Calculation of Photovoltaic Cable Line Loss

Reasons for Over - Configuration
- As mentioned, to reduce system costs, photovoltaic power plants often use over - configuration. By installing more solar modules than the rated capacity of the inverter, the system can capture more sunlight during peak hours and increase overall energy production. For example, in a location with abundant sunlight, an 110 - KW module can be paired with a 100 - KW inverter. This 1.1 - fold AC - side over - matching allows the system to take advantage of the high - intensity sunlight without having to invest in a larger - capacity inverter.
Impact on Cable Selection
- The over - configuration affects the cable selection process. Although there are more modules installed, the AC input current of the inverter will not exceed its maximum output current. So, when selecting the AC cable, we base it on the maximum output current of the inverter. In the example of a 100 - KW inverter with a maximum AC output current of approximately 158A, the cable should be able to handle this current without excessive line losses.

Theoretical Basis
- The line loss in a cable is mainly due to the resistance of the cable. According to Ohm's law (V=IR) and the power formula (P=VI), the power loss (Ploss) in a cable can be calculated using the formula Ploss=I2R, where I is the current flowing through the cable and R is the resistance of the cable.
- The resistance of a cable can be calculated using the formula R=ρAL, where ρ is the resistivity of the cable material (for copper, ρ=1.72×10−8Ω⋅m at 20°C), L is the length of the cable, and A is the cross - sectional area of the cable.
Step - by - Step Calculation
- Determine the Current (I): As in the example, the maximum output current of the inverter is the current flowing through the AC cable. So, I=158A.
- Determine the Cable Resistance (R): Suppose the length of the AC cable (L) is 50 meters, and we select a 35mm² copper cable. Using the formula R=ρAL, with ρ=1.72×10−8Ω⋅m, L=50m, and A=35×10−6m2, we have R=1.72×10−8×35×10−650≈0.0246Ω.
- Calculate the Power Loss (Ploss): Using the formula Ploss=I2R, substituting I=158A and R=0.0246Ω, we get Ploss=1582×0.0246≈612.3W.

Cable Material
- Different cable materials have different resistivities. Copper has a lower resistivity than aluminum, which means that for the same cross - sectional area and length, a copper cable will have lower line losses compared to an aluminum cable.
Cable Cross - Sectional Area
- A larger cross - sectional area of the cable results in lower resistance and thus lower line losses. However, larger - gauge cables are more expensive, so a balance needs to be struck between cost and line loss reduction.
Cable Length
- The longer the cable, the higher the resistance and the greater the line loss. Therefore, in photovoltaic power plant design, the cable length should be minimized as much as possible.

Q: How can I reduce the line loss in photovoltaic cables?
- A: You can reduce line loss by using a cable with a larger cross - sectional area, a material with lower resistivity (such as copper), and minimizing the cable length. Additionally, proper cable installation and connection can also help reduce losses.
Q: Does the temperature affect the line loss in cables?
- A: Yes, the resistivity of the cable material increases with temperature. As the temperature rises, the resistance of the cable increases, leading to higher line losses. It is important to consider the operating temperature of the cable when calculating line losses.
Q: Can I use a cable with a lower current - carrying capacity than the inverter's maximum output current?
- A: It is not recommended. Using a cable with a lower current - carrying capacity can lead to excessive line losses, overheating of the cable, and potential safety hazards. Always select a cable that can handle the maximum current of the inverter.

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