Help! Partial Flat-roof mount w LG 305 or Full Sloped-roof mount with SunPower 345

[esquivelso]

I have an interesting dilemma (at least I'd like to think so). Recently, I had a local San Diego installer price a system for me using LG 305's and this is what he came back with:

panels: LG 305
# of panels: 19
system size: 5.80
inverter type: central/optimized
inverter qty & model#: Solar Edge se5000 and 19 solar edge p300 power optimizers

*ALSO includes service panel upgrade*

cost (cash price) = $23,735 before 30% tax credit

Here's the issue though: the system includes mounting panels on my sloped roof as well as some on the flat part of my roof. I'm not a big fan of the idea and it would definitely involve re-roofing due to the age of the flat roof.

I thought it was a pretty good price from a reputable installer, but like a good homeowner I want to do my due diligence and get multiple quotes.

The second installer that came over proposed mounting the entire system, using SunPower panels, on the sloped portion of the roof. He thinks he can get, at a minimum, 15 345w panels on the sloped part of the roof which would cover most of my usage. The problem of course is the cost difference. See below for his quote on a 3.45kw system, which is much smaller than the aforementioned LG, but this is due to him not adding in expected usage from the EV I just got. Either I forgot to tell him about it over the phone or he forgot. Either way, this is the only cost I have for now from them; I'll update once I receive the revised quote (which WILL include either a service panel upgrade OR an RMA).

panels: SunPower 345
# of panels: 10
System size: 3.45
inverter type: SMA Sunny Boy 3000TL-US-22

*NO service panel upgrade needed*

cost (cash Price) = $16,387 before 30% tax credit

Cost seems high to me but it does solve the problem of having to install panels on my flat roof. I don't trust the roof and most homeowners in the area have had to re-roof multiple times since they were built (in 70's).

So my questions for all of you solar experts:

- Should I be worried about the flat-roof installation? Any direct experience out there?
- Is SunPower a worthwhile upgrade? Does it seem justified in this case?
- Is the cost for either/both systems in line with average solar install in San Diego (I'm specifically in San Marcos)?
- Anything else I'm missing?

Thanks in advance to anyone that takes the time to read this post, especially if you can offer any insight!home.jpg

[sensij]

Let's say for the sake of argument that if you can fit 15 of the Sunpower 345's on your sloped roof, you could also fit 15 of the LG305's. The dimensions aren't identical (the Sunpower is 3" shorter and about 1" wider), but they are close.

15 * 305 = 4575 W. Conveniently, that is about 1.2 * 3800 W, which is the largest size inverter you could install on a 20 A circuit, avoiding the panel upgrade.

4575 W might not zero out your bill, but by avoiding the panel upgrade, postponing the re-roof until it is necessary, and perhaps by using SDG&E's TOU rates for EV's, I would bet that would be the most cost effective PV installation for you. Shop it around and see if you can get someone respectable to bite at $3.50 / W. I can PM an installer if you are interested.

[thejq]

It's probably not a fair comparison when the two proposals have that much of difference in wattage and installation area. You either need the extra 2.35 KW or you don't. You should ask the 2nd installer to give you a proposal of 5.8KW SP + panel upgrade to be fair. But just based on price, assuming the panel upgrade is $2500 (normally $2-2.5K) your first proposal is $3.66/W which is ok, maybe a little higher. Did they have to use tilt mount for the flat roof which is a little more expensive? As for the SP, the price is $4.75/W which is a little higher too, but personally I don't think it's worth $1.1/W extra. BTW, 2.35KW extra will likely allow you to drive 15K miles/year. But with EV-TOU2 plan and you have a fast charger to push all charging to super off-peak, you can live with a much smaller system. As for re-roofing, if you think you will do it anyway in the near future, wouldn't it be better to do it with the solar, so at least you can claim some of it as part of your solar installation to get the 30% tax credit?

[esquivelso]

Let's say for the sake of argument that if you can fit 15 of the Sunpower 345's on your sloped roof, you could also fit 15 of the LG305's. The dimensions aren't identical (the Sunpower is 3" shorter and about 1" wider), but they are close.

15 * 305 = 4575 W. Conveniently, that is about 1.2 * 3800 W, which is the largest size inverter you could install on a 20 A circuit, avoiding the panel upgrade.

4575 W might not zero out your bill, but by avoiding the panel upgrade, postponing the re-roof until it is necessary, and perhaps by using SDG&E's TOU rates for EV's, I would bet that would be the most cost effective PV installation for you. Shop it around and see if you can get someone respectable to bite at $3.50 / W. I can PM an installer if you are interested.

Hi sensij,

I appreciate you taking the time to respond. As much as I wish I could fit 15 LG's, I don't think it's possible. My sloped roof is 292" x 225" so if the calculations are correct I'd have just enough space for 15 SP panels but not enough space for the same amount of LG panels (292"-36"-36" = 220" space. 220/42= 5 panels. 225"-36" = 189" space. 189/62 = 3 panels. Hopefully math is correct) . So that leaves me with either 12 LG's or 15 SP max on the roof. 12 LG's won't cut it so I'd be stuck adding panels to the flat part of the roof. Also, if I did 15 SP panels, I'd also need a panel upgrade or RMA so I'd have to factor in that cost too. Am I missing anything? Also, can you PM me the name of an installer you know? I'd like to get another quote or two before proceeding.

[esquivelso]

It's probably not a fair comparison when the two proposals have that much of difference in wattage and installation area. You either need the extra 2.35 KW or you don't. You should ask the 2nd installer to give you a proposal of 5.8KW SP + panel upgrade to be fair. But just based on price, assuming the panel upgrade is $2500 (normally $2-2.5K) your first proposal is $3.66/W which is ok, maybe a little higher. Did they have to use tilt mount for the flat roof which is a little more expensive? As for the SP, the price is $4.75/W which is a little higher too, but personally I don't think it's worth $1.1/W extra. BTW, 2.35KW extra will likely allow you to drive 15K miles/year. But with EV-TOU2 plan and you have a fast charger to push all charging to super off-peak, you can live with a much smaller system. As for re-roofing, if you think you will do it anyway in the near future, wouldn't it be better to do it with the solar, so at least you can claim some of it as part of your solar installation to get the 30% tax credit?

Hi thejq,

Thanks for the response, you've been an amazing help since I started this journey! I didn't think of the tax break for redoing the roof at the same time, nice call. I'm still skeptical of putting panels on there for the long term though. As is, water pools in certain areas of my roof when it rains. This, combined with the greater weight of the panels makes me really uneasy to install anything additional up there. I'll ask my neighbor today, who's a gen contractor and recently redid his roof to see what he thinks. Thanks again!