Inverter Testing--Continuing the thread [RE-wrenches]

[jeff.oldham at realgoods.com]

I recall a report that stated that on average a CEC calculated AC output was
running about 20-30% higher than actual field measurements. Bill, I know
that you did some of these earlier spot tests, what was your findings? I've
really been wanting to give my clients a much more realistic AC output
number (i.e. 30% less than CEC) but find that I cannot be competitive if I
quote a similar priced system with a 30% lower output than my competitor,
especially when their claims are backed by a State agency. It honestly tears
me up to quote and sell someone a 10# bag of nails with 7# in it. I'm just
as uncomfortable telling them that my competitors quote is rather
"optimistic", our industry is struggling enough for credibility. I hope I
can live long enough to see this industry really mature into a well
respected professional challenge to oil and global warming. 

> 	From the Solar, Wind & Hydro Powered office of:
> 	Jeff Oldham
> 	Gaiam- Real Goods & Jade Mountain
> 	Design & Consulting Group
> 	11755 Mid. Mtn. Rd.
> 	Potter Valley, CA 95469  USA
> 
> 	Ph: 303.222.3814
> 	Fax: 707.743.1820
> 
> 	www.solardevelopment.com
> 
> 	"When you turn to face the Sun all shadows fall behind you"
> 	- Old African Proverb
> 


-----Original Message-----
From: Bill Brooks [mailto:billbrooks7 at earthlink.net]
Sent: Thursday, April 18, 2002 3:31 PM
To: RE-wrenches at topica.com
Cc: Jeff Newmiller; Chuck Whitaker
Subject: RE: Inverter Testing--Continuing the thread [RE-wrenches]


Peter,

You have put your finger on an extremely common misconception. Most think
that PTC conditions on the CEC website were actually tested by someone other
than the manufacturer. Not so--the PTC module ratings are based solely on
manufacturer's information of STC and NOTC and those data are used to
calculate what the PTC would be. Nearly all manufacturers are on the low end
of +/- tolerance spectrum, so this number on the CEC website is almost
always 5-10% higher than what the rating would be from an independent lab.

Since you touched on the inverter efficiency ratings (as is this thread is
addressing), those numbers are strictly based on information from the
manufacturer. Sometimes we ask "is that your final answer" when we think the
number sounds unusually high, but if the answer comes back "that's my final
answer" then Regis hands out the $1,000,000 (actually Jeff Newmiller updates
the website). It is certainly possible that one manufacter is very
conservative with their numbers and others have a "rounding up" tendency.
There is no standard to prevent that. Have I depressed you yet?

Peak efficiency is a number to maximize the buydown and should never be used
to determine how much power or energy a PV system will produce. Ultimately
it is all about how much energy a PV system generates on a annual basis.
ACout divided by PVin on an annual basis is a much better metric than max
efficiency. 90% efficiency is a very high number and some inverters come in
at 80-85%.

Efficiency can be affected by temperature, voltage, and certainly power
level. As a manufacturer, you pick the right conditions that maximize the
number, round to the nearest higher digit and go with it--a little tongue in
check for fun but not too far from the truth. Without anyone telling them
how it must be done, I can't say that I blaim them--it just doesn't help the
wrench or the customer with anything other than a higher rebate.

Bill.


-----Original Message-----
From: asap at podnine.com [mailto:asap at podnine.com]
Sent: Thursday, April 18, 2002 2:50 PM
To: RE-wrenches at topica.com
Subject: RE: Inverter Testing--Continuing the thread [RE-wrenches]


Wrenches,

Does not the CEC's PVUSA test conditions, the infamous PTC ratings, kind of
tell the story and level the playing field with their eligible inverter
ratings?  Hasn't this been done before?

http://www.consumerenergycenter.org/buydown/certified_inverters.html

Anyone know how these ratings happen, how testing is done or what "based on
available documents" means, and who gets to decide on these peak efficiency
ratings?

Peter Duchon
ASAP POWER!

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