Selling tatic for MPPT [RE-wrenches]

Bill Loesch, Saint Louis Solar bill_loesch at compuserve.com
Sun Aug 8 04:03:50 PDT 2004


 

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YOur loyal fan is always looking out for ways to make Mr. Frank rich.

Thanks for the tip and perserverence with the Home depot CFL minispiral
instant on units. If they can locate any more I will buy them and put them
in my horde of very reasonably priced used Lightoleer track lighting. 

RE-wrenches said:
> Hey Phil;

>I'm aware and proud to share Nuevo Mexico with you, I was referring to the
 rest of the list and
>didn't want anyone to think I was suggesting these  methods for Higher
voltage grid tie.   I love
>your example and with your numbers, I would drop the cost even  lower by
doing a modest amount of
>Daisy chaining (3 modules would be  pushing it, but would still be around
10 amps actual operating
>current per  circuit. ) Assuming they're Siemens M50 modules, the
manufacturer's  literature
>clearly shows daisy chaining up to 4 modules. Then I would bring  the 2
circuits into a 2 pole QO
>box indoors with 2 15 A breakers.

>QO 2P box  $14.00 2 breakers    $15.88 60' 12-2 TC     $14.40

>Total   $44.28

>Three times cheaper.

>Perfect: no. NEC no, but Taos inspectors allow this all the time since its
in the  PV 
>manufacturer's instructions. (and I quote from the latest Siemens manual:
"  A small number of
>modules may be paralleled using the Junction box on the  back of the
module. Contact your local
>reseller for more information.") Is it safer than daisy chaining the whole
thing with no fuses: 
>Yes. Am I going to lose sleep over this arrangement going up in smoke , 
absolutely not, it won't.
>Are the power losses worth going to other methods:  Not without MPPT. The 
almost 1 volt drop while
>high, will not be noticed by a regular charge  controller. The modules
even hot will  produce close
>to full amps at 15  volts, leaving full current up to 14 volts at the
batteries. As the  batteries
>near full charge (over 14), the volt drop will only help taper  the
charging current slightly. (3%
>volt drop is too conservative for 12 v  systems and not conservative
enough at high voltages, 48
>and up. Instead I  use power drop as stated in previous emails) As noted,
jumping into an MPPT
>controller would solve many problems and  would be the next recommended
upgrade for this customer.
>The same lines at  24 v and 5 amps would only cause a total power loss of
5 watts or $25 worth  of 
>solar power. So the wiring holds for the MPPT upgrade too. Maybe I  would
run a third line and put 
>each series string on its own circuit then  too and everyone would be
happy.

>I'm sure a bunch of wrenches are rolling around thinking I'm cracked, but 
that's great. That's why
>I love this list and respect everyones' views; its  getting us ALL to
think and rethink about what
>we're doing.

>Ray

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