Solar newbie in Los Angeles - Sunpower vs. LG panels - seeking advice!!!

[Constellation]

Hi, we live in los angeles and are looking to install our first solar panel system in the next few months. I have met with two different local companies and thus far have received two quotes, for totally different systems. We have no shade or risk of shade where we would put the panels, and need a 7700-7800 systrm to cover 90 percent of our use.

Option 1: 27 305-watt panels (7930 watts), with emphase microinverters, mounting hardware
$3.74/watt before tax credit
Plus $1800 for new 200v electrical panel (not sure what brand this includes- any suggestions for what pe of electrical panel is best?)

Option 2: 27 305-watt panel, with solar edge single phase inverter and solar edge power optimizer, mounting hardware
$3.53/watt before tax credit
Plus $1800 for new main panel

Option 3: 24 e20-327 sunpower panels, with 2 sma America 3800TL-US-22 (240 V) inverters (or they said for the same price we could instead get a single bigger inverter), sunpower monitoring system and sma secure power supply
$4.75/watt before tax credit
Plus $2100 to $3500 for new main panel (200A solar rated MSP)

Any thoughts? Do these prices seem high, and what would people recommend between these options? If we have no shade and could do a central STRING inverter (and save money on the LG system), is that the way to go? For some reason I feel like the sunpower system has a better warranty but the price is so much higher, I am not sure it is worth it. Also, how great is the risk do you actually need to call on your warranty? Has anybody had issues with the LG panels and/or microinverters? Or the central solar edge inverters?

Again, I am so confused by all of the options and also feel like all three of the quotes are high. Any tips (especially from LA people) would be greatly appreciated!!!!

Thank you!

[DanKegel]

I'm in LA, too. Option 2 sounds better offhand, and is close to what I plan to get (and which was estimated at $3.35/watt a couple months ago).

Sunpower is too expensive for normal situations.

solaredge is probably a better choice than enphase (simpler per-module electronics -> cheaper and more reliable) and better than simple string (per-panel monitoring), but if you really have no shading, and all panels are pointed same direction, a simple string might be more cost-effective.

Half my panels will be pointed west, and there is some shading, so I pretty much need per-panel optimizing a LA enphase or solaredge.

[J.P.M.]

Welcome to the neighborhood.

This forum is replete with folks in similar situations to yours. A perusal of prior threads may be an eye opener for you. Your basic instincts seem in line with a lot of other opinion and ideas expressed here.

Reader's digest version:

No shade probably means no micros are probably necessary.

The prices you report seem about in line, +/- a bit for So. CA.

Run PVWatts on your own and confirm what the vendors are telling you for annual long term average estimated output. Keep in mind PVWatts is about 5-10% conservative using default system losses of 14%. Read the help info screens before you start. The learning curve is shorter that way.

If one of your goals is to lower your electric bill, get an energy audit and reduce your use before solar as much as suits your lifestyle. Know that solar is usually the most expensive way to lower a bill. Not using electricity in the first place is the cheapest and most cost effective. Smart money does what gets the most bang for the buck first.

Buy a book on residential energy conservation and solar energy. You're considering spending a lot of money. Invest 20 bucks in a book and a few hours reading it. Those 2 investments can have a very large return on investment.

Upcoming rate reform will affect how much you pay for electricity in ways not fully known at this time. Be aware that for large users, bills may well drop some in the near future - 3-6-9 months ??

If solar is still a choice, get your roof inspected/serviced. Cheap insurance.

Equal (electrical) size solar systems in the same location, orientation and duty will produce about equal annual output for as long or longer than most folks will own them, regardless of panel. Sunpower MAY be worth a slight up front premium (5 % maybe ??) but probably not the difference being charged.

Add: In LA, the system sizes quoted with conditions you describe, will probably generate 13-14,000 kWh/yr. It is probably not most cost effective to eliminate your entire bill, and not cost effective to overgenerate at this time.

What is your annual usage by month ?

[Constellation]

Welcome to the neighborhood.

This forum is replete with folks in similar situations to yours. A perusal of prior threads may be an eye opener for you. Your basic instincts seem in line with a lot of other opinion and ideas expressed here.

Reader's digest version:

No shade probably means no micros are probably necessary.

The prices you report seem about in line, +/- a bit for So. CA.

Run PVWatts on your own and confirm what the vendors are telling you for annual long term average estimated output. Keep in mind PVWatts is about 5-10% conservative using default system losses of 14%. Read the help info screens before you start. The learning curve is shorter that way.

If one of your goals is to lower your electric bill, get an energy audit and reduce your use before solar as much as suits your lifestyle. Know that solar is usually the most expensive way to lower a bill. Not using electricity in the first place is the cheapest and most cost effective. Smart money does what gets the most bang for the buck first.

Buy a book on residential energy conservation and solar energy. You're considering spending a lot of money. Invest 20 bucks in a book and a few hours reading it. Those 2 investments can have a very large return on investment.

Upcoming rate reform will affect how much you pay for electricity in ways not fully known at this time. Be aware that for large users, bills may well drop some in the near future - 3-6-9 months ??

If solar is still a choice, get your roof inspected/serviced. Cheap insurance.

Equal (electrical) size solar systems in the same location, orientation and duty will produce about equal annual output for as long or longer than most folks will own them, regardless of panel. Sunpower MAY be worth a slight up front premium (5 % maybe ??) but probably not the difference being charged.

Add: In LA, the system sizes quoted with conditions you describe, will probably generate 13-14,000 kWh/yr. It is probably not most cost effective to eliminate your entire bill, and not cost effective to overgenerate at this time.

What is your annual usage by month ?

Thank you so much!! Our actual usage is just over 14,000 a year. The LG panels were estimated at just over 12,300 for first year, sunpower estimated 13,335 for first year. We hope to get an electric car over the next two years so want to have enough to cover at least part of that going in (or get a system we can add to easily as needed). We are trying to get an energy audit over the next few weeks to see what else we can do. Also it looks like LG panels degrade three times faster than sunpower panels, so we want to get at least 90 % going in. Does that sound right?

If total panel watts = 7900, any recommendations for the best central string inverter? Is solar edge a good one, and is a SE7600A-US single phase inverter the right size for this system? Does it matter that the wall where this will be installed gets direct sun (in he valley where it is already very hot)?

[Alisobob]

Does your local power provider ( LAWP??) offer a "Time of Use".. or TOU program?

solar62.JPG

If your house is pretty quiet during the day, it allows you to feed solar generated power into the grid at higher pricing, then what you buy it back for at off peak times..

solar98.JPG

It could allow you to build a smaller system, but still hit your goals.

Its something to consider.

The other advice from JPM is spot on....

[J.P.M.]

Does your local power provider ( LAWP??) offer a "Time of Use".. or TOU program?

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If your house is pretty quiet during the day, it allows you to feed solar generated power into the grid at higher pricing, then what you buy it back for at off peak times..

[ATTACH=CONFIG]6658[/ATTACH]

It could allow you to build a smaller system, but still hit your goals.

Its something to consider.

The other advice from JPM is spot on....

Thanx for the kind words. Spot on for some. Opinions vary.

T.O.U can work but it's not a lock for everyone, and takes some knowledge of use pattern(s) and how T.O.U. works. Not quite a no brainer. Close maybe, but look carefully before you leap. If done correctly with some correlation with a realistic use pattern it can reduce optimum system size and save money at least under current tariffs.

[Ian S]

Does it matter that the wall where this will be installed gets direct sun (in he valley where it is already very hot)?

I'd avoid that if at all possible. These things can get quite toasty even when not in direct sun. See this thread for a recent discussion of SolarEdge inverter temperatures.

[russ]

Does it matter that the wall where this will be installed gets direct sun (in he valley where it is already very hot)?

Why not shade the unit?

[Constellation]

I'm in LA, too. Option 2 sounds better offhand, and is close to what I plan to get (and which was estimated at $3.35/watt a couple months ago).

Sunpower is too expensive for normal situations.

solaredge is probably a better choice than enphase (simpler per-module electronics -> cheaper and more reliable) and better than simple string (per-panel monitoring), but if you really have no shading, and all panels are pointed same direction, a simple string might be more cost-effective.

Half my panels will be pointed west, and there is some shading, so I pretty much need per-panel optimizing a LA enphase or solaredge.

Thank you! What do you think about the Sunny Boy (SMA) inverter, vs. Solar Edge with Power Optimizers? Also, it sounds like a very complicated analysis, but assuming I size the inverter for 27 panels, how many strings would be recommended? Why would an installer recommend two separate smaller inverters (vs. one larger one)?

[Constellation]

Why not shade the unit?

Can you explain what type of shading you are suggesting?

As another idea - further along the east side of our house we do receive more natural shading and perhaps could figure out some wall space, but none of the solar companies to come by mentioned that as a possibility. Do the inverters need to be close to the electrical panel (which unfortunately is in the direct full-day sun)?

[J.P.M.]

Thank you so much!! Our actual usage is just over 14,000 a year. The LG panels were estimated at just over 12,300 for first year, sunpower estimated 13,335 for first year. We hope to get an electric car over the next two years so want to have enough to cover at least part of that going in (or get a system we can add to easily as needed). We are trying to get an energy audit over the next few weeks to see what else we can do. Also it looks like LG panels degrade three times faster than sunpower panels, so we want to get at least 90 % going in. Does that sound right?

If total panel watts = 7900, any recommendations for the best central string inverter? Is solar edge a good one, and is a SE7600A-US single phase inverter the right size for this system? Does it matter that the wall where this will be installed gets direct sun (in he valley where it is already very hot)?

Sunpower yr/yr published performance degradation rate ~0.4%/yr., LG ~ 0.7%/yr., not 3X. In either case the # is small enough in terms of possible long term output diff. to not justify the S.P. premium. Also, according to a more sophisticated estimating program (SAM), LG 300's, 305's actually outperform S.P on a per kWh output/yr per installed kW, at least in my zip code.

[sensij]

Sunpower yr/yr published performance degradation rate ~0.4%/yr., LG ~ 0.7%/yr., not 3X. In either case the # is small enough in terms of possible long term output diff. to not justify the S.P. premium. Also, according to a more sophisticated estimating program (SAM), LG 300's, 305's actually outperform S.P on a per kWh output/yr per installed kW, at least in my zip code.

If you look carefully at how SAM performs its calculations, the extra credit given to the LG panels seems to be in the upfront STC rating, not necessarily in the conversion efficiency under given TMY data. SAM uses the CEC database for its equipment parameters, and I've not found anything that explains why this database treats the base rating of the panels differently. In any case, I think the safer assumption is that LG and Sunpower would be expected to perform the same in the same conditions, but opinions may vary.

[J.P.M.]

If you look carefully at how SAM performs its calculations, the extra credit given to the LG panels seems to be in the upfront STC rating, not necessarily in the conversion efficiency under given TMY data. SAM uses the CEC database for its equipment parameters, and I've not found anything that explains why this database treats the base rating of the panels differently. In any case, I think the safer assumption is that LG and Sunpower would be expected to perform the same in the same conditions, but opinions may vary.

The CEC rating is supposed to give a more "realistic" guess of output under "real world" conditions. At the end of the day, IMO, it doesn't matter as either way, you get to the same place. It was also used to figure CA solar rebates until money ran out. That's why rebates were never based on STC system sizes.

STC: 1,000 W/m^2 irradiance, 25 deg. C. cell temp., 1.5 airmass, ASTM G173-03 standard spectrum (whatever that means).

CEC: 1.) PVUSA test conditions (called PTC): 1,000 W/m^2 irradiance, 20 deg C. AIR temp., wind speed of 1m/sec. at 10m above ground level. Note that cell temp. is not specified.

Then, 2.) Output is adjusted for inverter efficiency.

The CEC rated output is lower than the STC rated output because the temp. of the panel is higher for the CEC rating method and the inverter efficiency is also in there.

If you start with the STC rating, estimate the panel temp. @ 1,000 W/m^2 using the Sandia temp. est. method and/or a heat balance/energy balance, w/1m/sec wind speed, back off (or up actually) from the STC efficiency using the temp. decrement of efficiency from the 25 deg. C. STC temp., and then multiply by the inverter eff., you'll get pretty close to the CEC number for panel output by ratioing the 2 efficiencies.

When a comparison is made at a given cell temp., the efficiency works out about the same with either method.

The CEC performance model SAM uses is the "5 parameter model" in some common use (See Duffie & Beckman for a decent explanation of basics). While not super easy to use, it does provide a reasonable guess at a cell/panel/system efficiency.

I've found I (or anyone) can get a decent first approx. of estimated output using the STC rating, the cell temp. and the P.O.A irradiance.

The trick is to have a pyranometer and a way to estimate wind speed.

Having measured array temps. up until about 3 months ago, and comparing those results to the Sandia model's method for estimating cell temps., I've found that what I've measured about 70 + times mostly agrees within about +/- 1 to 2 deg. C . with the Sandia temp. est. method, which is about what the folks at Sandia claim. I believe the wind vector variability is the source of most of the uncertainty.

[sensij]

While the previous post was informative, I was not referring to the difference between CEC (PTC) ratings and STC. SAM actually assigns the STC rating of LG300N1C-G3 panels as 302.72, while the Sunpower X21-345's are given an STC rating of 344.95. The source of the STC ratings is the CEC equipment database, which is not to be confused with the CEC performance tests that were used to support the CA rebates.

Perhaps this STC rating is back calculated from the PTC performance, or maybe it is based on some other testing that isn't shared. My point was that this difference accounts for most of the 3% or so difference in results that SAM predicts between these two panels, and is independent of any particular TMY data that might be used in the model. Since the most common LG panel being installed now is the N1C-B3, there might also be a difference there too. Without a better understanding of why SAM (or the CEC) treats the STC rating of these panels differently, I am uncomfortable citing the 3% modeled difference in performance as significant. I don't think the J.P.M. was necessarily treating it as significant either, but by stating the fact, it is possible that someone might misunderstand and be misled into thinking that the LG's were somehow more efficient, without knowing that the evidence that would support that hypothesis is not available.

[J.P.M.]

While the previous post was informative, I was not referring to the difference between CEC (PTC) ratings and STC. SAM actually assigns the STC rating of LG300N1C-G3 panels as 302.72, while the Sunpower X21-345's are given an STC rating of 344.95. The source of the STC ratings is the CEC equipment database, which is not to be confused with the CEC performance tests that were used to support the CA rebates.

Perhaps this STC rating is back calculated from the PTC performance, or maybe it is based on some other testing that isn't shared. My point was that this difference accounts for most of the 3% or so difference in results that SAM predicts between these two panels, and is independent of any particular TMY data that might be used in the model. Since the most common LG panel being installed now is the N1C-B3, there might also be a difference there too. Without a better understanding of why SAM (or the CEC) treats the STC rating of these panels differently, I am uncomfortable citing the 3% modeled difference in performance as significant. I don't think the J.P.M. was necessarily treating it as significant either, but by stating the fact, it is possible that someone might misunderstand and be misled into thinking that the LG's were somehow more efficient, without knowing that the evidence that would support that hypothesis is not available.

The max. power rating SAM uses is not back calc'd rom the CEC rating. It comes from the mfg. published data. It is the product of the rated voltage and the rated current for the specific model listed.

For the 345, those published #'s are (57.3 V) X (6.02 A) = 344.95 W. For the LG 300, it's (9.46 A) X (32.0 V) = 302.72 W.

Those #'s change slightly with model changes and minor adjustments are probably not too important in the bigger scheme of things, but they appear to come from data supplied by the mfg. the way I see it.

The CEC ratings come from the PTC test condition ratings.

The PTC rating of a module is a calculated number, not a measured number.

The PTC eff. uses the Nominal Operating Cell Temp. (NOCT), which is the mod. temp. at 800 W/m^2 (not 1,000 W/m^2), 20 deg. C amb. and 1m/sec wind speed. The NOCT and the temp. coefficient of power are then used to calc. the PTC power rating and thus to the CEC.

The PTC rating starts with the STC rating.