What is AC Solar?
DC Solar Systems
Conventional Direct Current (DC) solar systems consist of a number of solar modules wired together in series configuration to create ‘strings’ of modules, with a combined output voltage typically between 200 and 1,000 volts DC. This voltage is then fed into a centralised large inverter, which converts the power to 240 volts AC for connection to the utility electricity system. In the past, all solar power systems were configured as DC systems and even now, DC systems are often the cheapest and most common option. However there are several inherent problems with DC solar systems and these include; risks associated with high voltage DC circuits, sub-optimal performance in shaded locations and as systems age, lack of visibility over system performance, and the loss of the entire system output if a fault occurs anywhere within the series connection of the solar modules. In recent years, some centralised DC inverter manufacturers have implemented power optimiser technology at the solar modules to enable maximum power point tracking of each module. While this achieves some of the benefits of AC Solar systems, these are still high voltage DC systems and suffer from all the disadvantaged of this technology such as the need to install failure-prone DC Isolators, enclose all DC cables in heavy duty conduit and maintain minimum string sizes. They also have multiple single points of failure, each of which can cause a total system shutdown in the event of a problem.
Conventional Direct Current (DC) solar systems consist of a number of solar modules wired together in series configuration to create ‘strings’ of modules, with a combined output voltage typically between 200 and 1,000 volts DC. This voltage is then fed into a centralised large inverter, which converts the power to 240 volts AC for connection to the utility electricity system. In the past, all solar power systems were configured as DC systems and even now, DC systems are often the cheapest and most common option. However there are several inherent problems with DC solar systems and these include; risks associated with high voltage DC circuits, sub-optimal performance in shaded locations and as systems age, lack of visibility over system performance, and the loss of the entire system output if a fault occurs anywhere within the series connection of the solar modules. In recent years, some centralised DC inverter manufacturers have implemented power optimiser technology at the solar modules to enable maximum power point tracking of each module. While this achieves some of the benefits of AC Solar systems, these are still high voltage DC systems and suffer from all the disadvantaged of this technology such as the need to install failure-prone DC Isolators, enclose all DC cables in heavy duty conduit and maintain minimum string sizes. They also have multiple single points of failure, each of which can cause a total system shutdown in the event of a problem.
AC Solar Systems
Alternating current (AC) solar systems use microinverters (typically one microinverter per one or two solar panels) to convert the output of each solar panel directly to 240 volts AC. This eliminates the need to install DC cabling between modules or to install a large centralised inverter, and greatly simplifies the installation, monitoring and maintenance of the system. Microinverters provide all of the functionality of conventional string inverters – such as automatic disconnect and reconnect when the grid fails – and are required to conform to the same standards (including AS4777). The use of microinverters eliminates the safety risks associated with high voltage DC circuits, improves overall system performance under real life operating conditions, and significantly reduces the impact of a component failure on the operation and output of the system.
Alternating current (AC) solar systems use microinverters (typically one microinverter per one or two solar panels) to convert the output of each solar panel directly to 240 volts AC. This eliminates the need to install DC cabling between modules or to install a large centralised inverter, and greatly simplifies the installation, monitoring and maintenance of the system. Microinverters provide all of the functionality of conventional string inverters – such as automatic disconnect and reconnect when the grid fails – and are required to conform to the same standards (including AS4777). The use of microinverters eliminates the safety risks associated with high voltage DC circuits, improves overall system performance under real life operating conditions, and significantly reduces the impact of a component failure on the operation and output of the system.
Key advantages of AC Solar systems over DC systems
AC Solar systems have four key advantages over DC systems
Safety
Flexibility
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Performance
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Reliability
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DC Solar System wiring faults
These images show the result of electrical faults within DC solar systems. These faults usually occur due to water ingress, manufacturing defects in the equipment used, incorrect component selection, poor workmanship, or mechanical damage to the cabling after it is installed (e.g. rodents, birds, insects, people walking on cables) or simply as the DC solar systems ages (cable insulation degradation or corrosion of DC connections). As the DC solar system ages the risk of fire increases.
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What's the difference between AC and DC electricity?
Electricity is generated and distributed in two common forms - Alternating Current (AC)
and Direct Current (DC).
and Direct Current (DC).
Alternating Current
Alternating Current is the system used to generate and distribute electricity around our cities, homes and businesses.
This system is used almost exclusively by utilities worldwide to deliver electricity to their customers as it is inherently safer and easier to manage.
All of the modern electrical appliances found around our homes and businesses are designed to be powered by AC electricity. In Australia, New Zealand and much of Asia, the electricity supply is 230 volts AC. Because the flow of electric current alternates between positive and negative values fifty times each second, appropriately designed switches and circuit breakers can interrupt the flow of AC electricity relatively easily without significant arcing or burning. If a fault occurs in an AC circuit, a circuit breaker or safety switch will typically operate to isolate the supply and prevent the risk of further arcing or electrocution. This informative video demonstrates in very practical terms the different impacts of AC and DC arcs.
Alternating Current is the system used to generate and distribute electricity around our cities, homes and businesses.
This system is used almost exclusively by utilities worldwide to deliver electricity to their customers as it is inherently safer and easier to manage.
All of the modern electrical appliances found around our homes and businesses are designed to be powered by AC electricity. In Australia, New Zealand and much of Asia, the electricity supply is 230 volts AC. Because the flow of electric current alternates between positive and negative values fifty times each second, appropriately designed switches and circuit breakers can interrupt the flow of AC electricity relatively easily without significant arcing or burning. If a fault occurs in an AC circuit, a circuit breaker or safety switch will typically operate to isolate the supply and prevent the risk of further arcing or electrocution. This informative video demonstrates in very practical terms the different impacts of AC and DC arcs.
Direct Current
In Direct Current systems, the flow of electricity is in one direction only. Batteries are the most common source of DC electricity, which is typically used to power small lights and appliances which don't require a lot of energy. Solar modules generate DC electricity when exposed to the light.
At low voltages DC electricity is relatively harmless, however at higher voltages there is a significant risk of arcing. This is why DC is used for arc welders.
We've all seen the arc that is generated if a car battery is shorted out or the heat that arc welders generate when melting and joining metal. Because the electric current flows only in one direction without crossing the zero point at any time, DC arcs are much more difficult to extinguish. DC circuit breakers and switches are especially designed to quench the arc generated when a DC circuit is interrupted. Good quality DC circuit breakers are more complicated and cost more than AC circuit breakers. Even when good quality equipment is installed there are, unfortunately, numerous examples of situations where faults on DC circuits due to water ingress or other causes have resulted in continuous arcs that have caused significant damage and started fires that have destroyed solar systems and the buildings they are installed on.
In Direct Current systems, the flow of electricity is in one direction only. Batteries are the most common source of DC electricity, which is typically used to power small lights and appliances which don't require a lot of energy. Solar modules generate DC electricity when exposed to the light.
At low voltages DC electricity is relatively harmless, however at higher voltages there is a significant risk of arcing. This is why DC is used for arc welders.
We've all seen the arc that is generated if a car battery is shorted out or the heat that arc welders generate when melting and joining metal. Because the electric current flows only in one direction without crossing the zero point at any time, DC arcs are much more difficult to extinguish. DC circuit breakers and switches are especially designed to quench the arc generated when a DC circuit is interrupted. Good quality DC circuit breakers are more complicated and cost more than AC circuit breakers. Even when good quality equipment is installed there are, unfortunately, numerous examples of situations where faults on DC circuits due to water ingress or other causes have resulted in continuous arcs that have caused significant damage and started fires that have destroyed solar systems and the buildings they are installed on.
Microinverters
The world's largest manufacturer of microinverters is Enphase Energy. The next largest manufacturer is AP Systems.
AP Systems YC500 Microinverter
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Enphase Energy M250 Microinverter
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Enphase Energy S270 Microinverter
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