How did you decide? Microinverter vs Optimizer & PV Inverter

[jflorey2]

But saying I am throwing out things like being 10-15 degrees cooler in the shade of the panel/module? Ever stand in the sun and felt the heat? Ever stepped out of the sun and into the shade? Yes, it was a little bit cooler! I don't need to have a degree in physics or thermal dynamics to offer this observation.

Case in point -

We were in Thailand and the Thais had thoughtfully provided some packing tents. It was 90 degrees and 80% humidity. You would step out of the sun into the black tent and . . . immediately be hotter. The black tent absorbed all that sunlight and re-radiated it as infrared, and the slight reduction in wind (even though three sides were open) was enough to make it much worse.

So yes, in some cases, being in the shade is going to make you hotter. It all depends on mounting, amount of shade, amount of air circulation, and both the radiative and conductive thermal environment.

[J.P.M.]

I'll bet there're guys here who live in the hot southwest who can tell us based on panel voltage pretty accurately what temps panel silicon can reach. I'd like to get an inkling of that. Silicon diode voltage decreases by about -2.5mV/C. The actual frame of the panel will be somewhat cooler.

I can, but it'll take more space than available here. Been at it for ~ 2 1/2 years now.

Very short guess on array temps.: In winter, under something like 800-850 W/m^2 POA (Plane Of Array) irradiance, my roof array runs 23 - 23 deg. C. above roof ambient air temp. which runs about 3-5 C. above ground level ambient air temp. at midday under clear skies. In summer, Approx. same conditions, w/POA ~ 950-975 w/m^2 POA irradiance, the array runs about 24-26 C. above roof ambient air temp. which runs ~~ 4-7 C. above ground amb. air temp. One correlation I've found that gets pretty close to what I've measured:

T, array ~~ = 0.943*(Tamb. ) + (0.28 * (I) -1.528 *(wind) +4.3 (from NREL/ CD - 520-33586, yr. 2003.)

Where: Tamb, = amb. air temp., deg. C.
I = P.O.A. ( plane of array) irradiance - not GHI ( Global Horizontal Irradiance)g, in W/m^2
wind = wind velocity in m/sec.

I needed to change the last term to 3.82 to better fit my observations.

There are lots of other methods and correlations. One way to use Voltages: Observe/record array voltage at the inverter. calculate/estimate the array temp. using the above empirical correlation. Do this several times and see if a pattern/trend line emerges, or get the Voltages from your monitor. Either or any way, compare the slope of the voltage drop/deg. with published data for the temp. coeff. of Voltage for the panels in question.

That's the Reader's digest version. Some assembly is required. Your mileage will vary.

[DaveDE2]

Thanks JPM. Great answer.
...except when I use the NREL formula above I get wildly high numbers due to the 0.28 * I factor....

[J.P.M.]

Hi sensij,

The discussion that went over my head was this:

"To a first approximation, when A is close to B, A⁴ - B⁴ is proportional to 4(A-B) (Average)³ As the temp difference gets very large the heat transfer becomes proportional to the fourth power of the higher temperature. In between, it is messier."

I am comfortable saying that these sentences go over my head - and I am pretty well educated. But that is just it - I am "ok" not knowing everything. I'm here because I want to learn more and be an educated consumer. As best I can.

So, I truly enjoy how you make everything so personal. I will be sure to pass along to friends and acquaintances that honest comments, curiosity, and genuinely intended observations are not welcomed by you on this forum. Perhaps you don't realize how off-putting you are. Perhaps I ask questions (whether reasonable or ill-informed) that you feel impact your bottom line. You take my comments - which have no particular bent - in an unnecessary way.

The fact is (interpreting your unusually defensive postings) is that you are sensitive to the "perception" problem that the seeming temperature of a roof causes for a particular product. The perception problem may have no basis in fact - and you can shout people down all you want. But if you want to change the perception of your ordinary consumer, you might want to do more than just shout them down. Even my own post acknowledged the information from a product spec sheet - about ICE 61215 testing) may override any concern (again, real or perceived). (Just like you never admitted I was right about the integration of the Sun Power micro converter being physically integrated in a different way than the Enphase module. You insisted they were integrated in the same manner. You raced to excoriate me about my honest comment - about integration - only to be factually wrong yourself. Did I kick you about that?

But saying I am throwing out things like being 10-15 degrees cooler in the shade of the panel/module? Ever stand in the sun and felt the heat? Ever stepped out of the sun and into the shade? Yes, it was a little bit cooler! I don't need to have a degree in physics or thermal dynamics to offer this observation. Perhaps the logic is not born out in practice (perhaps the water in a tree is what absorbs the heat making the shade of the tree cooler). But I can admit I don't know the ultimate outcome - and I pretty much say so upfront. I rely on the experts (hopefully on this forum to point me in the right direction).

Perhaps you've watched the HBO show "Silicon Valley." Just yesterday the engineers on the show came to grips with the fact that their audience were consumers - not other engineers. And as such, they had to readjust the way they explain themselves and their products (otherwise the consumers just got defensive and left their company without anyone who wanted their product). All of use end-user consumers are the folks that write the checks at the end of the day... but I guess I still deserve all of your disdain for making honestly intended observations and comparisons.

I think back about how you had to be so very snarky in telling me about all the many mistakes in my evaluation, my contractor, my system, my expectations... almost like you were cheering for me to have a bad experience installing solar on my home... if there were enough people like you on this forum - displaying your complete lack of grace - this forum would slowly recede from anyone's notice. Then where would you be? All 3361 posts... down the drain.

There are far gentler ways of redirecting the misinformed. There are far gentler ways of informing me about the particulars of solar power, or the sheer brilliance of your brain power. So I will leave you to your 3361 posts... recognizing that once my system is installed, the likelihood of my posting again will drop off.... but seeing that you may be here for the long haul, you may (re)consider your tact.

Thanks.

You might consider investigating ways of getting a thicker skin and keep in mind that not everyone who tells you what you don't like is trying to hurt your feelings, as well as not considering advice you get here as an entitled birthright. You came here looking for advice/answers. You got some. Don't like them ? Ignore them. Want to learn stuff ? Stick around.

If you do stick around, I'd suggest your learning experience may be better with a modified sense of entitlement, but suit yourself.

Welcome to the forum of fewer illusions.

[entgegnen]

You might consider investigating ways of getting a thicker skin and keep in mind that not everyone who tells you what you don't like is trying to hurt your feelings, as well as not considering advice you get here as an entitled birthright. You came here looking for advice/answers. You got some. Don't like them ? Ignore them. Want to learn stuff ? Stick around.

If you do stick around, I'd suggest your learning experience may be better with a modified sense of entitlement, but suit yourself.

Welcome to the forum of fewer illusions.

JPM - Fair enough. FWIW, I only took issue with a single poster. Not the various diverse advice from everyone here. Not looking to sound entitled. Thanks for telling me I was. Thanks.

[J.P.M.]

JPM - Fair enough. FWIW, I only took issue with a single poster. Not the various diverse advice from everyone here. Not looking to sound entitled. Thanks for telling me I was. Thanks.

Understood.

[thejumpingsheep]

I didnt read all of page 3 in this discussion but I am working on my installation and just wanted to state why I moved away from Micro-inverters. Well there is more than 1:

1 - Not future proof. Well sort of. At the rate battery tech is moving, I fully expect batteries to be very affordable in 10 years and for folks to be moving off grid in droves for about $10k. To go from micros to battery you would need to convert the power back to dc... which is another loss of 2%-3%... then you need to invert it again to AC (even more loss)... that is just silly.

2 - As a guy with a long finance background, I dont see Enphase surviving because to be competitive they will need to keep up with string inverter prices +/- 10%... A lot of Chinese inverters are just now starting to penetrate the market. I bought a Solis 5kw inverter (they just partnered with Tigo) for $1200 and that is a lot compared to others. I have seen 5kw inverters with 2 MPPT's for as low as $800 but they are not UL listed (yet). But that tells me that they will eventually be that much if not less since the internals are no different than most of the inverters on the market now. Can enphase keep up with this price decline? In the finance world, we see this all the time and the answer is almost always no. A public company simply has too much overhead but there are exceptions every now and then.

3 - Cost. Cost is too high if you have more than 10 or so panels. In my case, I got a great deal on 30 190W mono panels. If I went with enphase I would need to spend $4k on inverters. That is too much. I could double the size of my array and get another Solis 5kw for the same price. It might make monetary sense if you had 10 or fewer 300+W panels.

As a side note, I like the Solaredge idea of optimizers but I hate the proprietary nature of their business and coming from the IT world originally (before I got into finance), this was always bad juju. I really like idea of Tigo but no one is using them yet so I am waiting to see more reviews and such. I can always install them later if I want to.

Anyway, thats just 2 cents from a newbie.

[entgegnen]

Since you have a background in finance, I was wondering if you had any opinion on the Solar Edge tech being licensed; eventually - as a way to further compete against micro-inverters... or is this wining a battle (optimizer vs micro inverter) just to lose the war (eventual knock-off brand optimizers). I was looking at the tech as akin to the brand-name vs generic drug market. With Tesla taking the reigns as an energy company (arguably this is how the last few weeks could be viewed) it may be less concerned with the SE patents as it is with the direction of the larger market.... based upon its core product lineups... making SE just an accessory to e.g. its vehicles...

The whole Solar City thing had me wondering why... e.g. was it just to have a customer acquisition infrastructure? It couldn't have really been in hopes of acquiring future PPAs...?!

[thejumpingsheep]

@etgegnen Let me get my crystal ball... in terms of the overall war against cheap competitors, I think both solaredge and enphase can compete since there is no reason why they cannot produce their product around the same price as their competitors (minus their corporate inefficiency plus corporate advantages).

As for the battle of micro vs optimizers, I think optimizers are already winning. Of about a dozen estimates, only 1 wanted to install micro-inverters. About 8 wanted solaredge optimizers, and the remaining few offered simple string configurations. That speaks volumes to me. I think enphase needs to switch gears fast and make their own optimizer/maximizer option. They can take all the market share back by making their optimizer non-proprietary. Further evidence is in the financial numbers. Enphase revenue has basically stalled since 2014 and the last 12 months dont look good at all (shrinking) whereas Solaredge revenue is still growing at above a 20% clip. Solaredge is also outselling Enphase overall ($464m vs $335m). That said, there are competitors in the optimizer market who I think will give SE a run for its money.

I believe that Tesla's purchase of Solaredge was purely altruistic. I think Elon didnt want to fire the folks at SC and didnt want to fire his relative at the helm. Simply as that. And you know what? That is ok with me. Money is not what makes the world go round, its actually productivity. Bankers and investors are generally worthless in the grand scheme of things so why protect them any more than workers who produce? The only thing I am worried about (and what I learned when I tried to help folks) is that most dont appreciate it anyway. I think that Elon is thinking that the amount being paid is peanuts anyway and when you look at acquisitions made by other companies that imploded, its really not a horrible deal in comparison. I mean... look at most acquisitions made by big companies like Apple or MS... they almost always never pan out and they are always overpriced. SC at least gets you in a few households by contract. You may be able to leverage them later to install batteries.

[J.P.M.]

Thanks JPM. Great answer.
...except when I use the NREL formula above I get wildly high numbers due to the 0.28 * I factor....

I created an error. The 0.28 *(I ) * IS WRONG.

The entire correct formula is:

T, array ~~ 0.943 * (T,amb.)+ (0.028) * (I) - (1.528) * (wind) + 4.3

The 0.28 from the post is incorrect. I meant to write 0.028.

I apologize for my error. Thank you for checking my work and finding my error. Part of the problem of being retired is that there is no one in the next office to check my work and vice versa.

FWIW, that empirical correlation agrees fairly well with actual measured temp. data from 60 trials once I changed the 4.3 to 3.82 as noted. It also agrees quite well with the Sandia method that SAM uses to estimate array temps. for the same 60 trials. All 3 methods seem to agree with the estimate of average array temp. calculated from string voltages taken at the inverter screen.

[J.P.M.]

Further to my 06/28, 8:22 P.M. post about my error, note that the empirical correlation used for temp. needs P.O.A. (Plane Of Array) irradiance, NOT GHI ( Global Horizontal Irradiance).

The two are not the same.

Example: My array , 18.75 deg. tilt, 195.75 azimuth, At min. array incidence angles:

June 20 (~~solstice), min. incidence angle = 8.37 deg. @ 1311 hrs. P.D.T, measured GHI = 986 W/m^2, POA est. = 991 W/m^2.

March 20 ( ~~ equinox), min. incidence angle = 14.80 deg. @ 1318 hrs. P.D.T., measured GHI = 833 W/m^2, POA est = 952 W/m^2.

Dec. 22 (~~ solstice), min. incidence angle = 38.46 deg. @ 1208 hrs. P.S.T., GHI = 555 W/m^2, POA est. = 772 W/m^2

Using GHI instead of POA irradiance will lead to less accurate estimates. Getting an accurate est. of the POA from either tabular, calc'd or measured GHI values is a bit of a PITA, but NREL has spreadsheets that can help. Still GIGO applies, and even with some instrumentation and care, getting within 1-2 % requires real care and precision of data collection and handling methods.

[DaveDE2]

How is POA measured real-time?
I guess another way to get array (silicon) temp vs voltage would be to put a thermocouple under the panel on the back side of the back sheet and monitor it with a data logger and compare that to the inverter reported voltage. Errors would be due to backsheet thermal resistance, voltage drop between the array and the inverter, and in my case differences between panel voltages within the string. The voltage drop could be easily accounted for since the inverter reports string current and the wire length and resistance is known. I have a thermocuple and a data logger. When I get bored I might try it. Once the correlation is understood I guess that could maybe be plotted on PVoutput but I'm not sure if PVoutput lets you include an equation to convert voltage to Temp.

[Supercharger619]

Which system (microinverter vs power optimizer) would use more wiring/cables, junction boxes, etc. leading to more money and time?