Solar power optimizers

rice81 · October 2015

I don't see much discussion about the use of power optimizers for PV systems. When I came across the concept, it seemed to fill the niche for a solution to being both off-grid and optimizing PV output. When I first learned about microinverters I understood that they were strictly designed for grid based systems as I finally understood that they had to be driving a load and that the grid provided the excess load after the loads of the home were satisfied. There seem to be a few 'hacks' to allow microinverters to function from a simulated grid, charge batteries and be shut off by a programmable variation in local grid frequency based on battery charge state. I'm not trying to discuss microinverter hacks, just providing a bit of background. Optimizers provide the MPPT function at the individual (or dual) panel level but deliver DC to a string instead of providing an AC output. They seem to simplify the inverter / charger system a bit by providing an optimized (MPPT'd) power source and I believe they are generally paired with a special inverter / charger that expects a particular optimized power source.

The point of this thread is to gather some insight into their use or lack of usefulness. I can't really tell from the specs how the strings are wired. Are optimized panels wired in parallel? If so, the voltages from the optimizers don't seem particularly high and I would think that would require excessively large wire gauge. My impression is that the optimizers put out a constant voltage. If they are constant voltage then they must have a varying current and varying output impedance and the inverter must then must load the string with the same varying impedance to optimize the system. But then this looks to me like an MPPT inverter to me. I believe there is a master communication box. Perhaps it gathers impedance info from the optimizers and feeds this info to the inverter.

Any thoughts on this?

rice81 · October 2015

Here is a decent discussion of a couple of optimizers.

rice81 · October 2015

Any experience with these? Seems like a module that could be 'built in' to solar panels to provide smart panels that could automatically balance their output for parallel wiring or provide series shunting when shading would diminish the performance of a string. At the very minimum they could monitor and report their own performance.

mike95490 · October 2015

optimizers are for problem systems that have shade on some panels at various times. Put all the panels in the full sun, and the need for optimizers goes away.

inetdog · October 2015

Since having modules of different voltage in parallel will not work out, the modules must be in series.
And to adapt dynamically to different power outputs from different panels, the optimizers must necessarily communicate with each other in some way. They need to agree on a common current target and the voltages will adjust accordingly.
It would be possible to build an optimizer with a fixed current target, letting each module aim for that target and letting the string output voltage fluctuate accordingly. This approach will cause problems for the MPPT input if the high and low voltage ranges are not constrained in some way.
Or the modules can interact to produce a collective target string voltage, adjusting the target current to match the available total module power.
This approach requires that either the modules communicate and come to a joint decision or as is the case for SolarEdge, the inverter collects data from all modules and assigns each one its operating point.

Solar power optimizers

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