How to choose the best solar panels for a motorhome

Spread the love

Drunkenpom contains affiliate links. This means if you click on one of the links and make any purchase I will receive a small piece of the pie at no extra cost to you!!.

Own a motorhome, campervan or RV and crave a little more freedom than being tethered to a campsite hookup offers!? Then you my friend, need a solar panel. Here’s how to choose the best solar panels for a motorhome/ your home on wheels.

For many people out there, understanding solar panels and the technical jargon that comes with them is understandably, a daunting task. However, for myself after spending 10 years as a trained electrician and just generally being technically minded and interested in this sort of stuff means I’ve got a decent grasp of it. Does that make me sad!?

I will use this knowledge to break it down as much as possible so that anyone reading this article will understand what solar panels are about, what their requirements are and if they could actually benefit from installing them.

This way you will have the knowledge and confidence to buy the best solar panels for YOUR motorhome.

What do solar panels actually do?

Right, so the first thing we’re going to touch on is what a solar panel actually does. The full scientific answer to this is pretty complicated and boring but if like me this type of stuff interests you then you can read a good article on it here.

For everyone else the short more interesting answer is:

  • Particles of sunlight (photons) hit the surface of the solar panel
  • These particles knock electrons free from atoms
  • A flow of electricity is generated.

Once the photovoltaic cells have converted the suns light into electricity its time to harness that electricity. For this you’ll need a charge controller and battery to store the energy created by the solar panel. Trying to use the electrical current produced by a solar panel on its own doesn’t work well at all.

It’s OK for charging say, your mobile phone but imagine connecting your 12v Tv directly to a solar panel charge controller, your TV would probably work until a cloud covered the sun. Solar panels only really produce meaningful amounts of energy on a clear day.

Thick cloud can mean less than 5% efficiency.

A soon as it went cloudy the TV would be out of juice. You NEED a leisure battery of some description to smooth out the power supply to your devices.

In a nutshell: Sunlight > solar panel > charge controller > leisure battery = stored usable energy

Why do you need solar panels for a motorhome?

In all truth you don’t but like us, you require a little more freedom than travelling from campsite to campsite then a solar panel or two is what you need.

Fill your motorhome with 100 litres of fresh water, food, 6kg of propane, empty the toilet cassette and you’re easily good for 3-4 days of “wildcamping”. With this setup the only limiting factor is electricity.

A motorhome without electricity is pretty much useless. After all, nearly everything in your motorhome needs electricity to function.

For example: The toilet needs electricity for the flush, water heater and fridge need it for the ignition to light the gas burner, blown air heating system uses an electric fan, obviously lights, charging devices and not to forget your 12v TV.

In short not much in your motorhome will work without electricity. Your £20,000 motorhome is now closer to a tent with a bucket in the corner…..

Another good reason to invest in solar power for your motorhome is that most people don’t use their motorhomes too often and if just let to its own devices the batteries will go flat. Just think, your motorhome alarm needs electricity to function.

To mitigate this problem people would normally plug in their motorhome on their driveway which isn’t ideal. Also, what if you can’t keep your motorhome on your driveway and you need to have it in storage with no power!?

A solar panel as little as 50w is the way to go. This system would keep your batteries topped up even through winter:

Can you not just turn the engine on to charge the batteries!?

Of course you can yes! Is it a good idea? Not really!

To charge your leisure batteries while you drive to your next destination is one thing but to run the engine while stationary just to charge the batteries is not a great idea. Mainly for these 4 reasons:

  • The price of diesel – A diesel engine idling will use somewhere between 0.5-1 litre of diesel per hour. £0.65-1.30 per hour
  • It would take hours – Alternators are not really designed to charge batteries they are designed to feed loads. Depending on your vehicle it could take anywhere from 2-6 hours to charge 2 x 100AH leisure batteries. (£1.30-£7.80)
  • You’d be given the daggers off everyone – No one wants to pitch up next to the person who is running their noisy diesel engine all night.
  • Solar power is green, diesel is not – Solar power is green energy burning our dwindling supply of fossil fuels so you can watch coronation street is not.

What can you run off a solar panel?

There no clean cut answer to this but I’ll try to explain the science around this and then we’ll look into what me and Agne run off ours.

Firstly how much electricity do everyday devices take?

To begin to understand exactly what you can run off a solar panel we first need to look at the amount of electricity that these individual devices need to function and the terminology used.

Terminology:

To try and break it down – Solar panels are rated in watts or W and leisure batteries are rated in Amp Hours or AH.

So for example a 240W solar panel is capable in perfect conditions of generating 240 watts of usable current.

A 100AH battery is capable of storing 100 Amp Hours of energy at 12 volts.

To get from Watts to Amps you simply need to divide the watts by the voltage.

For example: 240 watts divided by 12 volts = 20 Amps. If the solar panel was to produce 240 watts for exactly 1 hour then you would have 20 Amp hours (AH) produced by the solar panel.

To put this into context, if the same 100AH battery was completely flat (not advisable) and the same 240w solar panel was in perfect conditions for 5 hours then in theory it would be enough to fully charge the battery.

240 watts divided by 12 volts = 20 Amps x 5 hours = 100 Amp Hours OR

120 watts divided by 12 volts = 10 Amps x 5 hours = 50 Amp Hours

The reason I’ve talked about charging a leisure battery is because most of the electrical demand is in the evenings when the solar panel is not generating any electricity and you’ll be powering devices from the leisure battery.

So that’s the scientific mumbo jumbo over with, I hope I’ve not lost you. Now to look at what some of the most common devices take:

  • TV: 20-30 watts or 1.6-2.5 Amps
  • lights (3w LED): 3 watts or 0.25 Amps
  • 3 way fridge: 120 watts or 10 Amps
  • Laptop charger: 60 watts or 5 Amps
  • Fan for blown air heating: 12 watts or 1 Amp
  • Water pump: 20 watts or 1.6 Amps
  • Phone charger: 12 watts or 1 Amp
  • Low wattage kettle: 150 watts or 12.5 Amps
  • 12v hairdryer: 168 watts or 14 Amps

Now you know how much electricity common devices take, it’s now time to look at an example day of usage. So I will give a general estimation of a standard days usage:

  • TV: 2 hours @ 2A = 4AH
  • Lights: 2 lights for 4 hours @ 0.5A = 2AH
  • Laptop charger: 2 hours @ 5A = 10AH
  • Fan for heating system or cooling: 4 hours @ 1A = 4AH
  • Phone charger: 4 hours @ 1A = 4AH
  • Low wattage kettle: 2 hours @ 12.5A = 25AH
  • Hairdryer: 0.5 hours at 14A = 7AH

*I’ve not included “3 way fridge” in this calculation because it would flatten the Leisure battery in around 8 hours. It’s just not really feasible unless you buy 500w worth of solar panel and 4 x 100AH leisure batteries and live somewhere it’s sunny every single day.

Add all of that together and it equals 56AH used in a day. Considering you should never run a leisure battery down more than 50% means that the first day away from a power hook up you have already run out of electricity.

If this is example is close to what you would use then Ideally you’d have 2 leisure batteries wired in parallel to give a total of 200AH and 100AH of usable energy at a 50% discharge rate.

How long would it take for a solar panel to replace 56AH?

Well to work that out there are many different factors to look into, mainly:

  • total wattage of solar panels,
  • if it’s cloudy,
  • what time of year it is and
  • what latitude you’re at.

There’s no real way to put a time on it but our 275w panel on a clear summers day in July will easily kick out 200w or 16.5A between 10am and 2pm. At that rate it would take around three and a half hours to replace the energy used the day before.

However, on a cloudy day in April our 275w solar panel might only generate 40W or 3.3A of power between 10am and 2pm. At that rate it would take 17 hours to recharge the battery.

On cloudy days you’ve got to be more frugal with the electrons. It really does pay dividends to be aware of the weather forecast.

How much do we use?

The official figure is 5750AH in 6 months but what do we use to get this number?

We charge 2 laptops, 2 phones, 2 cameras, watch tv, use lights, water pump and never ever worry about running out of electric. As I said earlier we might be a little more frugal if its raining for days on end but in all honesty I don’t think we had to.

We even run the 3 way fridge off our leisure battery sometimes, if it’s a cloudless day our solar panel can produce more than enough power to run it.

What different types are there?

Although solar panel technology is advancing all the time, in both cell type and manufacturing process, there is only still 3 types that are of any use on a motorhome or campervan. Monocrystalline, polycrystalline and the thin film flexible ones.

Here’s the pros and cons of each:

Monocrystalline

Monocrystalline cells are made up of one silicone crystal. These panels are generally the most expensive on the market due to their more complicated manufacturing process.

Pros:

  • Most efficient (up to 22%)
  • Lower efficiency loss in warmer weather. (slight difference)
  • Look slightly better (can’t see it on the roof though)
  • Rated to last 25 years

Cons:

  • 2nd most expensive here (£150 for 200w)
  • Heavy (15.5kg for 200w)

Polycrystalline

Polycrystalline solar panels are made up of multiple silicone crystals and are easier to manufacture than monocrystaline panels.

Pros:

  • Cheapest here (£130 for 200w)
  • Rated to last 25 years
  • Slightly lighter (14kg for 200w)
  • Not the best but still pretty efficient (up to 20%)

Cons:

  • None really. Best all-rounder.

Thin film semi-flexible

Thin film or semi flexible solar panels are around the thickness of a human hair and are the newer solar technology.

Pros:

  • Very light (4.2kg for 200w)
  • Easy to install (some are sticky back)
  • Can be mounted on curved surfaces (overcab bed)
  • Rated to last 25 years.

Cons:

  • Expensive (£450 for 200w)
  • Least efficient (up to 13%)

To sum up which is the best type in a paragraph:

If you’ve got loads of roof space but little unused payload then go with semi-flexible. If you’ve got limited space but a big motorhome payload, go for the monocrystalline. Finally, if you’ve got a bit of both and want the most bang for your buck go with the polycrystalline.

Simples…..

What size is best?

Who says size doesn’t matter!? With solar panels it certainly does!

The bigger the surface area the more of the suns electric giving rays you can catch. First thing to do is measure the spare space on your roof. Decent wattage solar panels are big. Our 275w panel is roughly 1.6 meters tall by 1 meter wide.

Make sure you have enough space…

This all depends on what you want to achieve, whether it’s simply keeping the leisure battery topped up while your motorhome is not in use over winter. Or do you want to build the ultimate off-grid machine and never want to see another electric hook up unit in you life!?

To keep the battery topped up while your motorhome sits idle on your drive over winter, a 50w panel with a cheaper PWM solar charge controller will suffice.

On the other hand, if you want to run all of your home comforts as mentioned earlier then you’ll likely need at least 250w of solar panels, a decent 20A MPPT charge controller and two good 100ah leisure batteries.

From my personal perspective: We get by pretty well with our 275w panel but the more the better, especially for those prolonged cloudy days.

Are portable solar panels any good?

As well as permanent roof mounted solar panels there are also portable, folding solar panels but are they any good?

In all honesty, I have no first hand experience but the people I know that use them are pretty impressed by their effectiveness. As with everything, there are good points and bad points.

Some of the good points are:

  • You can use them in more places than just on your motorhome or camper Do you have a boat or allotment that could use some solar power?
  • No need for fitting – Either paying a professional or drilling holes into your motorhome yourself is never good.
  • You can adjust the angle – Solar panels being flat on the roof is not the most efficient way for them to be mounted. Having portable ones, you can adjust the direction and angle to follow the sun throughout the day to gain maximum power.

And the bad side of portable solar panels?

  • They ain’t cheap – You’re looking at over £300 for a 150w system but that also comes with built in charge controller.
  • They’re bulky to transport – The same 150w panel is 100cm by 50cm and weighs in at 15kg.
  • They can be stolen – leaving £300 worth of gear outside your motorhome while you go off exploring Lyme Regis…. I don’t think so!

Do I need an inverter as well?

In a word, no!

You don’t need an inverter as well, but do I find ours to be one of the best things we bought for our motorhome!? HELL YES!

A £60, 600w pure sine wave inverter, a few strategically placed double sockets and we have 230v mains power all over our motorhome no matter where we are camped.

What is an inverter?

An inverter is an electrical device that connects directly to your leisure battery and converts 12v DC from a leisure battery to 230v AC that your standard household appliances use.

Some people will disagree with me saying that it is a good investment because of the outdated notion that “they’re very inefficient and waste too much electricity”.

Maybe back in the day that was correct but I can assure you, this is no longer the truth. Just an old wives tale.

Fair enough, its never going to be as efficient as something that is designed to work on 12v but my inverter uses around 4w extra to power my 240v TV. At that rate it’s not really worth thinking about.

Especially by the time that you’ve spent lots of money buying all of the 12v adaptors to charge your laptop, your camera etc you could have just bought an extra 100w solar panel and mitigated the whole problem….

An inverter just makes life easier. Period!

Just whatever you do don’t go out buying a 3000w inverter so that you can plug in your domestic kettle. The inverter would be fine but your leisure batteries wouldn’t last until your 10th cup of PG tips.

What else do you need?

Buying a solar panel is only part of the equation as you can’t just wire solar panels directly to your leisure batteries because the solar panel will just keep charging, constantly. Resulting £200 worth of ruined leisure batteries.

Between the solar panels and leisure batteries you’ll need whats called a solar charge controller. A solar charge controller is used to determine the state of charge in the leisure batteries and than works out what voltage and current is best for topping them up. Once the leisure batteries are completely full then the solar charge controller switches to a trickle charge mode to keep them there.

There are two different types of solar charge controller. The cheaper PWM and the more efficient MPPT charge controller. I definitely recommend spending an extra £30-40 to get the MPPT charge controller as they are up to 30% more efficient than PWM ones.

As well as a solar charge controller, there’s lots more bits you’ll need in order to fit a solar panel to your motorhome:

  • Solar cable
  • Mounting brackets
  • Correct rated MCB with enclosure
  • Cable entry gland
  • MC4 connectors

The easiest way to make sure you get all the right pieces is to by a ready made kit.

Can I install solar panels on my own?

Of course you can. I fitted it onto our motorhome in less than 3 hours. Fair enough, I used to be an electrician but the fitting of solar panels is pretty simple for anyone who’s pretty handy with the tools.

The only real bad part to it is having to drill holes in the roof of your pride and joy. Holes in the roof is the last thing any motorhome owner wants but as long as you seal them up well with a bit of Sika 512, they’ll be no leaks!

I was in a rush when I fitted ours and forgot to take my camera along hence why I haven’t written a how to post on this but here’s a video on youtube.

What do we have?

Me and Agne have a 275w panel, a 20A MPPT charge controller and 2 x 75AH leisure batteries.

The panel: After much measuring and research into different size and wattage panels, it turned out that due to the layout of roof windows etc the best option was to get one big 275w panel. Even at 100cm x 165cm it was the most wattage we could get over buying multiple smaller panels.

The MPPT charge controler: Its a 20A Tracer MPPT charge controller. One of the plus points is that although its only rated up to 240w (20A) you can actually wire it up to 480W (40A) of panels without problems.

This means on a sunny day some energy (anything over 20A) is wasted but on a cloudy day you have twice the panels. So instead of generating maybe 90w your 2 panels are generating 180w.

You’re probably thinking why don’t you just buy a 40A MPPT controller? They’re expensive and need bigger, more expensive cables.

Also, The charge current should not exceed 20% of the AH capacity of the battery. As an example, one 100AH battery should not be charge at a greater current than 20A.

Another good thing about the tracer 20A MPPT charge controller is that you can buy an optional MT 50 charge monitor. Although it’s not really useful for telling you how much charge is left in the batteries (only a hydrometer or standing voltage can do this) it does enable you to tell when they are fully charged and how much energy is produced by the solar panel each day.

tracerer mt50
All-focus

At the time of writing this our 275w panel has produced 69 kilowatt hours or 5750AH since the beginning of March. Bare in mind though one the battery is full and there is no demand the charge controller stops counting.

So the 5750AH is what we have actually used in the 6 months. The solar panel could have produced much more.

It also lets you input your own charging parameters. This way if you have sealed lead acid batteries you’ll want one set of parameters and if you have some traction batteries you’ll want another set of charge voltages.

The batteries: These came with the van and are two cheap 75AH Lion leisure batteries. I was going to change them when we installed the solar panel but they work well so I’m leaving them until they die!

Where’s best to buy solar panels from?

Obviously the web is awash with companies selling solar panels and equipment. You really are spoilt for choice. Although there are different brands of solar panels, it is not something that you should pay too much attention to.

A solar panel is a solar panel. Some expensive German made one is only going to harvest as much energy as a cheaper Chinese one. Give or take 5%. Instead of buying a 100w branded panel for £200 you’d be better off buying a 200w cheaper brand panel for £200.

I bought my solar panel from Bimble solar as they had the correct size panel I was after at a very reasonable price. For the most convenient and biggest selection I recommend Amazon.

There are some really well priced kits including everything you need to install your own, plus you get the security of buying through Amazon as well as plenty of customer feed back and reviews.

For example this kit is perfect for people who love to wild camp:


Spread the love

Leave a Reply

Your email address will not be published. Required fields are marked *