’t matter.  Connect them all.  Run them all at the same time.  No additional protections or switching of any sort are necessary.  Chargers of all types are protected against reverse current flows and base their output on the voltage of the battery bank they are charging.  When a battery is getting charged by any source, it’s voltage will go up proportional to the amount of current being fed onto that battery.  In some situations where you have a particularly strong charging source, like an alternator or shore power, the high current fed onto batteries will drive the battery voltage up to the point that the solar charge controller thinks the battery is full.  When that happens, the solar charge controller will temporarily stop charging until the voltage returns to a lower level.

What charge controllers do you sell? 
We mainly sell Blue Sky Energy brand charge controllers because of their proven performance in RV applications.  We offer both PWM and MPPT charge controllers to satisfy a wide variety of customer needs.  Decades of experience have taught us what works and what doesn’t work in an RV.  The goal of our charge controllers is to maximize battery lifespan and improve system usability.

What is the difference between PWM and MPPT? 
PWM type charge controllers are simpler and less expensive than MPPT type charge controllers.  MPPT type charge controllers have the ability to convert excess panel voltage into higher charging amps, which means that they will produce about 15% more power than PWM type charge controllers.  Read more about this on our Charge Controllers page.

What charge controller should I use? 
Charge controller selection is based primarily on the panel wattage and corresponding charging current.  For every 100 watts of solar panels, assume that there will be about 6 amps of charging current.  The charge controller’s current rating needs to be greater than or equal to the total panel charging current.  For example, a system with four 100 watt panels can use a 25 amp charge controller.

Beyond the current rating, you should also consider the differences between PWM and MPPT charge controllers.  The MPPT charge controllers are usually more expensive, but can harness about 15% more power from the solar panels.

To learn more, visit our Charge Controllers page.

Can I use multiple charge controllers? 
Yes, multiple charge controllers can be used on the same battery bank.  Multiple charge controllers are used in situations where a single charge controller is not able to handle the entire output of a large solar array.  When multiple charge controllers are used, communications cables connect the charge controllers, and help them work in unison.  Read more about this on our Charge Controllers page.

How do I repair/upgrade my Heliotrope RV30 charge controller? 
The Heliotrop RV30 was a popular two-stage PWM style charge controller that has been discontinued.  If you have one that isn’t working properly, we can connect you with an engineer who can service the unit and provide replacement parts.  Or, you might consider upgrading to a modern charge controller.  Click here for more details.

How should I adjust my charge controller settings for optimum performance? 
It is very important that your charge controller system is properly tuned for your battery bank.  An improperly set charge controller can destroy an expensive battery bank.

Tuning for lithium battery banks is the easiest because they do not require equalization nor do they need regular full charges.  The BMS (Battery Management System) handles most of the thinking for you.  But if your charge controller or converter are configured incorrectly, and the battery bank gets too high of a voltage, the mistake could be very costly.

Tuning for lead-acid (Flooded or AGM) batteries requires the most steps.  The voltage and current limits for absorption, float and equalize have to be set.  You may also have to program for automatic equalization frequency and duration.

All systems installed by AM Solar are programmed to optimize battery life.  If you have questions about how to configure your AM Solar system call or email our Tech Support at (541) 726-1091.  We will need to know the make and model of your batteries and the charge controller system you are using.

Frequent Questions: Wiring

What is a series/parallel connection? 
A series connection is when you connect the positive of one solar panel, battery, etc., to the negative of another, leaving you with one free positive and one free negative.  With series connections, the voltages of the items connected in series sum [18V + 18V + 18V = 54V], while the current averages [(5A + 5A + 8A)/3 = 6A]. 

A parallel connection is when you combine the positive leads of solar panels, or batteries, etc. to make one lead and combine the negative leads to make another lead.  With parallel connections, the current from each of the items sums, while the voltages average.

If you have two six volt batteries and want to make a 12V battery bank, you would connect the two batteries in series.

If you have four six volt batteries and want to make a 12V battery bank, you would connect the batteries in two parallel groups of two batteries in series.

When a solar panel gets shaded, its current drops and its voltage remains roughly the same.  This is why we recommend parallel connections for solar panels.  In a parallel connection, a drop in current without a drop in voltage from one source will not have an effect on the other sources connected to it.  In other words, with solar panels connected in parallel, partial shade on one panel will not bring down the other panels in your system.

What gauge wire should I use? 
All of our SunRunnerTM System Cores come with an appropriately sized wire harness to minimize line losses and maximize value.  We use 10 gauge cable from the solar panels to the combiner box.  Since the panels in our systems are always connected in parallel you can assume about 6 amps per 100 watts of solar panels.  For cable run lengths typical in RV applications, we recommend 10 gauge wire for 20 amp systems up to 4 gauge wire for 40 amps systems.  If your system calls for more than 40 amps of charging current you will use multiple wire harnesses to multiple charge controllers. 

The cables going from the battery bank to the inverter have to be much thicker because they have much more current flowing through them (up to 250A in some situations).  These cables are typically limited to 10 feet in length and a 2/0 cable is most commonly used.

How should I route wires from my roof? 
With the majority of our installations, cables go from the solar panels to a combiner box (or boxes) on the RV roof.  Depending on your rig, these combiner boxes may be installed near existing roof penetrations, like vents, or a new roof penetration will have to be made underneath the combiner box.  The placement of these combiner boxes and cable routes is always planned very carefully before any holes are made.  An installer will want to keep cables as short as possible while maintaining structural integrity and preserving the vehicle’s aesthetics.

Do I need fuses or breakers?  Where? 
You aren’t going to get a surge from solar panels (unless maybe there was a very unusual solar flare, in which case you have bigger issues to worry about.)  Because of that, our kits do not use fuses between the panels and the charge controller.

To protect the charge controller in the event of a short-circuit or some other unforeseen event, we recommend a fuse or breaker on the positive line between the charge controller and the battery bank rated at the maximum current of the charge controller.

We also recommend a fuse on the positive line between the battery bank and the inverter.  To determine the size of this fuse, take the wattage rating of the inverter, divide it by 12 and multiply it by 1.25.  For example, a 2000 watt inverter would have a rating of about 200A (2000 / 12 x 1.25 ≈ 200).

Do I need grounding? 
Since your RV moves down the road on rubber tires, a grounding rod obviously isn’t going to be a part of your system.  Our systems are designed in such a way that a lack of grounding will not affect performance.

Frequent Questions: Batteries

How many batteries do I need? 
Batteries come in a variety of types and sizes.  Batteries are like gas tanks, in that some are bigger than others.  A better question would be “How many Amp hours of capacity do I need?”  

When dealing with lead-acid batteries you will want between 0.5 and 1.0 Amp hours for every 1.0 watts of solar panels.  If you have too much battery capacity your batteries may not be able to reach a full charge frequently enough to prevent sulfation.  Additionally, battery charging inefficiency will eat up an increasing amount of solar production as you add to your battery bank.  But, if your battery bank is too small, you will reach a full charge early in the day while there is still plenty of sunlight.  Solar panels connected to a fully charged battery bank cannot produce power and therefor become expensive roof decorations.

With lithium batteries you don’t need to worry about full charging or inefficiencies.  Get as much lithium battery capacity as you can afford as long as you have enough to store a full day’s solar production.

What is better, 6V or 12V batteries? 
If you are comparing similar battery types, from a chemistry perspective, there is no difference between 6V batteries and 12V batteries.  The only difference is that 12V batteries have twice as many of the same type of cells as 6V batteries.  In other words, aside from smaller plates, a 12V battery is just two 6V batteries in the same enclosure.  People choose one type over another based on space constraints and costs.  Two 100Ah 6V batteries connected in series will have the same electrical characteristics as a single 100Ah 12 battery.

Are lithium batteries worth the upfront cost? 
Many customers that factor in the longer lifespan and improved performance of lithium batteries conclude that in the long term they are cheaper than AGM batteries.  You can learn more about the advantages of lithium batteries on our Batteries page. 

What should I do to keep my AGM batteries healthy? 
The challenge with AGM batteries is managing the build-up of sulfate on the internal plates.  This accumulation of sulfate on the plates is a natural side effect of the battery discharging, but getting that sulfate off the plates and back into the electrolyte solution is an often-overlooked aspect of battery management.  If the sulfate isn’t regularly removed from the plates it will harden and reduce the conductive area of the plates, which will reduce the capacity of the battery.  

In order to remove the sulfate, the battery has to be fully charged.  But, if the battery is over charged the electrolyte will boil off.  A careful balance has to be maintained in order to get the most useful life out of your battery bank.  A well-tuned charge controller system can automatically regulate the charging cycle of your batteries.  

All systems installed by AM Solar are tuned specifically to optimize your battery bank.

To learn more about battery management check out our Batteries page.

How long will my batteries last? 
Batteries have varying lifespans depending on how they are used.  AGM batteries may last up to three years.  Lithium batteries are warrantied out to five years but can last longer than ten years.

What does Bulk, Absorption, Acceptance, Float & Equalize mean? 
These are all terms pertaining to the various stages of lead-acid battery charging.  

Bulk:  This is the stage where the battery gets about 80% of charge and where it can handle the highest current and voltage.

Absorption (also known as Acceptance):  This stage can be described with an analogy of pouring beer into a glass.  After the main pour (bulk stage) you have a lot of bubbles in the top part of the glass and you have to slow down the pour rate to keep from overflowing the glass.  The absorption stage is essentially a slower charge than the bulk stage.

Float:  The float stage is a very slow charge rate and how batteries are maintained long term when they are full.  Back to the beer analogy, the float stage would be like slowly replacing beer that evaporates as a glass sits full for a long time.

Equalize:  A battery is composed of cells that may not always be at the same charge level.  An equalization stage is a brief overcharge that brings all the cells to full (equal charge) to remove the accumulated sulfate on the battery plates.  In terms of beer, it would be like having several closely spaced shot glasses with a pitcher pouring beer all over them and only stopping when the last shot glass is full.  Some shot glasses will fill quickly and overflow, but in the end they will all be equally full.

To learn more about battery management check out our Batteries page.

How should I dispose of old batteries? 
Lead-acid batteries have lead cores that need to be recycled after they are spent. Most battery shops will accept lead cores, and some will even charge an extra fee if you purchase a battery without returning a spent core. Also, check with your local recycling centers to see which centers are willing to receive spent cores.

When lithium batteries have reached the end of their lifespans, they will also need to be recycled. We’re not quite sure what that will look like 10 years down the road, but we know lithium technology today should not be disposed of in the landfill.  Check with your local reclamation centers for additional information.

Frequent Questions: Inverters

What size inverter should I get? 
Inverter capacity is measured in Watts which should be higher than the total watts of all the devices that you plan on running simultaneously.  For example, if you have a 1500 watt microwave oven, a 300 watt refrigerator and maybe another 200 watts of lights, cell phone charging and misc., you will need at least 2000 watts of inverter capacity.  If you only have a 2000 watt inverter and you try to run all of that equipment plus a 1000 watt blender it will overload your system and your inverter will turn off.  

The size of an inverter system has nothing to do with how many solar panels you have or how much battery capacity you have, it is only relevant to the size of your AC loads.

Learn more about inverters on our Inverter page.

What is the difference between pure and modified sine? 
A pure sine inverter is universal and works with all AC appliances.  A modified sine inverter is usually less expensive and does not work well on devices with moving parts.  The output of a pure sine inverter is smooth and constantly changing as its output goes from negative to positive.

Learn more about different wave forms on our DC, AC, Pure Sine page.

What kind of efficiency would I get on an inverter? 
A typical inverter used in RV applications would have an efficiency of around 90%.  In mathematical terms, this means Voltage out x Current out x 0.9 = Voltage in x Current in, or if an inverter is driving a 2000W load, you would see 120V x 17A x 0.9 = 13V x 141A.

In addition to power conversion inefficiency there is also an idle wattage consumption of around 7 watts, just for having your inverter turned on.  A consumption of 7 watts over a 24 hour period works out to 168 watt hours, which is about half the daily production of a single 100 watt solar panel.

What extra features might I want on my inverter? 
Many inverters will have an option for a built-in DC charger for your 12V system when you are plugged into shore power or running from your onboard generator. Other inverters may have an option for a pass-through AC function that enables shore power (or generator) to bypass the inverter when you’re “plugged in.” Some inverters may even have both of the options described above. Of course, the price point changes with the addition of these options.

Is my inverter a good match for my panels? 
A better question would be “Is my inverter capable of supporting my load?”.  The solar panels and charge controller determine how quickly the battery bank charges.  The inverter determines how quickly power can be drawn off the battery bank and converted to Alternating Current.  The two systems don’t have any contact or influence over each other.

What happens to the onboard converter/charger when I install an inverter/charger combination? 
In our shop, we typically disconnect the onboard converter/charger from the circuit breaker in the AC distribution panel. We do this in order to prevent a feedback loop between the two chargers. Most often, we leave the onboard converter/charger in place, as a backup, in case the inverter/charger fails. For this contingency, you may want to leave the wiring intact, but label the circuit breaker to remain OFF at all times.

Frequent Questions: Mounts

Do I have to penetrate my roof? 
With standard fiberglass roofs, 3M double-sided tape and Dicor sealant are usually sufficient.  On rubber roofs, we recommend using ¾” stainless steel sheet metal screws, along with the double sided tape and DiCor sealant, to ensure that your rubber roof stays bonded to the plywood structure beneath it.  Go to our Mounts page to learn more about our mounting hardware.

What will I gain by using tilting mounts? 
When solar panels are tilted toward the sun their cross-sectional surface area exposed to the sun increases.  In other words, the panel looks bigger from the sun’s perspective and therefore it can collect more solar energy.  Tilted panels also transfer more of the sun’s rays to your cells, as opposed to reflecting them off the glass.

Tilting is especially beneficial in the winter months.  In Phoenix, AZ during the month of December, a panel tilted at 30 degrees off horizontal to the south, will produce about 73%* more power on an average day than a flat mounted panel.  In the month of June, that same tilt angle will actually decrease production by 10%* since the sun is higher in the sky during that time of year.

*PV Watts analysis by NREL, 77% Derate Factor

With tilted panels comes responsibility.  If you don’t put the panels flat before driving it will be much easier for wind to rip them off of your vehicle.

Can I get an automatic tilt or tracking mechanism? 
We do not sell any automatic tilting or tracking kits, but we have run across some clever engineers who have designed automatic systems for their personal use.  It’s our opinion that these systems are certainly impressive, but reliability concerns and costs limit their practicality to a very small niche market.

Has anyone had a panel blow off? 
In all our years of working with RV solar panels, not a single panel that we have installed has blown off.  We attribute this successful track record to our well-thought-out designs, tight quality controls and attention to detail.

Frequent Questions: System

How will my alternator interact with my system? 
Our systems are designed to work in conjunction with your vehicle’s alternator.  You will not need to disconnect your solar system when charging your battery bank with an alternator.  You can have both sources running at the same time.  With lithium battery systems we occasionally install an alternator disconnect switch.

How will a generator interact with my system? 
Our systems are designed to work in conjunction with a generator.  You will not need to disconnect your solar system when using a generator to power AC loads or charging your battery bank.  You can have both sources running at the same the time.

When do I need to turn off my solar? 
The short answer is never when outside.  A well-designed RV solar power system will have a charge controller that automatically detects when your batteries are at full charge, and tapers off the charging current from your solar panels to prevent overcharging.

When stored inside a garage or covered area, you will want to turn your solar OFF at the circuit breaker (or remove fuse) to ensure the solar charge controller doesn’t become a load on your house battery bank. Your normal house disconnect switch will not turn OFF your solar.

Frequent Questions: Service

Do you do installations? 
We do complete system installs, but you will want to set your appointment several months in advance.  Our installation department is always running at full capacity, and it isn’t unusual for us to be completely booked out six months into the future.

What do you offer for warrantees? 
Many of our components have their own warranties underwritten by the manufacturer, which range from 1-5 years with some proration; and, we do our best to ensure that all components are properly installed to the specifications. Our workmanship is 100% guaranteed, aside from normal wear and tear that transpires with RVs. Vibration and stress can cause connections to loosen over time, and we expect RVers to periodically have check-ups performed.

Frequent Questions: Misc.

How will your systems handle in the event of an EMP? 
An EMP (Electro Magnetic Pulse) can be the result of a solar flare or nuclear blast.  Coils, long runs of cables and microelectronics are especially susceptible to the damaging effects of an EMP. Solar panels would most likely be able to survive anything that your DNA can survive because solar panels are essentially just flat sheets of silicon.  Charge controllers, converters and inverters, on the other hand, would not fare as well because they contain coils and microelectronics.  One way to protect these components would be to enclose them in a grounded Faraday cage, which is basically a metal box with a cable going to a grounding rod.  Considering how impractical this would be in an RV, and all the bigger problems you would have with every other system being destroyed in your RV (and the world around you for that matter), we recommend just avoiding EMPs.