PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

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bbrock
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Joined: Mon Nov 23, 2009 8:55 pm
Location: CA

PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by bbrock »

Hi Bogleheads,
What started as simply wanting to improve our energy efficiency with doing attic air sealing, increasing the insulation to R-44, and replacing our HVAC system, has led me down many paths. Now, I have been researching and planning on having PV solar installed. I figure why not take advantage of this as well as the 30% solar tax credit while we can. We would pash cash for the PV solar system and the payback varies from 6-9 contingent on contractor and brand. The other variable that throws a wrench in this plan is that we have thermal solar (pool) and a stone coated metal shingle roof (Decra tile).

Re: the roof. The house was built in 1969 with wood shingle. The original owner of our house had the metal shingle placed over the wood shingle in Dec. 1986. This Decra tile was 50 yr. warranted, but of course that warranty was only to original owner. The metal shingle is aged 32 yrs. It generally looks good, however there are some dents in places. I had a reputable roofer out who only deals with metal roofs. He gave me a quote to repair of approx. $1300, but it would be higher to perhaps $1500 b/c he would charge hourly for any wood work and he suspects and sees some on the gables. With the repairs, he believes the roof would last another 25 years. His quote for a new metal roof replacement is ~$22k. The new metal shingle would be a shake look and is much easier to walk on and more durable. In addition to his quote, I have obtained some quote to replace the roof with a comp shingle. Those bids vary from $24k (30 yr comp) - $26k (lifetime comp).

The benefits of going again with metal are that the original wood shingle wood not have to be removed so less mess outside and in attic, the metal has better reflectivity and less conduction, the air gap between the metal and wood could serve as an insulator, the wood shingle would provide better ventilation vs. the plywood or OSB sheeting that would have to be put down for the comp shingle, the metal will last forever, metal is 100% waterproof, Tilcor metal shingle is a greener choice vs. comp. Cons: compared to comp shingle, it is still more difficult to walk on as some care must be taken even with the newer metal shingles, wider availability of roofers who work with comp. vs. metal roofs.

Now, re: PV solar. The contractor I'd go with for the Panasonic gave me a quote of about $20,500. The quote I have received for Sunpower is about $24,500. If I go with Sunpower through the roofer who intalls the metal shingle, his quote is $25,920. The Sunpower is the industry leader as far as panel efficiency and degradation; the production at year 25 is 92% vs. the Panasonic 330 HIT is %90.76 at year 25. Pros and cons for each manufacturer.

Panasonic:
Cheaper upfront
Like Sunpower, has 25 year full warranty on material, workmanship, performance
Better heat coefficient vs. Sunpower
Company has better bankability vs. Sunpower

Sunpower
Industry leader
Company was declared exempt from the Trump tariffs
Busbars are in back on panel vs. the rest of the industry which places them on front (This helps with long term solar production)
Uses copper back plates

The re-roofing option would be more upfront b/c it would also require that I replace my thermal solar, as it is 30 yrs old, and most thermal solar installers don't want the liability of removing and replacing this old of a system on a new roof. New thermal solar ranges from $5k-6k.

I am leaning to using the Panasonic PV b/c Panasonic is a known, is not going out of business and will back there warranties as such. They are less expensive upfront. If the minor improvement in long term efficiency and production of the Sunpower 92% comes at an upfront cost of ~$5k, that may be a wash in the long term given the Panasonics are at %90.76 at year 25. Regarding the roof or re-roof, I am at a bind and can't decide whether to replace (and replace with comp or metal) or repair.

I have done the cost benefit analysis of roof now vs. 25 years later. But just trying to make sense of the numbers and look at the situation not just monetarily but practically.

If I don't spend the~$25k on roof now, then in 25 years based on the 2.32% yield of Vanguard Intermediate Term Tax Exempt Admiral Bond Fund it is $44,626

my average price per kwh = $0.29
average usage last 13 mo. = 8018 kw
average cost per mo. = $167

savings over 25 yr based on my cost per mo. = $50,100
savings over 25 yr based on $0.29 * 8018 kw *25 yr = $58,131

cost of roof today ~$25,000
new roof in 25 yrs based on average inflation rate 3.22% = $55,212

25 yr savings on mo. electricity cost of $167 and investing savings annually in VCADX w/ yield of 2.32% = $68,727

Can anyone help me make sense of all these numbers and this situation both practically and monetarily? Thanks in advance for reading this long thread.
B

Edit 1: Doing roof now, part of it would fall under the 30% solar tax credit. I estimate 1/6 could based on plan placement on my roof.
bbrock
3504PIR
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by 3504PIR »

I would replace the roof with solar roof shingles from Tesla. I’m not sure if they are currently available, but if they’re not, they will be soon enough.
desiderium
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by desiderium »

How long will it take to pay off your investment in the solar panels?

For the cost of the installation, how much energy will it produce?
Subtract your tax credits and the savings on the roof and figure your cost/kwh X production
Allow for tiered pricing on the electricity and degradation of the panels
Any other state or local incentives to figure in?

How long do you think you will you enjoy your home?

This is perhaps the best way to understand the investment, IMO.

When I first looked into things, it way ~10 year payoff. Over the next 4 years it went down to payoff in 4 years and I went with it. Combination of state incentives and price drops on the panels over this period. Now close to being paid off Ongoing cash incentives will make money on top of the savings.
DrakeSRT
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by DrakeSRT »

I would remove the old metal and wood roofs and replace with composition shingle, then choose whomever you want for PV.
Topic Author
bbrock
Posts: 421
Joined: Mon Nov 23, 2009 8:55 pm
Location: CA

Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by bbrock »

Thanks for the reply so far.

There is always the thought and option to just replace the east face of my roof upon which PV solar would go. That side is not visible from the street, so it really would not be obvious, especially if I went with another metal shingle such a shake style which is easier to walk on.
bbrock
DrakeSRT
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by DrakeSRT »

I'm not a fan of metal roofs and you have one over the top of an old presumably bad / failing wood shake roof which is something I would never do but you bought it and are stuck with it. Your metal roof has dents if you use metal again you will have more dents after the solar is installed and or during maintenance/ cleaning.

At some point your roof may leak, with new stacked on old and repaired on top of that it will be very hard to determine where it is leaking. It might leak in one spot then drain down through the metal and wood and drip onto drywall appearing like that's where the leak is. You may then have to take the solar off the roof to repair (again) or replace. Then put the solar back on.

Don't compound what is already (IMO) a very janky roof. Tear it all off and put a proper roof back on.
Drake
bbqguru
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by bbqguru »

I vote for the metal roof. You may want to see if your home insurance is impacted by getting rid of the metal, many companies give a discount for metal vs asphalt. We have a metal roof on our home and receive a sizable discount (20-25%) off of our entire premium due to the metal roof being rated against wind/hail damage.

I'm inclined to have the same line of thought as DrakeSRT- tear the shingles off to the decking and only have one layer of new roof. You're able to repair any damage and you've removed the additional weight that doesn't need to be there.

As for the solar panels, I'd lean Panasonic for the reasons you are, primarily company longevity.
Valuethinker
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by Valuethinker »

bbrock wrote: Sat Sep 29, 2018 2:26 pm Thanks for the reply so far.

There is always the thought and option to just replace the east face of my roof upon which PV solar would go. That side is not visible from the street, so it really would not be obvious, especially if I went with another metal shingle such a shake style which is easier to walk on.
I think you are best to replace the roof now, because it will be big hassle and cost to do it once the solar array is on.
Dilbydog
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by Dilbydog »

Did the contractor provide a power production model for each system? I.E. anticipated annual kWH production for the SunPower system and the Panasonic system. I’ll assume the Panasonic modules are rated 330 watt given the model number you presented (I didn’t look that up so I could be mistaken), what wattage are the proposed SP modules?
SunPower thinks a lot of their modules, and charges a premium, thus I’m surprised at how closely priced the two systems are. Do you have any other options in module manufacturers? Trina, Jinko, LG, all make quality modules.
mouses
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by mouses »

I would not let the mess of removing shingles be considered a factor. That is a very short term situation.
applejack123
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by applejack123 »

Yeah, I would replace the roof before I worried about solar panels. Never just put a band-aid on it. My neighbor did this same thing, had no plywood on his roof, tried putting a metal roof on, and guess how long it lasted? He kept getting leaks around his chimney.

Did you mention where you live? Say northeast? Why are you not interested in architectural asphalt shingles? That’s all I would consider, unless say I lived in the southwest. And if I lived in Florida, and had lots of money laying around, I’d consider a tile roof.

In my opinion, and it’s just that, is that metal roofs look cool, but shouldn’t be on a house. In the northeast, snow comes shooting down, like an avalanche. The rubber grommets deteriorate in the sun, and then you have a potential leak everywhere there’s a screw. I hear they design them now with a seam that covers the screws, but we will see. Also, they are loud, get dents, etc. I mean there are pros and cons to everything and nothing lasts forever, nothing. So I don’t know what this “lifetime” price you said covers.

Is it 20+k for both, the roof and the solar? Or each? If it’s each, just do the roof first, the right way. Complete tear off, plywood preferably, not OSB. Then, do the solar. That’s what I’d do. I’d even almost further add, I don’t even know if I’d do solar just yet anyways. I mean it’s only gonna get cheaper and better, kind of like a tv, or tankless water heaters.

I bet if you did the work yourself, it would only be at most, five grand.
Last edited by applejack123 on Sun Sep 30, 2018 9:46 am, edited 1 time in total.
applejack123
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Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by applejack123 »

The other thing is please go with a reputable roofer. Roofers can really cut corners, say not stepflashing, or using the proper amount of nails per shingle. There’s so many places they can cut corners to make the job quicker and easier for themselves, and then they’re out.

My parents have a second home in SW Florida and after the hurricanes, you just see one roof and another go up. U can sit on porch listening to roofers nail shingles. Not good when you only hear three nail pops, when you should be hearing at least 5 and preferably 6. I feel bad when the owner will never know til their shingles fall off. Guess what, try and find that roofer then. Even I was burned one time on step flashing, and I grew up around construction and roofing.
Topic Author
bbrock
Posts: 421
Joined: Mon Nov 23, 2009 8:55 pm
Location: CA

Re: PV Solar (Sunpower vs. Panasonic HIT) & To Roof or Not to Re-roof

Post by bbrock »

Tx for the replies. I didn't get any notification of them. Moderators, can you let me know why please? I fortunately saw the replies the other day when I looked back at the thread.

To answer some of the questions/comments.
We reside in Livermore, CA.

Panels would be located on East roof face as I have 5 thermal solar panels on South face, and 1 thermal panel on West face. West face gets eventual shading d/t tall trees to West and South sides. I am not interested in relocating thermal solar even though that could be option especially if I re-roof. Actually, if I re-roof, it pays to just get a new thermal panel system as mine is from ~1988 from the research I did. Past it's life expectancy. But, kids love a warm pool, and in swim season, it's worth it to have the thermal on the South face to get the most sun to supply heat for the thermal panels right off the bat. So, relocating is not worth it when my East face will suffice for PV.

But, given that I am working with just my East face, I have thought that I may want to consider the most efficient panels given the space. If I can get the most efficiency given the space, then I could use less panels which in turn would save some space for if/when I need more panels d/t future degradation, electric car, etc. So, this gives a nod to Sunpower, but given the efficiency rates of Panasonic and Sunpower, I really don't think it is worth it to pay the premium for Sunpower.

The metal roof installer, who also installs PV, can install Sunpower or Panasonic. If Sunpower, he can install 17 of the 360 w panels (6.12 kw). This would be $4.50/w at a gross cost of $27,540. He estimates that it would produce 8223 kw in the 1st year. However, his Sunpower analysis tool shows that my usage is 8369 kwh for the last year. He also ran a Sunpower proposal for 20 of the 327 w panels (6.54 kw), which is estimated to produce 8777 kwh. This would be $4.30/w, priced at $28,122.

Another Sunpower dealer (non-roofer) ran a proposal on the 327 w panels. He estimated that with 19 panels (6.213 w), it would produce 8110 kwh. His estimates showed that I used 8320 kwh for the last year. Their cost: $24,955 which is $4.017/w.
[Sidenote: when I looked at my usage at PG&E for the last 13 months, which was as far back as I could go, I think I got a total usage of 8018 kwh]

Not a big difference in my historical usage per these two contractors, rather there is a difference in their cost per watt. Realize this is before any tax credit, as I am not considering that. I am more so interested in upfront cost per watt. Also, I seem to be averaging about a 31-35% coefficient on the amount of energy that these Sunpower systems will produce. I am not saying that that is a constant coefficient, but rather it generally helps me to compare different solar vendors claims of production.

I had the metal roofer also price out a proposal with Panasonic HIT 330 w panels. I asked for 18 panels b/c another Panasonic vendor did a thorough analysis with that number of panels. While the metal roofer did not analyze the energy production yet, he did provide pricing of $22,275. This is 18 panels 330 w (5.94 w) for $3.75/w. I asked him to run an energy production analysis for 18 and 21 Panasonic 330 w panels.

Basing the metal roofer's proposal on the Panasonic vendor (non-roofer) I was considering, for 18 Panasonic 330 HIT panels (5.94 w), they estimated my energy production would be 8088 kwh. This company's price per watt for the Panasonic is $3.45. Their energy production estimate is relatively similar to my 31-35% coefficient for energy production (again I can't base this on anything more than it appears that is what I can expect for system production). Whatever the case, perhaps 20 of these 330 w Panasonic panels would be enough to cover 100% of my energy usage based on past performance.

Factors which will most likely affect my energy usage going forward are that within the last month, we upgraded our HVAC from a 8 SEER AC to a 15 SEER, and furnace from an 80% single stage to a 96% 2 stage variable speed blower. Thus, the AC and furnace d/t variable power should lower our energy usage. And, after some attic air sealing, I'm planning for the attic insulation to be increased from R-16 to R-44.

Even though that one Panasonic contractor would do it for $3.45, I am less inclined to go with him if this metal roofer can re-roof and install the Panasonic system. That way I get one nice fat hefty bill that I can use for IRS purposes for the credit. Otherwise, I have been told that I need to have the roofer coordinate with the solar company so that the solar company can state that they subcontracted the roofer as it was necessary for my solar install. That could work, but if I also give all the business to the roofer, maybe I'll have some leverage for add-ons like gutters, etc.

And, I am leaning towards re-roofing, it's just that I have a hard time not wanting to add that amount in to what solar will be costing me per watt. If I didn't do solar, I would not be re-roofing. However, I would be needing some repairs regardless. But, I realize I can't really add the cost in on some levels. I am still leaning towards metal b/c the pricing I am getting for the metal re-roof is $22k vs. other roofers offering comp at $24k-26k for comp. The comp would include tear off of my metal and wood shingle down to the skip sheathing, and then laying down new sheathing and the comp over. The metal roofer would simply tear off my existing metal and put down a the new metal Tilcor Craftsman Shake shingle over the battens. This is acceptable, I read the installation instructions, warranty, etc., and have been in contact with the local distributor of the Tilcor to verify. Code allows 2 layers of roofing. Wood shingle can be the underlayment. The metal over is 100% waterproof, more durable, longer lasting, and a better value. For that money, I'm getting a much longer lifespan out of the metal vs. the comp. The comp will radiate that much more heat into my attic, which will pass through and fight my insulation to get into my housing envelope. The metal will reflect that much more heat vs. the comp.
bbrock
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