Am I Crazy?

[russ]

Oh ok, thats the road I was on originally - doing my own spreadsheet 'till I got offtrack by someone plugging pvwatts as the endall. No one is plugging PV Watts as an end all - it is a very useful tool to get you into the ball park for annual production

On the derate factor, all the quotes I had used 23-30% loss (.70 -.77), maybe do to possible shading issues. Probably - the derate used today is typically 82 to 84%

So the Energy Value $ in pvwatts is the estimated cost displaced by the solar system for the first year assuming no rate chgs and all other inherent assumptions. K, got it. The energy shown by PV Watts is the rate of the local POCO per kWh * total kWh per year generated according to the PV Watts projection.

So no canned programs exist that try to factor in rising cost scenarios? all the quotes I had the companies did this calculation using 4.75%/year. Seems rising costs is the key to determining savings in lease scenarios Full purchase and assuming no changes for 20 years seems to most always come out positive.
[ATTACH=CONFIG]4593[/ATTACH][ATTACH=CONFIG]4592[/ATTACH]

5% is salesman's BS and nothing more - every local is different. The higher the better as far as the salesman is concerned - I am surprised some fools hasn't gone for 10% or even 25%.

[Datacruncher]

Whats the formula for 100% efficientcy with 0 Derate

5% is salesman's BS and nothing more - every local is different. The higher the better as far as the salesman is concerned - I am surprised some fools hasn't gone for 10% or even 25%.

Not sure what you mean by "The higher the better" for what? and what is the 10%-25% you mention?

Pvwatts gave me a production of 7112 kWh/year using a default derate of .77 ; using 5kw system, 15 degree tilt, 192 Azimuth
0.77 is close to the value all the quotes I've gotten.

I was told that the production formula is [(Sys_Size * Solar hours * 365 days) - (LOSS)]

for zero loss that would provide a production value of 10037 kWh/year (using the 5.5 solar hours for my area; pvwatts calcs 5.46)

[russ]

Not sure what you mean by "The higher the better" for what? and what is the 10%-25% you mention?

Pvwatts gave me a production of 7112 kWh/year using a default derate of .77 ; using 5kw system, 15 degree tilt, 192 Azimuth
0.77 is close to the value all the quotes I've gotten.

I was told that the production formula is [(Sys_Size * Solar hours * 365 days) - (LOSS)]

for zero loss that would provide a production value of 10037 kWh/year (using the 5.5 solar hours for my area; pvwatts calcs 5.46)

If you read the posts on the topic you will learn the 77% is considered very conservative - the 82% to 84% range is a lot more realistic.

Some salesmen like to go for bigger numbers - more commission for them and to heck with the customer.

PV Watts is an estimation that with a reasonable derate factor should be more or less on over some long time period - say 10 years. There can be substantial annual variation.

[J.P.M.]

Not sure what you mean by "The higher the better" for what? and what is the 10%-25% you mention?

Pvwatts gave me a production of 7112 kWh/year using a default derate of .77 ; using 5kw system, 15 degree tilt, 192 Azimuth
0.77 is close to the value all the quotes I've gotten.

I was told that the production formula is [(Sys_Size * Solar hours * 365 days) - (LOSS)]

for zero loss that would provide a production value of 10037 kWh/year (using the 5.5 solar hours for my area; pvwatts calcs 5.46)

You were told wrong. That formula is of little even as a dart throw. "Solar hours" is an undefined term, no account is taken for azimuth or elevation and "LOSS" is undefined.

[Datacruncher]

Simple Formula to calculate PV annual production is close to PVwatts calcs.

You were told wrong. That formula is of little even as a dart throw. "Solar hours" is an undefined term, no account is taken for azimuth or elevation and "LOSS" is undefined.

A diff of 396 kwh/year for a 5kw system seems ball park to me. Enough with your negative vibes jpm. you make these generalizations with no backing.

PVWATTS yielded 7332 kwh (see attached)

My “dart” throw resulted in 7728 kwh a diff of 396 kwh. I’d say that is close.

PROOF: [(5kw) *( 5.5 solar hrs) * (365)]*.77 = 7728

and a snapshot of your beloved PVWATTS results;

same formula was used by Mike90250 back in 11/10/2009 -> http://www.solarpaneltalk.com/showth...hlight=formula

And if you don't understand loss when talking about PV solar systems, let me help - as in mechanical engines there is power loss to get the power from the engine to the wheels, PV systems also have loss in many areas, one of the easiest ones to understand is in the inverter, there is electrical loss in converting DC to AC. Do you need me to define DC and AC too? keep the brain flatulence to min, and remember - Not everyone who tells you what may be unpleasant or seems insulting is your enemy.

PVWATTS yielded 7332 kwh.jpg

[Ian S]

A diff of 396 kwh/year for a 5kw system seems ball park to me. Enough with your negative vibes jpm. you make these generalizations with no backing.

PVWATTS yielded 7332 kwh (see attached)

My “dart” throw resulted in 7728 kwh a diff of 396 kwh. I’d say that is close.

PROOF: [(5kw) *( 5.5 solar hrs) * (365)]*.77 = 7728

and a snapshot of your beloved PVWATTS results;

same formula was used by Mike90250 back in 11/10/2009 -> http://www.solarpaneltalk.com/showth...hlight=formula

And if you don't understand loss when talking about PV solar systems, let me help - as in mechanical engines there is power loss to get the power from the engine to the wheels, PV systems also have loss in many areas, one of the easiest ones to understand is in the inverter, there is electrical loss in converting DC to AC. Do you need me to define DC and AC too? keep the brain flatulence to min, and remember - Not everyone who tells you what may be unpleasant or seems insulting is your enemy.

This concept of solar hours is kind of intriguing. I've attached a plot showing my production today and wonder how I would determine the number of solar hours from it.
ScreenHunter_01 Aug. 05 20.56.jpg

[J.P.M.]

A diff of 396 kwh/year for a 5kw system seems ball park to me. Enough with your negative vibes jpm. you make these generalizations with no backing.

PVWATTS yielded 7332 kwh (see attached)

My “dart” throw resulted in 7728 kwh a diff of 396 kwh. I’d say that is close.

PROOF: [(5kw) *( 5.5 solar hrs) * (365)]*.77 = 7728

and a snapshot of your beloved PVWATTS results;

same formula was used by Mike90250 back in 11/10/2009 -> http://www.solarpaneltalk.com/showth...hlight=formula

And if you don't understand loss when talking about PV solar systems, let me help - as in mechanical engines there is power loss to get the power from the engine to the wheels, PV systems also have loss in many areas, one of the easiest ones to understand is in the inverter, there is electrical loss in converting DC to AC. Do you need me to define DC and AC too? keep the brain flatulence to min, and remember - Not everyone who tells you what may be unpleasant or seems insulting is your enemy.

I can't write for Mike, but, if I'm reading the correct post, I do not think what you wrote above is quite the same as what he wrote. Nor is your point the same as his in that post of 2009. I believe you're taking his post out of context. I did see his mention in that same post that PVWatts was a better estimator than his simple formula which you incorrectly copied.

I'd respectfully suggest you consider taking a deep breath, stop embarrassing yourself, and consider the possibility you are in over your head from a technical standpoint. It is however, a free country, so do as you wish.

If you continue making unsubstantiated and incorrect pronouncements of a technical nature (separate from opinion) that those of us who are knowledgeable know to be wrong, do not be surprised if those statements are challenged in an attempt to keep incorrect information from impeding progress toward a better energy future, same as other incorrect and misleading statements would be and are challenged.

BTW, to perhaps correct your thinking on one point: I think PVWatts is a decent first cut at a residential sizing tool. It's not gospel and I'm not enamoured with it. I've used stuff that, IMO, are better design tools and, FWIW, written stuff going back to FORTRAN and Visual Basic that is more flexible.

As far as my knowledge of solar energy and, as you say, "mechanical engines and power loss", I believe I can handle that part without your assistance, but thank you for the offer. My guess is I may have forgotten more about the profession of Mechanical Engineering and its technical aspects than you are likely to be aware of for some time to come.