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Solar panels and batteries; a complete 12V guide

There's a lot of confusion when it comes to 12V systems in 4WD's, Camper trailers and Caravans. It's not surprising, as there are more products on the market than ever before, and 12V gear isn't always straight forward. This post is aimed at making 12V systems simple to understand, so you can buy the right gear for your application.

I'm going to point out straight away that I'm not an electrical guru. In fact, I often don't enjoy working with it. However, I like to set things up once and do it properly, and that has forced me to learn enough about 12V electrics that I feel able to pass some information on.

For the electrical guru's reading this post, you may pick up terminology that is not perfect, and disagree with the way I've explained things. Feel free to leave a comment; I'm not perfect, but please know I am trying to explain this in a simplified way, and explaining that Voltage is the potential for energy to move is a little beyond the scope of this post.

Work out the figures for your system

I can't stress enough the importance of going through the math for your system. It's not complicated, and I'll show you how to do it. If you don't do this, you are wasting your time; anything you purchase may or may not suit what you want. Asking other people about their solar and battery setup is fine, but often the information is totally irrelevant as you will have different appliances, and use them differently.

Asking whether a 100W panel and 105ah battery will run your fridge is a waste of time without knowing what the fridge draws, what the ambient temperature is, and how you have attached the panels.

It takes time to look into these things properly, but its doable for everyone, and worth doing properly. Take the time to work it out and your system will function as you want it to, and you won't have to re-buy other bits of 12V gear to make your system work


Electrical terminology

Stay with me - this might look difficult to start with, but its actually very simple.

Watts - This is an instantaneous readout of power either being consumed or generated.

Amps - Amps is also an instantaneous readout of power either being consumed or generated, but it relates to voltage, which we won't cover.

Amp hours - Amp hours is the amount of power consumed (or generated) over one hour. You can work out amp hours by dividing watts consumed by 12. 600 watts of power used over 24 hours is equivelant to 50 amp hours.

Power consumption

We will start with the basics; how much power do you consume? Can you do anything to make them use less power? Are you running them in the most efficient way? A laptop charger for example, is extremely inefficient when run through a 240V inverter. Likewise, if you carry a generator around just to run your lighting there are better ways to do the same job. A fridge in almost every circumstance will use the most amount of power, so we will focus on these (especially when they are running as a freezer!).

Are your appliances energy efficient?


What power does your appliances consume?


3 way fridges

Inverters; what size and sine wave?



What type of battery should you use?

How many and what size batteries do you need?



Do you need a generator?


Solar panels

How does temperature and location affect solar performance?

Portable vs fixed solar panels

Solar panel regulators - PWR vs MPPT

DC-DC battery chargers

Cable size

Charging a trailer from your 4WD



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