MPPT controller per panel or not?

[davethedog]

Afternoon all,

Looking to install some semi flexible solar panels on my Hunter Legend 41 sailboat. Looking to put 2 x 100W semi flexible panels on the sprayhood soon and then add a further 2 or more to the bimini in the future when we head to the Med next year.

Now I know the best option is for an arch at the stern but we have enough metalwork there as it is and dont really want to spend £4000 or so for an arch.

So, the question is am I better having an MPPT controller for each panel wired in parallel to maximise the power output. Or would a single large capacity MPPT controller be just as good (with the capacity to handle the later purchased panels also)?

DTD

 

[lw395]

When you get any shading, or the panels point different ways, separate MPPT controllers will be a little more efficient.
The modern approach is to have separate MPPT controllers for smaller and smaller groups of cells within a panel.

The question is, will the little extra efficiency pay for the extra controller?
I'd guess not, but I could be wrong.

 

[William_H]

Nah just go for one controller. olewill

 

[Dantp]

We put to smaller ones for 2 reasons:
It was cheaper (victron mppt's)
It gave some redundancy if one fails we don't loose all our solar.
Doubt there is much benefit in performance but that is just me guessing.

 

[Bobc]

Buy your first 2 panels and a small MPPT now, and decide later (you can always sell the MPPT on here and get most of your money back). The common view is to wire pairs of panels in series to get about 40v to the MPPT, so for redundancy it might be better to have each pair going to it's own controller anyway. You may also find that 2 panels is adequate.

 

[cueball]

I purchased the voltronic duel battery MPPT. Excellent piece of kit very pleased, about the same price of 1 victron.

 

[davethedog]

thanks all and think will go for 2 controllers, one for the first lot of panels and then add another with the later panels.

DTD

 

[Mikedefieslife]

Two controllers are often cheaper than one larger one capable of handling the voltage or amperage.

A pair of victron 75/15 will do you nicely, and most likely be the same or cheaper than a 100/30

 

[ghostlymoron]

I thought that having 2 controllers going to the same batteries caused them to get confused by sensing the controller output voltage and thinking it's the battery voltage. I may have misunderstood though.

 

[chrisclaydon]

MPPT controllers perform better with a higher voltage, therefore you should connect enough panels in series to ensure the input voltage is well above your bettery voltage, even in low light, otherwise your charger will only operate well in direct sunlight. Also check the maximum input voltage for the controller and don't exceed it - panels can produce at least 20% over their rated voltage in tropical conditions with reflection off sails etc.

On the other hand, if your panels are connected in series then a small shadow on part of one panel will almost completely knock out the output from the whole string, therefore you should only do this if the panels in the series are all close together and pointing in the same direction.

The correct balance of multiple controllers vs series connection will depend on where you intend to use the boat (how bright the sunlight) and how likely the particular installation location is to have shade on just one panel.

If you find yourself contemplating connecting panels in parallel then multiple smaller MPPT controllers is almost certainly better.

We have 2 controllers with 2 adjacent panels connected in series on each plus 1 controller with 4 adjacent panels in series. this setup performs well in low light and is not too adversely affected by shade patches.

 

[chrisclaydon]

PS watch out - some of those semi flexible panels are absolute rubbish and a high proportion will fail completely after just a few months. Make sure you buy only branded panels from a reputable seller with a good warranty. We had big problems with the "Sunpower" panels. Like a shadow, one burnt out cell on one panel takes out the whole string! Avoid the cheap PET coated ones, false economy. Make sure they are ETFE coated to survive the marine environment.