System size confusion

[Ewp2308]

Hello, I have been researching residential solar panels for a weeks now and stumbled across this forum. We have met with 3 different companies and obtained 2 quotes. All 3 companies have stated we need a system around 6.2kWh to 6.6kwh to zero our monthly electric, however when I put my usage in a solar calculator it is telling me roughly around a 11kWh system. Obviously that's quite a difference, even one of the invoices from the company on a 6.6kWh system only estimated roughly 50 percent of electric usage per year. Here is my setup:

central florida
3100 sq ft. (New build, been in 6 months)
Oct 2016 roughly used 1530kWh and march 2017 was 897kWh.
No shading/trees chimney issues
roof faces pretty much dead south

first quote:
7.08kwh
24 canadian 295s
solar edge se7600 w/ 24 se300 optimizer
permitting installing and whole 9 yards for
$26020

Second quote:

6.55kWh
23 solarworld 285s
sb tl7000-us
Permitting installing and whole 9 yards for
$15299

thoughts?

Thank you for your time and response.

[sensij]

a kW is a unit of power, a kWh is a unit of energy. 1 kWh = 1 kW * 1 hr. Your system is sized in kW, the rated power that the system could produce under a certain set of conditions. The energy you consume is measured in kWh, which is usually what your bill is based on.

You can check out PVWatts to see how much energy a system with 6.5 kW power rating might produce, in your location. If you are on a TOU rate plan (I don't know if you have those in FL), it is possible that you can produce fewer kWh than you consume, but still offset your bill.

[J.P.M.]

Looks like your researching needs a little direction. Download and read "Solar Power Your Home for Dummies". Then run PVWatts after you spend about 20 min. reading the help/info screens.

A 6.5 kW (not kWh) system will probably get you something like 9,000 - 9,500 kWh/yr. Suit yourself, but depending on what your electric rates are and how you use electricity, a 100% offset of an electric bill may not be the most cost effective way to go.

Add: Why the price differential ? $10K differential for essentially very similar systems is not correct. I'm unfamiliar w/ FL prices, but one is $3.68/Watt, which seems in the ballpark, if high by maybe 10% or so. The other is $2.33/Watt, and that seems low.

[Ewp2308]

Thank you for replies. In the process of reading the dummies book. As far as the pricing differences, from what I can tell it appears each part has been marked up quite a bit. Not to mention a blanket charge of 2k for electrical services, which is aside from installation fees. Seems like added hidden b.s charges imo.

[J.P.M.]

Thank you for replies. In the process of reading the dummies book. As far as the pricing differences, from what I can tell it appears each part has been marked up quite a bit. Not to mention a blanket charge of 2k for electrical services, which is aside from installation fees. Seems like added hidden b.s charges imo.

You're welcome. Forgot to mention, an updated hardcopy is ~ $25 @ bookstores/Amazon. The download's a bit dated, but most of the bread/butter is still good.

As for the prices you got: Yea, but $10,000 ? Something is not correct.

[SunEagle]

You're welcome. Forgot to mention, an updated hardcopy is ~ $25 @ bookstores/Amazon. The download's a bit dated, but most of the bread/butter is still good.

As for the prices you got: Yea, but $10,000 ? Something is not correct.

I agree with you. Either they forgot to add something into the second price or they are installing used equipment. That $10,000 difference between the 2 proposals raises a question.

[Kuma]

New to this also. Have learned a lot in the past several weeks. imho - One thing that should be seriously considered when using solar calc tools for system sizing is panel efficiency losses over time. Generally speaking, panels lose 2-3% in the first year, .6-.7% every year following that, with no more then 20% loss in 25 years. It can be enlightening realizing the "actual" system size required for future proofing.

PVwatts -> system losses/loss Calculator -> age. Meaning, age of panels.

MOD Note. This info is incorrect. ThinFilm panels might degrade this fast, but they are not too much in circulation now.

[ButchDeal]

Generally speaking, panels lose 2-3% in the first year, .6-.7% every year following that, with no more then 20% loss in 25 years. It can be enlightening realizing the "actual" system size required for future proofing.

Generally speaking you should lose 1% first year. and 0.5% per year there after. Some

[Ewp2308]

Here is the exact break down on the invoice from the higher quote:

permits and design - $ 1800
se 300 optimizer - 24 x 131.125 = $3147
cs6k-295-ms-bf - 24 x 365.05 = $8761
se7600a-us - $2824.80
ru-2 vynckler transition box - $131.56
solar mounts/rails - 24 = $ 150
electrical services - $2000
installation labor - $3755.44
Total - $26020

As for the cheaper quote, I don't believe any of the equipment quoted was used but I will make sure I clarify that with them.

[J.P.M.]

I agree with you. Either they forgot to add something into the second price or they are installing used equipment. That $10,000 difference between the 2 proposals raises a question.

Or, looking at the post again, maybe a typo by the OP ?

[J.P.M.]

Here is the exact break down on the invoice from the higher quote:

permits and design - $ 1800
se 300 optimizer - 24 x 131.125 = $3147
cs6k-295-ms-bf - 24 x 365.05 = $8761
se7600a-us - $2824.80
ru-2 vynckler transition box - $131.56
solar mounts/rails - 24 = $ 150
electrical services - $2000
installation labor - $3755.44
Total - $26020

As for the cheaper quote, I don't believe any of the equipment quoted was used but I will make sure I clarify that with them.

If this is a turnkey system, the cost breakdown for equipment/services is not important to you. It's probably more/less B.S. anyway. What is important is the quality of the components, the quality of the vendor and getting the most bang for your buck. The best chance of getting the best mix of all three of those is to follow the path of self education.

[Ewp2308]

Yea I asked for the invoice to see exactly what items they were expecting me to purchase. The difference between the quotes provided obviously made me question as to what was going on. I agree with everything you said regarding vendor, components and bang for buck. Don't want to be that sucker that over pays when I could have achieved same result with a different company. Also forgot to answer above, there are currently no TOU's in Florida.

[SunEagle]

Yea I asked for the invoice to see exactly what items they were expecting me to purchase. The difference between the quotes provided obviously made me question as to what was going on. I agree with everything you said regarding vendor, components and bang for buck. Don't want to be that sucker that over pays when I could have achieved same result with a different company. Also forgot to answer above, there are currently no TOU's in Florida.

Keep us informed as to what they say about the second price and equipment.

If the prices look right I might be installing a ground mount pv system up in the Brooksville area of Fl next year. I am always interested in what others are getting.

[J.P.M.]

Yea I asked for the invoice to see exactly what items they were expecting me to purchase. The difference between the quotes provided obviously made me question as to what was going on. I agree with everything you said regarding vendor, components and bang for buck. Don't want to be that sucker that over pays when I could have achieved same result with a different company. Also forgot to answer above, there are currently no TOU's in Florida.

Most of my point was to perhaps take a different view of what constitutes the "best price" away from lowest initial cost - a fool's errand - to a longer view that looks at value for dollar spent in providing a fit for purpose, but not necessarily overbuilt array with unnecessary or unused and mostly useless frufra.

[Kuma]

Generally speaking you should lose 1% first year. and 0.5% per year there after. Some

..

The below chart from Revnu is inline with other panels I am considering, including Canadian Solar. Which is also a panel manufacturer the OP mentioned.

Is the" actual" degradation closer to your number where the listed warranty/guaranteed degradation is a conservative number? Designing and planning on the conservative side is a good approach anyway.

--------------------------
Hanwha Q.PLUS L-G4.2 330-340

"At least 97% of nominal power during first year. Thereafter max. 0.6% degradation per year. At least 92 % of nominal power after 10 years. At least 83% of nominal power after 25 years."

Csun CSUN340-72M

--------------------------

GUELPH, Ontario, June 12, 2015 /PRNewswire/ -- Canadian Solar Inc

• For polycrystalline module products, Canadian Solar guarantees the first year power degradation is no more than 2.5% from its nameplate power. From year 2 to year 25, the actual power decline will be no more than 0.7%. By the end of year 25, the actual power output will be no less than 80.7% of the nameplate power output.
• For the Diamond double-glass module, Canadian Solar guarantees the first year power degradation is no more than 2.5% from its nameplate power. From year 2 to year 30, the actual annual power decline will be no more than 0.5%. By the end of year 30, the actual power output will be no less than 83% of the labeled power output.

The performance warranty for standard monocrystalline cell modules will continue to be 3% degradation for the first year, and 0.7% power loss from year 2 to year 25.

----------------------------

HANWHA Q CELLS Q.PEAK G4.1 300W 32mm Black Frame Mono

HANWHA Q CELLS Q.PEAK G4.1 300W 32mm Black Frame Mono
Module Efficiency 18.6%.
25-year linear performance warranty and 12-year workmanship product warranty.
32 modules per pallet

Performance (Mono PERC)	Q CELLS	CSIQ	Trina	Jinko	JA	Hyundai
Annual Degradation	0.6%	0.7%	0.68%	0.7%	0.65%	0.7%
1st year	98.0%	97.0%	97.0%	97.0%	97.0%	97.0%
25th year	83.6%	80.2%	80.7%	80.2%	81.4%	80.0%
Product Warranty	12	10	10	10	12	10
Wp (WHT)	300-305	290-300	280-305	280-300	265-285	270-285