I’m pondering the role of an mppt and why it might be better to feed a higher voltage aka a series connection of panels so that on quite days when levels are low, there is still enough voltage to supply battery. This is because on the surface an mppt is a step down converter. If however an mppt is a step up then parallel will work because it will bump the voltage up. Does any one know if an mppt will in fact boost voltage output from low light conditions?
Is an mppt a dc to dc converter that goes up and down?
- Thread starter cdstaley
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Pierre
Somewhere down South
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- Dec 21, 2019
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The way I understand it is the SCC cannot boost the voltage ( determined by the battery ) so it increases the charge current instead. So you can almost say that it trades excess voltage on the input side for a lower voltage but higher current on the output depending on the state of charge of the battery. I am open to correction on this.
You do however get boost SCC as posted by @gnubie a while ago.
Series connected panels apparently favour low light conditions - that is why I wired the two panels on my RV with a change over switch to select series or parallel.
You do however get boost SCC as posted by @gnubie a while ago.
Series connected panels apparently favour low light conditions - that is why I wired the two panels on my RV with a change over switch to select series or parallel.
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So being an electrical engineer I understand power. Watts are watts. 10 amps at 20 volts is 200 watts. 5 amps at 40 volts same watts. My question was more directed at the dc to dc converter. In most cases a PV panel puts out more than 12 volts so the mppt aka dc to dc converter “steps down” the voltage but preserves the watts. Less the conversion efficiency. What I don’t know is can the mpg take for example 8 volts step it up to say 14.2. The current would drop but a battery is a voltage device. It needs a certain amount of Voltage to charge. If an mppt can do this parallel or series makes little difference other than wire size. I’d also need to see the conversion efficiency curves. Perhaps, dropping a higher voltage to a lower voltage is more efficiency than bumping up a lower voltage. I just can’t find any info about the step up step down profiles.
gnubie
Solar Wizard
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- Sep 20, 2019
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Most MPPT controllers are buck designs, but there are a few boost designs for going the other way. Unless you have a really niche panel the Vmp is always going to be higher than 12v nominal battery, hence buck is where most of them are.
genasun.eu
Genasun Boost MPPT's
The Genasun GV-Boost controllers are designed to step-up lower-voltage solar panels to charge higher-voltage batteries. Available for lithium, LiFePO4 and lead-acid batteries.
genasun.eu
Turns out the goal is to get the solar panel at the max power out as defined by the solar specs. That translates to keeping the input voltage close to the impedance of the converter. While a buck will work at higher voltages it may be less efficient. A buck-boost converter would work also.
To the last guy... smoke is the secret to all functioning electronics. After the smoke exits the item it won’t work anymore
To the last guy... smoke is the secret to all functioning electronics. After the smoke exits the item it won’t work anymore
rin67630
Solar Enthusiast
A plain buck converter does not care about the input voltage. It takes whatever it gets and tries to produce the requested output voltage as long as the output voltage is lower. On a solar panel, it may draw so much current from the input (panel) that it voltage will collapse and the whole thing just operates as a by pass. This is sub-optimal.
MPPT circuitry will reduce the input current -> increase the input voltage until the combination current/voltage reaches the maximum power that the panel can deliver.
MPPT circuitry will reduce the input current -> increase the input voltage until the combination current/voltage reaches the maximum power that the panel can deliver.
Whats-n-Watts
New Member
Resurrection of this thread to share this. https://www.mdpi.com/2227-9717/11/4/1087
400bird
Solar Wizard
What's the point? A solar edge optimizer is a buck/boost converter they when connected in series (with panels on each), with some communication from the inverter, will cumulatively hit 380 volts at 99% efficiency.
I stopped reading when the article said 90-96%
zanydroid
Solar Wizard
I read the first two paragraphs, and it felt like the uniqueness was going from a single 20V-40V module up to >350VDC bus voltage with a small component count. Note that microinverters also hit that efficiency and this output voltage (to be able to generate 240VAC) on the same voltage input, but much higher component count (not sure why you can't delete the inverter part of it).
One of the issues with optimizers in series (which I don't understand how is resolved, since everything I learned about power engineering is from this forum, and this forum has very few deep dives into optimizers) is that the string inverter or optimizers independently need to simultaneously ensure that the total string voltage does not exceed safety limits, while ensuring that no current blocking happens. Both Tigos and SolarEdge have independent operation mode that does not require central coordination.
You can avoid that with parallel wiring (and conceivably if IndOp drops the ball on some power when conditions change and they need to adjust boost/buck ratios, the efficiency of parallel wiring might end up being better).
Whats-n-Watts
New Member
i thought it might be relative and or helpful. My bad for wasting your time. Have a good one.
400bird
Solar Wizard
It's not a waste of time! I'm genuinely curious on the point of the thing. As Zanydroid pointed out, maybe it's lower parts count which should mean lower cost.
I'm pretty sure Solar Edge require central coordination unless you buy the unlocked ones. From what I gather the unlocked ones output a fixed voltage, current, or passthrough. I'm pretty sure you loose all the smarts with that "upgrade"
zanydroid
Solar Wizard
(article) I'm not sure what the quality of journal is. You have to scroll down to 4th author to get to the top school in the country.
Not sure exactly what you mean by losing all the smarts.
Some tea leaf reading for guessing the IndOp vs Standard algorithm. It teases some hints via describing the different specs/behavior you get from each mode. Instead of just writing up a clean whitepaper on what it is... (maybe my Google-Fu needs to be better).
Interesting tidbits are that the output current (10A) and VoC are lower. The VOC is capped at the PV module VOC, which is good because it means you won't boost the voltage up and kill the string inverter. It does not say that module level MPPT is removed. I don't know if the 3rd parties reprogramming SE are able to force them into boost mode.
For some reason it says minimum 4 optimizers per string. It is probably related to 1V safe mode when off (also on this datasheet)
Tigo works fine with distributed control and buck mode. I think adding their CCA/TAP primarily gives debugging and firmware upgrades.
One very simple way to do distributed control on the SolarEdge would be to always output 10A. If the buck ratio exceeds the range of the converter, bypass. This would be able to scale from 80W to 400W. However, the problem with this approach is that it might easily drop below the start voltage of the connected inverter. A patch to deal with that is for the optimizers to detect this and do a coordinated drop in current to reduce the buck ratio. EG, go to 9A, 8A, ... until the string starts again.
(On Tigos the maximum drop is somewhere in the 20%-33% range, so you can design the string against that to ensure that the string can still start)
As I posed a few messages up, parallel wiring would avoid current matching... just make them all run at 350VDC and peace out. I can sort of imagine that this will require switching to more expensive transistors that can handle 350VDC, or there could be tradeoffs in using these vs <100V ones. Maybe working voltage will jump up a lot when everything moves to higher breakdown transistors (MLPE, FET BMSes, ...)
Yes, SolarEdge has some kind of "constant global voltage" control. There's no way an individual optimizer can do that without feedback.
Not sure exactly what you mean by losing all the smarts.
Some tea leaf reading for guessing the IndOp vs Standard algorithm. It teases some hints via describing the different specs/behavior you get from each mode. Instead of just writing up a clean whitepaper on what it is... (maybe my Google-Fu needs to be better).
Interesting tidbits are that the output current (10A) and VoC are lower. The VOC is capped at the PV module VOC, which is good because it means you won't boost the voltage up and kill the string inverter. It does not say that module level MPPT is removed. I don't know if the 3rd parties reprogramming SE are able to force them into boost mode.
For some reason it says minimum 4 optimizers per string. It is probably related to 1V safe mode when off (also on this datasheet)
Tigo works fine with distributed control and buck mode. I think adding their CCA/TAP primarily gives debugging and firmware upgrades.
One very simple way to do distributed control on the SolarEdge would be to always output 10A. If the buck ratio exceeds the range of the converter, bypass. This would be able to scale from 80W to 400W. However, the problem with this approach is that it might easily drop below the start voltage of the connected inverter. A patch to deal with that is for the optimizers to detect this and do a coordinated drop in current to reduce the buck ratio. EG, go to 9A, 8A, ... until the string starts again.
(On Tigos the maximum drop is somewhere in the 20%-33% range, so you can design the string against that to ensure that the string can still start)
As I posed a few messages up, parallel wiring would avoid current matching... just make them all run at 350VDC and peace out. I can sort of imagine that this will require switching to more expensive transistors that can handle 350VDC, or there could be tradeoffs in using these vs <100V ones. Maybe working voltage will jump up a lot when everything moves to higher breakdown transistors (MLPE, FET BMSes, ...)
zanydroid
Solar Wizard
Another telling thing about the non-SE indOp mode is that it cannot match parallel strings.
400bird
Solar Wizard
I'm pretty sure you loose the communication, controlled/adjustable output voltage, and RSD. I think that just leaves panel side MPPT.
That's interesting. I hadn't seen a spec sheet for a Solar Edge optimizer that had independent operation out of the box.
zanydroid
Solar Wizard
Ah missed a subtlety. It does allow parallel strings of different orientations. My theorized mode of operation doesn't work with this.
Tigo does work with this which is more evidence that there's exists an independent algorithm out there to voltage match when operating in buck mode. Well, SolarEdge is selling it two so there's two.
fmeili1
Solar Enthusiast
The MPPT's inside one of these Voltronic based AIO's (like EG4-6500EX) using boost circuits (inductors, diodes, MOSFETs) to boost up the PV voltage to the required internal DC-BUS voltage of the AIO (between about 350-450V). So in this case, the PV voltage has nothing to do with the battery voltage. But this may be different in pure MPPT charge controller designs - but I don't know.
zanydroid
Solar Wizard
Ah yes those do have a boost in them. You still need PV higher than battery voltage in all cases though.
For stand alone MPPT the only DC bus is to battery.
For AIO there are various topologies. It could buck to battery and then 48V inverter boosts from that. For high voltage AIO I think they buck/boost to 350V and then buck down for battery charging.
You would still need to find a charge controller that can be appropriately programmed or auto-detect the power limit of the DC input.
