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stmbtwle

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Reply with quote  #1 
Ok I know it's claimed to "optimize" output, but to me that's just snake oil. You can CLAIM anything. What does it actually DO, and how does this affect power output?
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gbwillson

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Reply with quote  #2 
I'm not sure if this is the proper context Willie, but an "optimizer" is a device that throttles back a device to operate using less energy. Most devices, like an electric motor, use the most watts when first turned on. But the device often continues to use excess energy during normal operation. The optimizer senses the peak at startup, and lowers the energy as needed, to still allowing for proper function of the device. 

Another way to look at it is a car, which needs a lot of horsepower to quickly get up to 60MPH. But once up to 60, the car in motion needs very few HP to maintain a given speed. So the excess HP over the minimal amount needed to maintain 60MPH is wasted. A few car manufacturers have engines that actually shut down cylinders when cruising as the extra fuel is not needed.

Some electronic devices today, such as a refrigerator,  already "optimize" to be more energy efficient.

Greg in MN
stmbtwle

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Reply with quote  #3 
I'm talking about the so-called "optimizer" for solar panels. "Throttling back" would reduce output and be counterproductive, so what's the point?
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colinmcc

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Reply with quote  #4 
Ok, in short, the output from a solar panel is dependent on several things mainly temperature, solar incoming radiation and the panel's  resistance.

The optimizer you are presumably referring to is a device that sits between the panel and the load and by varying the load 'seen' by the panel adjusts the panel's Voltage/Current curve to obtain the maximum output from the panel. The subject is usually referred to as MPPT which stands for Maximum Power Point Tracking

Rather than write reams about this and how they work this wikipedia article goes into it in great depth.

https://en.wikipedia.org/wiki/Maximum_power_point_tracking

A quick google of "Maximum Power Point Tracking" will turn up lots of descriptions, some technical, some not ;-)

Such as: https://www.solar-electric.com/learning-center/mppt-solar-charge-controllers.html/
stmbtwle

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Reply with quote  #5 
All well and good, but it still doesn't explain how it works. I know how an MPPT charge controller works, it's sort of like a dc "transformer" or buck converter that changes the output voltage of the panel to what the battery needs. As it lowers the output voltage the current goes up. So far so good. However the optimizers as far as I can tell are intended to be used with string inverters, which have their own MPPT circuits, so why do we need the "optimizers" at all?

Also, in a series string, ALL components have the same current. So if you have say 10 panels at say 40v and 5a, they're all carrying 5a, even if one is shaded. Every panel I've seen has bypass diodes to allow that 5a to flow, even if the panel itself is not producing any power. The total string voltage would drop, but the MPPT circuit in the inverter can handle that.

So again, what's the point of the optimizer? I'm missing something, somewhere.


I think I found it: "Power optimizers are essentially DC-DC converters, taking the DC power from a solar panel at whatever voltage and current is optimal (via MPPT), then converting that to a different voltage and current that best suits the central / string inverter.

Some power optimizers are designed to work in conjunction with a central inverter from the same manufacturer, which allows the inverter to communicate with the optimizers to ensure that the inverter always receives the same total voltage from the panel string.[9] In this situation, if there is a string of panels in series and a single panel's output drops due to shade, its voltage will drop so that it can deliver the same amount of current (amps). This would cause the string voltage to drop as well, except that the central inverter adjusts all the other optimizers so that their output voltage increases slightly, maintaining the fixed string voltage required at the inverter (just at reduced available amperage while the single panel is shaded). The down side of this type of optimizer is that it requires a central inverter from the same manufacturer as the optimizers, so it is not possible to gradually retrofit these in an existing installation unless the inverter is also replaced, as well as optimizers installed on all panels at the same time." Wikipedia

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jjackstone

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Reply with quote  #6 
This link gives a little more explanation and a comparison between the different methods of power management from the panels.

http://scitechconnect.elsevier.com/differences-string-inverters-microinverters-power-optimizers/



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stmbtwle

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Reply with quote  #7 
Read essentially the same thing on another site. What most of them don't tell you is how the optimizer does what it's supposed to do. Just saying "optimize" is meaningless. I did finally determine that the optimizer adjusts the voltage so that the current remains the same as the other units. This is the reverse of a microinverter, which maintains a constant voltage (240vac) by adjusting current.

Though I have a string inverter, I would lean toward microinverters for safety reasons. As the microinverters are individually grid tied, cutting the grid means the entire array goes dead. With my string inverter, cutting the grid only kills the inverter, and the series array is still sitting there at 350-400 volts DC. Not the most comforting thought for say, a firefighter.

Whether optimizers would shut down I don't know. After more reading, it appears they do.

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Solar is like the wind. It may be free, but putting it to work isn't!
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