Solar electrical system in a camper van: how to design and install

Last updated on 24 Nov 2022 by Thierry

One important (among others) topic to deal with when working on a van conversion is your electrics. Ideally while being off-grid, you would like to be able to charge your phone(s), laptop(s), having a fridge, some lights, and maybe a water pump, pending which stage you want to go. The best way to achieve energy independence is to install a solar electrical system in your campervan. We have prepared this guide to walk you through the process, based on our experience.

“But why would I install a solar electrical system on a campervan?“, you may ask.

In a nutshell, even if connecting a cooling box on the 12V DC Lighter Socket Outlet of your vehicle or getting some light at the back is OK while you drive, it is certainly not OK if you intend to stay somewhere for a full day and maybe night. Except if you are not planning to go anywhere after because your battery will be flat… And you will be stranded, hopefully not in the middle of nowhere!

So, that’s where you need to plan your electrics for your conversion properly.

This article will go through the different steps, using our Mitsubishi Delica L400 campervan conversion as real-life material.

Disclaimer: This post describes how we have designed and installed our own solar electrical system. This is based on our own research, for your benefit. However, even if we have experience, we are not considering ourselves electricians. As working with electricity can be very dangerous, we suggest you read the different manuals that come with your components. And if you have any doubts, look for qualified help before performing electrical work.

Designing the solar electrical system for your campervan

Step 1: what do you want to connect

First, start by making make a list of what functionalities you need for your vehicle. For us:

• charging mobile phone (quantity 2)
• charging laptop
• having some lights (quantity 4)
• keeping food fresh
• washing capabilities (dishes/ basic shower)
• keeping the starter battery charged (trickle charging)

Trickle charging would be an option for most of the conversions. In our case, because we are not using our van during the cold months for extended periods of time, the starter batteries suffer, losing charge progressively with a risk of getting damaged. A solution to keep the batteries charged at all times is to have a trickle charger. Trickle charging can be done with most of the standard battery chargers you plug into your garage. Otherwise, if you don’t have a garage, like us, then a solar panel-based solution is a good solution. A standard solar trickle charger is a small solar panel left on your dashboard but if you are planning to install some solar panels on the roof, why not use them directly?

Step 2: understanding how this whole thing works

Before we start designing the solar electrical system for our campervan, it is good to know how this works in principle. The sketch below illustrates what the main components are and how they interact with each other:

• The Sun is providing the energy that we want to convert into electricity
• The conversion into electricity is made by the Solar Panel
• The electricity then transits via the Charge Controller, and from there:
  • Trickle charge the engine Starter Battery
  • Charge the Leisure Battery
• The Leisure Battery connects to Sockets:
  • USB or cigarette lighter outlets for 12V DC circuits
  • Home-type sockets for 110/ 240V AC if needed, via an Inverter. It is not shown on the sketch/ not part of our build at this point.
• The Leisure Battery feeds the Lights through the Charge Controller. The controller will disconnect the lights if the battery is running low.
• The Sockets feed the devices/ appliances (Phone, Laptop, Fridge, …together with everything else we plan to connect!)

Step 3: how much power each of your functions/ devices will use

The data should be available directly on your device, or otherwise from user manuals, datasheets, or the internet. Sometimes, it is a bit difficult to find out.

For chargers (phone or laptop), the information provided as input (e.g. 100-240VAC & 0.35A) can be misleading as it’s the maximum value the charger can accept.

For those devices, it is more realistic to consider the output values (5V & 2.0A). Calculate the power (P = UxI = 5 x 2 = 10W) and add a safety coefficient (there is some energy loss in the charger, that’s why they become warm). Standard charger efficiency is about 80% to 90%, so the corrected power would be 10W * 1.2 = 12W “worst case”

For items such as LED lights, where you do not really have a converter then the efficiency is 1. If it is not 1, that will still be of little impact.

To this first power usage list, which is per unit, you need to multiply per the number of each device type you might use, and then get the total power usage.

Based on our list from Step 1:

This value is the total maximum power draw you could have while using all your devices at the same time.

Notes:

1. LED lights are considered 100% efficient. If not, the difference will not be so massive.
2. 44W is the power-rated input (DC) from the manufacturer, which is basically what is fed into the fridge.
3. 25.2W based on voltage and current from the manufacturer datasheets.

Step 4: how many hours per day are you planning to use the devices

No explanation really needed here, it is quite straightforward (but let me know if it’s not!):

Note:

4. The fridge will be connected 24/7 but will not be running all the time. The average running time is estimated at 33% of a day = 8 hours (considering several sources giving “22 % average running time at 32 °C ambient temperature and 5 °C inside the unit” for a CFX-40W)

The grand total value is the maximum energy consumption you could have per day.

Ideally, you will add a margin if you wish to connect more appliances or the same but for a longer time. Rounding at 1000Wh means you have “space” for using another device for nearly 127Wh. For example, recharging the laptop for another 1.75h, or connecting an additional device.

Step 5: which leisure battery capacity for your system

Once you know how much energy all the devices together are going to use, you will need leisure batteries.

A leisure battery differs from a starter battery as it is designed to power appliances by releasing a low level of energy over a long period of time. In comparison, the starter battery provides a burst of energy to start the engine when required. Leisure batteries can use different technologies, the most common one being lead-acid-based.

To determine the size of the battery/ batteries, you need to know the Amps-hours you need (batteries capacities works in Amps-hours). To do so, you just need to divide the daily energy usage by the circuit voltage. As the vast majority of cases are a 12 VDC circuit, like for our campervan, then we have 1000/12 = 83.33 Ah

Important point: a lead-based leisure battery cannot be discharged more than 50% of its capacity. This would damage it badly and shorten its life.

Having this 50% limit in mind, in order to be able to use 83.33Ah we will need a 166.67Ah capacity battery, rounded at 170Ah for convenience.

From there, you would have 2 options: 1 single 170Ah battery or 2 smaller 85Ah (or close to this value).

Step 6: solar panel charging system

Getting the good solar panels

So now, having our batteries and knowing how much energy we will be using, we have to be able to charge them. This is done via solar panels. To calculate the power needed for solar panels, you need to consider the average hours of daylight.

Being in the UK, and probably not going to use our van before March maybe even early April, I will consider an average of 5 peak sun hours per day (where the solar panels will be the most efficient).

Because we will be using 1000Wh of energy per day, our solar panel system must be able to recharge our batteries by at least the same amount if we want to be self-sufficient and with no need to drive the van around to recharge the batteries.

That means the power of our solar panels will be: 1000Wh/ 5h = 200W

Now, this is a theoretical value.

Don’t forget there are clouds in the sky (nice title for a song/ book/ movie!). On cloudy days, your panels will still be charging but with a drop in efficiency of about 25%.

This means in our case that we should consider a solar panel system of 200W *1.25 = 225W minimum.

And the same question for the batteries, that we will need to answer a bit later: 1 single panel or 2 smaller units?

Solar charge controller

The solar charge controller is another key component of the solar electrical system that you need, located between the solar panels and the leisure battery.

The controller automates the charge of the battery and protects it, by:

1. preventing overcharging the battery:
   • It is as bad for the battery to get overcharged as to be discharged excessively. Overcharging would damage the battery, it might even explode!!
   • Solar panels are basic components, generating as much voltage as they can, not knowing they are generating too much for the battery. The controller protects the battery by reducing the voltage.
2. monitoring the voltage of the battery:
   • Another way the controller protects the battery is by detecting when the battery’s voltage is too low. If the voltage drops below a predefined level the controller disconnects the load from the battery to avoid it from being drained.
3. stopping reverse current at night:
   • At night, solar panels are not producing current. Because they are not generating, they receive current from the battery and they are not designed for this. The controller prevents damage to the solar charging system by stopping any current from flowing back into the solar panel.

They are 2 main types of solar charge controllers. Without entering into the details:

• PWM (Pulse Width Modulation): 75% to 80% efficiency
• MPPT (Maximum Power Point Tracking): 92 to 95% efficiency, but more expensive.

Up to 25% of the energy generated by the solar panels will not end in the battery with a PWM charge controller, and up to 8% for an MPPT controller.

These values need to be factored into our calculation for the solar panels. The corrected power for the solar panel(s) is 225 * 1.08 = 243W (MPPT) or 225 * 1.25 = 281W (PWM).

Trickle charging

At the beginning of this post, we listed trickle charging as one of the functions we need but it did not appear anywhere in the post so far. The reason is quite simple: the trickle charging function is not a device as such, but a functionality offered by a specific type of solar charge controller: dual battery controller. It allows connecting two batteries to charge (leisure battery and starter battery). The idea is to allow a small portion of the current to go to the starter battery when it is not full. Also, because we have a bit of margin in our system (remember the extra 127Wh from earlier), the trickle charging should go unnoticed.

Bill of Material: everything we need for our electrical system

Now that we have designed our campervan’s solar electrical system, we can list all the components we have chosen for our build:

…. And it is Coming soon!

Installing the solar electrical system in a campervan

That’s where the fun begins…. And it is Coming soon!

The final word

We have written this (quite long!) guide to share our experience with the design and installation of solar electrics. In this process, we have learned a lot and tried to put everything in writing, to answer all the questions we had.

We hope you have found in this post useful information for your own project, but if you have a question, or we got something wrong, or something is not covered, feel free to leave a comment 🙂