Matching MPPT controller to solar wattage.

[jonjo]

The Victron 75/15 mppt controller seems to represent the sweet spot in the range in terms of popularity and price. My plan is to fit 200 watts of solar capacity initially with provision to increase this to 300w in the future.

Would the output from a 300 watt solar panel array ever exceed 15 amps at an English Channel lattitude?

My understanding is that if the voltage of the panels (in series) exceeds 75 volts the controller will be damaged but if the panels are capable of producing more than 15 amps the controller will automatically limit its output hence the only downside is lost opportunity to pump more amp hours into the batteries.

 

[AntarcticPilot]

The Victron 75/15 mppt controller seems to represent the sweet spot in the range in terms of popularity and price. My plan is to fit 200 watts of solar capacity initially with provision to increase this to 300w in the future.

Would the output from a 300 watt solar panel array ever exceed 15 amps at an English Channel lattitude?

My understanding is that if the voltage of the panels (in series) exceeds 75 volts the controller will be damaged but if the panels are capable of producing more than 15 amps the controller will automatically limit its output hence the only downside is lost opportunity to pump more amp hours into the batteries.

It will almost certainly exceed 15 amps some of the time - watts = volts times amps, so at 12 volts you could get up to 25 amps. Of course, the voltage will usually be higher than that, but it is 15 amps at 20 volts. At my latitude (52.4567° N), I get a maximum of about 90% of the rated output of the panels on my roof, so at the English Channel, I'd expect a bit better than that, all else being equal.l

 

[Trundlebug]

If your panel performance is anything like mine then I think you'll rarely see anything like 15A..

I have a single 150w panel with this controller (thinking like the previous poster that 150/12= 12.5 A max.)
I therefore purchased this very same 75/15 MPPT controller, but have in reality never seen more than about 6.5A out of it, in mid June full sun around midday. In Norfolk.

So from my experience I think you'll be fine with this controller, even if theory may indicate otherwise.
With 300w you may get double what I get, but I doubt you will get more than 15A very often or for very long so it probably isn't worth getting a bigger controller.

Note, I have a semi flexible panel fixed across my curved sunroof.
If you have rigid panels which can be angled towards the sun, performance may be better.

 

[jonjo]

Note, I have a semi flexible panel fixed across my curved sunroof.
If you have rigid panels which can be angled towards the sun, performance may be better.

I forgot to mention that the panel mounting would be flat and horizontal without a facility to angle the panels.

In other respects your numbers are a touch lower than my initial pessimistic guess about peak amps.

An often quoted pragmatic formula is Rated Wattage divided by 20, times by an assumed 4 to 5 hours at peak amps = 15 amps max and 60 to 75 amp hours on a good sunny British day for a 300w array.

I have the panels and wanted to order the controller so that that I can experiment with series/parallel configurations in the garden.

 

[Trundlebug]

In that case I think you'll be fine with that controller.

From what I've read on this forum wiring in series is the option for best results.

 

[macd]

I have the panels and wanted to order the controller so that that I can experiment with series/parallel configurations in the garden.

If you're being that thorough I'm sure it's occurred to you to experiment with different degrees of shadowing in both series and parallel, but just in case...

We have 340W (4 x 85W) of horizontal panels which routinely reach 25A at a nominal 12V. That's in the Med, where the midsummer sun is about 7 to 15 degrees higher than your area, but I daresay yours will exceed 15A from time to time, if only by a little. Ours are wired in series on a stern arch and are usually subject to relatively little shadowing. Had shadowing been more of an issue, I'd probably have gone for port and starboard pairs.

Be very interested to learn what you garden research throws up.