What do you think of my quote for 6KW in SoCal?

[J.P.M.]

Well, several people (and forum threads) recommended against me choosing micro-inverters unless absolutely necessary. I REALLY want them because I like the precise data on a per panel basis that they provide. But, it was a "want" for me and likely not a "need" (pending shading analysis) and people's concerns over longevity and reliability certainly got me thinking twice.

So, today, after instructing my contractor to re-layout my roof again (they were unnecessarily avoiding my rooftop heat exchanger that is non-functional). My suggested layout removed the heat exchanger and conveniently allowed future expansion of 2 more panels on my south facing roof. Next, we discussed the shading analysis which indicated I have a next to no shading in my layout. After some philosophical conversations about micro vs central, I expressed my concern that the micros might not be cost effective (or necessary) for me and asked my project manager what the monthly production difference between micros and central would be. After plugging in the 96.5% efficiency for micros vs 95% efficiency for the Fronius IG Plus V 6.0-1 UNI he estimated (I think he approximated in his head) about 50 kwH/month difference. This seems too high to me... I could run some numbers to check that (I probably will), but instead I said I'm paying $2,600 for micros and gateway that give me about 50Kwh/mo. I asked how much would it cost to put the extra 2 solar panels up there NOW instead of the micros and gateway....after some quick calculations, he said about $1,750 installed. I told him I would rather have 2 extra panels and save $850 ($2,600 inverters - $1,750 panels) than have micro-inverters. I felt like that is more the common belief around here by the SMEs and I think I've even convinced myself of that fact (and now my contractor), so I'd like to hear that you guys approve...Would you guys choose 6.5kW central + $850 savings vs 6.0kW micros? With the prospect of the loss of my micro-inverter data, I'm looking for comfort!

Also, does anyone think 26 x 250 kWh (SolarWorld SW 250 poly / Version 2.0 and 2.5 Frame) is too much for the Fronius IG Plus V 6.0-1 UNI? I suspect they weren't going to automatically upgrade that.

This is still somewhat conversational at this point. I still need to see the details of the change order and see if it materializes to what we verbally discussed.

1.) The inverter efficiencies are estimates, not gospel. Mine runs about .97 or so most of the time. Spec sheet sez. .955 or so.

2.) Back of envelope stuff : A 6 kW system under good conditions in Ventura co. will probably produce about 10,000 to 10,500 kWhrs./yr. The 1.5% diff. (.965-.95 = .015) in eff. as claimed amounts to ~~ (10,500 X .015) = 158 kWhrs./yr. = 13 kWhrs./month. At say, $.37/kWhr. = (13 X $37) = $4.86/mo. TOPS !

3.) I neither approve or disapprove. I would suggest your project mgr. may need to get a bit tighter in the estimating area.

[bcroe]

After plugging in the 96.5% efficiency for micros vs 95% efficiency for the Fronius IG Plus V 6.0-1 UNI he estimated (I think he approximated in his head) about 50 kwH/month difference. This seems too high to me...

My Fronius IG Plus V 6.0 claims 96% efficient at 240 VAC out. Half a percent of a month's
output might be .005 X 6000W X 30 days/mo X 4H/day = 3600 WH / mo = 3.6 KWH / mo

Pretty slipshod. Bruce Roe

[insaneoctane]

...
Also, does anyone think 26 x 250 kWh (SolarWorld SW 250 poly / Version 2.0 and 2.5 Frame) is too much for the Fronius IG Plus V 6.0-1 UNI? I suspect they weren't going to automatically upgrade that.
...

The Fronius IG Plus V 6.0-1 UNI specs show it's good up to kWp of 6.9, so it should work....

Does anyone know of a graph that would show the Fronius IG Plus V 6.0-1 UNI (or comparable) efficiency as a function of load/output? As I push it from kWp 6.0 to kWp of 6.5, I'm wondering what efficiency delta is. (This is were someone tells me that will only happen for 2 minutes per year and not to worry about it probably)

[silversaver]

I have total of 28 panels of 255W @ 7.1kW, and I'm still using the SMA TL-6000 inverter. There is nothing wrong with this setup.

If you want high eff, the SMA TL6000 to 11000 claim 98.5% eff. But, since you are installing your solar array in 2 roofs, then SMA TL6000-US-22 with dual MPP tracker rated 97% eff. might be your pick. They are compact with emergency plug support up to 1500W.

[insaneoctane]

... But, since you are installing your solar array in 2 roofs, then SMA TL6000-US-22 with dual MPP tracker rated 97% eff. might be your pick. They are compact with emergency plug support up to 1500W.

I'm sorry if I implied I was using two roofs...just my south facing:
RevB Layout_.jpg

[silversaver]

If you want more output at same roof space, then tell the installer to use 265W to 275W panels since the price isn't much different compare with 250W panel (old for 2014 unless the price is crazy cheap). I highly recommend SMA 6000TL-US-12 inverter, it has highest 98.5% eff rating.

[bcroe]

I highly recommend SMA 6000TL-US-12 inverter, it has highest 98.5% eff rating.

98.5% is a pretty impressive number, how do they do that? Are they universally accepted
by the utilities? I might look for such a number if there comes a time to replace my inverters.
Its pretty hard to check up on that; you have to measure input & output power to 4 decimal
places, so that subtracting the output from input gives 2 decimal places. Bruce Roe

[silversaver]

98.5% is a pretty impressive number, how do they do that? Are they universally accepted
by the utilities? I might look for such a number if there comes a time to replace my inverters.
Its pretty hard to check up on that; you have to measure input & output power to 4 decimal
places, so that subtracting the output from input gives 2 decimal places. Bruce Roe

With 345v min voltage required makes it unpopular for installer to pick this inverter. Single MPP tracker limited to single roof installation. But you can't beat it's high efficiency.

[insaneoctane]

If you want more output at same roof space, then tell the installer to use 265W to 275W panels since the price isn't much different compare with 250W panel (old for 2014 unless the price is crazy cheap). I highly recommend SMA 6000TL-US-12 inverter, it has highest 98.5% eff rating.

I'm at the right size at 6.5kW to completely offset my PUC usage, so it was really down to 2 more 250W panels or micro-inverters...

How does the SMA with it's 98.5% eff do on shady/overcast days compared to the Fronious? I'm thinking the SMA upgrade might be an additional $2k (plucked from you know where).

[J.P.M.]

98.5% is a pretty impressive number, how do they do that? Are they universally accepted
by the utilities? I might look for such a number if there comes a time to replace my inverters.
Its pretty hard to check up on that; you have to measure input & output power to 4 decimal
places, so that subtracting the output from input gives 2 decimal places. Bruce Roe

I'm not sure I understand why all the concern about relatively small differences in inverter efficiency. It's hard to measure, changes as f(input, temp.), and over time as well. Quoted efficiencies are maximums, and are different depending on location/governing authority/measurement method. System performance will probably decrease more in the first month of operation from burn in and fouling than any standard, spec sheet stated difference in inverter efficiency.

FWIW, I'd spend my time learning about reliability vs. initial cost/maint./service requirements.

Separate from that, I think Bruce's use of significant figures is different than how I remember learning it.

[bcroe]

I'm not sure I understand why all the concern about relatively small differences in inverter efficiency. It's hard to measure, changes as f(input, temp.), and over time as well. Quoted efficiencies are maximums, and are different depending on location/governing authority/measurement method. System performance will probably decrease more in the first month of operation from burn in and fouling than any standard, spec sheet stated difference in inverter efficiency.

FWIW, I'd spend my time learning about reliability vs. initial cost/maint./service requirements.

Separate from that, I think Bruce's use of significant figures is different than how I remember learning it.

I have trouble understanding the need for monitoring systems all the way down
to panel level, hour by hour, accessible 24/7 from wireless devices, with elaborate
spread sheets, etc etc.

My own concern is to put numbers on all the important numbers of the system DESIGN,
verify those numbers in operation, and periodically check for changes or deterioration.
Seems it is FAR MORE IMPORTANT to peg numbers that will directly affect system for
the decade or two it will operate, than tracking exactly what is happening this moment.
Obviously output is directly impacted by wire loss, converter efficiency, and panel
output new & over the system life. Reliability is ALSO important, so are a list of other
considerations. I find that getting exactly what I want is considerably more important
than initial cost, because I may have to live with it for a very long time. In truth,
equipment that runs cooler typically is MORE reliable.

Burn in on solar, what is that? The wiring loses will not change; if they do, better
find the fault before it starts on fire. If panels do have an initial loss (who says that?),
then its just one more number to understand in the design; it doesn't cancel the need
to understand the rest of the system numbers. And the inverter losses are NOT
going to change unless there is a failure. An inverter running 97% efficient is
dissipating that 3% loss as heat. if the loss increased to 4%, that inverter would have
to deal with a 33% increase in internal heating, a big problem. Furthermore, the
increase almost certainly would be concentrated in a specific circuit, so its heat
issues would be far greater, we are talking imminent failure.

Inverter efficiency is output power divided by input power, no legislation will change
that. Sometimes it needs to be a curve over load instead of a single number, and
there may be other factors: mine is specified as affected by line output voltage.

I don't plan to measure my inverter efficiency; anyway I already bought it. Its not
easy to do. Suppose I measure input at 1000W with a measurement accuracy of
1%, and output at 970W with a measurement accuracy of 1%. So the real input
power might be from 990W to 1010W. The actual output power might be from
979.7W to 960.3W. If I divide 960.3 by 1010 I get .951 or a loss of 4.9%; if I
divide 979.7 by 990 I get .9896, or a loss of 1.04%. If I want to know the losses
a lot more accurately than between 1% and 5%, my measurements will need to
be MUCH MORE ACCURATE than 1%. Bruce Roe

[J.P.M.]

I have trouble understanding the need for monitoring systems all the way down
to panel level, hour by hour, accessible 24/7 from wireless devices, with elaborate
spread sheets, etc etc.

My own concern is to put numbers on all the important numbers of the system DESIGN,
verify those numbers in operation, and periodically check for changes or deterioration.
Seems it is FAR MORE IMPORTANT to peg numbers that will directly affect system for
the decade or two it will operate, than tracking exactly what is happening this moment.
Obviously output is directly impacted by wire loss, converter efficiency, and panel
output new & over the system life. Reliability is ALSO important, so are a list of other
considerations. I find that getting exactly what I want is considerably more important
than initial cost, because I may have to live with it for a very long time. In truth,
equipment that runs cooler typically is MORE reliable.

Burn in on solar, what is that? The wiring loses will not change; if they do, better
find the fault before it starts on fire. If panels do have an initial loss (who says that?),
then its just one more number to understand in the design; it doesn't cancel the need
to understand the rest of the system numbers. And the inverter losses are NOT
going to change unless there is a failure. An inverter running 97% efficient is
dissipating that 3% loss as heat. if the loss increased to 4%, that inverter would have
to deal with a 33% increase in internal heating, a big problem. Furthermore, the
increase almost certainly would be concentrated in a specific circuit, so its heat
issues would be far greater, we are talking imminent failure.

Inverter efficiency is output power divided by input power, no legislation will change
that. Sometimes it needs to be a curve over load instead of a single number, and
there may be other factors: mine is specified as affected by line output voltage.

I don't plan to measure my inverter efficiency; anyway I already bought it. Its not
easy to do. Suppose I measure input at 1000W with a measurement accuracy of
1%, and output at 970W with a measurement accuracy of 1%. So the real input
power might be from 990W to 1010W. The actual output power might be from
979.7W to 960.3W. If I divide 960.3 by 1010 I get .951 or a loss of 4.9%; if I
divide 979.7 by 990 I get .9896, or a loss of 1.04%. If I want to know the losses
a lot more accurately than between 1% and 5%, my measurements will need to
be MUCH MORE ACCURATE than 1%. Bruce Roe

???

[Ward L]

Real Life Issue?

Seems strange I heard all about inverter efficiency and other technical details but nothing about cleaning the panels before buying. From my limited 2 month experience with panels, it seems like it would have been good to know I need to clean my panels regularly to keep them at their peak performance. I have to figure out the best way to rack my panel fouling.

[silversaver]

Seems strange I heard all about inverter efficiency and other technical details but nothing about cleaning the panels before buying. From my limited 2 month experience with panels, it seems like it would have been good to know I need to clean my panels regularly to keep them at their peak performance. I have to figure out the best way to rack my panel fouling.

OP is still in design stage and there's no need discuss about cleaning the panels. There are few posts about clean the panels. All you have to do is read. I don't think it is necessary to "clean" the panels before "buying" the panels. You can clean your panels every month or every other month, really depends on how easy to access to the roof.

I think you are prpbably the solo Graph Solar owner I seen on this forum. How is the Graphe working out for ya?

[insaneoctane]

I was looking for concurrence that opting for 2 extra panels vs micro-inverters on a near zero shade roof was the right choice. It's probably rhetorical. Honestly, I probably should not do EITHER. I should probably use 24 panels and hope to get 9.8kWh/yr out of them (my current yearly needs). BUT, my baseline was micro-inverters and when the opportunity to maybe remove them and save $2,550 I reacted by asking about 2 additional panels. My thought was it was probably the cheapest time to put them up (I could easily be wrong on that assumption), because it's just "2 more panels". The contractor essential seems to have scaled the price....26 panels is (26/24) x original quote. Which really tells me there is really NOT any savings, per say. It's probably cheaper than paying them in 2 years from now to go plop 2 more panels up there, though. The other reason I'm considering it (besides thinking now was a way to get a "deal" on them), was to give me some breathing room. We really don't run our AC much, because it's expensive. Our house is pretty regimented on electricity usage (remember Seinfeld's "Soup Nazi"?)...2 additional panels MIGHT buy me some additional comfort. Plus, the wife might catch on to the fact that what little power we do buy from our PUC is cheaper than it used to be (our TIER 4 is $0.34), so our usage might well go up.

But, I'm realizing what most people already know, which is the tail end of your Solar power is the worst ROI. I just ran a few calcs and the 2 additional panels delivering approximately 833 kWh/yr, displacing TIER 1 at $0.14/kWh currently takes 11 years to recoup the $1,225 post-tax cost (no power cost inflation accounted for). So I'm just not sure if I save my $1,225 and stay in the "Energy Nazi" mode or go for it and live fat!