Introduction: Calculate the Right Size and Type of Battery and Solar System for Your Motorhome | Solar Calculator 12V

By FreeGroup

Modern motor homes have a real hunger for energy due to their technical equipment. If you want to be independent and not always only on parking or camping sites, you can not avoid a solar system. How to calculate your solar system for your camper simply I show you in this post.

Since not everyone knows their energy needs ahead of time, I'd like to give you a few avatars or pointers here.

Step 1: Find the Consumer

Step 1 is usually always: Find all your consumers and calculate their power consumption. But this is exactly the problem. Usually you don't have any feeling for what it means when I say in advance that I want to charge 2 laptops, 3 cell phones, a hair dryer or even cook with electricity.


For this purpose I have built a software with which you can enter all your typical consumers in a MindMap and then you get automatically told by the software the power consumption and immediately sees the consequences - how long do I get around the rounds with my battery?


The software is free and available on Github and can be used for free. Open a new and clean canvas to create your own layout on https://freegroup.github.io/CampingElectricCalculator/#/map/new or use an already existing one as a good starting point: https://freegroup.github.io/CampingElectricCalculator/#/map/Aboveaverage200wLightCooler


Step 2: Choose Your Battery

The key element in such a system is always the battery. Typically, this is also the most expensive part. We take a relatively inexpensive battery at the beginning and see how far you can get with it. Of course, this can be easily changed and adapted it later on.


Choosing A Battery For Your Camper Or RV: The Cliff Notes

  • Economical choice: Flooded lead acid. This is the oldest technology in the bunch. If maintained properly, they still are the cheapest short-term and long-term. Maintenance is more involved and must be managed more carefully due to ventilation and liquid acid inside. It is not hard to do, but for small amateur systems they aren’t as appealing.
  • Low maintenance: AGM Deep Cycle. Over the long term, this is the most expensive battery because they wear out faster than the other two. In the short term, they are cheaper than lithium. They are common and all around a good starting point for most amateur installers.
  • Premium choice: Lithium LiFePO4 These batteries are just around the corner from being the best choice for everyone. Unfortunately, the high up front cost is a barrier to many.

However, if you calculate the used Ah over all charging cycles and lifetime of a battery, you get the cheapest with a modern LiFEPO4 battery. However, yes - the acquisition costs are much higher and pay off only over the lifetime of the battery.

Step 3: Add Some Fuses and Main Switch

The MindMap is designed in such a way that the simple rules of a circuit are naturally taken into account, thus helping the user to make as few mistakes as possible. A really important point is a main switch and an absolutely necessary fuse of the right size.

Thus one can insert the usual consumers only if one has inserted a switch+fuse into the MindMap. Let us do this first

Step 4: Add the Consumer

Now we add our first consumers. You can see very quickly and nicely how long the battery can run these devices without having to recharge the battery. You can now change the battery and see very nicely how the service life changes.  But what are the already 2 days autarkic? Then a little power should flow back into the battery. 

That depends on whether I am much with the vehicle on the road or I stay longer in one place. I assume that I am on average 4 days in the same place. The consequence is now, I need solar on the roof.

Step 5: Add Solar to Your System

However, you can't just clip a solar panel to the battery. The voltages and the charging curve simply do not fit together. Here you must first connect a so-called "booster" in between which adjusts the voltage and thus optimally supplies the battery.

After that, you can choose a solar panel that best suits you in terms of performance and price. You can then immediately see how the runtime and the charge level of the battery is adjusted.

As you can see from the charging booster, the duration of use is set to 4.5 hours/day. This corresponds to the average of sunshine hours / day within Germany. You can adjust this value according to the region you want to travel to. 


Step 6: Closing Thoughts

I find that the tool is very nice to have your needs and budget in focus. You can see very well why you need a larger solar system or whether you prefer to connect a charger coupled with the alternator of the car, because you are anyway not longer than 2 days in one place and you can thus charge his auxiliary battery with the alternator.


With all the testing you will of course quickly discover that not all configurations make sense. The tool warns you for this and tries to offer you a better alternative.


You can also click on the connection lines. Here, depending on the currents flowing between the components, the correct cable cross-sections are suggested. Well - it could hardly be better - could it?


So I wish you a happy configuration session and special requests and feedback are as always very welcome.