• Maximizes battery life
  • Helps keep batteries charged with pure DC power directly from the sun
  • Helps prevent deep discharges of batteries – lengthens battery life
• Low maintenance
  • No fuel to hall around or consume
  • No moving parts to go bad or make noise
  • Just keep the solar panels clean and make sure all the electrical connections are good
• Electrical independence
  • A properly sized system with the appropriate components can allow you to go where you want without the worry of wondering where your power will come from
  • You are not dependent on a shore plug or a noisy generator

• Power needs
  • What are you trying to accomplish with your solar array and solar charge controller?
    • Do you just want to keep up with basic draws while traveling down the road?
    • Are you a serious “Boondocker” with high power usage?
    • Do you fall somewhere in between?
• What does solar provide in an RV environment?
  • Solar in the RV world is different than solar in the residential world
    • In the residential world, solar power is typically inverted directly to 120 volt power and fed into your home and the grid
      • It actually supplies useable power to run appliances or turn your meter backward
    • In the RV world, solar is typically used as a power source to recharge your battery bank
      • In other words, it is really dependent on the storage capacity you have available
      • It can also supply “free” power to run DC appliances, DC lights, etc. in addition to recharging your batteries

• Panels
  • Produce DC power from the sun
• Mounts
  • Hold panels to the roof of your RV
• Charge Controller
  • Regulates the amount of energy put to the batteries
• Wiring
  • How everything is connected to allow the energy to flow
• System Monitor
  • Optional, but important
  • Keeps track of your system’s performance

• Solar Panel Basics
  • There are currently three general types of solar panels available on the market
    • Amorphous (thin film)
    • Poly-Crystalline (multi-crystal)
    • Mono-Crystalline (single crystal)
  • Which type is best?
    • Amorphous panels are about 6 to 8% efficient
    • Poly-Crystalline panels are about 14 to 16% efficient
    • Mono-Crystalline panels are about 15 to 17% efficient
  • Mono-crystalline and poly-crystalline panels of the same physical size will produce about the same amount of energy
    • This is because mono-crystalline cells are more round and can’t be packed as tightly on a panel as the poly-crystalline cells. Therefore, a panel of similar physical size will produce about the same amount of power due to the number and efficiency of cells available on the panel
    • These numbers vary slightly by manufacturer, but are good general rules
• How are solar panels rated?
  • Panels are rated in Watts of output
    • This wattage is derived by multiplying a panel’s peak power voltage (Vmp) by its peak power amperage (Imp)
      • Watts = Volts x Amps
• Standard Test Conditions or STC
  • The solar industry uses a set of standard test conditions to rate a panel’s output
  • These conditions assume:
    • Sunlight intensity of 1000 watts per square meter
    • The time of day is solar noon
    • The sun is perfectly perpendicular to the panel
    • No dust or particulates are in the air
    • Air temperature of 77 degrees Fahrenheit
    • The atmospheric density is 1.5
  • These conditions are obviously idyllic and are not real world conditions
    • Use these numbers for wire size calculations to keep voltage drop to a minimum
    • We can never reach these conditions even on a perfect day in North America
• Normal Operating Cell Temperature or NOCT
  • These are a more realistic set of ratings adopted by municipalities and utilities to more accurately calculate applicable rebates and tax credits
  • These conditions assume:
    • Sunlight intensity of 800 watts per square meter
    • Air temperature of 68 degrees Fahrenheit
    • An average 1 meter per second breeze with the panel at a tilt angle of 45° and its back side open to the breeze
  • These conditions are still difficult to attain in an RV environment
• What does all this mean to you?
  • Your panels may never attain their full wattage potential so size your system accordingly
• What affects panel power output?​
  • Sun Angle​
    • When the sun is not perfectly perpendicular to the panel some of the light will reflect off the surface of the panel and will not provide power to the panel​
  • Light Intensity/Shading​
    • The brighter the sunlight the more power a panel will produce​
  • Shade caused by obstructions such as trees, antennas, satellite dishes, air conditioners, roof vents, etc. will greatly affect the output of solar panels​
    • It is very important to avoid possible shading of panels (especially true of panels wired in series)​
  • Cell Temperature​
    • Solar panel cells are dark and are much hotter than ambient air temperatures (think of putting your hand on a black car at high noon in full sun)​
    • The hotter the cells are, the lower the operating voltage​
      • The lower the voltage, the lower the wattage (Volts x Amps = Watts) ​
      • This is why it is important to use higher operating voltage panels​
    • An RV solar panel should be no less than 17 volts nominal (for a 12 volt system)​
      • This will account for basic voltage drop due to heat and inherent inefficiencies in wiring​
      • Higher voltage is better if your charge controller can handle it​
  • Wiring​
    • Poor connections and improper wire size will affect panel output​

• Panel Installation
  • Determine the location for each of your panels
    • Use a cardboard cutout to make sure they will physically fit and shading will not be an issue
    • Make sure you also have room for mounts – these will be wider than the panels (typically)
    • Measure and double check everything before you commit to a particular panel
  • Determine the type of mount to be used
    • Tilt mounts or solid mounts
    • Individual feet or rails/angle iron
      • Installations on flat roofs can use either
      • Installations on curved or sloped roofs are easier with individual adjustable feet to compensate for the curvature of the roof
    • Fiberglass or metal roofs
      • Mounts can be secured with 3M VHB tape without any roof penetrations
    • Rubber roofs
      • Require mounts to be screwed to the roof with appropriate sealant applied to protect the penetrations (use stainless hardware)

• Tilting
  • Tilting panels allows for better orientation relative to the sun and less light reflection off the panels
  • Tilting is most effective in winter months and in northern latitudes
  • Tilting requires you to physically get on your roof and manually tilt your panels
    • There is currently no good method to automate this process in the RV world
• Is it worth it?
  • Maybe, maybe not
    • If you are limited on physical space on your roof, tilting can compensate for fewer panels by providing higher output for those panels
    • If you are not limited on roof space (or budget), you can add additional panels to make up for not tilting them and get the same power output
    • Do you want to get up on your roof every time you set up and break down your RV or when there are strong winds?

• Solar Charging is no different than any other charging source
  • Solar panels convert sunlight into usable power through a solar charge controller to charge your batteries
    • This is no different than a charger converting shore or generator power to charge your batteries
  • Make sure your solar charge controller is a “smart” controller with temperature compensation
    • Three stage charging is best for Lead Acid or AGM batteries
  • Remember, lithium charge characteristics are different so make sure your charge controller can handle lithium batteries if you have them

• Solar Charge Controller Basics
  • Primary types of controllers used in the RV world
    • Pulse Width Modulation or PWM
      • The simplest and usually the lowest priced
      • PWM controllers operate by regulating a pulsed, direct connection from the solar array to the battery bank
      • As the battery bank approaches a full charge, the length of the connection pulses decreases to gradually taper off the charging current from the solar array
      • On a 12 volt battery bank, PWM charge controllers can only be used with a solar array that has an open circuit voltage of 24.0 volts or less
        • This excludes large 60 cell or 72 cell residential panels from use with a PWM controller
      • In systems with multiple solar panels of different voltages (e.g. 32 cell panels mixed with 36 cell or 40 cell panels), PWM charge controllers are preferable to MPPT controllers because their operation algorithms are less finicky
  • Maximum Power Point Tracking or MPPT
    • The MPPT type charge controllers use a much more efficient method of feeding power from the solar array to the battery bank
    • Instead of a regulated direct connection, MPPT type controllers transform the optimum balance of current and voltage from the solar array into something that can safely be fed into a battery bank
    • This means excess voltage from the solar array is transformed into more charging current
      • For example, with a PWM charge controller you may have a solar panel operating at 19.0 volts and 6.0 amps, feeding 6.0 amps into your battery bank (ideal conditions)
        • If your battery bank is at 13.0 volts you are only getting 78 watts (13.0V x 6.0A = 78W) from the panel
      • With an MPPT charge controller on that same panel you will be able to use the extra 6 volts (19.0V – 13.0V = 6.0V) and turn it into more current (amperage)
        • 6 volts is approximately 46.2% of 13 volts (6 / 13 = .462)
        • That remaining percentage of power is converted to amps by the MPPT controller
        • 6 amps plus another 46.2% is approximately 8.8 amps (6 x 1.462 = 8.772)
        • Your charging current will be about 8.8 amps and you will be getting about 114 watts (13V x 8.772A = 114.036 watts) from the same panel with an MPPT controller vs. a PWM controller

• Selecting a solar charge controller
  • Performance vs. Price
    • MPPT charge controllers cost more but can harvest more power out of an array
      • If roof space is at a premium, use higher voltage panels and an MPPT charge controller to harvest more power
      • If you are on a limited budget or have modest power needs, a PWM controller can work well for you
  • Array Voltage vs. Battery Voltage
    • The solar array needs to have a higher voltage than your battery bank in order to push a charge into the bank
  • Voltage Limits
    • Don’t let your array voltage exceed your controllers capabilities
    • PWM controllers are limited to 24 volts on a 12 volt system
    • MPPT controllers can be rated for as much as 150 volts or more depending on the model selected
    • To avoid damaging your charge controller, make sure the Voc (Voltage open circuit) for each panel does not exceed your charge controller’s limit
      • The Voc is usually printed on the label on the back of the solar panel
  • Current Limits
    • Charge controllers are rated on their output current (from the controller to the battery)
    • As long as your panels are connected in parallel (recommended for an RV) you can determine the maximum output current by summing the operating current, or Imp (Current maximum power point) for each panel
      • The Imp is usually printed on the panel label
  • Multiple Charge Controllers
    • If your desired solar array has a charging current that exceeds the current rating of your preferred charge controller, you can use multiple charge controllers
    • These charge controllers would be connected in parallel to each other across the battery bank
      • Not all charge controllers have this capability
  • Charge Controller Setup
    • It is very important to set up your charge controller properly
    • Set the correct system parameters within the controller such as maximum panel voltage, total battery bank capacity, etc.
    • Some controllers allow for a myriad of customized settings (often through remote controls) while others have only simple options available to them (often through dip switches)
  • Battery Temperature Compensation
    • It is important to incorporate battery temperature compensation on any system with AGM or Lead Acid batteries
    • Avoid charge controllers that do not allow for battery temperature compensation on these type of systems
  • Monitoring
    • It is very important to incorporate some type of monitoring system
    • Whether this is through an integrated monitor or a stand alone system, you need to know what is going into and coming out of your batteries to properly maintain their life and longevity

• Parallel
  • Voltage stays the same
  • Amperage is cumulative (adds together)
  • Connect positive (+) terminal to positive, connect negative (-) terminal to negative in the combiner box
• Series
  • Voltage adds
  • Amperage stays the same
  • Connect positive (+) terminal of first panel to negative (-) terminal of next panel
  • The remaining positive (+) and negative (-) terminals can be connected to the combiner box
    • Series is less desirable with solar panels due to shading issues, but can be used effectively to take advantage of smaller wire sizes
• We put solar panels together to increase the solar-generated power
  • Connecting more than one solar panel in series, in parallel or in a mixed-mode is an effective and easy way not only to build a cost-effective solar panel system but also helps us add more solar panels in the future to meet our increasing daily needs for electricity
• How to connect your solar panels depends on:
  • The type of your solar panel system
  • The solar power you want to generate
  • The other system components, such as a charge controller, battery, and inverter
    • You connect solar panels in series when you want to get a higher voltage
    • If you, however, need to get higher current, you should connect your panels in parallel
    • Should you need both a higher voltage and a higher current, you have to apply both connection modes, which means a series/parallel type set up 
  • The most important thing to remember is both connection modes provide you with a higher wattage
    • If the power output of a single solar panel cannot meet your daily electricity needs, you should think of adding more such panels to it, whether in series or in parallel
• Panels
  • Determine their placement on the roof (use cardboard cutouts – avoid shading)
  • Wire in parallel (preferred) or series (if called for)
  • Multiple panels are wired to a combiner box somewhere on the roof or just below the roof
• Wire
  • Use high grade, quality, flexible wire
  • Any exposed wire should be UV rated to prevent degradation of the wire
  • Use MC4 connectors or good quality, heat shrink sealed butt connectors to connect wire to panels
  • Wire used between panels and the combiner box is smaller gauge wire – typically 10 gauge
  • Wire from the combiner box to the charge controller is larger gauge wire to handle the higher amperage of the combined panels
  • Wire from the solar controller to the batteries is also larger gauge wire to handle higher amperage
  • A wire calculator should be used to determine proper wire size
    • Bigger is better as it allows for future expansion and less voltage drop
    • It is better to run a larger wire the first time than to have to run larger wire later if you decide to expand your system
• Combiner Box
  • Determine the location for your combiner box
    • Needs to be convenient for wire runs – both on the roof and from the roof to the solar controller
    • If on the roof, make sure it is a weather tight enclosure
      • Place it under a panel for even more protection
  • Determine how you are going to get your wire from the combiner box to the solar controller
    • This is the single hardest part of the installation
    • Did your RV come with wire pre-run?
      • If it did, is this wire properly sized for the application?
    • Typical aftermarket wire runs
      • Behind a refrigerator (if not located in a slide)
        • There is usually an open space from floor to ceiling in the RV behind a refrigerator
      • Along a vent pipe
        • Vent pipes run from the belly of your RV to the roof and provide a convenient way to fish wires
        • Sometimes wires can be fished along side a vent pipe, but in most instances wires have to be fished through the vent pipe
          • This requires holes to be drilled at the top and bottom of the vent pipe and those holes must be resealed properly to prevent odors from escaping inside your RV
        • Through an interior wall, cabinet or closet​
          • If there is good access, these can be convenient wire run locations​
• Solar Controller Installation
  • Determine the best location for your solar controller
    • The solar controller should be located as close to the batteries as practical to keep wire runs short
    • Do not install the solar controller in the same compartment as lead acid batteries
      • Any electronic component could provide an ignition source of gasses emitted from lead acid batteries resulting in a potential explosion
• Circuit Protection
  • Install some type of circuit protection between the panels and the charge controller
    • This can be as complex as individual panel breakers (instead of a combiner box) or as simple as a disconnect
      • You want to be able to isolate the solar array from the system
  • Install some type of circuit protection between the charge controller and the batteries
    • This needs to be some type of circuit breaker or fuse to prevent damage to the system
      • Size this appropriately for the application and place it near the batteries

• Mixing solar panels of various voltage or wattage, or produced by different manufacturers, is a frequently asked question
  • Though mixing different solar panels is not recommended, it’s not forbidden and things would be ok as long as each panel’s electrical parameters (voltage, wattage, amperage) are carefully considered
    • When you intend to wire two panels produced by different vendors, the vendors are not the problem
      • The problem is in different electrical characteristics of the panels, together with different performance degradation
• When you connect solar panels in series, the total output amperage of the solar array is the same as the amperage passing through a single panel, while the total output voltage is a sum of the voltage of each solar panel
  • The latter is only valid provided the panels connected are of the same type and power rating
  • For example:
  • Wiring solar panels of different ratings in series
    • Here is a series connection of solar panels of different voltage ratings and the same amperage rating:
      • You can see if one of the solar panels has a lower voltage rating (and the same amperage rating) compared to the remaining panels, the output power is lower than in the previous example but the loss is not significant
    • Things, however, are entirely different if you connect panels of different amperage ratings in series
      • You should keep in mind the amperage produced from а solar panel depends on the ambient temperature, solar cells temperature, and solar irradiance
      • If the lower wattage solar panel is from a different series or a different brand, it might behave differently under the same ambient conditions
        • For example, if under the same environmental conditions the solar panel of the different wattage (i.e., 136W) has a lower amperage (for example, 7.5A), it would drag the performance of the whole solar array down, because it would limit the solar array’s current to 7.5A
    • The performance of the solar array is only as strong as the performance of the weakest element
      • In a series connection, such a weak element is the solar panel with the lowest amperage
        • The following example reveals this in more detail:
          
        • In this picture, you can see a total of three different types of solar panels are used
          • Each panel type has its own voltage, amperage, and power rating
          • The total amperage here is determined by the panel of the lowest amperage rating and, as a result, the total wattage is severely reduced (by 40%) compared to the previous example where the loss of output power was not so significant
          • Furthermore, if you take a look at the first panel in the row, and assume you wired four such panels in parallel, then the total output power would be: 4 x 85W = 340W
            • Just compare this to the dramatically reduced wattage of 365W, and you’ll find out if you connect solar panels with different voltage and amperage ratings in series, the total output power is determined mostly by the solar panel of the lowest rating!
            • What is more, let’s imagine an ideal fictitious situation where the amperage does not influence the performance of the solar array – the total harvested solar power would be 515W (85W+126W+152W+152W)!
• Connecting solar panels in parallel is just the opposite of series connection and is used to increase the total output amperage of the array, and hence the total output power while keeping the same voltage
  • When you connect solar panels in parallel, the total output voltage of the solar array is the same as the voltage of a single panel, while the total output amperage is the sum of the amperage of each panel
    • The latter is only valid provided the panels connected are of the same type and power rating
    • Here is a parallel connection of solar panels of different voltage ratings and the same amperage rating:
      • • As you can see, things are getting worse, since the total voltage of the array is determined by the solar panel of the lowest voltage rating
          • We received 11% loss of installed solar power in the above example
      • Let’s see what happens when we bring even more diversity and connect solar panels of different voltage and amperage ratings in parallel:
        • Things are steadily getting worse, but it’s evident what you lose here as wattage is much lower compared to connecting different solar panels in series
• Both in series and parallel connection, plugging a panel of a lower power rating to the array drags the whole output power down
  • The lower the rating, the higher the loss of solar generated power
    • This, however, is much more evident for panels connected in series
  • If you want to get the maximum power from your solar array, you should only connect similar panels
  • Mixing different panels, whether connected in series or in parallel, ALWAYS reduces the installed wattage
  • If you don’t have any other option than wiring dissimilar panels, you should know:
    • For series connection – the same current rating of the panels is more important
    • For parallel connection – the same voltage rating of the panels is more important

• What size system do I need?
  • There is really no one size fits all answer to this – It really “depends”
    • Everyone has different power needs, budgets and space
    • How do I size my systems?
• General rules of thumb for sizing
  • Basic battery maintenance on travel trailers and 5th wheels = 100 watts solar
  • Basic battery maintenance on a motorhome = 200 watts solar
  • Conservative electricity usage = 200 to 300 amp hr battery capacity & 200 to 300 watts solar
  • Moderate electricity usage = 400 to 600 amp hr battery capacity & 400 to 600 watts solar
  • Heavy electrical usage (serious Boondocker) = 600 to 800 amp hr battery capacity & 800 or more watts solar

(Size your panel wattage at least as big as the amp hour capacity of your battery bank or greater – I prefer at least 1.5 to 2 times solar wattage vs. battery amp hours and closer to 3 times as much for Lithium battery based systems)

• Sizing by actual usage
  • Go out and use your RV “unplugged” (no shore power or generator)
    • You need a good way to monitor battery usage for this method
      • This could be a built in battery monitor or a voltage meter with a corresponding voltage table to indicate battery state of charge
  • Use electricity like you normally would (whether it be 12 volt or 120 volt), don’t change your habits (assumes you already have an inverter installed to meet 120 volt needs)
  • Go until your batteries are depleted to the lowest level you are comfortable with
    • This should never be below 50% SOC with lead acid or AGM batteries
      • I personally do not like to go below 65% SOC
    • If you are lucky enough to have a lithium bank this number can be as low as 10-20% SOC (or lower)
  • How many days did it take you to get to your low point and how much power did you use?
    • These numbers will be highly dependent on your battery bank size
• As an example (in idyllic conditions):
  • Assume a battery bank size of 250 amp hrs
  • Assume you can go two days before drawing your batteries to 50% state of charge
    • You would have used 125 amp hrs (250 x .50)
    • This means you used an average of 75 amp hrs per day (125 / 2)
  • Now we need to determine how many solar watts it will take to replace 75 amp hrs per day
    • A typical 100 watt panel produces an average of about 6 amps per peak sun hour
      • There are on average 5 peak sun hours per day (this is an industry standard number)
      • So a 100 watt panel produces about 30 amp hrs (6 x 5)
  • For the above example, two and a half 100 watt panels will replace the 75 amp hrs used per day
    • 75 / 30 = 2.5
    • Since we cant cut a panel in half, three 100 watt panels will supply the power needed with a little cushion

• Sizing a system for modest usage (there is a lot of math here so not the best method for a large system)
  • If you only want to power a few small appliances in your RV, you can determine the power consumption of those items and build a system around those numbers
  • First, determine the wattage of each appliance you wish to power
    • This can be done by the ratings on the appliance label or with a device such as a Kill-A-Watt
  • Multiply the wattage by the total run time of the appliance (here are some examples)
    • Hair dryer uses 1000 watts for 7 minutes per day (7/60) x 1000 = 117 Watt Hours per day
    • TV uses 100 watts for 2 hours per day 2 x 100 = 200 Watt Hours per day
    • Satellite receiver uses 8 watts for 2 hours per day 2 x 8 = 16 Watt Hours per day
    • Microwave uses 1500 watts for 10 minutes per day (10/60) x 1500 = 250 Watt Hours per day
  • Sum the total daily watt hour consumption 117 + 200 + 16 + 250 = 583 Watt Hours per day
  • To convert this to Amp Hours, divide it by 12 volts 583 / 12 = 48.6 Amp Hours
    • (Remember Volts x Amps = Watts)
  • Add this number to your existing base load (12v lights, 12v appliances, parasitic draws, etc.) for your total usage
  • For this example, assume 40 Amp Hours of base load 48.6 + 40 = 88.6 Amp Hours total
    • 88.6 / 30 = 3 (approximately)
    • Three 100 watt panels in this example will supply the power needed with no cushion

• Physical roof space
  • The physical roof space available on your RV will be the biggest limiting factor on the number and size of panels available to you
• Obstructions and possible shading
  • Don’t install panels up against large objects such as air conditioners, antennas or roof vent covers because these objects will shade your panels
• Find panels of smaller physical size to take more advantage of available roof space
  • It’s a game of Tetris and you want to see how many blocks (panels) you can jam in a confined space
• Remember to leave pathways on the roof for maintenance and inspection (of the panels and the roof in general)
• Remember to take into consideration the available carrying capacity of your RV as well
  • You don’t want to overload it