enphase s280 with LG315N1C-G4

[jetsurgn]

You mentioned you added two panels to your system, did you have to go through the whole process again? Or can you just add a couple without anyone knowing?

[J.P.M.]

I'm thinking more about payback and ROI (I had to look up "LOCE"). Think about it this way, you could over pay for your system by $1/kw but under-sizing (or should I say "not right-sizing") without consideration for change (that is a given) could cost you much more over the system life.

Ah well, certainly worthy of it's own topic, maybe if I get around to it.

LOCE is one way of many. My point was that folks may be looking for the most long term bang for the buck, and there are as many ways to do that as there are people to make the effort. One other way is to do some comparison of alternative type analysis. For example, and depending on one's view of the future and time horizon, it's certainly possible to compare 2 scenarios ( or any # for that matter) and see what may happen to a sum of money over the chosen time frame when invested in each alternative, with the possible goal of choosing the one alternative that, in the opinion of the asset holder the best combination of risk/benefit. Bury in the ground - zero return and suffer the ravages of inflation, but close to zero risk of loosing any capital. Stock index fund - depending on risk tolerance, better. Corporate bonds - some risk, probably a nominal to decent return and a fair chance of return of all capital at the bonds' maturities, as well as some access to the capital in an emergency. Solar - lower electric bills, and a bunch of tax credits, but a bit more uncertainty in the analysis, partly because of a lot more variables to consider.

Not all considerations are financial, but the financial ones are usually considered and usually top the list.

[Willaby]

That's great, I would NOT cancel that 2nd order either. I tend to wait and over-analyse which causes me to miss out from time to time.

[rsilvers]

I was 16th in line on the first day and got my order in around 10:07am EST. Given the 50 or so dealers on that time zone, I should be in the first 800.

They accidentally charged my card twice, so I have two orders. I was going to cancel one, but then didn't.

When preparing my load center for solar, I moved some circuits to a sub-panel and freed up enough space for 200 amps of car charging.

If I have an electric credit, I can always use electric space headers.

[Willaby]

If the most cost effective, long term solution is one of the goals, one way to look at it is to size a system that produces the lowest LOCE for the parameters the person paying for the system and the resulting bill sets. Unfortunately that often take a bit of homework.

I'm thinking more about payback and ROI (I had to look up "LOCE"). Think about it this way, you could over pay for your system by $1/kw but under-sizing (or should I say "not right-sizing") without consideration for change (that is a given) could cost you much more over the system life.

Ah well, certainly worthy of it's own topic, maybe if I get around to it.

[Willaby]

I want my system oversized for my current usage because if I had lower-cost power, I would not suffer with minimal air conditioning going forward. Also I have a Tesla Model-3 on order. 10,000 miles on the car will be about 3.5 MW a year.

My thoughts exactly. I wanted to use about 500kw extra worth of AC per year. I bought a Volt before solar, so I knew my EV usage. Sadly, I'd like a Tesla 3, but with 500k now on order I think that's a 5+ year wait and the tax credits will be gone. Too late to the party for me. I am considering a base Model S, but I'll likely talk myself out of it.

[rsilvers]

Also SREC2 in MA are worth about $250 per MW. Electricity costs about $230 per MW, so the SRECs are worth more than the electricity. So even if your system is larger than you need, and even if you run a negative balance on your electric bill, you still won't lose due to the SREC value.

And besides, if I had a negative balance on my electric bill, I would just turn on resistance heaters in the winter and use up the power, saving on heating oil.

[J.P.M.]

Interesting statement (I don't sell solar, btw). For someone considering solar in San Diego (or California in general), and say they were reasonably able to project their usage, what defines "oversize"? Or, maybe better asked, what is the "right size". Is it 60%, 70%, 99%? For me, the lowest rate on my bill is ~18c kwh, I'd want to cover that and up because the ROI is good. Certainly current TOU periods are not likely to shift, right, so that shouldn't affect calculations much? What specifically is the ignorance and what are the myths? Would there be any scenario for a larger system today that might make sense later?

If the most cost effective, long term solution is one of the goals, one way to look at it is to size a system that produces the lowest LOCE for the parameters the person paying for the system and the resulting bill sets. Unfortunately that often take a bit of homework.

[rsilvers]

I want my system oversized for my current usage because if I had lower-cost power, I would not suffer with minimal air conditioning going forward. Also I have a Tesla Model-3 on order. 10,000 miles on the car will be about 3.5 MW a year.

[Willaby]

Oversizing a system, whether intentionally or not, costs your customers money. You can choose to perpetuate the ignorance and myths that are embedded in the industry, or you can choose to objectively look at the data and try to help people understand that they don't need to offset 100% of their usage to come out ahead, especially (in many cases) with TOU plans..

Interesting statement (I don't sell solar, btw). For someone considering solar in San Diego (or California in general), and say they were reasonably able to project their usage, what defines "oversize"? Or, maybe better asked, what is the "right size". Is it 60%, 70%, 99%? For me, the lowest rate on my bill is ~18c kwh, I'd want to cover that and up because the ROI is good. Certainly current TOU periods are not likely to shift, right, so that shouldn't affect calculations much? What specifically is the ignorance and what are the myths? Would there be any scenario for a larger system today that might make sense later?

[J.P.M.]

Yes agree but as sensij said it's probably not a horrible rough idea


Good to know



Horizontal



Awesome! I've got a Vantage Pro2 with the trimmings. I'm also soon mounting mine above the array, let's compare notes.

See my last post. While Sensij's comment describes a method that is for sure better than using the inverter heat sink temp. (as I assume what you were referring to), I'd not put a lot of faith in reported microinverter temps. without getting up on the roof and getting some data for comparison and/or calibration, or understanding more about how Enphase, or any monitoring system measures or estimates cell temps.

So far there are 3 posters I know of with Davis Pro II + instruments - you, me and Sensij. I'm working on pyranometer changeout and calibration check. I'm SWAGing mine's drifted ~ 1.8 - 2.3% or so over the last 8-12 months and is underreporting GHI by about that much. Can't/won't speak for Sensij, but it looks like he may have high readings due to albedo effects. This is not an exact science by a long shot.

[J.P.M.]

I would guess that using the temperature reported by the Enphase microinverter, mounted directly underneath the panel, is not a terrible way to correlate panel temperature.

Better than using the inverter temp.

Short ans: Without knowing the apparatus and method of attachment of the temperature sensing method(s) used, I can't offer an intelligent response to your question in the form of an opinion.

See: "Photovoltaic Array Performance Model", King, et al., Sandia, 2004, and other sources for some discussion/information on array or cell temp. measurement. I've found the Sandia method workable for my situation, and it seems to give reproducible results. In general, my opinion is that stand off (detached) methods of temp. sensing - IR thermometers - have advantages over "attached" methods (thermocouples, etc) that may be more numerous that the disadvantages of the attached methods. Lots to consider.

I'm closing in on a short description of my results of a comparison of estimating array average instantaneous cell temps. using array voltages vs. actual measured panel temp. measurements (I know, it's been gestating for a long time now - give it a pit drip induction as my bride would say). Film at 11 or when bulletins break.

[Engineer]

More later, but the inverter temp. has little if any relation to the panel temperatures.

Yes agree but as sensij said it's probably not a horrible rough idea

FWIW, this time of year, and from a lot of measurements I've done w/ an IR thermometer from under the array, the ave. array temp. runs about 25 - 30 C. above roof ambient under clear skies at min. incidence angle time, a bit less as f(P.O.A.) off min. incid. angle.

Good to know

What's the orientation of your Davis solar sensor ? If horizontal, that 998 W/m^2 needs to be adjusted to P.O.A. irradiance for what you're measuring. For a bit more precision, the solar sensor reading needs to be corrected for temp. effects (~ -1/1500 per deg. F. above/below 77 F.).

Horizontal

I've got a Davis Pro II +, located about 4 ft. north off the N-S axis of my array. Been measuring/recording this type of stuff for a bit over 2 years or so.

Awesome! I've got a Vantage Pro2 with the trimmings. I'm also soon mounting mine above the array, let's compare notes.

[ButchDeal]

no you are not getting it. I never claimed that a larger inverter on the under sized module would produce more. I claimed that a larger inverter on a larger module would produce more than that same module on an inverter that clips.
lets use an example. say with a S280 vs SolarEdge and 350W pv module and 300W pv module:

the enphase report is claiming (correctly) that
an S280 will produce more power with a 350W module vs the same S280 with a 300W module

the S280 with 350 would produce more than S280 with 300W correct
however solaredge with 350W module would produce even more than the S280 with the 350W module


As you state the paper demonstrates that funds are better spent on a larger module than a larger inverter, However, they assume that the inverter is the same cost. Solaredge and other larger micros are cheaper than enphase, so you would have more funds to put towards a larger module....

[sensij]

More later, but the inverter temp. has little if any relation to the panel temperatures. FWIW, this time of year, and from a lot of measurements I've done w/ an IR thermometer from under the array, the ave. array temp. runs about 25 - 30 C. above roof ambient under clear skies at min. incidence angle time, a bit less as f(P.O.A.) off min. incid. angle.

I would guess that using the temperature reported by the Enphase microinverter, mounted directly underneath the panel, is not a terrible way to correlate panel temperature.