When are DC to DC optimizers economically feasible?

Re: When are DC to DC optimizers economically feasible?

It is questionable what benefit these devices would give to bypassing a shadowed panel.

The block diagram claims they have an MPPT power optimizer. The question is what that means to a series connected group of these optimizers. Having two MPPT processes in series (one at panel optimizer and one at central inverter) seems questionable. The data sheet makes a statement "Single panel MPP tracker compatible with all Power-One inverter models" implies they may only work with Power One's central inverters, not other manufacturers.

They also have a Zigbee short range RF data link shown in their block diagram.

I would be concerned about what these series connected optimizers mean to overall voltage delivered to the central inverter and the possiblity of losing control over the maximum voltage delivered to central inverter, possibly causing damage. Maybe they are using the RF link to mitigate this but there is not enough info in their data sheet to know.

Power One also recently introduced a micro-inverter which seems to address the electrolytic capacitor concern of the Enphase micro-inverter. Both the optimizer and micro-inverter are just recently introduced products. It appears the original company is Italy based but pretty much worldwide now with headquarters in Camarillo, CA.

Also press announcement:

"On June 17, 2011, Power-One Renewable Energy Solutions LLC (“Power-One RES”) acquired the assets of National Semiconductor’s SolarMagic monitoring business."

Re: When are DC to DC optimizers economically feasible?

rollandelliott wrote: »

http://www.youtube.com/watch?v=pkoT5vNTtn8&feature=player_embedded

http://www.tigoenergy.com/our_products.php

another company that makes a similar product.

"patented impedance matching technology", the spin doctors :roll:

From a quick patent search, it looks like their modules may help equalize panel production variation more then do much for a shaded panel. The shading benefit may depend on how many bypassing diodes are incorporated in a given panel. It looks like they have a simple voltage boosting circuit, along with the monitoring function. Because the voltage boost ratio is very low, the efficiency loss is minimal.

When panels are put in series the central inverter's MPPT point voltage will be distributed across the series connected panels. Production variation in the PV panels can be up to +/-5%, or so, in their illumination/current production. Actually, cell production has greater variation but the panel manufacturer sorts them into 'bins' that group them in tighter matching. This is why the same shape and size panel from a manufacturer can have 180 watt, 190 watt, and 200 watt models.

Because all panels are wired in series they must produce the same amount of current (Kirchhoff's law). When there is variation in the panels ability to produce more or less current for a given illumination level, the individual panel's loading voltage will divide up the central inverter's MPPT voltage loading point unequally. This can cause an individual panel to be operated at a voltage loading point slightly off its individual optimum MPP voltage point. So the strongest panel must be compromised in its optimal loading voltage to make it produce the same amount of current that the weakest panel in the series produces.

So the question is how much extra will you pay, per panel, to squeeze the last 3 or 4% of power production out of your array? $50 per panel, $100 per panel, ??? I think not. I think you will be more likely to pay for the performance monitoring function. This is, in my opinion, the only thing that makes them even close to a viable product.

Re: When are DC to DC optimizers economically feasible?

rollandelliott wrote: »

checked with one distributor and it is $40 per unit.
not sure if you need them on every panel or just the shaded ones.

Thanks for the "This is why the same shape and size panel from a manufacturer can have 180 watt, 190 watt, and 200 watt models."
I always wondered about that.

Pretty sure they have to be on every panel. There has to be communication on each panel's performance to know how to divide up the overall central inverter's loading voltage.

I also believe the primary MPPT function is still done by the central inverter. The individual panel's optimizer just does slight voltage conversion modification to induce the central inverter's MPPT function to find a better overall loading point. The panel optimizers have to be very careful (do it slowly), so not to sent the system into an unstable MPPT hunting exercise that would lose even more power then any possible gain by the optimizer.

By the way, although I call it a voltage conversion modification, the boost circuit switcher is still operating as a current source so by true definition, it is an impedance matching device.

The panel unit circuit board is only about 2"x 2". Attached picture is poor resolution but gives you an idea of what it is.