[RE Marketing] 400 ft DC voltage drop [RE-wrenches]

[Joel Davidson]

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Hello Steve,

Bob-O Schultze and Bill Brooks are right. Granted, supply shortages and the 
dollar/Euro value are important business factors, but minimizing voltage 
drop is important because a 1% increase in voltage drop means a cumulative 
1% decrease in the total output of your PV system over its lifetime.

I do not know of a PV system sale that was lost to a competitor because of 
the price difference between 2% and 5% I2R loss wire. On the other hand, I 
know jobs that were won because the customer selected the system with the 
highest peak (not average) inverter efficiency. PV customers want efficient 
systems.

In the 1970s, some PV system designers referenced NEC 215 and rationalized 
5% wire loss because 36- and even 33-cell solar modules could charge 
batteries under most conditions. By 1984 when NEC 690 was first published, 
many designers had switched from 5% to 3% and some designers were used 2% 
wire loss to squeeze every watt out of the system. In 2002, John Berdner got 
designers' attention by recommending 1% to 1.5% loss on the AC side. Since 
then some wrenches have posted that higher than 2% wire losses are 
acceptable (maybe to them but not to me).

A Ferengi Solar Rule of Acquisition states that money today is worth more 
than money tomorrow and its corollary states that first-cost is most 
important. Thus, it is believed by some beings in this galaxy that the 
lowest price PV system is best. However, I say design PV systems with 2% or 
less wire loss, invest in copper wire, and reap the kWh rewards for decades.

Joel Davidson

"Conventional energy economics is a value system masquerading as 
mathematics. At its heart is one key assumption: the future is worthless and 
the environment doesn't matter. Fie on future generations, who needs 'em? 
What have my grandchildren done for me? For 80 years, our culture has had 
cheap power on a pedestal. In most contexts, cheap means 'shoddy' or 
'second-rate.' Cheap is schlock, cheap is shunned. Think of your own 
purchasing behavior. Do you buy the cheapest ice cream, put powdered dairy 
creamer in your coffee, drive a Yugo? Of course not. But when it comes to 
electricity, cheap is best. If similar thinking prevailed in the underwear 
industry, Calvin Klein would sell only burlap bras and boxer shorts. 
Scratchy sure, but cheaper than cotton. A Public Underwear Commission would 
ensure that he didn't try to blend some pricey silk garments with the burlap 
ones. If consumers complained of a rash, the PUC would say, 'Quit itching. 
Americans want cheap undies. Burlap is best.'" - from The New Frontier: 
Grid-Connected PV, James R. Udall, 1998.




----- Original Message ----- 
From: "Bob-O Schultze, Electron Connection"
To: <RE-Markets at topica.com>
Sent: Thursday, May 01, 2008 6:55 AM
Subject: Re: [RE Marketing] 400 ft DC voltage drop


> I'd go with D if possible, but E would be fine too. Losing expensive  PV 
> watts in wire losses is bad design and economically foolhardy when  you 
> consider the lifespan of the system.
> Bob-O
>
> On Apr 30, 2008, at 10:18 PM, Steve Johnson wrote:
>
>> I have a 400 foot run on an output circuit to combiner, 23.5 amps.
>> Should the DC VOLTAGE that is used as the system voltage to calculate
>> voltage drop be:
>> A) Voc at low temperature
>> B) Voc at high temperature
>> C) Nameplate Voc
>> D) Vmp at high Temperature
>> E) Nameplate Vmp


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