- Light Intensity. The brighter the sun shines, the more power is produced. As an example, if an installed panel receives 1000 watts per square meter of sunlight, (a Standard Test Condition*), it will produce its fully rated output wattage. If the sun produces 500 watts per square meter of light intensity, then the panel can only pump out half its rating. 100% of a panel’s output rating is basically only attainable at high noon and a few hours on either side.
* Panel manufacturers apply what is called “Standard Test Conditions” (STC), to calibrate panels
during the manufacturing process. Solar panels are subjected to a “flash test” to calibrate
the panel to deliver the equivalency of 1000 watts per square meter of sunlight intensity while
maintaining a cell temperature of 77-degrees F. The flash test determines a panel’s STC rating.
It is akin to the EPA mileage ratings for new automobiles. Not really reality, but something
constant for the sake of comparison.
- Shade. RV applications are always susceptible to periodic shading of solar panels. Antennas, satellite domes, storage pods, air conditioners, campground trees, local topography, etc., can all occasionally cover a portion of the cells on solar panels, thereby reducing its relative output rating. Tests have shown that only a partial shade covering just a few of the individual cells can reduce the panel output as much as 50%.
- Cell Temperature. Plainly put, the hotter each cell in the panel, the more voltage drop is experienced through that cell and subsequently through that panel. Always opt for a panel that can produce an operating voltage of 17.0 volts or more; the higher, the better.
- Sunlight Angle. Unless equipped with a motorized mount that can track the sun across the sky and keep the panels squarely pointed at it throughout the day, some of the sunlight will be reflected off the surface of the panel, resulting in some power reduction. Tilt mounts exist that can minimize this loss, but personally I feel it’s better to simply have enough panels up there to offset losses attributed to the angle of the sun’s rays.
- Poor Electrical Connections. All electrical connections have an integral resistance that leads to voltage drop and reduced effectiveness and the poor connections have even more resistance. Correct conductor size and the proper types of connectors used are important considerations with any RV solar installation. Clean, dry and tight are appropriate attributes to strive for concerning all electrical connections.
- Parasitic Drains. Most battery display monitors and charge controllers are predestined to consume some of the electricity produced by the solar system they are monitoring and controlling. Such “self consumption” is typical for powering the LED display, internal logic calculations, etc.; current use that will never reach the battery bank, but must be factored in when “sizing” a solar charging system nonetheless.
Some controller models incorporate full-time 45-amp charging capability with temperature compensation and battery equalization. (The equalization charge is basically a very slight overcharge at regular intervals to help prevent battery plate sulfation and to allow all cells in each battery to reach the proverbial full charge). Advanced charge controllers employ user-defined parameters for battery voltage, size and type. Typically, the four charging stages found in the top of the line controllers are: bulk charge, absorption charge, float charge and the previously mentioned, equalization charge.