Update on system quote in NM

[renormalize]

In March I posted on this forum asking for feedback on two bids for installing PV on a 2700 sq ft residence under construction in Las Cruces, NM. Since then, I've asked both vendors to up-size their proposals to include 24 low-profile panels (the max that can fit on my flat garage roof), where the added power is intended to assist with the charging of a future electric vehicle. They have responded as follows:

Vendor L
System Size: 7,200 W DC
Year 1 Estimated Production: 12,304 kWh
Panels: (24) LG Electronics LG300N1C-G4 modules with 10 year product & 25 year linear power warranties
Inverter: (1) SMA America SB7000TL-US-2 7000 W
Mounting Type: Ballasted roof mount at 10 deg tilt
Total Investment: $27,100
System Cost per DC Watt: $3.76

Vendor S
System Size: 7,848 W DC
Year 1 Estimated Production: 14,106 kWh
Panels: (24) Sunpower SPR-E20-327 (WHT) modules with 25 year product & 25 year linear power warranties
Inverter: (1) Sunpower SPR-7702m (AFCI, 2MPPT w/SPS) 7700 W
Mounting Type: Ballasted roof mount at 10 deg tilt
Total Investment: $28,613
System Cost per DC Watt: $3.65

Comparing the two proposals, the Sunpower system has a 2.5x longer panel warranty (for what it's worth) and is 3% cheaper per DC watt than the LG system. So to me the Sunpower system looks like the better deal, but maybe I'm missing something. Are there any reasons that I might prefer the LG proposal? Or any other comments? Thanks!

[J.P.M.]

1.) Are the systems ballasted because the garage roof is horizontal ? If so, will the roof take the dead and live (wind) loading ? If you have not done so already, check it out.
2.) Are those prices before of after fed. tax credit ?
3.) At that tilt and your climate, expect a pretty robust and frequent cleaning schedule. Not a knock, but Las Cruces is one of the dustiest places I've ever been to, and I lived in
NM for several years. Performance will probably suffer more there than other places due to panel fouling.
4.) Forget about the economic worth of any alleged warranty benefits. Outside of down/out failure, performance claims are about impossible to verify. Fortunately, most quality panels seem to beat spec performance out of the box.
5.) You could do worse than those prices, and maybe a bit better on the LG's depending on the local market, but something seems amiss. Sunpower systems commonly cost ~ $1.00 or so more than other equipment before tax credit, and in any case > ~~ $4.25-$4.50/Watt. I'd say if you can verify the price and quality - not used, or sloppy seconds, or stolen, etc., the S.P. might be worth a sniff, but I'd remember if a deal sounds too good to be true, it probably is. There's something not right about that S.P. price, especially for a ballasted system.