What is Voltage Rise in Solar?

Voltage rise in solar specifically refers to an increase in voltage within a solar photovoltaic (PV) system beyond its normal operating range. This phenomenon is particularly important to address in solar installations due to the potential for equipment damage and safety risks.

Voltage rise is a phenomenon that occurs in electrical systems, particularly in solar power installations. Here are the main causes of voltage rise:

When a solar system produces more power than the home is consuming, the excess electricity needs to be exported back to the grid. For this to happen, the voltage from the solar inverter must be slightly higher than the grid voltage to “push” the energy from the inverter to the grid. This difference in voltage is what creates the voltage rise.

The resistance in the cables between the solar inverter and the grid connection point plays a crucial role in voltage rise:

• Cable length: Longer cables have higher resistance.
• Cable thickness: Thinner cables have higher resistance.
• Cable material: Different materials have different resistances (e.g., copper vs. aluminium).

According to Ohm’s Law (V = IR), when current flows through a resistive cable, it creates a voltage drop across the cable. This voltage drop manifests as a voltage rise from the grid to the inverter.

Voltage rise is most pronounced during periods of peak solar production, typically around midday when sunlight is strongest. At these times, solar systems are generating maximum power, pushing more current through the cables and exacerbating the voltage rise effect.

The baseline grid voltage can fluctuate throughout the day. When grid voltage is already high, even a small additional rise from solar generation can push the total voltage above acceptable limits.

In multi-phase systems, unbalanced loads across different phases can contribute to voltage rise. This is particularly relevant when single-phase solar systems are added to multi-phase electrical installations.

Improper system design can exacerbate voltage rise issues:

• Undersized cables for the solar system capacity
• Inverters placed far from the main switchboard
• Lack of voltage regulation features in the inverter

Understanding these causes is crucial for designing and maintaining efficient and safe solar power systems. Proper cable sizing, inverter placement, and system balancing can help mitigate voltage rise issues.

Ohm’s Law plays a crucial role in understanding and managing voltage rise in solar systems. Here’s how it applies:

Ohm’s Law states that voltage (V) equals current (I) multiplied by resistance (R):

V=I×R

In the context of solar systems, this formula helps explain why voltage rise occurs and how it can be managed.

When a solar inverter exports excess electricity to the grid, it needs to “push” this energy by creating a slightly higher voltage than the grid voltage. This difference is what we call voltage rise.

1. Current (I): This represents the amount of electricity flowing from the inverter to the grid. During peak solar production (typically midday), the current is at its highest.
2. Resistance (R): This is determined by the cables connecting the inverter to the grid connection point. Factors affecting resistance include:
   1. Cable length: Longer cables have higher resistance
   2. Cable thickness: Thinner cables have higher resistance
   3. Cable material: Different materials have varying resistances

Using Ohm’s Law, we can calculate the voltage rise:

Voltage Rise = Current × Resistance

For example, if a 5kW single-phase inverter generates 21.7A of current (5000W / 230V), and the cable resistance is 0.21Ω, the voltage rise would be:

21.7A × 0.21Ω = 4.557V

This is just within the maximum allowable voltage rise of 4.6V (2% of 230V) according to Australian standards.

Understanding Ohm’s Law helps solar installers and engineers manage voltage rise:

• Reducing Resistance: Using thicker cables or shorter cable runs can lower resistance, reducing voltage rise.
• Three-Phase Systems: By dividing the current across three phases, the current in each cable is reduced, leading to lower voltage rise.
• Inverter Placement: Placing the inverter closer to the main switchboard reduces cable length and, thus, resistance.
• Cable Material: Choosing cables with lower-resistance materials can help minimize voltage rise.

By carefully considering these factors and applying Ohm’s Law, solar system designers can ensure that voltage rise stays within acceptable limits, maximising system efficiency and compliance with grid regulations.

If a voltage drop occurs in a solar power system, it can have several negative impacts:

1. Reduced power output: A voltage drop decreases the solar system’s overall power output. This means less electricity is generated and available for use or export to the grid.
2. Lower system efficiency: The voltage drop reduces the overall efficiency of the solar power system, as some of the generated electricity is lost in transmission.
3. Poor performance of inverters: If the voltage drop is significant, it may prevent the solar inverter from receiving enough voltage to operate properly. This can lead to reduced performance or even failure of the inverter.
4. Overheating of cables: Excessive voltage drop can cause increased current flow, leading to overheating of cables. This poses a safety risk and can potentially damage the system components.
5. Inconsistent power supply: Voltage drop can result in fluctuations in the power supply, which may affect the performance of connected appliances and equipment.
6. Decreased lifespan of components: Continuous operation under voltage drop conditions can stress system components, potentially reducing their lifespan.

To mitigate voltage drop in solar systems:

1. Minimise wiring length: Keep the distance between solar panels, inverters, and connection points as short as possible.
2. Use larger wire sizes: Thicker wires have lower resistance, reducing voltage drop.
3. Proper inverter placement: To minimise voltage drop effects, position the inverter closer to the lower-voltage end of the circuit.
4. Regular maintenance: Perform routine electrical maintenance to ensure tight connections and components function correctly.
5. Consider voltage drop in system design: Factor in potential voltage drop when designing the solar system, especially for longer cable runs.

Addressing voltage drop issues can maximise the efficiency and performance of your solar power system, ensuring optimal energy production and longevity of the installation. If you have any questions about your solar panel installation, don’t hesitate to contact the friendly staff at Skyline Solar.