Unorthodox Shared Busbar and Solar Array Theory with Victron MPPT Controllers

[CityFullOffgrid]

I need some feedback from Victron Engineers since I worked out a Theory that’s very “out of the box” so to say…

Before everyone Jumps on the instant “No that’s Not Possible” Response, let me explain the idea and the reasoning behind it.

So, to my understanding works a Smart mppt, let’s say an 100/30 , with a internal Shunt to measure real-time the Current /Voltage coming from the Solar Array.

So here an for most people weird and very Unorthodox Theory.

In this setup, you’re using two Victron 100/30 MPPT controllers connected to a shared busbar system. Unlike the traditional approach, where each MPPT controller might be connected to an individual, isolated solar array, this configuration combines the solar array’s output at the busbar level before feeding it to both controllers. This design takes advantage of Victron’s advanced MPPT capabilities, specifically their internal shunt and continuous tracking features, to optimize power distribution without the issues that can arise with older MPPT systems.

In classic solar setups, each MPPT controller is typically connected to a separate section of the solar array. The primary reasons for this approach stem from:

1. Power Loss During “Hunting”: Traditional MPPTs briefly disconnect to measure and adjust to the MPP, potentially causing oscillations and “hunting” when multiple controllers share an array, leading to inefficiency.

2. Independent Tracking: Controllers track MPP independently, and without synchronization, sharing an array could lead to interference, with controllers attempting to adjust simultaneously, causing performance conflicts.

Theory Behind the Shared Busbar with Victron MPPTs:

Victron MPPT controllers overcome these traditional limitations with continuous real-time tracking enabled by an internal shunt. The internal shunt ensures that:

1. Seamless Monitoring: Each controller continuously tracks the MPP without needing to disconnect, so multiple MPPTs can operate on a shared array without disrupting one another.

2. Enhanced Synchronization: The controllers can make micro-adjustments in real-time without “fighting” or “hunting” for the best power point, allowing for a smoother and more efficient energy harvest.

This modern approach allows for parallel operation on a shared array, with each controller tracking independently while respecting the shared voltage of the busbar.

Key Advantages of the Shared Busbar Design with Victron 100/30 Controllers:

1. Reduced Cabling Complexity: With a shared busbar, you simplify the wiring by consolidating the solar array’s output, which reduces the total length of cable runs and minimizes resistance losses.

2. Optimized Voltage Utilization: Your setup benefits from the array configuration (e.g., 2S2P setup with a rooftop busbar feeding down via a 25mm² cable), which maintains voltage levels to maximize power input into the MPPTs.

3. High Efficiency from Victron’s Real-Time Adjustment: The Victron controllers’ continuous, non-interrupting tracking means that they handle minor fluctuations smoothly, even when shared on a busbar. This design enables maximum solar energy capture without the performance trade-offs seen in classic MPPT setups.

Misconceptions with Classic MPPT Knowledge:

Most traditional objections to using a shared busbar come from an outdated understanding of MPPT controllers, which operated on different principles. The classic limitations don’t apply here because:

Victron’s Internal Shunt and Adaptive Tracking: These features allow the controllers to work in harmony without the “pause-and-measure” approach, which avoids disruptive interactions.

Built-in Coordination Among Controllers: Victron’s smart MPPTs can adjust to one another’s activity through real-time data without compromising efficiency or stability on a shared array, something conventional MPPTs could not achieve.

So to come to a conclusion…

The shared busbar and solar array configuration using modern MPPT controllers represents in theory an evolution in solar system design, leveraging advanced tracking technologies to overcome the limitations traditionally associated with parallel MPPT setups. By utilizing continuous, shunt-based tracking, these systems avoid the “hunting” issues that arise from periodic disconnections in older MPPTs, allowing for seamless, real-time adjustments to the maximum power point. This design theoretically optimizes power capture, minimizes wiring complexity, and provides stable performance, even with multiple controllers on a shared array.

In contrast to conventional approaches, which often insist on isolated arrays per MPPT, this setup demonstrates that shared busbars could be highly effective when paired with advanced MPPT technologies. The result should be a streamlined, efficient solution that maximizes solar energy harvest and challenges outdated assumptions, ultimately this is an out of the box approach to solar energy management in multi-controller configurations.

[alexpescaru]

Don’t say that wont work, but did you try it practically?
And compare the results with classical configuration?
Because Kirchoff’s laws say that the gain could be at best marginal…

PS.
Sorry, english not my first language, but “out of the box” or “outside the box”?

[CityFullOffgrid]

Neither it’s mine, so it might have been my Native tong that messed up the sentence a bit

You get the point tough

Thinking outside the box

Yess a test setup is as we speak up and running, and so far doing alright, although the first Sun just came through so it’s too early for any conclusions but I’ll keep an eye on it and will share some experiences later on

[CityFullOffgrid]

@alexpescaru

Don’t say that wont work, but did you try it practically?
And compare the results with classical configuration?

I had to dive a bit deeper into this.

In theory, Kirchhoff’s current law implies that the power sharing might not be perfectly balanced at all times, especially under varying conditions like partial shading.…

While Kirchhoff’s laws govern current distribution, the controllers shouldn’t simply split the current—their algorithm dynamically adjust based on the solar input and battery demand. This means in Theory each controller could operate at its own optimal point, minimizing interference and effectively maximizing power capture. In practice, any loss should be minimal because each controller’s MPP tracking is sophisticated enough to handle these conditions.

It’s up and running, so let’s see how well the theory survives the Real World

[JohnC]

@CityFullOffgrid

The Victron controllers’ continuous, non-interrupting tracking

When did this happen? I’d still be watching for the ‘triple dip’ every 10 minutes…

[CityFullOffgrid]

Could this indicate a periodic recalibration or synchronization cycle of the MPPT controllers as they attempt to track the maximum power point of the solar array?

At least to me it suggest a periodic MPP tracking recalibration.
Caused by the algorithms that occasionally “sweep” the voltage to find the true maximum power point, especially under variable conditions. To my understanding the process involves briefly adjusting the load to confirm they’re operating at the most efficient point, which can indeed result in those temporary dips in power output.

However, with Victron’s modern smart controllers, these synchronization issues are generally minimal. Victron controllers algorithms should manage shared inputs better than older models, theoretically reducing the likelihood and impact of such conflicts. In most cases, any misalignment should be brief and not significantly affect overall performance. The controllers would quickly stabilize and resume efficient power tracking without prolonged interference.

At least, that’s the theory so far…

Let’s see how that holds up in the field

[alexpescaru]

When a controller does a full sweep, it goes from open circuit to full short circuit with the panels.
For sure that will create some interference and confussion with the other(s) controllers, that will consider that a change in light conditions.
It’s even possible that they’ll also decide to do a full sweep.
And for sure that sweep is taking place, at least in my controller case.

[CityFullOffgrid]

I need to find out how to attach Pictures, but maybe I’m still a too low level to not be allowed attaching those (yet) so I’ll do my best to try and find a way how to post them here as well.
Otherwise I’ll add them somewhere later this week after a prolonged test.

Our observations so far.

1. Peak Synchronization: Both controllers reach their peak wattage close to the same time, around noon, with the original controller reaching about 334W at a voltage of around 61.74V, while the second controller peaks slightly lower at 295W with a similar voltage of 62.18V. This close timing suggests both controllers are drawing power effectively under optimal conditions and respond in sync with sunlight changes.

2. Voltage Behavior: The voltage for both controllers fluctuates in a similar pattern throughout the day, reflecting the varying sunlight levels. The voltage peaks just before the wattage peak, which is typical in MPPT controllers as they adjust to find the maximum power point with changing solar conditions.

3. Cloud Impact and Variability: The sporadic drops in both wattage and voltage hint at intermittent cloud cover. Both controllers appear to maintain similar power and voltage levels, indicating that the shared busbar setup does not introduce noticeable power loss or imbalance under cloudy conditions.

The Live graphs from the Victron App help confirm that this dual-controller setup for so far is working as intended, with both controllers adapting dynamically to changes in solar irradiance.
Today was a very Cloudy day, and it’s just a small setup to test the Theory, but the combined Yield was on par with last days with the single 100/30 controller.
There’s 3 independent Solar systems at this place with each their own Battery banks, and all had comparable Yields for this Cloudy day.
On a sunny day this setup should ideally yield even higher combined output, allowing to evaluate the configuration’s full potential. If I will continue to observe this close synchronization without voltage or power imbalances, it should indicate the shared busbar is functioning effectively with the two controllers.

[CityFullOffgrid]

There’s a small additional 12volt setup (directly next to the 2S2P panels to the Busbar) with a single 450W panel managed by a Victron 75/15 controller (Yess it’s overpanneled, just temporarily setup like this), and this Graphs demonstrate an interesting comparison. The fact that the 12V battery bank reached full charge early, likely entering float mode around 12:05, aligns with the peak timings seen on the 24Volt shared busbar setup.

Notably, the solar voltage here also peaked around the same time, despite the separate configuration and 12V system. This suggests that the solar irradiance conditions affected all our systems similarly, causing simultaneous peaks across each. The 75/15 controller, managing a smaller battery bank, simply had a quicker charge cycle, showing it entered float earlier thus around noon the Wattage dropped to Float range.

This consistency in peak timings across our systems indicates that the shared busbar configuration on the main 24V setup is not causing timing misalignments, as all systems respond to solar conditions in unison. Observing these patterns on clear days will further clarify if this alignment continues, solidifying the efficiency of the combined system.

[CityFullOffgrid]

[Toopy (Alan Toop)]

Is the current path into the busbar balanced? And to the mppt’s.

Similar to this,

[CityFullOffgrid]

Balanced as in, everything has exactly the Same cable length?

Only the cables running from both the MPPT’S to batteries are slightly of set, will adjust them at a later stage.
All batteries are connected with exactly (on the centimeter precise) same length & spec cables to their respectively Plus and Minus Busbar. So between batteries there’s no offset in the connections and all pairs have a Balancer. The inverter is connected with Plus directly to those bushbars coming from the Batteries (but with a Off-switch and fuse inbetween), and the minus of everything runs trough a 500Amp smart shunt, including the MPPTs.
The inverter Cables are also exactly the same length from the busbars, except that the Minus has said Smart-Shunt in between.

Also, incoming cables from roof to shared Array Busbar exactly same length, plus both pairs between the MPPT’s on the Solar side are exact same size and length.

Only the Cable length differs slightly between Both MPPT’s to Battery Busbars. This needs to be adjusted to get the best efficiency

It’s a pretty small system, so no fancy equipment in this setup, purely some basics.
I forgot to mention a bunch of fuses, but overal they are where they need to be and when two pairs run somewhere than both are the same specs as well.

[Toopy (Alan Toop)]

So it’s possible then that the slight variation between the 2 MPPT is due to this. Very interesting test, looking forward to seeing the outcome