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choosing the right solar roof system for your home (buy or lease)

I have three current quotes for a solar installation on the roof of our home in Marin County California.

Two of them offer a lease option (as an alternative to a purchase).
One of them offers a discount through the 1BOG group purchase plan.

I am having a hard time choosing between the bids.

Any advice would be appreciated.

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Replies to This Discussion

Permalink Reply by Deep Patel on July 28, 2009 at 12:21am: Thomas,

thanks for posting this important question. First I would compare the equipment, are all the quotes offering the same solar panel / inverter combination? Also are you consider to own the system or lease it? If you were to own the system would you pay cash or your obtain your own financing through home equity?

looking forward to your response!; ▶ Reply to This

Permalink Reply by Martin Herzfeld on July 28, 2009 at 11:59am: Financially: Think one would be a residential Power Purchase Agreement (PPA) and think the other would be a solar lease.

"... monthly payment varies each month based on the production of the system, whereas the SolarLease payment does not change month to month, but increases 3.9% per year." Think there are also differences in the terms in comparison. Additional information, for instance:

http://www.renewableenergyworld.com/rea/news/article/2009/01/reside...

The competitive options would be for instance, municipal financing or Clean Energy Municipal Financing (CEMF)

http://rael.berkeley.edu/financing/seminar
http://sites.google.com/site/raelfinancingseminar/Home

The potential issue with the CEMF would be if the first would allow a second from the municipality.

Concur, "First I would compare the equipment ..." although specialize on ground mounted arrays, if roof mount, check requirements for flashing, and the height the modules are going to be about the roof 4 or 6 inches? Also would the installer be placing modules with a 3 foot for residential - page 13 and page 14, which impacts the number of modules on the roof.

http://osfm.fire.ca.gov/pdf/reports/solarphotovoltaicguideline.pdf

Concur, " ... financing through home equity.." as an option - to consider the cost of capital of other options including the IRR and NPV. The issue would the other options would be the cost of money and solar as a service recurring costs. Since solar energy systems require little to no maintenance, you may have to wash the modules with a garden hose twice a year. And from debris data, it appears once in July and once October, depending on location:

"It appears from the performance index with regards to the soiling appears to best twice a year for 12-16 panels in July [5% - 15%] and in October [5% - 20%]"

If California, there are "Secured Financing for CA/TX" also with the option to "Learn more"

http://www.cleanpowerfinance.com/solar/residential-loans/
http://www.cleanpowerfinance.com/guaranty-bank/

Technically: In addition to the solar modules and inverters, would be the conductors. Larger conductor sizes result in a reduced power loss which results in increased energy. Simply, solar integrators may minimize conductor sizes with regards to the code, but from a consumers perspective, the larger conductor sizes may be of benefit with regards to energy. This may be calculated by using the National Electrical Code Chapter 9, Table 8 to calculate the resistance of a conductor at a specific temperature. to calculate power based on the current of the modules, time - since current increases and decreases during the day. For example a #10 AWG cost typically more than a #12 AWG, but installers may just use a #10 on the Direct Current (DC) side because of simplicity which benefits the customer.

Another issue may be the azimuth of the array. If the array may be adjusted as to the value of energy based on time, would result in a decreased kWh, but increased value and increase the return on investment with a smaller array based on usage. In other words, the more you used, the more a 3kW array would provide benefit. Depending on your usage, a 3kW array < 4kW typically the average, would be what you would require.

Also you may wish to look in your breaker panel. In accordance to NEC 690.64(B) you should have an available position, to save you a substantial cost. For instance, if there is no space in the breaker panel, the incremental cost may be substantial if the installer is unable to reduce the size of the main depending on the current rating of the buss bar.

In other words, a smaller systems, may provide the greater return on investment.

Remember, a module consists of two wires a positive and negative. You may wish to think about the style of the modules for aesthetes. Also, the roof may not be the only viable option, have you considered a various options of ground-mounts? For instance, but one,

http://www.renewableenergyworld.com/rea/partner/products/view?id=22...

Would you consider the equipment before financing options, or financing options before equipment?; ▶ Reply to This

Permalink Reply by Thomas Luehrsen on August 10, 2009 at 10:32am: I can't say I really understood everything in the above post...but I do have another question:

All other things being equal, do either of these two systems look "better" or "higher quality" than the other one?

Thanks for any advice!

System #1:

CEC Rated kilowatt Output (PTC): 3.932 kW AC
MFG Nameplate Rating (STC): 4.725 kW DC

27 Panels - Suntech STP175S-24/Ab-1 Black 25 Year Manufacturer Warranty
Inverter(s):

Inverter: 1 - SMA SB 4000 US(240) 10 Year Manufacturer Warranty

System #2:

4.725 kW DC Power (STC)
4.099 kW (PTC)
3.935 kW AC Power (CEC Size)

27 Panels:
Sharp Corporation Model: NT-175UC1
175W Monocrystalline Module with locking connector

Inverter:
Qty. 1 SMA America Model: SB4000US (240V)
4kW 240Vac Sunny Boy Utility Interactive Inverter with display

Both systems are offered with a straight purchase option or a lease option (through SunRun).; ▶ Reply to This

Permalink Reply by Deep Patel on August 10, 2009 at 1:30pm: Hi Thomas,

The systems compared are very similar in terms of CEC AC output. I would say the SunTech Black Label solar panels have a higher aesthetic appeal since the frame, solar cells and backsheet are black they give your system a low profile look.

On the other hand, Sharp is a well diversified conglomerate, they've been around since 1912 and develop many consumer electronics. Since solar panels have long warranties, at least 25 years. Owning the Sharp solar panel may give a buyer more confidence in the warranty.

I would run the CSI calculator for both of the systems you are comparing to find how many kWh (kilowatt-hours) you'll generate per year: http://www.csi-epbb.com/default.aspx

If you're going to lease the system, I suppose warranty will not matter as much since most likely to lessor would be responsible for the equipment. Although if you're looking to purchase and own the system then I would say if you were to compare the strength of the Sharp warranty versus Suntech then obviously Sharp would be the clear winner because of the company's financial position.

Also Sharp manufacturers their solar panels in New Mexico versus SunTech which are primarily made in China, I'm not sure if that also influences your purchasing decision.

I hope this helps, good luck!; ▶ Reply to This

Permalink Reply by Thomas Luehrsen on August 10, 2009 at 3:25pm: Thank you Deep, for your help!; ▶ Reply to This

Permalink Reply by Martin Herzfeld on August 10, 2009 at 7:00pm: Respectfully, both design options there is a substantial issue. Strongly suggest whom you are working with alternate system designs.

1. Light Induced Degradation (LID) likely to be an issue over time and voltage depression during hot days
> 113 F #2 worse than #1 at > 122 F with regards to MPPT, depending on location.
2. Strongly suggest, depending on location, ~24 modules if lowest ambient temperature, for instance, 14 F and maximize string size along with NEC 690.7.

In other words, although maximizes system size, if the modules too hot, won't be able to track the maximum power point around solar noon, modules degrade over time, ... and other reasons. Would you like to talk about best practices?; ▶ Reply to This

Permalink Reply by Thomas Luehrsen on August 10, 2009 at 7:14pm: The house is in Marin County CA (94925).
We rarely get over 100 degrees F and never under 25 degrees F.

By 24 modules, do you mean 24 panels?
Don't understand.; ▶ Reply to This

Permalink Reply by Martin Herzfeld on August 10, 2009 at 8:40pm: http://www.weather.com/weather/wxclimatology/monthly/graph/94925?fr...

1. The cell temperature of the modules in sunlight which would exceed > F. Greater than highest ambient temperature.
2. In accordance with NEC 690.2 definitions.

I. As defined in NEC Figure 690.1(A) Identification of Solar Photovoltaic System Components.

a) "Panel. A collection of modules mechanically fastened together, wired, and designed to provide a field-installable unit."
b) "Module. A complete, environmentally protected unit consisting of solar cells, optics, and other components, exclusive of tracker, designed to generate dc power when exposed to sunlight."
c) "Array. A mechanically integrated assembly of modules or panels with a support structure and foundation, ..."

For our discussion only: A cell > module > panel > array. Therefore, 27 modules may be 3 panels | strings or 1 array or 24 modules may be 2 panels | strings or 1 array.

3. If rooftop, also would suggest adjust conduits in sunlight as FPN using NEC 2008 along with thermal expansion calculations among other things.

Now, would you like to talk about best practices?; ▶ Reply to This

Permalink Reply by Martin Herzfeld on August 10, 2009 at 9:36pm: 54.6 degrees Celsius = 130.28 degrees Fahrenheit?

Also for your information only: IR imaging from a ground mounted array in the east bay other modules for discussion only:

When temperature increases, voltage decreases. In addition, there is the temperature coefficient of voltage which is factor ... both really about the same in you example, but one greater than the other -> Vmin.

In other words, would suggest you keep it - solar - simple - maximize modules and minimize panels.; ▶ Reply to This

Permalink Reply by Thomas Luehrsen on August 10, 2009 at 10:25pm: 1. temperature increases, voltage decreases
2. maximize modules and minimize panels

OK! This I understand now!
Are you saying I should find another vendor, like Sunpower?
I know they have more efficient panels.; ▶ Reply to This

Permalink Reply by Deep Patel on August 11, 2009 at 10:50am: Martin brings up a great point, in which when ambient temperatures increase the ability of your solar panels to maximize its harvest decreases. Most solar panels, including Suntech and Sharp have a lower temperature coefficients unlike Sanyo solar panels which are made of a crystalline / amorphous silicon blend which gives it a higher temperature coefficient. Solar panels with a higher temperature coefficient you will harvest the most electricity even when the temperatures are the hottest.; ▶ Reply to This

Permalink Reply by Thomas Luehrsen on August 11, 2009 at 11:01am: I wonder which vendors offer the higher temperature coefficient panels, like the Sanyo product?
I know that SolarCity uses panels by First Solar.; ▶ Reply to This