Replies

1. 
   user-2453173 | Aug 31, 2015 05:55pm | #1

   There are too many brands out there to be able to give a blanket statement on which is better, or even how to tell.

   What brands are being proposed?

   PTC vs STC rating, Warranty, company bank-ability, temperature characteristics, what brands you installer works with/is used to using, etc.... all are factors that come into play.

   Comparing solar modules isn't like comparing HVAC equipment, or appliances. The rules are a bit different, since we're talking about paying for something that MAKES energy, rather than something that consumes it.

   Where are you located that Duke is offering $1/watt as a rebate?

2. 
   SC dave | Aug 31, 2015 06:10pm | #2

   I live in Greenville, SC. Attached are 2 types panels. One company states that the panels will provide 70% and the other states 79%. Both offer similar warranties.

   
3. 
   user-1137156 | Aug 31, 2015 09:23pm | #3

   You might want to visit: http://www.solarpaneltalk.com/forum.php
   It appears that the first proposal uses all the available roof with the most efficient panel, giving the greatest output. The LG panels are also well regarded but will give about 7% lower output. The Qcell panel is even less efficient and would give 16% less output. If you had abundant roof area you could use more panels to make up for the efficiency. If the competing bids are covering the same roof area with less efficient panels yet claiming higher output, something is WRONG! Another "observation" about the first proposal is that they are bidding invertor capacity equal to the panel output rating where usual practice is 90% which in actual use causes only a percent or 2 of reduced AC output, sized as they propose every bit of output is obtained.

4. 
   SC dave | Sep 01, 2015 04:15am | #4

   thank you; I will visit that forum. However, I did make a mistake earlier. The LG and Qcell are both offered by Alder Energy. I left out the ones that are being offered by Sunstore Solar. I am attaching both complete proposal from each company. Thank you for your help. Only 1 file for sunstore that I wasnt' able to upload due to size....that is the inverter

   
5. 
   user-2453173 | Sep 01, 2015 08:42am | #5

   If you assume that all three types of modules are going to perform (i would assume that is true, they are all well known brands). Then what you need to consider is this: Which is more important; how much of you utility bill is covered by the system, and how much does the system cost vs how many kWh it produces in a year (what you pay, for what you get).

   Sunpower gives the best total kWh production for the roof space (18,555kWh @ a cost of $56,898)
   The Q-cells option is only slightly lower on production, for a better overall cost (18,303 @ $52,847)
   Did not see anything for the LG option, i imagine it would be somewhere between these two options though.

   The $/kwh for the first year are: (this is all pre- rebate, pre tax credit, which just exaggerates the differences. Depending on how you plan to pay for the system, you might want to use the numbers after all incentives.)
   Sunpower= $3.066
   Q-Cell= $2.887

   Purely based on this, the Q-cell option is favorable to me.

   As for inverter size vs solar array size. Having the inverter as small as 75-80% of the array size is workable, the 90% rule of thumb has shifted lower over the years as the solar module cost lowered. Even at a 75% inverter to array ratio, the clipping losses due to an undersized inverter are relatively low, on the order of 2% (climate, array tile, array azimuth, and module temperature characteristics affect the exact amount of clipping, and it is simulated by PVWatts) But now that the modules are 1/3 the cost of what they were 5+yrs ago, it's worth sacrificing a small amount of energy if it saves a significant amount of money (goes back to the bottom line $/kWh produced).

   Also take into account the installation companies. How long have they been in business, do they have good customer reviews/references to share. Good parts thrown together by a bad installer increases the chances of problems down the road, true of many trades.

6. 
   charlie_sullivan | Sep 01, 2015 01:38pm | #6

   Reputation of the installer is probably more important than small differences in cost or power produced.

7. 
   user-1137156 | Sep 01, 2015 02:14pm | #7

   It appears that Alder energy is able to get 48 panels on your roof, I'd ask that they verify this. Alder is proposing micro inverters, usually a more expensive option. With micro inverters you'll lose the "emergency power" Getting the LG panels instead of the Q cells is wasted with the micro inverters which clip at 250 watts input. Did Alder offer a "string inverter" alternative to the micro inverters? If you are convinced they really can fit 48 panels on your roof, then using the LG panels and string inverters you could have a 14.64KW array which would yield about 13& more output. The choice between string inverters and micro inverters is complicated. At $4/watt (Alder) and $4.32/w(Sunstore) the prices are toward the high end. Alder should be able to offer the 14.64KW system (with 2 7KW string inverters) for a tad less than Sunstore is asking.

8. 
   SC dave | Sep 01, 2015 03:47pm | #8

   Thank you all for your input; very helpful. As far as the String inverter....here is an email on this that Alder sent me followed up by another email dismissing the string inverter. So it seems that is off the table? And I am not clear if the 79% was if I went with the string inverter or if it would be due to using the LG panels (I suppose I should ask him that:

   Hello Mr. Sanda,

   I have attached the most updated proposal. The offset goes up to 79%. A string inverter is the most economical way to go solar when comparing inverter options. We use the individual string inverters when shade and multiple roof angles are present. A system with Micro Inverters also has a 25 year warranty. On the other hand, a string inverter has a 10 year warranty (life expectancy is 12 to 15 years) but we have found that even with a replacement in that time for a new inverter is more cost effective than a micro inverter system. I spoke to our president at Alder, and he recommended using a string inverter because a micro inverter system is a bit of overkill. Your final cost does go up a bit for the more powerful LG 305 panels, but the added offset still makes for great economics.

   Let me know what you think. Thank you for your time.

   THEN HE EMAILE BACK WITH THIS:

   Hello Mr. Sanda,

   I am going back against what I was saying in regards to the string inverter. Your system is larger that what I normally deal with in a residential system, especially with one roof surface. All other systems of this size have multiple roofs and require Enphase Micro inverters from the begining and I do not explore the string inverter option.

   If you look at the Cash Flow page on the proposal with the SMA string inverter, you will see in year 20 that the cost for inverter replacement is $5124. This is twice the amount normally seen there because you have two inverters. SMA does not make a single inverter that would size appropriately to your system I have attached a proposal with Enphase Micro Inverters and the cost is $1835 more than the system with the string inverter. This will eliminate the cost of replacing an inverter. The savings from going with the Enphase Micros would be $3289 over the life of the system.

   Again, I do apologize for my mistake with this, but after looking everything over, the Enphase Micro Inverter system will be less expensive in the long run without the cost of replacing the 2 inverters. Essentially, the additional cost of the micro inverters is absorbed in the tax rebates and proves to be the less expensive option for the life of the system.

   Thank you for your time and involvement in designing a quality system. If you have any further questions, please let me know. I will remember this for future systems and will not make that mistake again.

   Sincerely,

9. 
   user-2453173 | Sep 01, 2015 07:20pm | #9

   Jerry, the 250w micro inverter is not a waste on the 305w LG. The 250w inverter is 82% the size of the 305w module. On a flush mounted system (higher average module temps than on a ground mount, therefore the module is less efficient during the peak power producing hours) you will end up losing about 0.6% of it's potential annual energy output due to inverter clipping. I got this from the professional simulation software we run in our office. The 80% rule of thumb is long since lost its applicability, now that modules have gotten so much less expensive, and now that our modeling software can account for these losses in detail and allow us to optimize systems in more ways than before. I also am skeptical of fitting 48 of those modules on that roof, i second the idea of asking them to verify this.

   In regards to the string vs micro decision, i'll add this (i am in the string inverter camp at present, full disclosure). In terms of replacement schedules and costs, it is a gamble either way. Enphase is only 2 yrs into this generation 4 inverter, the first two generations were discontinued as they had some horrific failure rates. gen 3 has not shown such rates as of yet, nor has gen 4, but they are both still barely started on their expected 25yr life. SMA, on the other hand, has been around making relatively bullet proof inverters for decades, but they only have a 10yr warranty. I say this, take inverter warranties with a grain of salt, they are not necessarily an indicator of true lifetime, they may just be a marketing gimmik. As i said, it really end up being a gamble, i honestly am of the believe that the two inverters will have similar life expediencies, and when it's time to replace, enphase only gives the installer so much $ to actually do the work you may have to cough up something before the 25yr warranty expires, you can also buy a 20yr warranty for the SMA inverters if it puts your mind at ease.

   $4/w for a 10+kw system also seems high to me, but people tell me i'm high relative to other regions (i'd ballpark a 13kw system with black framed US made modules on a 4/12 shingle roof at roughly $3.20/w and that's with the 20yr add on to the inverter warranty). If they have to trench from the garage over to the other building to connect to the grid, then i could see maybe $3.50 ish. You have some nice incentives though, so i can see the installers in your area not having much price pressure......yet.

10. 
    user-1137156 | Sep 01, 2015 08:00pm | #10

    I'm sure that the 79% offset was based on a larger system, about 14.5KW, using the LG panels AND a pair of string inverters. The argument about replacement string inverters ignores the fact that a 20 year warranty is available on SMA inverters, it costs about 20% of the inverter price.. You have a single array with negligible shading which takes away the usual argument for micro inverters. Micro inverters put the electronics on the roof, where access is expensive and also use considerably more electronics, all of which has a falure rate that rises with ambient temperature. Enphase does include a 25 year warranty, but will they be in business?. I'm not a fan of micro inverters!. What is the price difference for 48 LG panels and 2ea 7KW SMA string inverters (14640W, 14KWAC)? vs 48 Qcell panels and Enphase (13.2KW DC, 12KWAC)? Installing a string inverter is not the same as installing Enphase, If Alder is not experienced installing string inverters, which is what it sounds like, it is best to let them work in their comfort zone and use the Qcell panels and Enphase system..