Solar panel / charge controller matchup

[Ziggy]

I'm planning to install a solar panel on my boat. My main constraint is very limited space, so I would like to squeeze out as much power as possible from a small panel. I'm currently considering a single 160W Renogy RNG-160D-SS panel with a Victron MPPT 75/15 charge controller. I have 2 Group 24 FLA batteries holding ~80 Ah each (no room for anything bigger). I sail mostly in Maine, with occasional cruises to Canadian Maritimes.



My question is this: the Victron Owners Manual states that he controller will not turn on until the panel voltage is at least 5V above battery voltage and they recommend 36 cell panels, assuming 0.5V per cell. The Renogy panel is only 32 cells, but according to their specs Voc = 22.9V and Vmp = 20.2V, so in theory it should work fine with the Victron. Can anyone confirm that it does or offer any practical experience with this combination in a climate typical of New England, Canada, or Northern Europe? How many Ah /day could I reasonably expect?

[sailorboy1]

5v above battery voltage is nothing to a mppt controller. Might delay the charge starting for 5 minutes in morning. Don't worry about it, you will get more power with the 22v panels and mppt controller. Don't over think it was it all averages out not matter what you think.

[kenbo]

+1 on what sailorboy1 said. You can expect about 40 to 45ah per day. More if you can orient the panel perpendicularly to the sun several times a day.

[Ziggy]

Originally Posted by sailorboy1

5v above battery voltage is nothing to a mppt controller. Might delay the charge starting for 5 minutes in morning. Don't worry about it, you will get more power with the 22v panels and mppt controller. Don't over think it was it all averages out not matter what you think.

I agree, if the panels really behave as advertised. I guess the only way to be sure is to buy a panel and try it.


I was less concerned about the start-up delay than about performance on a cloudy or foggy day

[Nord Sal]

I'm using that same charge controller with a single 100 watt Renogy panel having similar voltage specs, Voc = 22.3v and Vmp = 18.6v.

I've been really pleased with the performance at 55⁰30' N in southeast Alaska. There's no problems with the solar charge starting up early in the AM even with the frequently overcast weather (120 inches annual precip). I'm pretty sure you'll do better yet in Maine, especially with a bigger panel.


Victron Energy has a calculator that you can taylor to your location to estimate solar energy yield.

https://www.victronenergy.com/mppt-calculator

In June and July, the above calculator shows I will get an average of 0.4 kwh charging energy per day (400 watt hours/day at my new location in Hood Canal, WA. To convert that to amp hours/day, divide by the average voltage during daylight (charging) hours. So 400wh/13.5v ~ 30 amp hours /day for a 12 volt system. This again is for my 100 w system at my new location in Hood Canal, WA, your proposed system should be higher.

[Ziggy]

Originally Posted by kenbo

+1 on what sailorboy1 said. You can expect about 40 to 45ah per day. More if you can orient the panel perpendicularly to the sun several times a day.

Thanks, that's about what I was hoping for. I did find a link to Mainsail's test (https://marinehowto.com/mppt-vs-pwm-solar-controllers/) where he reports an average of 31 Ah/day with a 140W panel. This would scale to about 136 Ah/day with a 160W panel.

[Nord Sal]

31 Ah/day from a 140 w panel would scale to about 36 Ah/day. Bear in mind that that test was in early May and that the weather during the test per the author "could not have been worse." So the 40-45 Ah/day Kenbo mentioned is probably more accurate during the height of summer.

[kenbo]

It all comes down to the panel's orientation to the sun.

[sailorboy1]

Originally Posted by Ziggy

Thanks, that's about what I was hoping for. I did find a link to Mainsail's test (https://marinehowto.com/mppt-vs-pwm-solar-controllers/) where he reports an average of 31 Ah/day with a 140W panel. This would scale to about 136 Ah/day with a 160W panel.

Doubt it. In real life I could count on my 290w panel doing a 100Ah in Salem Ma. Maybe 150 on an excellent day in mid summer. I am currently in the Bahamas and can normally get close to 200ah out of 640w of panels. You can only get max power ifyour batteries are greatly oversized compared to your solar.

Good luck

[Ziggy]

Originally Posted by sailorboy1

Doubt it. In real life I could count on my 290w panel doing a 100Ah in Salem Ma. Maybe 150 on an excellent day in mid summer. I am currently in the Bahamas and can normally get close to 200ah out of 640w of panels. You can only get max power ifyour batteries are greatly oversized compared to your solar.

Good luck

Sorry, you're right. I meant to say 36Ah, not 136.

[Ziggy]

Originally Posted by Nord Sal

31 Ah/day from a 140 w panel would scale to about 36 Ah/day. Bear in mind that that test was in early May and that the weather during the test per the author "could not have been worse." So the 40-45 Ah/day Kenbo mentioned is probably more accurate during the height of summer.

Good point.

[OS2Dude]

Something else you may consider is putting another panel on the lifelines while at rest. We used to keep two 100W panels on the lifelines of our boat. You could disconnect the one on the lifeline and leave the other when underway. It is a bit of a pain to undo and store them before getting underway, but while stationary they worked fine. I recently replaced them with a Renogy 175W flexible panel lashed to the cabin top. It is out of the way enough so I can remove/replace the sail cover without having to stand on it and I don't have to stow it before going out.

[mitiempo]

Originally Posted by Ziggy

I was less concerned about the start-up delay than about performance on a cloudy or foggy day

Lots of cloud and/or fog will result in very little or no charging with solar.

[LoudMusic]

I think your hardware pairings are just fine. But I also think you'll be increasing everything as soon as you can when you discover how useful it is

"Hmmm, now where else can I bolt more panels to this boat ..."

[mitiempo]

Originally Posted by LoudMusic

I think your hardware pairings are just fine. But I also think you'll be increasing everything as soon as you can when you discover how useful it is

"Hmmm, now where else can I bolt more panels to this boat ..."

While I agree it will be tough to place many more panels on a Contessa 32.

I would plan a battery bank capable of running loads for 3 or 4 days without sun, and plenty of power conservation. All leds for sure and the less power hungry devices the better.