[RE-wrenches] PV System Design Compromises (was solid vs stranded AC vs DC)

Matt Tritt solarone at charter.net
Wed Aug 5 13:29:57 PDT 2009


Joel,

Changing any wires connected to a SW to solid core would be virtually 
impossible because of the almost impossible to connect with stranded 
wire connection blocks. Remember how ^$*! tight the spaces are in those 
babies? Living with a marginally relevant inefficiency from stranded 
seems a low price to pay for being able to connect the bits and pieces 
to each other. Non?

Matt T

Joel Davidson wrote:

> Dave, I agree. but are we talking about 2% voltage drop, resistance, 
> or power loss?
>
> What I got from this discussion about solid vs. stranded wire (1) use 
> solid copper wire and (2) keep I2R losses low and (3) if you use 
> stranded wire, be very diligent when tightening connectors. Anything 
> else?
>
> Wrenches make design compromises every day. My 11 year old grid-tied 
> system is an example:
> - Siemens SP70 modules because SP75s were unavailable.
> - Trace SW4048 at 65% efficiency because higher efficiency non-battery 
> inverters were less reliable.
> - Low-rise, low-tilt angle array because Culver City did not allow PV 
> arrays to be visible from the street.
> - And now, making improvements on a system that is working flawlessly 
> for almost 100,000 hours does not make cost vs. benefits sense.
>
> Joel Davidson
>
>
> ----- Original Message ----- From: "Dave Click" <daveclick at fsec.ucf.edu>
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Sent: Wednesday, August 05, 2009 5:58 AM
> Subject: Re: [RE-wrenches] solid vs stranded AC vs DC
>
>
>> 2% loss is significant, but I think that Darryl was saying that the 
>> resistance for stranded wire was 2% higher than solid. So if you had 
>> a 3% voltage drop in your system with stranded wire, you could rewire 
>> the system with solid wire and have a voltage drop of (3% x 0.98) 
>> 2.94% at peak production; that's less than 1 kWh/yr per kW installed.
>>
>> DKC
>>
>> -------- Original Message --------
>> Subject: Re: [RE-wrenches] solid vs stranded  AC vs DC
>> From: Joel  Davidson <joel.davidson at sbcglobal.net>
>> To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
>> Date: 2009/8/3 20:31
>>
>>> 2% loss from any resistance source over 25 years is significant.
>>>
>>> ----- Original Message ----- From: "Darryl Thayer" 
>>> <daryl_solar at yahoo.com>
>>> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
>>> Sent: Monday, August 03, 2009 2:04 PM
>>> Subject: Re: [RE-wrenches] solid vs stranded AC vs DC
>>>
>>>
>>>
>>> Yes, that is what the code book and my electricians handbook says, 
>>> but 2% is very little.  I would think that passing through a conduit 
>>> hole is larger than that.
>>> Darryl
>>>
>>> --- On Mon, 8/3/09, Matt Tritt <solarone at charter.net> wrote:
>>>
>>>> From: Matt Tritt <solarone at charter.net>
>>>> Subject: Re: [RE-wrenches] solid vs stranded  AC vs DC
>>>> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
>>>> Date: Monday, August 3, 2009, 3:49 PM
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Darryl,
>>>>
>>>>
>>>>
>>>> Say what?! This would seem to indicate that solid core is
>>>> actually
>>>> better for DC than stranded wire. Can this possibly be
>>>> true??
>>>>
>>>>
>>>>
>>>> Matt
>>>>
>>>>
>>>>
>>>> Darryl Thayer wrote:
>>>>
>>>>   I looked in the code book and found stranded wire
>>>> has about 2% higher DC resistance than solid, Chapter 9
>>>> table 8, and that for AC resistance the same value as DC
>>>> resistance to within the table accuracy Chapter 9 Table 9
>>>>
>>>> This table points out that for AC resistance it is
>>>> important to know the conduit system, as the reactance will
>>>> have an effect.  With AC it is important to never allow a
>>>> single wire to pass through a metal surface as this will
>>>> induce eddy currents and magnetic effects into the metal
>>>> causing voltage drop and heating.
>>>>
>>>> --- On Fri, 7/31/09, jay peltz <jay at asis.com>
>>>> wrote:
>>>>
>>>>
>>>>
>>>>     From: jay peltz <jay at asis.com>
>>>> Subject: Re: [RE-wrenches] solid vs stranded  AC vs DC
>>>> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
>>>> Date: Friday, July 31, 2009, 10:01 PM
>>>> Hi Darryl,
>>>>
>>>> But what are the differences and when do they come into
>>>> play?
>>>>
>>>>
>>>>
>>>>
>>>> On Jul 31, 2009, at 7:25 PM, Darryl Thayer wrote:
>>>>
>>>>
>>>>
>>>>       Well there is very slight differences between AC
>>>> and
>>>>
>>>>
>>>>     Dc But this
>>>>
>>>>
>>>>       difference
>>>> is so slight that it has no effect on anything we will
>>>>
>>>>
>>>>     do.
>>>>
>>>>
>>>>       Darryl
>>>> --- On Fri, 7/31/09, jay peltz <jay at asis.com>
>>>>
>>>>
>>>>     wrote:
>>>>
>>>>
>>>>
>>>>         From: jay peltz <jay at asis.com>
>>>> Subject: [RE-wrenches] solid vs stranded AC
>>>>
>>>>
>>>>
>>>>     vs DC
>>>>
>>>>
>>>>
>>>>         To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
>>>> Date: Friday, July 31, 2009, 7:00 PM
>>>> HI All,
>>>>
>>>> I'm trying to understand this wire issue.
>>>>
>>>> Whether or not there is a difference between
>>>>
>>>>
>>>>
>>>>     stranded or
>>>>
>>>>
>>>>
>>>>         solid wire for DC or AC.
>>>>
>>>> Any takers on this one?
>>>>
>>>> thanks,
>>>>
>>>> jay
>>>>
>>>> peltz power
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