MPPT controller size and Renogy/ Canadian Solar thoughts

[HelenLo]

Hey all!

We live onboard a sailboat. We went through the process of installing a DIY bank with EVE 280 cells. We're very happy.

At the same time, we had a solar arch built and doubled our solar to 700w comprising of 4 x Victron 175w mono solar panels, each wired into their own 75/15 MPPT charge controller (into a cerbo and controlled by a REC BMS). For reference we have an 840ah bank of lithium at 12v.

The panels just aren't performing. Some shading but even in peak, direct sunlight without shading, the max input I've seen across the 4 panels is 550w out of 700w. That's best case scenario. The standard is averaging about 100w per panel.

This is rendering our hard work building the arch as useless as we're not keeping up with our energy demand to keep our bank topped up.

I've looked at taking out the two middle panels and replacing with one Canadian Solar 705W TopBiHiKU7 (CS7N705TNAG) Bifacial panel. This is 24v and our system is 12v. I believe this is fine as long as I don't exceed the specs for the MPPT

In addition, I want to take off the two outside panels and replace with two Renogy RSP200D bifacial panels.

Being the Renogy panels are bifacial, should I increase the size of the charge controller to benefit from the increased input. If so, what size? The Victron calculator keeps crashing on me and seems to freeze on suggesting 150/60. Which I think is too big. Or am I missing something? Would the current 75/15 controllers be OK?

150/60 seems to be the preferred size for the 705w panel.

 

[sunshine_eggo]

MPPT charge controller (into a cerbo and controlled by a REC BMS). For reference we have an 840ah bank of lithium at 12v.

The panels just aren't performing. Some shading but even in peak, direct sunlight without shading, the max input I've seen across the 4 panels is 550w out of 700w. That's best case scenario. The standard is averaging about 100w per panel.

Sounds GREAT!

Panels are rated for CELL temperatures of 25°C. In full sunlight it's rare that they're cooler than 45°C. This cuts power by at least 10%. Consider also that you're not perfectly perpendicular to the sun and 550/700 = 78.6% of rated is actually pretty good.

Check the NOCT ratings for the panels for more of a real-world expectation of performance.

I've looked at taking out the two middle panels and replacing with one Canadian Solar 705W TopBiHiKU7 (CS7N705TNAG) Bifacial panel. This is 24v and our system is 12v. I believe this is fine as long as I don't exceed the specs for the MPPT.

Correct.

In addition, I want to take off the two outside panels and replace with two Renogy RSP200D bifacial panels.

Being the Renogy panels are bifacial, should I increase the size of the charge controller to benefit from the increased input. If so, what size? The Victron calculator keeps crashing on me and seems to freeze on suggesting 150/60. Which I think is too big. Or am I missing something? Would the current 75/15 controllers be OK?

MPPT are rated in OUTPUT amps.

15A * 14.4V (peak LFP voltage) = 216W

Check the specs on your MPPT, it show a similar max power. You put anything more than 216W on the MPPT, and it won't use it.

150/60 seems to be the preferred size for the 705w panel.

705/14.4 = 48.9, so a 100/50 would be better and more economical.

The idea that you're going to get a major boost in harvest with bi-facial is likely optimistic. You'll get some, but what coming from the back side is about what you get from a cloudy sky...maybe 10%. In full sun, high off the ground and snow on the grown, you can get some significant gains, but be prepared for disappointment as it's unlikely you'll exceed rated.

 

[Rocketman]

Per the data sheet the mppt 75/15 can only deliver 220w or 15amps @12v. Since they are mounting flat-ish you never get full power out of them. I would not change them out. You will never see enough time above 220w to justify the expense. It is fine putting the higher voltage into these - it just helps them start earlier in the morning.

Now your center 705w panel - I figure you have two choices:
1. A mppt 100/50 - can handle 700w. This is probably what I would go for. Being flat - probably will not get enough more power to justify anything else. But you may get clipped occasionally- depending on how well the Bifacial work for you. So maybe the 150/60 might be better.

2. A mppt 150/60 - you will capture everything with this one. But it will cost more.

You didn’t give specs for the big panel - so I assumed it’s Voc is below 75v? If not then go with the 150/60.

Remember you will need probably #4awg wire between the mppt150/60 and your batteries/bus bar.

Good Luck

 

[mikefitz]

150/60 seems to be the preferred size for the 705w panel.

Seems OK. Since the charge voltage for most of the charge profile will be 13.5 volts or slightly higher, the 60 amp unit will have capacity to 800 watts .

Renogy RSP 200D. Verify they are actually bifacial , the info I have seen suggests not. However they are 1/2 cet PERC cell panels, thus very efficient and handle shading better when in a series string.
The Renogy RSP220 DT is bifacial.

The 200 watt panels panels should be OK with the 75/15 giving 14 amps , assuming you get the full 200 amps.

The 220 bifacial would still be OK with the 75/15, but you loose a little around noon if you get maximum output. No experience with these panels, but unlike other bifacial they don't seem to use glass on the rear face. I may be wrong so check on this form of construction.

I suggest a Victron 150/45 with the two 220 bifacial in series, as an alternative.

The Canadian Solar 705 watt panel is huge and heavy at 38 kg, have you considered smaller panels for ease of instalation and redundancy?

550 watts out of 700 watts is not too bad when you consider the power reduction with temperature. In South Portugal, on my boat I have seen panel temperatures over 60 deg C.
Mike

 

[mikefitz]

Duplicate post

 

[HelenLo]

Thanks all.

This is really helpful.

The 705 watt panel is perfect to replace the two smaller panels without leaving any gaps. I can get a 555w Longi from Leeroy Merlin but it's not bifacial - but it is already in the Canaries. I'm struggling how to get the Canadian Solar 705w for a non trade sale!!

And a great point on wiring- this will have to go external to our arch.

 

[yabert]

I can get a 555w Longi from Leeroy Merlin but it's not bifacial - but it is already in the Canaries. I'm struggling how to get the Canadian Solar 705w for a non trade sale!!

You will not have a huge increase of solar power from a bifacial panel. Maybe 5-10% more.
Don't worry to use regular solar panel available.
If you don't want to spend a lot of money on high amps MPPT, I suggest you to stick with 4 panels in the range of 200-300W because with Victron 75/15 you are limited to around 195W (13V x 15A).