I was lucky to inherit two 100w solar panels with the van – they just need to be wired in.
I used an external waterproof junction box mounted on the roof of the to take the panel cables into the van via compression glands and then into the MPPT solar controller charger (MPPT30 solar charger – bad choice in hindsight, see last section of this post).
For more about the electronics see the 12V electrics and wiring
A look at my solar panels
Like most things of this nature, I like to poke around for a while with a screwdriver and multimeter to see what’s what before I do anything else.
The panels came with no labels on them; no indication of min/max voltage or power ratings. I googled ‘mono-crystalline solar panel’ and the ones with 4 by 9 solar cells are 100W so its probably safe to say my panels are 100W each.
Back in November I checked that each panel was giving the same voltage – if they disagreed then it would probably indicate a dead cell somewhere but all seemed well. Despite some cells having visible hotspot damage (scroll down to photo), both panels gave the same voltage of 18V and a closed current of 4.33A so around 80W of power. Not bad for November, although it was a clear sunny day and the panels were directly pointing to the sun.
Installation and wiring
I wired the panels in parallel just because there is no point wiring in series (higher voltage) unless you have an MPPT controller with decent DC-DC converter. Maybe I will experiment with other configurations at some point in the future
Solar panel damage- hot spots?
It took me a while of searching and asking on forums what these marks were on the solar cells. I’ve decided it must be hot spot damage from prolonged shadowing of a cell. The loss in power due to the shadowed cell will be dissipated across that cell causing hot spots and eventually burning the cell out.
Solar charge controller
I found out there are 2 types of solar controller; normal PWM (pulse wave modulation- pulses of varying duration) and MPPT (maximum power point tracking – efficiently down-converts a higher DC voltage from the panels to the lower voltage used to charge the batteries)
Without much further research, I went straight onto Ebay and bought an MPPT controller for £42.
I asked for a part refund and just forgot about the chances of getting super efficient MPPT charging for now. This unit does have some nice features such as load shut-off setting so the batteries will not discharge less than, say, 11.8V and also overload protection.
Lessons learnt
This post deserves to end with a ‘lesson learned’ :
- Cheap Ebay stuff from China really is hit and miss
Just cannot resist.
In hindsight, I would buy this MPPT solar charge controller instead of this half arsed MPPT30.
Great setup. Maybe worth looking into finding a cover while on the road flying debris, stuff falling from trees while stationary and if they aren’t cheap quite an expensive loss. Have you got engine charging up your battery supply as well?
Alright Andy, yeah that is a good point. I never thought of something as sensible as that. I guess I’ll have to just be careful and see how it goes (no parking under coconut trees etc). There are so many precautionary measures I could take but things would never get finished if I did them all. Its going to be the case of if a potential problem does cause a fair bit of trouble then I’ll solve on the go. I have split charging from the alternator for backup so its all cool.
I know I’m late to the party, but I was wondering if it was possible to put the panels UNDER the rack, that way you have a grating over them that will act as protection. Of course, that might block some of the sunlight and affect output.
Hey Jon, yeah it would be possible but more difficult mount on the plastic hi-top roof. Also, like you say, the output will be affected — quite dramatically as well. And will cause damage to the panel due to one cell being more shadowed than another; hot-spotting.
Has anyone ever had a broken panel on their van roof?
I picked up small 16V O/C panels on Ebay, will use 2 in series for my 24V boat. Lots of pairs in different places will simply add the currents together into the controller – so no shadowing problems.
Do you know much power your using on a daily basis?
Thinking of doing the same with mine but with a split relay from alternator i was thinking maybe an 80w solar panel would do the job but im not sure how much power id end up needing reallly.
Did a similar thing on my boat down the Thames. However I knew the panel I used had a Vpp voltage when it gives maximum power is about 26 Volts, so not much power lost with a simple, cheap 24V controller.
There is no blocking diode at the back of the panel. It is always a bypass diode.
The blocking diode is normally present in the Charge controller unit.
I thought the same, but when I looked at the back, one diode is in parallel with all of the cells (the whole panel) and the other diode is in series, with its cathode floating on the positive terminal – that’s the one I’m calling the blocking diode. But yeah a charge controller wouldn’t let the batteries charge into the panels anyway.
I was surprised that the cells were not split up with more bypass diodes though
Yes it could be MPPT (I have an electronics degree). But where is the definition of MPPT? – there are millions!
It may well try a 3 or 4 panel voltages/currents, do a quick V * I = Power calculation and stay with the best. Whether that is better than a bog-standard battery voltage controller is debatable. If your panels have a maximum power point of about 14Volts you won’t need an MPPT, because a cheap and cheerful 13.8V regulator will automatically produce maximum power. Yours have an O/C of 18volts and I bet they do fine at 13.8volts [look at the V/I curves of most panels and superimpose your 18V OC..see how they are close to the peak power at 13.8V]
Anyway, driving to a sunny country and parking the panels facing the sun will produce far more power than being in the UK!
I mean, yeah to some extent it could be MPPT – they all vary in resolution and sweep rate etc. But, I’d expect an MPPT controller like this to have an efficient DC-DC converter (a buck converter, right?) and I don’t see one. It’s no big deal though for me. This controller has worked really well over the past 15 months and has some nice features with the display
Hi there,
Where did you get the junction box to?. Need one of these to put cables through my roof.
Cheers, Gary.
Not sure if you are still rocking this setup, but If possible consider a bracket where u can alter the angle of the panels (front hinged say) when stationary, 45 – 30 degree would be great ( depending where you are) but you will see yield jump quite considerably!
Hi Mike,
I am just getting on to my solar panels. I went for a single unit 200w with a 20amp MPPT controller. Anyway, I have been using your book a lot and looking at your diagram I cannot see any fuses between the panels and the controller, or between the controller and the battery. Would you say this is needed or not? I was thinking a 10A inline blade fuse in each case? Also, I am using 4mm wire though 5mm is recommended. What do you think? 4mm is rated at 36A so way more than it will produce. Would really appreciate the help.
Hi Mike, love the conversion and the ebook. Could you tell me whether I have to earth the solar controller direct to the battery or can I do this to the chasis? And does this mean I can still earth the various electrical items to the chasis?
Thanks craig
Are those panels hail resistant? I want to use this method on my van.
What is the maximum voltage for solar panel on t converters ?
Hi,
Can you tell em what size cable you used to connect the solar charge controller to the battery and fuse box? I was thinking of using 10mm but it is too big to fit in the charge controller.
Hey Mike, curious, was a 30A controller enough to run all the appliances through the controller? I want to wire mine up like this, but i’m worried lights/diesel heater/fridge/water pump will be too much draw? Whats the benefit in wiring the load through the controller?