Buck-boost converter with solar panel?

[smily03]

This is just a theoretical...

By reading through countless threads on the forum here, I've learned (among many other things) that solar panels are current sources, not voltage sources, and thus it's more of the available current that changes based on environmental conditions, not the voltage that changes (eg. more sun == more current, less sun == less current; voltage staying about the same.)

What I'm curious about is -- instead of using a charge controller (off-grid/hybrid) or inverter (grid-tied), could you theoretically use a generic DC buck-boost converter? I know that it wouldn't be a guaranteed output, and that it wouldn't allow the panels to operate even remotely efficiently, but I'm just curious -- if I were to have a small solar panel, and a buck-boost converter that could handle the maximum voltage and current that the panel can output (with a margin for cold days, etc.) (something like this :: https://www.amazon.com/DROK-Adjustab.../dp/B00C9UAE28 ) could I theoretically run a voltage-dependent load off of the panel, without needing a battery, charge controller, or inverter?
)
My brain tells me that this would theoretically work. But I know that I don't know all that much in reality, so I wanted to ask folks that know a whole lot more than I do

[SunEagle]

I would say that adding any piece of equipment into the circuit will reduce the overall efficiency and increase losses.

Also just because that device generates a boosted output it is still dependent on the input which can be changing.

A small capacitor will "ride through" short voltage dip but will not provide any output for an extended (more than a few seconds) outage. That buck boost device does not have any storage so it's output will drop if the input drops enough. A battery is a much more stable power source between a pv panel and a load.

[smily03]

Cool, totally understand there. I was just curious if it would work at all, or if the whole "current source vs voltage source" thing would make it not functional (or potentially just release the magic smoke from the converter.)

[sensij]

It can work, but without storage, the useful applications are limited. There was a thread at one point in which the op wanted to power a raspberry pi this way. A fun engineering exercise, but not really an alternative to the commercial equipment available.

[bcroe]

What I'm curious about is -- instead of using a charge controller (off-grid/hybrid) or inverter (grid-tied), could you theoretically use a generic DC buck-boost converter? I know that it wouldn't be a guaranteed output, and that it wouldn't allow the panels to operate even remotely efficiently, but I'm just curious -- if I were to have a small solar panel, and a buck-boost converter that could handle the maximum voltage and current that the panel can output (with a margin for cold days, etc.) (something like this :: https://www.amazon.com/DROK-Adjustab.../dp/B00C9UAE28 ) could I theoretically run a voltage-dependent load off of the panel, without needing a battery, charge controller, or inverter?

Here is an example of what could go wrong with using a generic DC-DC converter. Suppose your load running requires 12V @ 2A,
a 24W load. You have a 100W panel with enough sun to develop 70 W. Its Vmp is 50V and Imp 2A. With this sun it can actually
deliver 1.4A at Vmp. A generic converter usually will turn full on, initially unregulated, at 1.4A and wait for the load voltage to rise to
the regulation level of 12V. If it did, the converter would go into switching mode, in fact varying the output voltage very slightly (at
high frequency) about the desired 12V level. Power drawn from the panel would be roughly 52V @ 0.5A.

However here 1.4A will not fully power the load, so it never sees 12V. The converter doesn't see 12V, so it doesn't go into the switching
mode. The system "stalls" at around 8.4V because it can't get started. Maybe your load will operate erratically or be damaged?

If your panels are large enough to supply any voltage and current your load might need, it could work (when the sun shines). This
can be done but becomes impractical for large systems.

There are ways deal with the problem, such as fixed duty cycle switchers or linear current boosters. But the common solution is to
insert a battery to keep the system on target for difficult operating points.

This question keeps coming up, because a simple converter might appear to meet the load requirements at a single point of operation.
In the real world complete operating curves must be satisfied. In general converters are designed to have a constant source of power,
larger than the load power, and regulated at the load side. PV converters have different feedback loops and modes of operation.
Bruce Roe

[Sunking]

Every MPPT Solar Charge Controller and Grid Tied Inverter is a form of Buck/Boost power supplies. The Magic they perform is to balance Panel Resistance against a Dynamic Resistance tuned to match the panels Optimum Power Point. Short story makes the load look like a variable resistor to the panels. The Magic is the Controller controls that variable resistor to match the Panels Impedance. When you match the source and load resistance, you maximize energy transfer.

Catch is with any Current to Power Converter is there is just a small range of resistance the source circuit can supply power. If my source battery is 20 volts and max current is 5 amps, I have a 100 watt panel at max power is 4 Ohms. Four Ohms is as low of an impedance the panel can source Only goes up to Infinity as panel power fades. Example at 4 amps (80 watts) the resistance rises to 5 Ohms, at 2 amps (40 watts) r = 10 Ohms, 1 amp r = 20 Ohms.

So here is the problem. How would you match your Dynamic Load Resistance to match those of the solar panel Maximum Power Point. The Maximum Power Point of the panels change every second That means you have to match its maximum power point. Might be 90 watts, then 30 seconds later a cloud pases and you are down to 5 watts until the cloud passes.

Now I can tell you the device is already made to run a piece of equipment off solar only. Known as Current Booster to run DC Water Well Pumps. The Controller is tuned and matched with the panel and motor. So you get a motor that runs slow to fast depending on how much sun energy is striking the panels. Works great on motors. Suks for everything else.