Multiple solar panels to a common bus bar?

[Mike OReilly]

A bit late to the party here, but for what it's worth, my 400 watts from four separate and parallel panels are wired via a single MPPT. It works great.

I'm sure I'm losing some potential power production by not using four separate controllers, which I agree is the optimal setup, but my sense is that it's not a huge loss. I routinely see charging amps in the mid-20s, and that's on a boat in the upper mid-latitudes (50ºN).

I also have a wind gen, which runs through its own controller.

[Hoohaa]

Originally Posted by goboatingnow

I have 4 panels now. One set of wires through the starboard arch piping , the other through the port side

No biggie really

I’m adding a wind gen

My 2 cents worth.
I've had my wind gen for around 9 year's. It's D400 mounted on a pole attached to the toe rail.
It's allot of weight swinging around up high.
It produces decent amps in wind over 15 knots but not much between 5 and 10.
If I had the choice again, I would go with more solar. And probably spend the money I saved on a high amp alternator.

[goboatingnow]

Originally Posted by Hoohaa

My 2 cents worth.
I've had my wind gen for around 9 year's. It's D400 mounted on a pole attached to the toe rail.
It's allot of weight swinging around up high.
It produces decent amps in wind over 15 knots but not much between 5 and 10.
If I had the choice again, I would go with more solar. And probably spend the money I saved on a high amp alternator.

Yes , that’s certainly a strong argument

[Mike OReilly]

Originally Posted by Hoohaa

My 2 cents worth.
I've had my wind gen for around 9 year's. It's D400 mounted on a pole attached to the toe rail.
It's allot of weight swinging around up high.
It produces decent amps in wind over 15 knots but not much between 5 and 10.
If I had the choice again, I would go with more solar. And probably spend the money I saved on a high amp alternator.

I know this is a bit off-topic, but...

I've had two wind gens over the years. My current one, a Silentwind (400 watt generator), contributes roughly 15% of my power needs, with the rest being made up by the 400 watts of solar. I rarely need to run the dino-generators to keep my batteries happy.

Solar is definitely the biggest amp bang for the buck, and I always suggest maximizing panels before considering a wind gen. If my wind gen died tomorrow, I'd be hard-pressed to replace it.

That said, a wind gen remains an excellent compliment to the total power generating system. Even though wind is a smaller overall contributor of power, it often excels when solar is sucking. I was reminded of this during the past season when, anchored out (of course), we had an extended period of heavy overcast but windy weather. Without the wind gen we would have been running dino-generators.

While my wind gen tends to produce smaller amounts of power, it can do so 24/7. Having even a moderately windy night at anchor makes a huge difference to my SOC in the morning.

So personally, I think the optimal setup is to have both. But if a choice need be made, solar is definitely the better option.

[B25Matt]

Re parallel versus series: it depends on your panels. The 100 watt flexible panels only have 19v out put, for these series is the only workable option because once you acount for system losses etc. the effective voltage leftover to charge the batteries is about 15v and that's not enough to drive a lot of current into the batteries.

If your panels are larger and have a working voltage of something in the 50v range, parallel is probably the best as the partial shading argument starts to have valid relevance.

[Mike OReilly]

Originally Posted by B25Matt

Re parallel versus series: it depends on your panels. The 100 watt flexible panels only have 19v out put, for these series is the only workable option because once you acount for system losses etc. the effective voltage leftover to charge the batteries is about 15v and that's not enough to drive a lot of current into the batteries.

If your panels are larger and have a working voltage of something in the 50v range, parallel is probably the best as the partial shading argument starts to have valid relevance.

This has not been my experience with my ~21v panels. But shading is definitely a significant issue. Even minor shading, like that cast by a stay or shroud, can have a serious impact. This is why most parallel is recommended for most sailboats.

[Martkimwat]

I refer to Nigel Calders, 'The Boat Owners Mechanical and Electrical Manual' 3rd Edition and I am pretty sure I recall he advocates a separate controller for each panel if possible. The issue to be aware of, if connected in parallel, is the likelihood of the fully exposed panel feeding some of its energy to the shaded panel, unless you put a diode in between each panel. The problem with that is that the diodes also reduces the voltage seen by the controller. If you have separate controllers, they do not allow back feeding so no diodes necessary and no corresponding voltage drop. I appreciate, it is not a huge amount, about 0.3~0.5Volts but that might be the difference to allow your panels to continue to charge for just a little bit longer on a cloudy day or approaching dusk. Since we should all strive to get maximum efficiency unless you're fortunate enough to have a 50 foot cat covered in solar panels, it is a consideration that needs to be taken into account. Since MPPT controllers control the voltage to maximise the power to the battery, (ramping up the voltage and reducing the amps as the battery gets full) I've often wondered whether putting two matched panels (12v each) in series (24V) and connecting them to a 12v battery bank via a MPPT controller that was capable of taking the potential 34~36V output from the two panels and controlling it down to the required voltage for the batteries, might work and would definitely alleviate any problems from shading, since the combined voltage would still be well above the minimum required by the controller and I would have thought that if the controller was ramping the voltage down to the amount required by the battery, it would in turn need to ramp up the amps to absorb the power available (it's got to go somewhere). Does anyone have any ideas or knowledge of that aspect of MPPT controllers?

[goboatingnow]

Mppt works better where the panel voltage is a good bit higher then the battery voltage as it’s easier to find the Vmp if it’s well above the battery.

Hence mppt will maximise the power from a series string , whereas a pwm tends to loose power in a series string.

Ps “ power isnt ramped “ loads control consumption.

[Pete7]

Originally Posted by Martkimwat

If you have separate controllers, they do not allow back feeding so no diodes necessary and no corresponding voltage drop. I appreciate, it is not a huge amount, about 0.3~0.5Volts but that might be the difference to allow your panels to continue to charge for just a little bit longer on a cloudy day or approaching dusk.

Surely that assumes the whole panel is shaded, which isn't normally the case.

Instead, larger solar panels are split into strings, mine have always been 3 strings, you can see them on the panel surface.

If one string is shaded by say the mast, then the other two strings will continue to produce voltage, just at a lower current. Therefore, both panels continue to produce the same voltage.

A recent YT episode by Andy in the Off Grid Garage did some extensive testing with a variety of panels into shading and explained this quite well.

Originally Posted by Martkimwat

I would have thought that if the controller was ramping the voltage down to the amount required by the battery, it would in turn need to ramp up the amps to absorb the power available (it's got to go somewhere). Does anyone have any ideas or knowledge of that aspect of MPPT controllers?

GBN is right and you can see it. When the MPPT drops to float the voltage drops but so do the watts from the panel.

[Mike OReilly]

Originally Posted by goboatingnow

Mppt works better where the panel voltage is a good bit higher then the battery voltage as it’s easier to find the Vmp if it’s well above the battery.

Hence mppt will maximise the power from a series string , whereas a pwm tends to loose power in a series string.

Ps “ power isnt ramped “ loads control consumption.

Agreed, in a non-shaded environment, series will likely always be best. But on your typical smallish cruising sailboat, it's hard to find places shading is never a problem. This is why parallel is generally better.

[Martkimwat]

Originally Posted by goboatingnow

Mppt works better where the panel voltage is a good bit higher then the battery voltage as it’s easier to find the Vmp if it’s well above the battery.

Hence mppt will maximise the power from a series string , whereas a pwm tends to loose power in a series string.

Ps “ power isnt ramped “ loads control consumption.

I presume you are answering my message, in which case, I am aware of the difference between PWM and MPPT but did not even mention PWM controllers so why you mentioned it, I am not sure. As to the performance of MPPT controllers, the way they work is to increase the voltage and correspondingly reduce the amperage as the battery approaches full charge, as that way the battery will continue to accept as much 'power' as possible. That is 'ramping up' the voltage in my parlance. I don't what you would call it.

[Hoohaa]

Update
I've installed my new twin 350 Watt panels.
Everything is working but is it normal to only get a maximum of 290 watts out of both the combined panels. Combined they are theoretically 700 watts.
I was told that this is normal but.
Any thoughts?
If this is the case then why the hell did I just spend over $400 upgrading my victron MPPT to A 100/50?

[emilecantin]

I have 600w of solar on my Victron 100/30. Yes, that means the max my panels will ever output is around 430W, but my issue wasn't peak power, it was all the other times.

I've found panels are pretty sensitive to shade (I have one on the dodger; I always need to move my boom around) and sun angle. At this time of the year, the sun doesn't come up as high in the sky as it did during summer, and accordingly my solar panels don't peak as high. Also, days are much shorter so they don't produce as long.

I expect I'd be able to gain a good 30% in daily production if I was able to aim my panels towards the sun.

[Adelie]

Originally Posted by Hoohaa

Update
I've installed my new twin 350 Watt panels.
Everything is working but is it normal to only get a maximum of 290 watts out of both the combined panels. Combined they are theoretically 700 watts.
I was told that this is normal but.
Any thoughts?
If this is the case then why the hell did I just spend over $400 upgrading my victron MPPT to A 100/50?

That depends.

When you checked output were the panels tilted up and turned to directly face the sun or were they flat and the sun down in the sky some amount?
How much shading? Was there even a backstay wire shading a panel?

If the panels are flat, the rule of thumb using an MPPT controller is daily output will average around 1/3 of panel nameplate in Watts = number of Amp-hours to battery.

So for 700W of panels you can expect around 233Ahr production at a nominal 12v (really around 14.1 or so but the same number of Ahr will come back out at 12v, that's entropy for you).

[Mike OReilly]

Originally Posted by Hoohaa

Update
I've installed my new twin 350 Watt panels.
Everything is working but is it normal to only get a maximum of 290 watts out of both the combined panels. Combined they are theoretically 700 watts.
I was told that this is normal but.
Any thoughts?
If this is the case then why the hell did I just spend over $400 upgrading my victron MPPT to A 100/50?

Assuming you're measuring in optimal conditions; clear noonish sky, no panel shading, panels oriented as much as possible toward the sun... then it does seem low, unless you're in a pretty high latitude. I've never hit my theoretical max of 400 watts on my system, but I often see over 300 watts, although the norm is more around 200. I run a Victron MPPT 100/30.

If all the more obvious problems are ruled out, are you sure both panels are producing? Sounds like the right peak amount from just one panel.