Solar power systems for Recreational Vehicles have traditionally been roof mounted. While this is a convenient location and makes efficient use of unused space, it may not be the most ideal location. Since optimal energy production is the ultimate goal, the position of the panel(s) is critical. A 120 watt solar panel may be very powerful , but pointed in the wrong direction, angled incorrectly, or in the shade of a tree can cut daily energy production by 50% or more, or worse, render your expensive investment in solar useless.
For optimum performance, solar panels must be facing directly south (called azimuth). In Arizona, solar panels should be angled at about 33 degrees (called tilt). A slightly steeper tilt in the winter (50-60 degrees) and lower tilt in the summer (8-15 degrees) further improves energy production. Ideal tilt angles change with latitude. Therefore, the further north you travel, the higher the ideal tilt angle becomes.
PV and Marine solar systems are simple and require three main components. The first is the Solar Panel itself. For this application the panel should produce 16v-21vdc. There are many different manufacturers of these panels including Sharp, Kyocera, Solarland, and dozens of others, and they come in many shapes and sizes. The second component is a simple charge controller which prevents battery overcharging. The controller should be sized correctly for the type and number of solar panels. There are many different manufacturers of charge controllers including Morningstar, Blue Sky, Solarland, and many others. The third component is a suitable mounting system. Unirac is a very common manufacturer of solar mounting accessories. A mounting system that enables adjustable tilt is highly recommended. Drill some holes in your roof, add a few lengths of 10awg wire and a connection to the accessory batteries and you're in business. Or, avoid your drilling anxiety go portable.
Recently, portable solar power systems have appeared on the scene. These systems usually employ either Thin Film or Crystalline solar panel technology, are usually ground mounted, have adjustable tilt legs for optimum tilt angle, have a built in charge controller, gives you your choice of various battery connection accessories, and can be folded up and stored safely in a padded carrying bag. When you arrive at your destination the set up process takes less than 5 minutes. Unpack the bag, unfold the panels, adjust the tilt legs, set on the ground in a sunny location pointing south, and finally connect the wires to your battery. Thin Film systems are usually lighter and more flexible than Crystalline, but Crystalline systems are usually 4 times more powerful and take up much less space.
Charge controllers regulate the power coming from the solar panels to the batteries. They are a key part of any off-grid system and prevent batteries from over-charging. We will discuss two kinds of charge controllers: PWM and MPPT.
PWM (Pulse-Width Modulation) controllers are cheaper than MPPT but create large power loses. Up to 60% of power can be lost. This is because PWM controllers do not optimize the voltage going to the batteries. This limitation makes a PWM controller a poor choice for a large system. However, in smaller systems their low price makes them a viable option.
MPPT (Maximum Power Point Tracking) controllers optimize the voltage coming from the solar panels so that the maximum amount of energy is transferred to the battery bank. The maximum power point, or the optimal conversion voltage, will fluctuate with changes in light intensity, temperature and other factors. The digital optimization process performed by the MPPT controller find and adjusts to the maximum power point quickly. Sophisticated electronics are needed in MPPT controllers to do this, which explains their high price. There is a significant pay-off though: MPPT controllers are 93-97% efficient in converting power.
Solar charge controllers are usually mounted inside the passenger compartment of the PV and recessed in a wall cavity. While this installation looks good, it can sometimes be problematic. On larger PV solar systems where 20-40 amps of current flows through the charge controller, a great deal of heat is produced. Heat must be dissipated otherwise the charge controller will fail. Recess-mount a charge controller inside a hollow, unventilated wall cavity and then raise the ambient temperature to that of an ordinary summer day, and the charge controller will quickly overheat and fail. This is a very common problem. Instead, consider a surface mount controller with a good heat sink and mount it inside one of the storage lockers or somewhere good ventilation is found. Since some controllers are not waterproof, care must be taken to select just the right location. Oh, and never, ever locate the charge controller in the battery compartment. There are many reasons for this, the biggest of which are corrosion caused by battery off-gassing and the potential for fire should there be a spark.