Solar power for motorhomes – an introduction

If you wild camp in your campervan or motorhome for extended periods of time, solar power is for you. Opting to keep your appliances powered and your batteries topped up with free energy is a no brainer. Although, getting your head around the different options available can be a tad daunting. Hopefully this article will simplify the components, systems and help the decision making process if you are considering solar.

Without solar your starter battery and leisure battery will be reliant on your engines alternator for charge whilst wild camping. However, for a one off cost you can install a solar charging set up. A relatively small panel system costing around £300 could provide enough energy for all your off-grid camping.

Overview

A solar charging system for your campervan will generally consist of three main elements:

  1. Solar Panel – traditionally roof mounted.
  2. Solar controller – regulates and directs power generated by the solar panel.
  3. Battery – stores controlled power for use.

Solar panels for your motorhome

Motorhome and campervan roofs can be cluttered with vents, aerials and various different fittings. The roof space you have available will dictate the size of solar panel/s you can fit and the power generated. There’s a lot of info online to calculate the power typically used by the appliances you have and therefore the size of solar panel you require. These calculators are a good place to start in gauging what accessories and appliances are using the most power

Once you have an understanding of your consumption, my advice is to fit a panel as big as your roof space allows. If a 100w panel will satisfy your needs but your roof will allow a 200w panel, my advice is to fit the bigger panel.  The more power you can generate the more options you have to store it and make use of it.

Solar panel size, weight and power

One 200w panel will require less space and will weigh far less than two 100w panels. The cost of a single 200w panel will be less and the installation will be simpler. You can’t generate too much power, the solar controller will regulate the power supplied to your batteries. If you have two batteries the controller will charge them simultaneously until full. Once one is full, the controller will concentrate its charge to the depleted battery until that too is fully charged.

Polycrysytalline or Monocrystalline Solar Panels

Simply put Monocrystalline panels are more efficient. Monocrystalline panels will be smaller than Polycrystalline panels of the same power output. Monocrystalline panels are more expensive but if you’re tight for roof space compare the dimensions of equal power outputs in both types of panel. For instance my Ford Transit Leisuredrive has only one position suitable for mounting a solar panel. I can fit a 100w Monocrystalline panel (£170) within this roof panel. The biggest Polycrystalline panel I could fit in this space is 80w (£80).

Solar panel charge controller MTTP or PWM

It seems it’s the controller that is most debated in solar power discussions. MTTP is the most efficient type of charge controller but work best with larger panel systems. I noticed that manufacturers and dealers put their smaller panel kits together with PWM controllers. I contacted several manufacturers for their opinion and they all said the same:

The advantages of MTTP over PWM is only noticeable when the panels output is significantly higher than the batteries charging voltage”.

For instance, the 100w monophonic panel that I’m planning to install has a charging output of 17.5 volts. A car batteries charging voltage is 13.8 volts.

MPPT controllers also boost the amount of current going to each battery, this varies in amount depending on weather, temperature, state of battery charge, and other factors. There are no downsides from using a MPPT controller on a solar panel with a voltage close to the battery voltage but the benefits are much lower than those gained from a larger panel system

Dual Battery Solar Controllers

If you want your solar panel to charge both your leisure and starter batteries you’ll need a dual battery solar controller. You can also use a dual controller to charge a starter battery and a bank of multiple leisure batteries too. A dual battery controller will allow a basic amount of user control over directing the charge to each battery. Adding a control panel to your controller will give even more control and display info back from your batteries and solar panel. A dual battery controller can be used for a single battery system too and should you want to install a second battery in the future, you’ll be ready.

Batteries

A cranking battery plus a leisure battery is a fairly standard motorhome set-up. Cranking batteries are designed to provide a big surge of power instantly. They cannot withstand being ran down much below full charge for any length of time without suffering permanent damage. A leisure battery can regularly be ran low and even flattened without any detrimental affect.  Make sure you are using the correct battery type for the intended job. Good quality batteries in top condition will accept charge efficiently and hold their charge longer.

If you have a battery meter in your van keep an eye on how much charge your batteries are holding and how they deplete from regular use. If you’ve not got a battery meter like what you’d find on a ‘zig board’ you can use a normal multi-meter.

Monitor the batteries in all conditions and through periods of normal and heavy use. Remaining fully charged constantly would suggest that your setup is delivering more than enough power. If you have enough power through strong sun days but your battery levels dip during cloudy times it maybe worth you considering fitting another or a larger capacity leisure battery. Just bear in mind the added weight that additional batteries add to your vehicles weight. However, an additional battery may make full use of the power you’re able to generate which could be used to see you through a dull period until the sun’s shining again.

3 thoughts on “Solar power for motorhomes – an introduction

  1. Sadly, much of the detail here is simply incorrect.

    No monophonic or polyphonic (that’s synthesisers) but monocrystalline or polycrystalline.
    And the distinction between them is not as you assert either.

    In every case, mppt is better than pwm, but on a small system the extra cost might not be worthwhile. In fact, mppt is more important for a smaller panel, becasue there is less power to waste.

    • Hi,
      Thanks for the input.
      Regarding the controller, I think that’s the articles summary. The quoted paragraphs are from two solar experts and dealers. All info shared is the result of speaking to solar system dealers whilst researching my own components. Can you let me know what you consider incorrect?
      Thanks again

  2. Like it says in the article, “It seems it’s the controller that is most debated in solar power discussions”!

    I think the article is helpful and does not contradict the expert advice. Iain says the panel gives out 17.5v and he only needs 13.8v, therefore any small loss is tolerable.

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