Beginner's Challenge

[BCSailing]

Hi All,

I am trying to secure correct advice on sizing the Smart Blue MPPT Controllers for my boat-mounted solar charging system.
I have tried to do my due diligence in reading here and many other sources about the proper sizing of controllers for my PV Panels but I am coming up with different advice on how to go about sizing the controller from suppliers, videos and much of the materials I have studied.

This is my first build and I have tried to be very careful in learning all I can about sizing, mounting and wiring specifically for my energy needs and the Marine Environment.

My system is set up using 6-6V Trojan T-105, Flooded, Deep-Cycle GC Batteries (215ahrs Each) wired in Series Parallel to produce 645 ahrs of energy. A careful energy audit onboard has verified my needs for approx. 850 ahrs/24 hr. day while on passage. This aforementioned is my house bank and is the only batteries I will use the solar for. Engine Start is facilitated by an isolated, if-need-be 12vdc Start battery, charged by the auxiliary engine's alternator.

Being a newbie to the craft, I originally planned this, my first build in stages. I have recently completed a rack that will be as free from shading as possible and that will enable mounting of 3 Panels.
The next stage is the mounting of the first two panels which will be 210W each. The following stage will see the addition of another 2 panels (210W) each, along the side rails at the stern.
I would like to go ahead now and purchase 2 MPPT controllers. Each Controller is to service 2- 210W Panels Each. (2 Starboard and 2 Port) total of 4. It is my wish to wire each side (2 panels X 210W = 420W total) in parallel to their own controller to help minimize any shading that might occur.
The last stage of the build will add an additional 380W panel on the rack above and it will live on it's own controller, to be added later.


Most everything I have read here speaks of sizing a controller by dividing Watts by battery voltage (12V). this leaves me with about 35 amps which I would size up to a 100/50, Smart Blue MPPT Controller.

This is where I get confused.
The supplier I am working with, a reputable solar supply and system business, has spec'd out and quoted me a pair of 100/30 controllers.
Am I missing something here?
Of course, I would like to buy the lesser cost 100/30's but it seems doubtful to me that they will be sized appropriately for the two panels each, that will be wired in Parallel.

Specs on the 210W panels are as follows:
Voltage at PMax=17.0V
Current at PMax= 12.35A

I would really like to wire each side of these 210W panels in Parallel.
Can anyone help me to clarify this mystery?

 

[sunshine_eggo]

My system is set up using 6-6V Trojan T-105, Flooded, Deep-Cycle GC Batteries (215ahrs Each) wired in Series Parallel to produce 645 ahrs of energy.

Using more than 50% of FLA batteries dramatically shortens their life. You have 322.5Ah of usable capacity.

A careful energy audit onboard has verified my needs for approx. 850 ahrs/24 hr. day while on passage. This aforementioned is my house bank and is the only batteries I will use the solar for. Engine Start is facilitated by an isolated, if-need-be 12vdc Start battery, charged by the auxiliary engine's alternator.

322.5Ah of usable battery capacity seems well short of 850Ah. I assume you'll be running off generator or pulling charge from the engine?

Being a newbie to the craft, I originally planned this, my first build in stages. I have recently completed a rack that will be as free from shading as possible and that will enable mounting of 3 Panels.

Even the smallest amount of shading can destroy panel output.

The next stage is the mounting of the first two panels which will be 210W each. The following stage will see the addition of another 2 panels (210W) each, along the side rails at the stern.
I would like to go ahead now and purchase 2 MPPT controllers. Each Controller is to service 2- 210W Panels Each. (2 Starboard and 2 Port) total of 4. It is my wish to wire each side (2 panels X 210W = 420W total) in parallel to their own controller to help minimize any shading that might occur.
The last stage of the build will add an additional 380W panel on the rack above and it will live on it's own controller, to be added later.


Most everything I have read here speaks of sizing a controller by dividing Watts by battery voltage (12V). this leaves me with about 35 amps which I would size up to a 100/50, Smart Blue MPPT Controller.

This is where I get confused.
The supplier I am working with, a reputable solar supply and system business, has spec'd out and quoted me a pair of 100/30 controllers.
Am I missing something here?

420W/14.82V = 28.3A

Additionally, you'll likely never see 420W out of your array.

Victron MPPT can happily be over-paneled. Don't exceed 100Voc input or 35A Isc PV input.

Of course, I would like to buy the lesser cost 100/30's but it seems doubtful to me that they will be sized appropriately for the two panels each, that will be wired in Parallel.

Your confusion is due to your optimism that your panels will ever produce rated power.

In perfect conditions, with perfect sun at high noon with the panels perfectly perpendicular to the sun, you'll pull 420W. In every other moment, you'll pull less. With even partial shading, you'll pull markedly less.

There might be a few seconds here and there where you produce more than the unit can handle, but it's going to be infrequent. 100/30 is fine.

 

[BCSailing]

Using more than 50% of FLA batteries dramatically shortens their life. You have 322.5Ah of usable capacity.



322.5Ah of usable battery capacity seems well short of 850Ah. I assume you'll be running off generator or pulling charge from the engine?



Even the smallest amount of shading can destroy panel output.



420W/14.82V = 28.3A

Additionally, you'll likely never see 420W out of your array.

Victron MPPT can happily be over-paneled. Don't exceed 100Voc input or 35A Isc PV input.



Your confusion is due to your optimism that your panels will ever produce rated power.

In perfect conditions, with perfect sun at high noon with the panels perfectly perpendicular to the sun, you'll pull 420W. In every other moment, you'll pull less. With even partial shading, you'll pull markedly less.

There might be a few seconds here and there where you produce more than the unit can handle, but it's going to be infrequent. 100/30 is fine.

Thank You!
Clear, concise answers with explanations.

I am well-aware of the FLA 50% limitation being that it almost drove me to the expense of Lithium power. Had it not been for the fact that my bank is only 8 months old, I would have followed that path. Next Time for Sure.

The additional 2-210W and 1- 380W panels to be added in subsequent stages of the build should help, (I hope) chop that Ahr replacement figure down somewhat. The 850Ahr/day figure was very accurate on load requirements as I checked every piece of individual equipment with an accurate meter, but the audit was also very heavy on usage time. Weather can sometimes cause sailing conditions that are very taxing on 12V energy usage. Additionally, this figure is for passage-making which is much more intensive than at anchor or moored. However, I thank you again as I haven't yet found anyone till now that has been that straightforward with their answer.

Finally.. You are indeed correct in your mention of my optimism getting in the way here.
Admittedly, it is something that I didn't consider and would do well to remember as I continue with the project.