2 Solar Controllers

[fritzdfk]

I have 2 50 watt panels wired parallel to a single mppt controller. The panels are subject to shading sometimes from a couple of antennas. I understand that using two controllers might give me more yield from the panels. I have read that with multiple controllers it is good to have them communicate with each other. My one controller now is a Victron with a bluetooth dongle. If I added another Victron with a dongle is it right that they will then coordinate with each other? How important is this?

[Kian]

I'm just a newbie myself, so take this with a grain of salt, but my understanding is that with a mppt controller you should wire your panels in series up to the voltage that your mppt can handle. If you have 2x 12V panels, if you wire them in series they would present a voltage of up to 24V to the mppt. I'd be surprised if the mppt can't accept 24V (or even 48V, if they're 24V panels).

The mppt then takes the input and draws the optimum power out of the two of them to feed the batteries. You would add a second controller if you had another isolated battery bank you wanted to feed as well, or if you had so many panels that wiring them in series raises your voltage above what the mppt can handle.

[Lazy1]

if wired parallel two separate controllers wont make a difference. If one panel is shaded the diode will prevent the shaded panel from absorbing output from the other panel, thats an issue with series wiring

VE.Smart Network is what you might want to get multiple controllers to talk to each other.

[Lazy1]

I could see two independent controllers getting in to a race condition theoretically reducing your charging

[fritzdfk]

Originally Posted by Kian

I'm just a newbie myself, so take this with a grain of salt, but my understanding is that with a mppt controller you should wire your panels in series up to the voltage that your mppt can handle. If you have 2x 12V panels, if you wire them in series they would present a voltage of up to 24V to the mppt. I'd be surprised if the mppt can't accept 24V (or even 48V, if they're 24V panels).

The mppt then takes the input and draws the optimum power out of the two of them to feed the batteries. You would add a second controller if you had another isolated battery bank you wanted to feed as well, or if you had so many panels that wiring them in series raises your voltage above what the mppt can handle.

I am not an expert either but it is my understanding that parallel is better than series in a situation where there might be shading.

[Kian]

Here's an article explaining how to mitigate that issue when using a mppt controller and your panels in series: https://www.mpptsolar.com/en/solar-p...in-series.html Basically you can conditionally exclude a panel when it drops below the point where it contributes to the system with a bypass diode.

[fritzdfk]

This is what I would like to do. Perhaps it is not an issue to have two controllers connected to one battery bank. Also with this configuration there are no diodes.

[Cthoops]

Originally Posted by fritzdfk

This is what I would like to do. Perhaps it is not an issue to have two controllers connected to one battery bank. Also with this configuration there are no diodes.

Thus is exactly what we have (including the Genasun controllers), except we have two batteries connected in parallel. We have two 100 watt semi-flexible Renogy panels, each connected to its own Genasun controller with their own fuses, and two Firefly batteries. Easy-peasy - we didn’t even bother to replace the Balmar battery monitor after it crapped out one month past warranty because by then we had a good handle on our daily usage and how cloudy days would impact the battery capacity.

Been cruising with this set up for 26 months now and we have zero complaints.

[Dsanduril]

@fritzdfk,

The picture you posted is pretty much best practice for boat installations where one panel may become shaded. Premium practice would be to use the Victron VE (or similar) networking to join the controllers. If nothing else it means you can easily make sure the programming is the same on both controllers. For that both controllers (for Victron) need to have Bluetooth Smart.

Having said that, it is pretty rare that you’ll get much problem with two controllers into one battery. In most cases they’ll be just fine, if you reach absorption voltage there’s a chance one controller will drop back to float and therefore not contribute anything while the other will be alone in trying to get the very top of the charge. If you need that maximum output while trying to top of the last of the charge coordinated units are better, otherwise you‘ll generally be fine without coordination (YMMV).

[Lazy1]

Originally Posted by fritzdfk

This is what I would like to do. Perhaps it is not an issue to have two controllers connected to one battery bank. Also with this configuration there are no diodes.

The panels should have diodes, you dont have to provide them

[Lazy1]

Panels are designed with cells in several series to achieve desired voltage.



Example

- 3.5 volt cell times 5 equals 17.5 volts for a typical 12 volt panel

- a panel may have 3 rows of 5 cells in parallel to achieve 3x amps while keeping 17.5 volts
- each row has a diode in standard panels, expensive panels may have a diode per cell
- cells that are shaded are parasitic meaning they will consume energy from other cells behind the same diode.
- if a row cannot match voltage it is lost power but not parasitic ( reduces watts but not overall voltage )


I just think you might be throwing away money adding a controller unless it is needed for amp or voltage limits of the controller you have


Victron will answer your questions as well instead of trusting us!

[noelex 77]

Originally Posted by fritzdfk

I have 2 50 watt panels wired parallel to a single mppt controller. The panels are subject to shading sometimes from a couple of antennas. I understand that using two controllers might give me more yield from the panels. I have read that with multiple controllers it is good to have them communicate with each other. My one controller now is a Victron with a bluetooth dongle. If I added another Victron with a dongle is it right that they will then coordinate with each other? How important is this?

Multiple MPPT controllers, ideally one per panel, will produce a higher output on a yacht than the alternative of series or parallel connection.

However, the difference is not great and a small amount of the improvement is lost to the higher self consumption of multiple controllers. Basically it takes some power to run the controllers tracking and monitoring functions. This power is generally greater for multiple small controllers than one larger controller.

Modern controllers such as the popular Victron line have very low self consumption, so this factor is generally very minor, but it does become a consideration with a very small solar array. A 50w solar panel only produces a small amount of power so the controller’s self consumption starts to become a more significant factor in the overall total output. With such small panels most of the gain produced by the superior tracking of multiple controllers will be lost to this extra self consumption.

For this reason, with small panels as in this example, the advantage of multiple controllers becomes much smaller. Providing your single controller is rated for 100w, in this case I would connect both panels in parallel to this controller and forget about the cost and complication of a second controller.

If you do still want to use multiple controllers, synching the controllers is not essential, but it does help. With the Victron smart range of controllers it requires some additional hardware. The cheapest way is with the Victron Smart Battery Sense (buy the newer, longer range, blue version rather than the older black version). This is less than $50. As well as charge synchronisation it also provides more accurate voltage information by eliminating the voltage drop between the controller and batteries, so the low cost is worthwhile if you have more than one controller. It can also provide better battery temperature information although the limited Bluetooth range means this is not possible on all systems.

I am not 100% sure if this networking will function with the older Victron controllers that used an external Bluetooth dongle rather than the newer models with the Bluetooth built in. I would check with Victron first, to be sure, if you have the older controllers.

[Sailing Ohm]

Running them in series will be the best long term especially with a mppt. Even if a string is shaded it still has some voltage just not amps so it is a less of a negative effect especially with the newer panels available these days. In series wiring the mppt reads the panels as simply one panel so whatever values you have from the panels the mppt will work out the best scenario for your battery. In parallel wiring each panel is more isolated yes but the power all gets recombined back at the controller and cleaned up/modified anyways so why not let the smart mppt controller do what it’s supposed to do? Series wiring allows for smaller wire and smaller holes for the wire to run through.

Now if one panel is entirely shaded frequently you have other issues and need to think of a solar arch or something. Adding a separate controller to a panel that isn’t producing isn’t going to do much outside of your bank account. If the panel isn’t producing power you can’t buy something to make the panel produce power when it feasibly can’t.

Really you need to get better panels. 50w panels are basically useless outside of maintaining a single battery from self discharge.
Your money would be better spent on a quality single high wattage panel (and voltage since you have mppt) than spent trying to make a 2 50w panel functional.
Panels are also cheaper than a decent mppt controller.

Find out how high a voltage your mppt controller can handle and get the highest voltage of panels (less than 15% of mppt max) you can fit. Either by wiring in series or even a single high voltage panel (I have 2 panels that operate at 60v nominal wired in series and the mppt figures out the rest).

I believe having Multiple mppt controllers starts coming into play with very high wattage systems. I think our single mppt can handle up to 250V and 2600 watts.... so quite a lot

This is my observed knowledge from designing multiple solar panel systems for sailboats.