Using 100% of the solar your panels produce [DC / AC ratio]

[Bitslizer]

I would like to see that quantified. For it to be significant, there would need to be significant difference in inverter efficiency between, say, 60% and 90% of rated power output.

Cheers, Wayne

Inverter clipping: How to maximize solar project value

Inverter clipping, or “inverter saturation,” occurs when DC power from a PV array exceeds an inverter’s maximum input rating.

www.solarpowerworldonline.com

 

[wwhitney]

People also tend to forget, you GAIN production during the "shoulder" before and after clipping, usually that exceed or offset the clipping

OK, the article you just posted doesn't discuss inverter efficiency at all. So apparently I misinterpreted your statement the first time around.

Now I take your statement above to mean that you are comparing (a) an inverter of size X with size X of panels, (b) an inverter of size X with size X+Y of panels, and (c) an inverter of size X+Y with size X+Y of panels. And if Ea is the energy produced by system a, your statement is that Eb-Ea > Ec-Eb. In effect that you getting over half the benefits of adding both panels and inverter by adding just the panels alone.

That's probably true for ratios of Y/X of up to at least 0.4 or 0.5. But it's a pretty arbitrary comparison to make. It doesn't in any way mitigate the clipping.

To be clear, DC/AC ratios below 1.3 are generally not economically optimal.

Cheers, Wayne

 

[wwu123]

Yes I agree that the efficiency is better when the inverter is driven at higher wattage. But I'd argue that this is a very small difference compared to the clipping loss.

I do think the industry could with minimal effort put out some studies, or even just some basic calculations, to explain both the energy AND cost efficiencies of oversizing vs undersizing vs right-sizing.

It might be true that the efficiency differences between 80% capacity vs 100% capacity are fairly low, I looked at say some SolarEdge inverter curves and the difference seemed like 0.1% or less.

But in general I think folks with oversized arrays relative to inverter over judge two things:
-One, they look at how long they are clipping during the best part of the year, and overestimate how much energy they are losing. Even if one is clipping for say three hours - the actual area (energy) lost under the curve can be pretty tiny, because the insolation curve is pretty flat if you clip for "only" three hours. The energy lost that day is a few %, and this only happens for a few months of the year. At ratios above say 1.3-1.4, the area is larger, but you have to be clipping for 4-6 hours a day.
-Two, they overlook the losses during the worst parts of the year. At least three months of the year, my array barely peaks at 50% of DC rating. Which also means half the day it's operating at below 25% of DC rating. Looking at the SolarEdge inverter curves, some of them lose about 1% efficiency between 20-40% power, maybe 5% efficiency between 0-20%. Of course at those lower power periods, you're losing that efficiency on smaller amounts of power - so it does take some pretty complex calculus to estimate. But if we just wing it that 3 months of the year, I would not be surprised at all if 1% of energy was lost all production over the ENTIRE winter season - and that's assuming perfect insolation (no storms, clouds, etc). Then let's add in all the cloudy days in spring and fall, plus the beginning and end of every day all year round, where the inverter is operating at 0-40% capacity.

So while I don't have full technical understanding nor the calculus to make the full analysis, I wouldn't be surprised at all if inverter ratios of 1.0 to 1.2 generate NO greater energy over the entire course of the year period, i.e. no economic value even if a larger inverter were free. And economically even worse off if you have to make a big step up, say going from a 7.6 to a 10 kw inverter (which is a 33% increase in capacity, even if free (so it's not about being only $300 more to upsize an inverter) - because it greatly increases those periods of the year where you're operating below 20% and 40% respectively, where inverter efficiency really drops off.

 

[DrSmile]

I'm not quite following your logic regarding peak production. Even on Winter Solstice, on a sunny day I'll peak at 80% of inverter DC rating. Are you talking about shady days? I think on shady days you may have a point, but the counter-argument to that is that your production is pretty low on shady days and don't contribute that much to your annual production.