Off-Grid Solar System

Nate Murphy
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The solar system is probably the coolest part about the van conversion.

After three months I have not connected up the split charger (the cables are just laying beside the battery should I need to) and nor have I had to connect the van up to mains.

Off-Grid Solar System the van conversion guide

Solar power is AMAZING. This single panel on the roof of my van easily gives two people ALL the electricity that we need and want and, apart from the set-up, it is essentially free forever.

Solar Basics

The solar system comprises of the following key components;

  • Solar panel
  • Cables
  • Solar Charge Controller
  • Batteries
  • Remote monitor

The solar power goes in to the panel, to the solar charge controller – which intelligently distributes this power, either to the battery, or to your appliances that you may be using.

The Solar Charge Controller (if you get a good one) also does a few other clever things – like intelligent battery charging, preventing over voltage and maximising the usable energy from your panel.

Types of panel

You could go into crazy amounts of technical detais – but there are two main types; poly-crystaline and mono-cyrstaline.

Honestly I did not care to research enough in to the difference, I do not think there is enough of a difference to worry about and, in reality, for your van conversion it does not matter too much. Just get something with enough Wattage and from a reputable supplier.

This is my panel spec:

  • Manufacturer: Perlight Energy
  • Type: Mono-Crystaline
  • Model number: INE 300MB-72
  • Wattage: 300W
  • 2m cable attached
  • Pretty cool guarantees:
  • 10 year manufacturing guarantee
  • 12 year performance warranty of 90% of original power output
  • 25 year performance warranty of 80% of original output

This panel is really designed to go on a roof of a house. When I ordered it they assumed I wanted to order by the pallet load.. but when I said I only needed one the supplier kindly posted one for about £30 postage.

You can get all sorts of different panels; flexible glue on ones, a set of smaller panels for an array… but I like simplicity and to have just one big panel works well in my mind. It cost about £190 (including shipping).

How big do I make the solar panel array?

Basically, based on the calculation of Watt Hours of your power needs – just work out how many useable sunlight hours you might have and divided the Watt Hours by that. This will give you what you need for your solar system.

Sunlight hours



Energy required



< Amount of output required per hour to deliver Watt Hours

Div by sunlight hours



<Watts delivered per hour - needed based on above sunlight hours

So technically I need a 100W panel to serve my needs. However you sometimes get cloudy periods, end up parking under trees and in winter, with shorter days and a lower sun – you get harvest less power.

On that basis I want my panel to deliver 3x the above Wattage. Hence getting a 300W panel.

This means even if there is a week or so of bad weather, where only 30% of the normal sunlight reaches the panel through the cloud my batteries will stay nice and charged.

My system

I have a single 300W solar panel on the roof this is linked up to a 40Amp charge controller. I use 2x 140AmpHr batteries.

Originally I bought a 10Amp charge controller – but I was quickly getting an ‘over voltage’ warning. Over voltage is essentially damaging to your batteries.

When I bought the charge controller I had no idea that you have to get a charge controller that matches the Wattage of your solar panel system. I didn’t realise there would be such a variation in size for smaller systems.

Solar Charge Controller

Beware there are some cheap 'MPPT' solar charge controllers.. which just are not.

In Europe these brands have presence;

I am using this one; EP SOLAR Solar Charge Controller; 40 Amp MPPT

I think this is not a bad alternative. SOLAREPIC Solar Charge Controller, 40 Amp MPPT

In the US Morning Star, I think, are a pretty popular choice.

What size Solar Charge Controller?

To work out the Ampage solar charge controller you need you can use the following basic formula;

(Solar-Panel-Wattage / Voltage) x 1.25 = Charge controller Ampage

The ‘x 1.25’ bit is just a bit of margin for safety.

For my system:

(300W / 12V)*1.25 = 31.25

I decided to just get a 40Amp charge controller. Perhaps more than I need but at least I know for sure that it can easily handle my panel and prevent potential over voltage.

Solar Charge Controller type

There are two types, standard and MPPT. Go for MPPT if you can afford it. If it is really cheap it is probably not MPPT – there are a few chinese ‘mppt’ charge controllers which just aren’t.

MPPT (Maximum Power Point Tracking) Solar Charge Controllers can be 25 to 30% more efficient. If you are getting a good solar array – you might as well get a good charge controller to get the best out of it.

You can also get a remote monitor so you can see what is going on with the solar panel. It is not a need-to-have but it is pretty cool to see what is going on. I recommend having one – they are not too expensive either.

Note: the MT-50 as shown below did not seem to work with the 10Amp EPSolar charge controller that I got in the first place (it was too small anyway).

Off-Grid Solar System the van conversion guide

MT-50 Remote monitor

Attaching the panel to the roof

As part of my stealth agenda I wanted to have the solar panel have a profile as low as possible.

My van came with these attachment point rails along the sides – I cut these up to make a bracket. The bracket folds one way – I probably will not need to use this feature – but it is useful to have – and it means I am flexible when it comes to doing repairs to the panel.

Off-Grid Solar System the van conversion guide

I bolted the panel to the roof using four 6mm stainless steel bolts. Once tight, as the nuts would be behind my gladding work, I used glue/sealant and spread it over and around the nut inside the van to help keep it secure.

Off-Grid Solar System the van conversion guide
Off-Grid Solar System the van conversion guide

Hinge side – double nuts to make it more secure. I put a couple of stainless washers between the two hinging ends.

Off-Grid Solar System the van conversion guide

Lift side (bolt holds bracket in place)

Bringing the cables inside

I used a junction box with a hole cut in the bottom to take the cables from the solar panel into the van. This actually sits underneath the solar panel and I glued this on with ample amounts of sealant glue.

The cables follow down one of the areas I left with a gap in the insulation.

Additional Cables

I needed to buy a couple extra cables to reach my solar charge controller. The cable type you will probably need to search for is 'MC4' cables.

Off-Grid Solar System the van conversion guide

MC4 connectors

Off-Grid Solar System the van conversion guide
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