Solar panel / charge controller matchup

[David B]

Originally Posted by Ziggy

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

Yes, in theory, another few volts from the panel should give you more output in the post-dawn and pre-dusk periods.

[DanielI]

At the risk of slightly derailing the thread: this is basically the setup I’m looking at, except I’m thinking of starting with the 100W version of that panel, and assuming I’ll add a second 100W panel in the near future. Two questions:

1. Is it better get the Victron 75/15, which can handle 220W? Or get the 75/10, which is rated 145W, and get a second controller when I get a second panel?

2. I’m looking at the Blue Sea mini-ACR to allow me to charge both banks. There are more expensive units, are they worth it for a system this size?

Thanks.

[mitiempo]

Originally Posted by DanielI

At the risk of slightly derailing the thread: this is basically the setup I’m looking at, except I’m thinking of starting with the 100W version of that panel, and assuming I’ll add a second 100W panel in the near future. Two questions:

1. Is it better get the Victron 75/15, which can handle 220W? Or get the 75/10, which is rated 145W, and get a second controller when I get a second panel?

2. I’m looking at the Blue Sea mini-ACR to allow me to charge both banks. There are more expensive units, are they worth it for a system this size?

Thanks.

1. Depends on where the panels are to be located. If one is likely to get shaded 2 75/10s can make sense. I like to use separate controllers for panels on each side of a boat. Actually right in the middle of an install with 200 watts on each side to their ow Victron controller.

2. The Blue Sea mini ACR is a good choice as is the Victron Cyrix. Both good products but the Cyrix will probably cost less. An ACR is definitely worth it in my opinion.

[Nord Sal]

Originally Posted by DanielI

At the risk of slightly derailing the thread: this is basically the setup I’m looking at, except I’m thinking of starting with the 100W version of that panel, and assuming I’ll add a second 100W panel in the near future. Two questions:

1. Is it better get the Victron 75/15, which can handle 220W? Or get the 75/10, which is rated 145W, and get a second controller when I get a second panel?

2. I’m looking at the Blue Sea mini-ACR to allow me to charge both banks. There are more expensive units, are they worth it for a system this size?

Thanks.

I'm using a victron 75/15 with a 100W Renogy panel. I oversized the charge controller thinking about possible expansion. The system works great, but I think a shouldve saved the $20 and got the 75/10 model. When/if I do expand, I'll add a second controller. Individual controllers will work better with different panels/shading.

I'm using a victron cyrix and it works great. Combines batteries when voltage goes up from charger/alternator is working and opens when voltge drops to 12.8 (I think). Mine is a 120 amp unit and was about $40 something. I'm very pleased with it.

[Ziggy]

Originally Posted by mitiempo

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.

The only way I could get significantly more battery capacity would be to replace FLA with lithium ion. But that's a pretty pricey upgrade. Perhaps Li batteries will come down in price as electric cars gain market share.

[noelex 77]

Originally Posted by Ziggy

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?

It is a good question, unfortunately without a definitive answer.

There has been concerns about a possible slow start up in some situations even with 36 cell panels. In practice this does not seem to be a problem, but I wonder if some users are simply failing to recognise the issue, leading to underreporting of the problem?

My best guess is that with typical 36 cell panels this is unlikely to be a problem unless you have relatively low voltage panels, hot conditions, poor panel ventilation or other charge sources such as wind running overnight. It probably needs a combination of some of these factors before there is likely to be a practical issue.

The problem is far worse with 32 cell panels and I would generally follow Victron’s advice and not use these controllers with 32 cell panels in parallel.

In this case, the Renogy panels have a high voltage for a 32 cell panel. The voltage is similar to a typical 36 cell panel. This reduces the risk of encountering a problem. I doubt you will have an issue, but if there are alternatives available these would be a safer choice, especially if some of the factors mentioned in the third paragraph are present.

[Ziggy]

Noelex,
Thanks--this pretty much summarizes my concern. I do believe that if the Renogy specs for Voc and Vmp are met, the panel would be fine. But I don't know how trustworthy these specs are. For example, to get 22.9V, would require diode voltage per cell to be almost 0.72 V. This is not impossible, but it would be unusually high. The spec'ed diode drop per cell for the 33 cell 100W panel is 0.65 V, which is more reasonable.


I will probably just order the 160W panel, test it it in my back yard, and return it if it doesn't perform as expected. My other option is the 200W panel (40 cells) which would fit in the space I have if I can figure out a reasonable mounting scheme.

[Dsanduril]

I would trust the specs (but verify). The current per-cell commercially produced maximum VOC of monocrystalline silicon cells is about 765mV, so the claimed spec is within the range.

Startup occurs with discharged batteries (say 12.8V for argument’s sake) and open circuit on the solar panel. All you need to reach the is about 18V on the panel for startup to occur, this should happen at somewhere between 25-75 W/m2 (the voltage curve is very steep with low light intensity, the current curve is pretty close to linear). At that light intensity you’re down at less than 10% of nominal production and it doesn’t contribute much to total energy harvest.

Ideally, sure, a slightly higher voltage would be nice, but if you’ve found quality panels that fit in your space and a layout that works I wouldn’t be overly concerned at those specs.

[Nord Sal]

I checked my open circuit voltage on my 100w Renogy panel before installing it. It was
over 22 volts (spec is 22.3v).

My system turns on early in the day and is producing some (not much) charging current right about sunrise. Production is worse on cloudy days but it still turns on early. Other than daylight hours, Maine will have better conditions than southeast Alaska for solar power production.

I don't think that your solar charger turning on 'late' due to insufficient panel voltage will be a problem at all for you. The bigger question regarding performance is related to how much energy you consume vs how much charge energy you extract from solar, i.e., your energy budget.

[SouthBaySailor]

Can anyone comment on where the output of charger is connected? It seems that when shore power charger and solar charger are running at the same time there would be a conflict of charging currents potentially causing damage to one of the chargers. Are the charger's outputs protected from current feeding backwards into the chargers?
Haro

[mitiempo]

Originally Posted by SouthBaySailor

Can anyone comment on where the output of charger is connected? It seems that when shore power charger and solar charger are running at the same time there would be a conflict of charging currents potentially causing damage to one of the chargers. Are the charger's outputs protected from current feeding backwards into the chargers?
Haro

It will not damage either charger. All they see is voltage. As the batteries charge at a certain point one charger will go into float but by then the batteries will be close to fully charged and not accepting much current in any case.

Multiple charge sources will not damage anything.

[SouthBaySailor]

Mitiempo, thank you.
Haro

[LostDog88]

Originally Posted by mitiempo

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

Very little charging on cloudy/foggy days. Yes.

No charging? Not true. If there is light it is charging. Sometimes I even get .1 amp from a full moon at night!

I have a 200W Rich Solar and Epever 40A charger controller. As soon as daylight breaks. Foggy, rainy, cloudy, whatever. I can watch the voltage on the controller start to rise. As soon as it hits battery voltage it starts pumping in amps. Very slow to start and then builds based on conditions. IE: On a very sunny day I can hit as much as 11 amps when batteries are below full charge.

On foggy and rainy days like we just had this last weekend while we were out I still was getting as much as 3 amps from the solar panel.

I sail the Puget Sound and have two very cheap batteries and even on crappy days I can almost charge them all the way on a very rainy crappy day. Much better than I expected based on Will's test results.

I hope this helps. My advice. Buy as much solar as you can afford. You will want it and need it. Conditions vary where I live. Constantly. Boats swing on anchor and constant adjustment of panels becomes very monotonous. So you don't do it. When you have more panels you can point them different ways and get power from them without the constant babysitting. This translates to less generator run time.

I run my panel flat with the deck on a rail mount without any adjustment. I could adjust but I'm lazy and don't. I get what I need with little help from the generator on a sunny day. Rainy days. Sure. I have to supplement with other charging schemes.

[wholybee]

Originally Posted by 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.

Why not leave them on while sailing? I never take my panels off the lifelines. I do need tie them so the wind doesn't flip them upside down. And in a strong gale I tie them in a down position. But after 30,000 miles they have survived fine. The have even gone in the water a couple times when the tow-rail gets buried.

I might replace the upper wire with 1" tube at some point, but other than that upgrade, it's a great place for them.

[Ziggy]

Originally Posted by LostDog88

Very little charging on cloudy/foggy days. Yes.

No charging? Not true. If there is light it is charging. Sometimes I even get .1 amp from a full moon at night!

I have a 200W Rich Solar and Epever 40A charger controller. As soon as daylight breaks. Foggy, rainy, cloudy, whatever. I can watch the voltage on the controller start to rise. As soon as it hits battery voltage it starts pumping in amps. Very slow to start and then builds based on conditions. IE: On a very sunny day I can hit as much as 11 amps when batteries are below full charge.

On foggy and rainy days like we just had this last weekend while we were out I still was getting as much as 3 amps from the solar panel.

I sail the Puget Sound and have two very cheap batteries and even on crappy days I can almost charge them all the way on a very rainy crappy day. Much better than I expected based on Will's test results.

I hope this helps. My advice. Buy as much solar as you can afford. You will want it and need it. Conditions vary where I live. Constantly. Boats swing on anchor and constant adjustment of panels becomes very monotonous. So you don't do it. When you have more panels you can point them different ways and get power from them without the constant babysitting. This translates to less generator run time.

I run my panel flat with the deck on a rail mount without any adjustment. I could adjust but I'm lazy and don't. I get what I need with little help from the generator on a sunny day. Rainy days. Sure. I have to supplement with other charging schemes.

LostDog,
Very good feedback, thanks. In my case, the cost of the panel is not an issue (within some limits), since it amounts to only a fraction of the cost of building even a simple arch and mounting it. The real limit is the available space.



I decided against rail or lifeline mounts because they would interfere with other stuff and boarding.