Before you order solar panels for your RV, it would be wise to determine how many solar panels you will need to meet your power demands. Determining how many solar panels you will need to sufficiently charge your RV batteries seems like a daunting task. In fact, it is not that difficult but it does take some thought and planning. In some instances it may even take some educated guessing on your part.  The good news is that if you make an educated guess and you are wrong, it is not that hard to add additional panels. The key is to leave yourself with some wiggle room with the equipment that you buy so that you can accomodate additional panels down the road if needed.  If you purchase a 10 amp charger and the solar panels you have are already producing 10 amps, then you have no wiggle room and lack the capacity to add additional panels unless you plan on buying a larger solar charger.  If, however, you plan carefully as I have and leave yourself some head room, then you can easily upgrade by adding additional panels later.

So let’s get started. In order to determine how many solar panels and what capacity solar panels you will need, it is important to try and figure out:

  • How many Amp Hours of energy will you be using per day and drawing from your batteries, and therefore, how many Amp Hours of energy you will need to replace each day.

The reality of the situation is that these are not easy questions to answer. In fact, what most people find (as I have) is that once you have estimated and calculated the amount of Amp Hours you think you are going to use and thus need to replace, you will most likely be wrong. Why is that? Well, as hard as you may try, you are most likely going to underestimate, overestimate, or forget about something important such as the “phantom loads” on your electrical system which are also drawing power from the batteries. “Phantom loads”? What the heck is that? “Phantom loads” are appliances that are constantly drawing power from your batteries without you even realizing it, such as the CO2 detector, refrigerator, or radio memory. It is hard to determine in advance how many hours of TV you are going to be watching or to know exactly how long you will listen to the radio each day. Similarly, our habits change, and we do not use our equipment the same way every day. So for the most part, this is going to have to be an educated guess that you have to test out in reality before you hit the road.

Just because you are likely to be wrong, however, it does not mean that you can skip this step. Although it is difficult to estimate your exact power needs, you still need to try in order to give yourself a good idea of how much energy you will need to replace each day so you can determine how many solar panels and what size solar charger to install. Additionally, this exercise will help you to determine how many batteries you will need to store all the energy you plan to use each day. I am not going to discuss batteries here; that is a topic for another day. Additionally, I will leave the energy calculations for a separate article about estimating power needs. For the purpose of this article, I am going to use some hypothetical numbers to demonstrate how to determine how many and what size solar panels you will need.

Before we go on, let’s define an Amp Hour so there is no confusion. In the simplest of terms, 1 Amp Hour is equal to a battery supplying 1 Amp of energy for one hour.  Therefore, if a battery can hold 5 Amp Hours of energy, then it can theoretically supply 5 Amps for 1 Hour or 1 Amp for 5 hours.  If it holds 50 Amp Hours, then it can supply 50 Amps for one hour or 25 Amps for two hours (25 Amps x 2 hours = 50 Amp Hours), etc.

Let’s assume for the purpose of this article that you have determined that you are going to consume 100 Amp Hours of energy per day and that you have sized your battery bank appropriately so that you can store that amount of energy without draining them below 50% capacity. Knowing that you need to replace 100 Amp Hours of energy each day allows you to determine how many panels you will need in order replace the energy that you plan to use. Since you can technically use any size and number of panels to meet your needs, the decision is really going to be determined by cost, space, and suitability to task.  To make things easier, I suggest that you use the smallest number of the largest panels that will meet your needs.  Mounting and installing 3 large panels is much easier than installing 10 smaller panels to meet the same need.

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