Location: Wire Voltage Drop

Examples of Voltage Drop Across a Wire

Wires are not perfect conductors of electricity, as such there are inefficiencies. This will explain those voltage drops. To illustrate the importance of wire, let us show a few examples of how a wire can negatively effect a very nice set of components around it. We will even do some math to prove it. We will look at how the choice of a wire can really make or break the installation.

Example 1 Johnny's Solar Install

Johnny wants to install solar panels to save money. He purchased the finest panels, the nicest inverter, and then chose to have a base rate installer accumulate the parts, inlcluding the wires, and put them on his home. The original installer chose very nice parts, but when it came to the wire discussion, Johnny opted to go with the thinner guage. Now 2 years into his solar power generation, he notices that he isn't quite getting the power production he expected. HIS QUESTION IS WHY?

Johnny's Kit:
1.5 kw solar panels
2.0 kw inverter/charger
400 ah sealed batteries
60 amp charge controller
Panels to batteries 200' @ 120 VDC, 14 AWG copper
Batteries to inverters 25' @ 24 VDC, 2/0 AWG copper
Find the problem with the system???

If you focus on the wire from the panels to the charge controllers, at 14 AWG, you have the culprit. By choosing a bit smaller wire here the client saved about $50 on copper, was able to purchase an outdoor wire at the locar hardware store, and got er done. However, losses over time are a bundle more.Without the wires to move the power from those pretty panels, it is lost. When you run the math on the voltage drop calculator here you see that the wires to and from the panels drop nearly 11 percent of the total power generated. This is then magnified by each component along the way.
96% efficient panels
95% efficient inverters
95% efficient charge controller
90% efficient batteries
88% efficient wires??? hmmm, that should be 95% or better!

.96*.95*.95*.90*.80 = .69 percent of the power to the grid or home
If you made the wires 97% efficient, the math changes to this
.96*.95*.95*.90*.97 = .76 percent of the power to the grid or home
When you run this out over a month, or a year, it becomes very obvious.

(1.5kw of panels) x (5hrs of sun /day) x (30 days a month) X .69 efficient system = 155.25 kw
vs.
(1.5kw of panels) x (5hrs of sun /day) x (30 days a month) X .76 efficient system = 171 kw
That is over 15 kw a month, or 1/10 of the power you wanted. Over a year that equates to 180 kw of loss.
At 25 cents per delivered watt (transportation charges, taxes, etc) they could have paid for that wire every year with what they throw away.


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Electrical How To Info:
 Electrical Breakers
 Electrical Fuses
 Wires, Sizing Wires, & AWG
 Solar Charge Controllers
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