Considerations for Aluminum
- The cost of copper continues to rise while the price of aluminum remains relatively stable.
- The cost of copper, on a “per amp” basis, is significantly higher than that of aluminum.
- The lower weight of aluminum per lineal feet means it’s easier to handle during installation.
Considerations against Aluminum:
Aluminum wire has to be larger than copper wire to achieve the same ampacity per circuit efficiency, resulting in larger raceways and potential size range incompatibility with inverter and combiner box terminals. Some cases have shown a 2x increase in wire size moving form Copper to Aluminum conductors.
- Thermal Expansion
Aluminum has a greater tendency to creep over time, because it has a far higher coefficient of thermal expansion. This constant expansion and contraction creates tension and compression at terminal points. The repeated expansion and contraction results in the terminals loosening, leading to a poor connection and thus, heat. Excessive loosening and lack of maintenance can lead to electrical fires. Newer aluminum alloys have addressed these issues, but ambiguity can persist across the electrical industry. If you’re going to use Aluminum conductors in your PV system, please consider the importance of regular maintenance cycles and infrared heat inspections to locate problem areas.
Oxidation is to aluminum what rust is to iron. A white powdery substance, called aluminum oxide, forms on the surface of the aluminum. Oxidation forms because of moisture. When the wires oxidize at electrical termination points, it creates resistance. The side-effect of resistance is heat which can become significant enough to start a fire. An anti- oxidation compound should be used at all aluminum terminations to combat this problem.
A seasoned electrician knows never to nick a wire when stripping it to make terminal connections. A nick creates a stress point, leading to eventual wire breakage. Qualified electricians use specialist tools to strip the wire, so only the insulation is cut. An unqualified person does not understand this and perhaps just uses a pocket knife or box blade to strip the insulation. Aluminum is a very soft and weak metal. Over time it will break at the nick point due to stresses. Breakage leads to loose conductors, heat and ground faults. Only a qualified electrician should have installed aluminum wire, since a nick-free installation is critical.
- In Summary
Each situation is unique with a balancing between material cost, installation cost, system efficiency, maintenance and LCOE (Lowest Cost of Energy) on a plant basis. It is extremely important to hire a good experienced engineer who can help work through the pros and cons for your exact situation and optimize the conductor sizes for the underground or rooftop photovoltaic system.