Installing a solar charging system can have great benefits for RV owners looking for an alternative way to keep RV batteries charged. If you are a do-it-yourselfer, you may be thinking of designing and installing your own solar charging system. There are many DIY videos (like my own) to learn from, yet each situation tends to be unique and many questions go unanswered — like this one:
“I have *** solar panels, how should I hook them up?”
This is a difficult question to answer without simply saying “Well, that depends…” So here are some general answers to related questions that may help guide you towards a solution to your specific situation.
Question: How much solar charging power do I need?
Calculate the total Amp Hours capacity of your battery bank (the one you want to charge with solar). Simply match the number of Amp Hours with Watts from your solar panels. For example, a 400 Amp Hour battery bank should have approximately 400 Watts of solar charging power to adequately recharge within a typical day of use.
Question: How should I connect my solar panels to my solar charge controller?
This really depends on what kind of panels and solar charge controller you have or are planning to buy. When connecting multiple solar panels, it is usually better if all of your panels have the same specifications. Connecting them in series or parallel will then depend on the type of Solar Charge Controller you plan to use.
PWM charge controllers will use the incoming voltage needed for to charge your 12, 24 or 48 volt battery bank. Voltage generated above the charge voltage in a PWM system will simply go unused. For example, if you have a 12 volt system, then your PWM charge controller will use the voltage it needs for 12 volt battery charging (usually up to 14.6 volts). Any voltage generated above that amount will get discarded.
Solar panels designed specifically for 12, 24, or 48 volt systems will work very well with PWM charge controllers. When wired in parallel, they will maintain the appropriate voltage output. For higher voltage solar panels, it is better to consider an MPPT charge controller.
MPPT charge controllers are designed to accept higher voltage levels. They are also able to convert excess voltage to additional charging amps. This is one of the big advantages of an MPPT charge controller. Multiple solar panels can be wired in series to output higher voltages. The MPPT charge controller will take all of the incoming voltage and convert any excess into more amps. As an added bonus, higher voltage from your solar array results in lower current (amps). This allows you to use smaller wire between your solar array and your charge controller.
Question: Should I wire my solar panels in Series or Parallel?
If you have an MPPT charge controller and closely matched panels, then wiring them in series or parallel should yield the same result. Watch the experiment in the video for a demonstration of this.
If you have a PWM charge controller, it will be better to wire your solar panels in parallel keeping in mind you may need thicker cable.
Finally, if you have mismatched panels, using an MPPT charge controller and wiring your panels in series will give you the best result.
For more answers to common RV solar questions, go check out our RV Solar Frequently Asked Questions.
Good luck! As always, do your research and know your limits before taking on any project.