What Is Power Factor For Solar?

What is Power Factor?

Power factor is a measure of how efficiently electrical power is being used in an AC circuit. It is defined as the ratio of real power (measured in watts) to apparent power (measured in volt-amperes). Real power performs actual work, while apparent power is the product of voltage and current in the circuit (source).

Power factor depends on the amount of reactive power in the system, which is power stored and released by inductors and capacitors but does no actual work. A low power factor indicates the current and voltage are out of phase, resulting in energy loss. The ideal power factor is 1, when voltage and current are perfectly in phase and all the power is real (source).

Power factor matters because apparent power determines the size of cables, transformers, and other equipment needed to distribute electricity. A lower power factor requires larger infrastructure investments. Utilities often charge fees for low power factor loads to recoup costs.

Power Factor Basics

The power factor of an AC electrical power system ranges from 0 to 1. It is a ratio that compares the real power (kW) supplied to the load to the apparent power (kVA) in the circuit.

A low power factor indicates that there is a large difference between real power and apparent power. This means that more apparent power is required relative to real power in order to do useful work. The closer the power factor is to 1, the more efficiently the electrical power is being used.

The power factor is affected by inductive loads like motors, transformers, fluorescent lighting and welding machines which require magnetizing current and by capacitive loads like capacitor banks or cables. Inductive loads consume reactive power and cause the current to lag the voltage. Capacitive loads produce reactive power and cause the current to lead the voltage. These phase differences between current and voltage affect the power factor.

Why Power Factor Matters

Low power factor strains electricity infrastructure, causes excess heat and power losses, and may result in utilities charging fees. Specifically, a lower power factor means more current is needed to deliver the same amount of power. This leads to overheating, increases line losses and voltage drops, and wastes energy. High reactive power flow also burdens equipment like transformers and generators and requires oversized facilities (Clifford). This can compromise reliability and distribution capacity. Utilities must generate and transmit extra power to compensate for low power factor loads. They often charge higher rates or penalties to commercial and industrial customers with low power factors to recoup these added costs (Sciencedirect). In summary, improving power factor reduces waste, enhances efficiency and capacity, lowers energy usage and costs, and avoids utility penalties.

Improving Power Factor

There are several ways to improve power factor in electrical systems and facilities:

Adding power factor correction capacitors is a common method to improve power factor. Power factor correction capacitors provide reactive power which helps offset inductive loads that create lagging power factor. Properly sized correction capacitors can raise power factor closer to unity. According to Eaton’s guide, “You can improve power factor by adding power factor correction capacitors to your electrical system. Adding capacitors effectively increases the size of the capacitor in the circuit and directly affects the phase angle between voltage and current.” (Source)

Replacing outdated motors and transformers with newer, more efficient models can also help improve power factor. Older styles of motors and transformers tend to have lower power factors. Newer models are designed for improved efficiency and power factor.

Installing newer switching power supplies can also help. Switching power supplies can have near unity power factors compared to older linear power supplies. Upgrading power supplies can bring facilities closer to unity power factor.

Power Factor and Solar

The integration of solar production can impact the overall power factor of an electrical installation and lead to issues with leading power factor (according to https://www.electrical-installation.org/enwiki/Power_factor_-_impact_of_solar_self-consumption). This is because solar inverters often cause capacitive loading on the electrical grid, which results in a leading power factor.

Leading power factor is problematic as it can lead to increased current in the system wires and transformers, resulting in excess heat generation and reduced efficiency. Smart inverters with reactive power control capabilities can help mitigate leading power factor from solar installations by dynamically adjusting their operating mode (according to https://www.smartcommercialsolar.com.au/resources/a-smart-guide-to-power-factor-power-factor-explained).

Power Factor Standards

Utilities often set minimum power factor requirements that customers must meet. These standards help utilities operate their systems more efficiently and avoid issues like voltage drops. According to the Electric Power Research Institute, typical utility power factor requirements range from 0.9 to 0.95^1,2.

If a customer’s power factor drops below the utility’s minimum requirement, the utility may charge penalties or require the customer to install equipment to improve their power factor. Power factor correction involves adding capacitors to cancel out inductive loads that cause poor power factor.

Power Factor Correction

Power factor correction aims to bring the power factor of an AC power system closer to 1 by compensating for reactive power. There are two main methods for correcting power factor:

Capacitors are commonly used for power factor correction. Capacitors supply reactive power to the system, reducing the burden on the utility supply and improving voltage regulation at the load. They are simple, reliable, and economical. However, capacitors can interact with harmonic currents which necessitates careful design considerations. Synchronous condensers are electrically similar to capacitors but are actually rotating electrical machines without any mechanical load. They provide smoother power factor correction compared to capacitors but have higher maintenance requirements (Ware, n.d.).

Power factor correction can be installed at an individual load, at a distribution board supplying multiple loads, or at the utility supply level. Automatic power factor correction systems switch capacitors in and out in response to the reactive power demand to maintain a high power factor under varying load conditions (Electronics Tutorials, n.d.).

Ware, J. (n.d.). Power factor correction (PFC). Retrieved from https://electrical.theiet.org/media/1687/power-factor-correction-pfc.pdf

Electronics Tutorials. (n.d.). Power factor correction (PFC) tutorial. Retrieved from https://www.electronics-tutorials.ws/accircuits/power-factor-correction.html

Power Factor Monitoring

To monitor and measure power factor, there are several options including:

Digital power meters can be installed at the load or service entrance to measure power factor. These provide real-time readings and data logging capabilities to track power factor over time.

Larger electrical equipment like motors and transformers often have built-in power factor monitoring. This allows the equipment’s power factor to be monitored remotely.

Remote monitoring systems can also be implemented to aggregate power factor data across multiple points in a facility or circuit.

Power Factor for Solar Buyers

If you are looking to install solar panels, it’s important to consider power factor requirements set by your utility. Some utilities charge fees or penalties if your solar system operates below a certain power factor threshold. Check with your utility to understand their specific regulations. Power factor can become an issue if your solar inverter operates with a lagging power factor, which is common as inverters convert DC electricity from solar panels into AC electricity for your home’s wiring (Relation Between Solar Power Inverter and Power Factor).

The good news is that many modern inverters, known as smart inverters, have power factor correction capabilities built-in. This allows them to dynamically adjust their operating power factor in response to the grid’s needs. So installing an advanced smart inverter may prevent power factor issues altogether. If your inverter lacks these capabilities, you may need to install separate power factor correction equipment to comply with utility requirements. Overall, it’s wise to consult with solar professionals to ensure your system meets local power factor standards.

Improving Solar Power Factor

There are a few key ways to improve power factor for solar PV systems:

First, it’s important to size inverters optimally for the expected solar array output. Oversized inverters can lead to poor power factor, so make sure the inverter is matched properly to the solar array’s production capacity based on the number of panels and their ratings. Consult inverter sizing guidelines when designing the system.

Second, you can install power factor correction capacitors either at the inverter or on the utility side of the interconnection. Capacitors counteract inductive loads to improve power factor. Work with an experienced solar installer to determine if capacitors are recommended for your specific system and application.

Finally, utilizing smart inverters with reactive power control capabilities allows actively managing power factor across a range of solar output levels. Smart inverters can inject or absorb reactive power from the grid as needed to maintain a target power factor. This provides dynamic power factor correction compared to fixed capacitors.

Paying attention to these key aspects of the solar system design and equipment selection can help ensure optimal power factor and interconnection compliance.