[Spam] Re: proper inverter [RE-wrenches]

Bob-O Schultze, Electron Connection econnect at snowcrest.net
Wed Mar 22 07:15:38 PST 2006


<x-flowed>
Your free subscription is supported by today's sponsor:
-------------------------------------------------------------------
First Month Free! Save up to 50% on your phone bill. 
Free Activation, Free Equipment! Packet8
30-day money back guarantee. 1-877-868-1135
http://click.topica.com/caaexdQbz8Qcsbz9JC9a/ TMONE
-------------------------------------------------------------------

Bill,
while I certainly agree with you to stay away from the minimum input  
voltage, I also try to say away from the Max input voltage as well.  
That's got little to do with giving the inverter an over voltage  
condition. All inverters have a "sweet" spot range where they  
operated most efficiently. For anyone who has taken the Fronius  
installer training, for example, they explain that in detail. Other  
manus, not so much. A competent, conscientious installer will press a  
manu for that data and try to hit it as a service for his/her clients.
Bob-O
On Mar 21, 2006, at 10:48 AM, Bill Brooks wrote:
>

> Darryl and William,
>
> As those of you know who have been to my courses, I strongly caution
> installers when using the string sizing programs from inverter  
> companies.
> The biggest caveat when using an inverter manufacturer's string sizing
> program is to stay away from the minimum voltage options given.  
> Always try
> to put as many modules in series as possible to stay under the Vmax  
> of the
> inverter. For the Fronius at 500Vmax, 18 modules in series would be  
> the max,
> but if they are wired in strings of 4, you would have to set up two  
> parallel
> strings of 16, which is fine.
>
> As I said earlier, it is clear they are currently wired in series,  
> but it is
> equally likely that the strings of 4 modules are run down to the  
> inverter
> since there is a large conduit, and this joker would not have  
> installed a
> larger conduit than absolutely necessary. Getting on the roof and  
> verifying
> the wiring seems like a costly job, so if the groups of 4 can be  
> tested at
> ground level, you are good to go.
>
> If these are KC120 modules, it is also possible that the modules have
> problems, so that the strings will need to be tested prior to  
> connecting
> them into strings. It could be that the array needs to be replaced  
> under
> warranty, so it would sure be good to know that prior to spending a  
> lot of
> time.
>
> Incidentally, Voc and Isc tests will not always detect the ribbon  
> problems
> in the KC120 module and other modules from other manufacturers that  
> have
> exhibited similar problems. It must be tested under load of the  
> inverter, or
> with a $20,000 IV curve tracer, or with a large power resistor  
> sized to
> operate the array near the maximum power point, or on a partially  
> charged
> 48-volt battery (assuming the strings are available in groups of 4  
> modules).
>
> If you are testing 48-Volt strings, you can size a power resistor  
> to operate
> the array near max power at 800 W/m^2. So how do you do this? What  
> a great
> problem for a PV exam. It requires knowing the main parameters of the
> module. Let's use the KC-120 as an example.
>
> KC-120
> From the module label
> @STC (1000 W/m^2, 25C cell temperature)
> Voc = 21.5 Volts
> Vmp = 16.9 Volts
> Isc = 7.45 Amps
> Imp = 7.10 Amps
> @NOCT (800 W/m^2, 47C cell temperature)
> Vmp = 15.2 Volts
> Imp = 5.74 Amps
>
> So what to use from this? The NOCT data is the proper data set.  
> Since Ohm's
> law is V=IxR, then the resistor value should be R = V/I = 15.2V/ 
> 5.74A = 2.65
> Ohms. Finding an resistor of that value might be tough, but you can  
> play
> around with power resistors in series and parallel until you have a  
> resistor
> bank with the correct resistance, and the correct power dissapation  
> (400
> Watts minimum). Or you can try to rent an IV curve tracer. Or you  
> can feed
> each string into 48 volt battery at partial state of charge and  
> test the
> operating current and voltage of string separately (maybe the  
> easiest).
>
> Good luck,
>
> Bill.
>
>

Your free subscription is supported by today's sponsor:
-------------------------------------------------------------------
Shopping for a new car? 
Pay 2-3% below invoice on a new car of your choice. 
Save thousands with our free car discount finder service!
http://click.topica.com/caaexd6bz8Qcsbz9JC9f/Dealix
-------------------------------------------------------------------

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address: www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------

</x-flowed>



More information about the RE-wrenches mailing list