Looking at two systems

[russ]

I agree the SP-245 price is lower than the SP-327 that I got quoted. I think they have room to move on the LG's but I have not pushed to hard. The reason I was told was because SP is discontinuing the SP-245 and replacing it with either a 255 or 250 ... as such SP is discounting the 245's and they could not give me that pricing on the 327's. The installer has been up-front with me from the start and as far as I can tell not tried to feed me BS but I agree 100% on trust but verify. I will do my part to make sure they keep to their word and not change things towards the end.

You have chosen a good path.

[Digital21]

You have chosen a good path.

Thank you. To say this forum has been helpful would be an understatement.

[sensij]

Thank you. To say this forum has been helpful would be an understatement.

It seems like some consensus has been reached so you may not be interested in another take. However, I tried to model your system in SAM and a couple things caught my attention. I selected a Long Island weather set (typical meteorological year) and put one string facing southeast (135°) and the other southwest (225°).

1) How many inverters are you using, or what is the planned string configuration? At reference conditions, the Sunpower E20-245 has a Vmp of 40.5 and an Voc of 50.8. The Sunnyboy inverters typically tolerate 600 Vdc max, and 480 Vdc max MPPT. If I select more than 13 panels on a string, it starts throwing errors about the 600 V limit being exceeded. I guess the 8.8 kW quote had more than one inverter?

2) To avoid errors, if I scale the system down to two strings of 13 (26 panels) on one inverter, for a 6.4 KW system size, it yields 8190 kWh in year 0, with some assumptions about system losses. If you are a Sunpower fan and believe they will degrade 2% in year 1 and only 0.25% per year thereafter, in year 14 the generation would be 7769 kWh.

If those Sunpowers cost $4.00 / W, that would be a system cost of $25480. If you took that same budget and bought the LG 270's for $3.80 / W (or $3.775 to make the math work out), that would buy you 25 panels. Let's say the LG's perform at the warrantied performance limit of 3% degradation in the first year, and 0.7% per year thereafter, and otherwise, the system has the same loss factors. In a smaller footprint, that system would produce 8765 kWh in year 0, and 7760 kWh in year 14. The total production difference would be 3783 kWh in favor of the LG's through those 14 years, and it would take the Sunpowers another 14 years to make up that difference.

I could definitely see an argument that the Sunpowers' out performance later in the system life is worth more, since electricity rates may be higher then and those kWh replaced will be more expensive. If it was me buying this system, I would be feeling out the LG quote a little more carefully, since their performance in the time horizon I'm most interested in appears to be a better value by this analysis.

Food for thought maybe... I don't think there's a wrong answer here, especially with the incentives you have going for you.

[Digital21]

It seems like some consensus has been reached so you may not be interested in another take. However, I tried to model your system in SAM and a couple things caught my attention. I selected a Long Island weather set (typical meteorological year) and put one string facing southeast (135°) and the other southwest (225°).

1) How many inverters are you using, or what is the planned string configuration? At reference conditions, the Sunpower E20-245 has a Vmp of 40.5 and an Voc of 50.8. The Sunnyboy inverters typically tolerate 600 Vdc max, and 480 Vdc max MPPT. If I select more than 13 panels on a string, it starts throwing errors about the 600 V limit being exceeded. I guess the 8.8 kW quote had more than one inverter?

2) To avoid errors, if I scale the system down to two strings of 13 (26 panels) on one inverter, for a 6.4 KW system size, it yields 8190 kWh in year 0, with some assumptions about system losses. If you are a Sunpower fan and believe they will degrade 2% in year 1 and only 0.25% per year thereafter, in year 14 the generation would be 7769 kWh.

If those Sunpowers cost $4.00 / W, that would be a system cost of $25480. If you took that same budget and bought the LG 270's for $3.80 / W (or $3.775 to make the math work out), that would buy you 25 panels. Let's say the LG's perform at the warrantied performance limit of 3% degradation in the first year, and 0.7% per year thereafter, and otherwise, the system has the same loss factors. In a smaller footprint, that system would produce 8765 kWh in year 0, and 7760 kWh in year 14. The total production difference would be 3783 kWh in favor of the LG's through those 14 years, and it would take the Sunpowers another 14 years to make up that difference.

I could definitely see an argument that the Sunpowers' out performance later in the system life is worth more, since electricity rates may be higher then and those kWh replaced will be more expensive. If it was me buying this system, I would be feeling out the LG quote a little more carefully, since their performance in the time horizon I'm most interested in appears to be a better value by this analysis.

Food for thought maybe... I don't think there's a wrong answer here, especially with the incentives you have going for you.

Thanks for taking a more detailed look into this setup. The system as it is mapped right now will be two array's one with 16 panels the other with 20 panels. It will come with 2 SMA TL-22 inverters with 20 year warranty (the extended warranty will be included). But this may change if I decide to move forward (signup) and get the sight survey done to see how much and location of the shading on the roof - I think it is very minimal but will let the experts decide.

The reasons I am leaning towards SP is because of the lifetime degradation rate is better than other panels currently available in the market and the 25 year warranty. I don't give too much weight to the warranty because the company may just refuse to honor it 15 years form now - if they are still around. But it is still good to know it is there...it also becomes a selling point I am looking to sell the house 15 plus years from know.

[Digital21]

Just to update:

Went with the SP 245's and SMA inverters for an 8.8 kW system at $4 per watt. This will cover about 83% of annual usage. Had the site survey and they noted a low level of shading and space to put more panels.

Considering adding 3 more panels to bring the system size to 9.6 kW to cover 90% annual usage. This would add another approx. $3000 to the cost. The reasoning behind increasing the system size is 1) as I replace appliances in the house with more efficient appliances my usage will be offset closer to 100% and 2) NY may one day have SREC's in place so the extra production will help build more credits and their value will add to the payback assumptions. But overall since this is major, long term purchase this is the time to make any changes and make sure I end up with a system that does not require tweaking. BTW the installer has been totally neutral on this and has not tried to push me in one direction or the other. Any suggestions would be helpful ...