Even if you are remotely familiar with solar PV and electricity, you must have heard the terms three-phase power and single-phase power. However, for those with little to no technical background, understanding the differences can feel quite complicated.
AC power is mostly used for electricity supply to commercial buildings and houses. Unlike DC, AC involves a change in the current direction periodically.
Before we get into it, it is essential to understand what a “phase” is in electricity. Simply put, phase refers to a variation, a cycle, or a state change. Theoretically, one could say that the change in any state with respect to time would be a phase.
However, in electricity, phase refers to a sinusoidal pattern in which the voltage shifts between the negative and positive maximum (amplitude).
In even simpler terms, the voltage between the neutral cable and the current cable would always be in phase. So, any system with a single phase in an office, shop, or home will have two wires. On the other hand, up to 4 (and usually 3) wires will be used in a three-phase AC power system.
What is single phase power?
Single-phase power refers to the distribution of AC current through a system that involves voltages in unison. In a typical AC power system, you would find two wires, i.e., the live wire and the neutral wire. The voltage between these wires is always in phase and is typically 240V with a 50 Hz frequency. Though, this can vary based on where you live.
This is the most used power for household applications. For instance, it can be used to power the television, lights, and other devices such as heaters, small ACs, coolers, and a lot more.
Some facts about single-phase power?
· In single-phase power supplies, a single conductor is used.
· It employs only a single-phase configuration.
· One distinct wave cycle.
· The voltage difference is typically 240V.
· Only one live wire is present in single-phase systems. So, in the case of a fault, the entire power supply will fail.
· Commonly used to supply power to houses and offices to run small appliances.
· Single-phase power supplies feature two wires, i.e., one phase wire and one neutral wire.
· Single-phase power supply has less efficiency in comparison with three-phase supplies for an equivalent circuit.
· These systems are prone to failure.
Advantages of single-phase power
1. Well suited for use in residential and domestic settings to supply power to small appliances such as televisions, lights, refrigerators, fans, and heaters.
2. The operation and design of a single-phase circuit are ordinary.
3. Best suited for low horsepower units.
Disadvantages of single-phase power
1. Additional circuitry is required for smaller single-phase motors, such as motor starters. These are similar to starter capacitors found in pumps and fans. That is because the supply is usually not sufficient for a start-up.
2. Cannot be used to power up industrial motors that require higher loads.
What is three-phase power?
In comparison, three phases power three alternate currents with separate electric services. In total, a three-phase power supply would use four wires, out of which 3 are conducting wires and the fourth one is neutral.
The current in the three conductor wires is slightly out of phase, with a phase angle of 120 degrees. Furthermore, the three-phase power supply is more commonly employed in industrial and commercial facilities.
Some facts about three-phase power
· The three-phase power supply offers higher conductor efficiency.
· Less amount of copper is required.
· Minimal risks for employees working in a facility.
· Can operate over a wider range of power loads.
Advantages of three-phase power
· The ability to run larger roads. Hence, most suited for industrial and commercial applications where higher electric loads are required.
· No need for additional starters due to sufficient phase difference, which provides the initial torque needed for industrial motors to work.
· Lesser conducting material is needed to transmit electricity. So, in the long run, they are more economical.
· The DC voltage becomes smoother with an increase in the number of phases.
Disadvantages of three-phase power
· Due to a high system voltage, the motors and power supplies require more insulation, resulting in higher maintenance costs.
· These power units are unable to handle the overload. So, the repair costs are significantly higher because replacing the individual components would be expensive.
A comparison between single-phase and three-phase power supplies
| Features | Single-Phase | Three-Phase |
| Circuit Connection | Requires a single wire for connection | Requires three wires for a connection |
| No. of Conductors | Requires single conductor | Three conductors are required |
| Output Voltage | Usually delivers 240V | Delivers 415V |
| Type of Phase | Split phase | No specific name |
| Power Transmission | Minimum capacity | Maximum capacity |
| Complexity of circuit | Easy to generate | Construction is comparatively complex |
| Power failure | Frequent | Less frequent |
| Loss | Maximum loss | Minimum loss |
| Efficiency | Minimal | Maximum |
| Cost | Less expensive | More expensive |
| Application | Typically used in residential settings | Utilized in commercial and industrial settings |
The number of phases and solar PV inverters
Solar inverters are critical components of any PV system. This helps convert DC electricity into AC electricity, which can be exported to the grid or used to power up the devices in your home. Furthermore, inverters also help control the system voltage so that maximum available power can be extracted. Furthermore, through a screen, modern solar inverters also provide in-depth reports on the performance of the solar energy system.
Single-phase power
If single-phase power is present, the inverter must also be single-phase. If you live in Australia, you can install inverters of up to 5 kW on properties that have single-phase power.
If you use a single-phase unit, then the electricity from the solar PV system will go through a single conducting wire. Hence, voltage rise could be a risk, but that can sometimes be addressed by increasing the size of a live wire.
Three-phase power
Three-phase power gives a lot more freedom. If you own a property with three-phase power, you can technically install both three-phase and single-phase inverters. However, an imbalance throughout the phases is usually not preferable. This means that you can either install a single-phase inverter on any phase or a single three-phase inverter.
For those who choose to install a single-phase inverter on any particular phase, the one with the heaviest load is preferred. However, there are some downsides to this approach. These are:
· The inverter can trip out if the phase voltage becomes too high (typically happens when the solar PV system is too large).
· An imbalance in the flow of energy between the phases.
A good workaround would be to let professional solar installers figure out which phase is the most viable. Otherwise, installation on any wrong phase could result in the solar energy getting wasted.
An alternative option is the installation of three single-phase inverters on each of the individual phases. However, this option is significantly more expensive.
Nevertheless, some property owners prefer 3-phase inverters over single-phase inverters because they reduce the risks associated with voltage surges. That is because the unit will send the energy back to the grid through three conducting wires and not just one. On the other hand, you can also solve the problem of voltage rise in a single-phase unit by increasing the size of the cable to reduce the resistance.
Checking whether you have three-phase power supply
The simplest way to check whether you have single-phase, or three-phase power is to check the meter box. If your house receives single-phase power, then the meter box would contain only a single fuse cartridge.
On the other hand, if you receive three-phase power, the meter box will feature three cartridges.
Alternatively, you can also check the switchboard. If the main switch is only a single pole wide, then your property is receiving single-phase power. On the other hand, if the main switch is three poles wide, your property is receiving three-phase power.
If this is something that sounds too complex, worry not, because a single call to your electricity provider can uncover the mystery.
Conclusion
Both single-phase and three-phase power have their advantages and disadvantages. However, property owners are typically limited by choice. Converting a property from single-phase to three-phase is often expensive, with several limitations from the service providers.
However, if you have the choice, then choosing between the two is usually a question of necessity, practicality, and economy. So, considering the practical needs is extremely important. This is where professional solar PV installers and circuit specialists can guide you.
Next Steps…
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