Enphase microinverter efficiency

[DrLumen]

Does Enphase make an iq6+ micro-inverter that can output 400 Watts AC power?

And that lost energy only occurs on the BEST DAYS, which I have very few of.
All winter there would be no clipping, no lost lost energy.

Ahh, ok. That makes more sense. Thanks.

[max2k]

I will probably regret this but...

The illustration does well to show what you mean for the quicker "saturation" (for lack of the proper or better term). But, how is leaving ~3600kwh of the clipped part on the table an advantage? Why not use micro-inverters rated to the panel output?

I guess I missed something.

those inverters don't exist in Enphase line up but if they did exist they would be more expensive so you'd lose money on inverters.
Then panels age and lose their output. If system was designed to harvest all possible Wh without clipping on the next year and all the rest inverters would become underutilized.
Utilities in CA and I believe other states introduced TOU rates where middle of the day costs cheaper than the evening. In this case having system which performs well in the late afternoon could allow for extra production at higher TOU rate.

in the light of above clipping design might not be as cost inefficient as it might look.

[JSchnee21]

Just to take a step back for fresnoboy ,

Is there a particular reason you're only considering an Enphase solution? SolarEdge solutions are similarly priced, have equivalent (or perhaps better IMHO) monitoring capability, and at least equivalent (many would say much better) reliability. Total system efficiency (if you can use the newer HD inverter) would be at least as good, if not better than the Micros. And SE offers DC optimizers which can harvest the entire output of a 400 watt (and larger) panel. For example the P400 optimizers I have on my 330W panels. They even make P800 and various other sizers to which you can connect two panels.

While NEOH is correct that panels rarely generate at their STC nameplate levels, pairing a 280W micro with a 360W panel seems a little over the top. Though if you figure that most of the time you panels will peak at 80-90% of their STC rating, that's 288W-324W.

Is this a residential application? With 72-cell panels? 240 VAC? How many kW? What is the anticipated production (kWh per PVWatts) versus your annual consumption? How much are you looking to offset with PV?

[JSchnee21]

Ooops, sorry. I missed the residential and HAM piece. I'm not a HAM person myself, but I've seen several posts on this board talking about Micro RF. So it seems like both Enphase and SE might have some RF concerns. But the benefit, I think, for SE is that all of the RF is in the inverter (aka localized, shieldable, and substantially less for the HD models? perhaps TBD). Where as the distributed nature of the Micros can be an issue. I've not seen posts suggesting the DC optimizers are RF sources.

[sensij]

Fresnoboy has other threads with more details. A big one is interference with radio, eliminating Solaredge from consideration.

[JSchnee21]

Thanks sensij, yes, sorry. I just remembered where I had seen those other posts. Sorry, I'm a day late and a dollar short. Please disregard my questions/comments.

[J.P.M.]

In the real world, there is a lot less clipping than you show unless you live in Arizona.

In the real world, there's also a lot less power production to be clipped than shown on max's graph as well.

[AzRoute66]

It seems to me that some in here are rationalizing a 280W output from a 400W panel as acceptable. That don't spread on my toast. If you want longer solar days, put some panels facing easterly or westerly. I don't mind bouncing photons off the panels, but not in this manner.

[J.P.M.]

It seems to me that some in here are rationalizing a 280W output from a 400W panel as acceptable. That don't spread on my toast. If you want longer solar days, put some panels facing easterly or westerly. I don't mind bouncing photons off the panels, but not in this manner.

Yea, FWIW, something on all this seems inside out to me as well. Design right and then either get smaller panels or higher capacity inverters.

[sensij]

It seems to me that some in here are rationalizing a 280W output from a 400W panel as acceptable. That don't spread on my toast. If you want longer solar days, put some panels facing easterly or westerly. I don't mind bouncing photons off the panels, but not in this manner.

A quick PVWatts run offers some insight.

400 W on 280 W inverter is a DC to AC ratio of 1.43.

For San Diego, using Miramar TMY, premium panels, roof mount, 180 deg azimuth, 30 deg tilt, 8% losses... modeled annual output is 1.75 kWh / kW.

Same conditions, but reduce the ratio to 1.0 and point the panels east... annual output is 1.45 kWh / kW.
Same conditions, but reduce the ratio to 1.0 and point the panels west... annual output is 1.55 kWh / kW.
Same conditions, but go to 0 deg tilt... annual output is 1.60 kWh / kW.

One more, south facing ratio 1.0... output is 1.82 kWh / kW... suggests the clipping penalty to energy production is ~4%. Changing the orientation to reduce clipping in a net metered, grid tie system doesn't look very rational to me.

[max2k]

It seems to me that some in here are rationalizing a 280W output from a 400W panel as acceptable. That don't spread on my toast. If you want longer solar days, put some panels facing easterly or westerly. I don't mind bouncing photons off the panels, but not in this manner.

guilty as charged . Seriously I think clipping has merits. The issue is 'impedance' mismatch between inverters capability to convert power and panels ability to produce power: inverters have flat 'curve' as they're capable of converting 24x7 at max output. Panels have bell shaped output curve and as a result you're fitting round thing into square hole one way or the other meaning you'd spend extra on panels (clipping) or inverters (not clipping) + few other factors already mentioned.

[fresnoboy]

guilty as charged . Seriously I think clipping has merits. The issue is 'impedance' mismatch between inverters capability to convert power and panels ability to produce power: inverters have flat 'curve' as they're capable of converting 24x7 at max output. Panels have bell shaped output curve and as a result you're fitting round thing into square hole one way or the other meaning you'd spend extra on panels (clipping) or inverters (not clipping) + few other factors already mentioned.

So would you say that high output panels are a waste of money? Stay to 300W or so, or what do you think the optimum panel output should be?

[sensij]

So would you say that high output panels are a waste of money? Stay to 300W or so, or what do you think the optimum panel output should be?

If you determine that the IQ+ inverters are most appropriate for your needs, I would suggest that you model the performance with lower output panels and with higher output panels. Then, you can compare the difference in cost and output for those systems, and come up with a marginal cost per kWh for the difference in size between the two. With that, you can decide whether you are better off with the smaller system (and paying the utility the difference), or going with the larger system.

[SunEagle]

So would you say that high output panels are a waste of money? Stay to 300W or so, or what do you think the optimum panel output should be?

IMO high output panels would be a better fit with a string inverter instead of using micros. Sometimes the ease of using micro's creates a bottle neck and output loss due to clipping. Unless you have shade issues going with a string inverter would be a cleaner and provide a higher array output.

[jflorey2]

Sorry, I don't understand. You are saying it's only going to produce 280 watts out no matter what, even if the panel can produce more power than that? This seems like a broken definition of efficiency as well.

Efficiency is technically power in to power out. If the panel CAN generate 400 watts, but is actually generating 290 watts, and 280 watts of that goes to the grid - the inverter's efficiency is 96.5%.

I am still confused as to why they say to use the iq6+ if I had a panel that went up to 400W. Why don't they make an inverter that doesn't clip?

Because it's more cost for a limited increase in power.

I'll use my system as an example. It's an older Sunpower system with 9680 watts worth of panels. However, the two inverters, together, are rated at 8700 watts. Why is this OK? Because most of the time the panels generate closer to 7000 watts and the inverters have no problem using all of that. The only time I've ever seen close to 8700 watts are right after rain, when the panels are clean and cool and there's a little cloud lensing going on.

In your case, depending on many things (angle, insolation, typical weather, temperatures) a 400 watt panel will produce about 280 watts at full sun. That means the Enphase will work well for you. Under certain conditions (the first sunlight after a rainstorm) the panel will generate close to 400 and you will clip - but those cases will be relatively rare.

Want to see this for yourself? You can get a panel and a curve tracer (they are getting cheaper now) or just a panel and a variable resistor and mount it outside your house. Measure the panel's power periodically and see what you get. This will give you a good sense of how much power you will see vs the panel's actual rating. Make sure you leave the panel outside for a while so it picks up a "typical" layer of dirt, as all panels do.