What is the best solar panel?

[jflorey2]

The one factor I think PTC is better at is higher operating temp. While 120F may be high (100F ideal?), IMHO is closer to real world than the 75F of STC.

Agreed - but - it really doesn't matter, since you can calculate the panel's performance at any given temperature as long as you know the tempcos and the performance at _any_ temperature. 25C is as good as 45C. The critical issue is that all panels be tested the same way, and that's what STC is intended for - since it's relatively easy to flash every single panel at 25C.

[Old_Man]

For the benefit of the metric-deprived, 75F is 24C, one degree Celsius shy of the goal, here.

This has been an interesting thread. Based on what I've read here, the solar, "industry," such as it is, is as corrupt as the music business and we KNOW what Hunter S. Thompson said about that, a statement I can personally verify. I'm putting solar on my truck but a friend was looking into real estate and installing it until he found out how much HASSLE it'd be. So he bought a house with it already installed. He doesn't have to go through what can only be called the insanity of trying to buy solar on your house, installed by some booger-picking kids with a gnat's knowledge about what they're doing, coupled with a commensurate attention span.

I don't know if Bob's system is *hit-tied, but I will suggest he go off grid. Power companies? No f-n' way I want any piece of that. Off grid or nothing would be for me.

[J.P.M.]

All good reasons not to use PTC, always good to question a standard.
The one factor I think PTC is better at is higher operating temp. While 120F may be high (100F ideal?), IMHO is closer to real world than the 75F of STC.

The cell and ambient temp. for the STC method is 25 C, not 75F.

Not a standard, but empirical correlations exist that get pretty close to estimating a panel's cell temp. relative to ambient air temperature using the P.O.A. irradiance and wind velocity. I've helped develop them in the past with some solar energy society folks and have one specific to my array that's good for estimating my array's cell temp. +/- a couple deg. C or less for winds < ~ 8 m/sec. Given an average cell temp. and a Global Horizontal Irradiance (G.H.I.) from a Davis weather station that gets converted to P.O.A. (Plane of Array) irradiance by conversion algorithms I and others have written, along with ambient air temp. and wind velocity from the Davis, my calc'd array power output is quite close (~ +/- 0.25% or so) to that of a clean array. I've used that method for a bunch of years to estimate how fast my array fouls under various conditions over the past 9 years or so. Long, boring story, but I'm pretty confident of my data and methodology.

If you know the P.O.A. and the wind speed you'll not have to screw around using panel test methods to estimate cell temps. and so panel efficiencies and so panel output. You'll be able to get panel output in ways similar to how PVWatts and for that matter most other PV panel modeling stuff models output in one form or another.

If you would like the temp. correlations, I'll post them once I get back home where all the data and the array are located.

[GoingElectric]

- The first one being too many variables that can change under real world conditions.

All good reasons not to use PTC, always good to question a standard.
The one factor I think PTC is better at is higher operating temp. While 120F may be high (100F ideal?), IMHO is closer to real world than the 75F of STC.

[J.P.M.]

Yes, as you more clearly wrote, in space limited area need higher PV production density.

Then I see STC, a new term for me, so I look up
“Standard Test Conditions”

then see
“Photovoltaics for Utility Scale Applications Test Conditions” or PVUSA Test Conditions; more commonly “PTC.”
Under PTC, everything is heated up as if it were in the sun. The solar cells within the panel are raised to their “normal operating cell temperature” which is typically around 113°F (45°C). The ambient temperature is set to 68°F (20°C), and a 2.2 mph (~1 meter/second) breeze blows across the panel. Here is a summary of the two sets of test conditions:


PTC is a much better metric to look at, closer to real life conditions.

I do not believe PTC to be a better measure of panel performance for several simple reasons.
- The first one being too many variables that can change under real world conditions.
- What's the panel orientation ?
- What if the wind vector changes in either magnitude or direction ? BTW, wind vectors are seldom steady and also have a vertical component. PTC makes no mention of how those variables may affect the output.
- You left out that the panel is tested 10m above the ground. Does that mean the panel has nothing under it ? If on a flat surface, what's the clearance under the panel ? That clearance will affect the NOCT more than being 10m above the ground, especially if the velocity vector's magnitude is fixed at 1 m/sec.
- The panel's tilt is not specified in the PTC method. A non horizontal panel's performance will be more affected by wind than will a horizontal panel.

- Another reason I don't think the PTC is a good thing to have around is it's not as universally applied to all panels.
- Having more than one test method only muddies the waters when trying to compare panels.
- Test methods should not be used to estimate operating conditions.

Any test method ought to be used to compare panel performance between and among panels but not site performance.

The STC method, or any test method is in that sense similar to vehicle mileage numbers posted by vehicle manufacturers.
The numbers will most likely never be achieved under operating conditions which are never the same from one site and setup to the next.
To say that the PTC method is closer to real life conditions is simplistic. The PTC method is probably more accurate at estimating performance when site conditions match the PTC test conditions.
Use PVWatts to model expected performance using site conditions. The method is reasonably fast and with reasonably accurate inputs will give results a lot closer to reality than using any test condition standard.

[GoingElectric]

If space is a concern, the panel STC wattage matters little. What counts most is the panel's STC wattage per area and a low(er) power degradation as f(temperature)

Depending on the available space and its layout, physically larger panels by themselves may actually be a drawback.

The only real benefit to larger panels besides maybe a bit less $/STC watt for the panels is probably a bit less wiring for the array.

Yes, as you more clearly wrote, in space limited area need higher PV production density.

Then I see STC, a new term for me, so I look up
“Standard Test Conditions”

then see
“Photovoltaics for Utility Scale Applications Test Conditions” or PVUSA Test Conditions; more commonly “PTC.”
Under PTC, everything is heated up as if it were in the sun. The solar cells within the panel are raised to their “normal operating cell temperature” which is typically around 113°F (45°C). The ambient temperature is set to 68°F (20°C), and a 2.2 mph (~1 meter/second) breeze blows across the panel. Here is a summary of the two sets of test conditions:


PTC is a much better metric to look at, closer to real life conditions.

[J.P.M.]

Personally,
I ended up focusing on lifespan, or "degradation per year".
End result is more collected power over lifespan.
Look for approximately 88% in 20 years.

The one exception is space vs demand, then I would get a higher W / area instead (410+ W sizes)

If space is a concern, the panel STC wattage matters little. What counts most is the panel's STC wattage per area and a low(er) power degradation as f(temperature)

Depending on the available space and its layout, physically larger panels by themselves may actually be a drawback.

The only real benefit to larger panels besides maybe a bit less $/STC watt for the panels is probably a bit less wiring for the array.

[GoingElectric]

For a person who live in California, and use Edison, and need about 8kW,
what is the best solar panel and how much we can save money by using the panel?
How much do we have to pay for the panel after rebates and incentives?
We might purchase one small house. If we can save $$$ money, we want to install the panel before California change law which pay less money to people.

Thank you.

Personally,
I ended up focusing on lifespan, or "degradation per year".
End result is more collected power over lifespan.
Look for approximately 88% in 20 years.

The one exception is space vs demand, then I would get a higher W / area instead (410+ W sizes)

[Old_Man]

I'm a big fan of Longi, as a company.

[bcroe]

9 years ago I went with those that had reached the status of a commodity.
Best watt/dollar value, and most likely to be available over the life of the
array, in case a storm throws a branch through one, etc. That was a
6 X 10 cell arrangement, 250W back then. The latest may have upped
the watts a bit, but they can still be swapped onto the system no problem.

I have some 6 X 12 panels, 5 of these placed end to end can directly
replace 6 of the above. The landscape mounting means snow has less
distance to slide (or be pushed) off. Bruce Roe

[solarix]

Solar PV panels are amazing. They virtually all have great reliability and pretty much are just a commodity now. Stick with "Tier 1" manufacturers, find what looks aesthetic to you, go for the best dollars/watt and you will be fine.

[Will792]

Best panel is the one that best matches your requirements. These aspects come to mind:
Price
Efficiency
Physical size
Thermal coefficient
Voltage compatibility
Expected reliability
Expected ability of manufacturer to service warranty claims
Expected efficiency drop as panels age
Tolerance for partial shading

forgot one more:
aesthetics

[silversaver]

Depends on your roof size, how big of system needed and choose the correct panel fit your budget. If you have enough roof space, you really don't need to buy the most efficient panel on the market, but with limited roof space, you will have no choice but to pick the most $$$ panels.

[DanS26]

Tier 1 solar manufacturers only....if you don't know what that means....Google is your friend....

[jflorey2]

what is the best solar panel

No such thing.

For a "typical" roof installation - get whatever single crystal panel is cheaper.
For an installation in a limited area - get whatever high efficiency (20%+) panel is cheaper. (Sunpower Maxeon 6 is currently leading at 23% but there are lots of others out there.)
For a ground mount installation - get a bifacial.

How much do we have to pay for the panel after rebates and incentives?

Panels are running from 40 to 75 cents a watt right now. You need a lot more than panels though.