When it comes to solar power for your 4WD, Caravan or Camper trailer, the age old question is this; should you go with fixed panels, or portable ones? People will argue all day over which is better, and I’m here to settle it once and for all.
Fixed panels are attached to your vehicle or trailer in a way that makes them difficult to remove. Usually this means bolts, but sometimes they are riveted or siliconed in place too. You’ll find them mounted to roof racks, on top of caravans, on boat loaders and sometimes even angled as wind deflectors on the top of 4WD’s. These are wired up permanently, and feed power into your batteries whenever the sun is out.
Portable panels are plug and play – you pull them out of their case or bag, plug them into wherever they need to go, and face them into the direction of the sun.
What are your individual circumstances?
There’s no one size fits all here, and this is what makes all the difference. Some people only run a small 12V fridge and can comfortably get away with an 80 watt panel and a portable battery pack. Others, like us, run a myriad of lights, chargers, a 55L fridge and also a 55L Freezer, and our solar needs are dramatically different. Once you start needing more than about 200W of solar though, portable panels become a struggle as the physical size and weight is just too much to move around.
If your power consumption is relatively low, you might get away with a single set of folding panels that you move around a couple of times a day. However, if you are using a fair bit of power you need to have a think about different options.
Whats the difference in performance between fixed and portable panels?
Solar panels work the best when they face directly at the sun. In the morning, as the sun is coming up, you want them almost vertical and facing the direction of the sun, to capture the rays. As it moves up, and north, you want them to tilt down, until at mid day where they should be almost flat, and then doing the exact opposite of the morning in the afternoon.
Where you live, and what season it is will determine the angles your panels should sit at, bearing in mind that you want them to face directly towards the sun for maximum charge.
Now, I found a very interesting table, which tells you how much power you will generate in different parts of Australia, relative to the angle your panels are sitting at, and the direction they are facing.
It’s interesting to note that in most cases, as long as your panels face north and somewhere between 25 and 70 degrees, the difference in power generation throughout the day is fairly insignificant. You can check this out here - Solar pitch and angle table.
You will get best results if you angle your panels correctly and move them around to follow the sun. There’s no doubting this, and many fixed commercial solar systems automatically track to follow the sun. For the 12V world on 4WD's, caravans, camper trailers and boats, how much moving of panels do you want to be doing each day? Can you get away with fixing a few panels instead?
What should you consider?
Amount of power used
This is the starting point for determining your solar and battery requirements. You need to ensure that the solar setup you purchase is going to easily cover what ever you remove from your batteries.
You can work out total consumption fairly easily, in amp hours. From there, your solar needs to easily be able to replace what you consume every day, in about 4 - 6 hours of sunlight. Although you will probably get more hours of daylight, the actual period where solar will generate decent amounts of power is substantially less.
Available space for fixed panels
A huge constraint for many people is where they can mount fixed solar panels. Caravans have it super easy; you have more roof space than you can poke a stick at.
Camper trailers are almost impossible to mount big, fixed panels on unless you make use of a boat loader, like we have. 4WD’s are also not the easiest; if you mount them on top of roof racks, then you lose the ability to put gear up there, or if you do, it wont generate any power when you have things on top. Some people have made slides under their roof racks, which can work very well.
If you mount them as wind deflectors at the front of a roof rack then you don't lose any space, and you get the benefits of better fuel economy.
Ambient temperature where you are travelling
I mentioned above that fridges use a lot more power as the temperature rises. They say 5% more power for every degree of increase in outside temperature. Lets say it goes from 25 degrees outside to 40, you are going to use a whopping 75 percent more power to maintain the same temperature in your fridge. For those who do their first trip to the tropics, it can be a shock to see their batteries and solar system not keeping up, as you need that much more energy to keep things cold.
Over size your panels
A good method regardless of fixed or portable panels is to over size your solar. Cloudy days, high ambient temperature and shade all hugely affect the amount of solar power you need, and its always better to have more than less.
How often you have access to other charging
A lot of people do no free or low cost camping, and that’s fine. It makes it real simple; if you have power from your vehicle as you are driving along, and then power from 240V camp sites when you arrive, solar is barely a problem.
However, if you try and avoid 240V sockets at all costs, then you may find your solar needs a serious setup. Some people never stop for more than 24 hours at a time, and this too means your vehicle can do most of the charging. We often stay in one spot for many days without running our vehicle and as a result have to rely 100% on solar keeping up without the aid of 240V chargers or the vehicles motor.
Battery bank size
There’s no point having a massive solar system and no where to store the power. Come sun down you will go through a fair bit, and if you haven’t got enough you will be in trouble quickly. Unless you go down the path of Lithium, try and keep your batteries above 50 percent state of charge. That means, for every 100 amp hours of batteries you have, you should only be using 50 of them. Want to know more? Check this out - Are you damaging your 12V batteries?
How much you want to spend
Set a budget, and stick to it. Solar and batteries are substantially cheaper today than they were 5 years ago, but you can still spend a lot of money on a good setup. I blew the budget for our camper trailer solar setup, and although it is magic, it wasn't cheap.
A decent solar regulator will make all the difference in getting power out of your solar panels. MPPT chargers are ideal, and something reputable is a good idea. Victron, Enerdrive, Redarc and Projecta are well known gear.
Decent thickness cable
The best solar system will be hugely let down by cheap, thin copper cabling. Make sure that the cable you run suits the amount of power you are moving, and the distance you are moving it. If you are running panels 10 metres away, you want copper cable that will comfortably move the power without huge voltage drop and causing excess heat.
Keep your panels out of the shade
A lot of people don't realise that just a hand print can drop your solar panels efficiency by about 50%. You only need one branch shading your panel, and you will be generating almost nothing. Having a way of seeing this in real time is absolutely fantastic. Many regulators will show you this, or you can buy an inline amp metre, which is absolute gold.
Have a think about what happens when things go wrong. Can you make your vehicle charge your trailer? Can your trailer charge your vehicle? If your solar regulator dies, is it all game over when you are thousands of kms away from the nearest town? What will that mean for you?
Solar, batteries, chargers and copper wiring isn't light. I have seen some caravan setups that are over 150kg, and that is a lot of weight to carry around. If you are already pushed for weight capacity, then it could put you over the edge. If you don't know what your vehicle or trailer weighs, you need to head to a weighbridge ASAP.
What are the benefits of fixed solar panels?
- No setup time or effort; they are constantly running and you don’t have to move anything around
- They can be big panels as you aren’t moving them on a regular basis. Some people even use house panels, with the right regulator
- They can double as wind deflectors, if you mount them in such a way
- Theft of panels that are bolted or glued down is much harder. Portable panels are very easy to steal!
- Not moving them around, so less chance of damaging them
What are the issues with fixed solar panels?
- They won't track with the sun
- Parking in the shade results in little to no power generation
- Exposed to the dirt and dust, so you need to clean them (and this can be very hard if they are hard to get to - think a 3 metre tall caravan!)
- You often end up setting up camp around the sun for solar, and not around the best location for comfort, access or shade
Can fixed panels be made portable?
Now, I will quickly point out that some clever people have designs where fixed panels can easily be removed, and relocated if necessary. This is a very smart solution; only moving the panels when there is a need to do so, otherwise they just stay in their ‘fixed’ position. In my mind, this is the best solution as they only come off when you really need them to, otherwise you can kick back and enjoy your camping experience!
What do we use?
We started off with a permanent panel on the previous 4WD which only just kept up, and bought a set of folding panels to substitute. I soon got sick of unpacking them, setting them up and moving them around before packing them away every time we left that I went back to permanently mounted panels.
We now travel with 200W on the Dmax, and 400W on the camper trailer, which are all permanently wired up and charging when the sun is out. I still carry the 180W folding solar panels for dire emergencies, but hate having to use them. I reckon they might come out 5% of the time, and that's the way I like it.
The conclusion; fixed or portable solar panels?
For us, the conclusion is very simple. Fixed panels, if you can mount them in a decent way, are far better than portable ones. We never have to spend time moving panels around, and if you oversize your fixed panels then you should be in the same situation.
However, there will be times where fixed panels are a pain, and won't do what you need them to (think setting up under trees) and having a set of portable panels that you can fall back on is clever.
The final conclusion is this - you need a solar system that is going to suit your requirements. They may be the same as us, or they may be wildly different. I prefer to kick back and enjoy my camping rather than worry about battery voltages and moving portable panels around.
What do you use? Does it work well? Do you want to change it?