The solar industry's standard way to quote a solar panel array is in DC watts, but there is also an AC rating for your solar electric system, which leaves many customers confused. Don't worry; we're here to help clarify the difference between DC and AC ratings in solar electric systems. Let's get started!
What is DC and AC?
DC stands for Direct Current, while AC stands for Alternating Current. These terms describe the flow of electric current in a system.
Direct Current (DC):
DC is the type of current produced by solar panels. It flows in a constant direction, like a straight line. When sunlight hits the solar panels, it creates DC electricity. However, this type of current cannot power the appliances we use in our homes directly.
Alternating Current (AC):
AC is the type of electricity that powers most of the appliances and devices we use daily. It flows back and forth, changing its direction periodically. AC electricity is what we find in electrical outlets in our homes.
Why is there a difference in ratings?
The difference in ratings between your DC rating and the AC rating of your solar electric system is due to a few factors:
Conversion Efficiency:
The DC electricity generated by solar panels needs to be converted into AC electricity for use in our homes. This conversion process takes place in an inverter, which transforms the DC current into AC current. During this conversion, a small amount of energy is lost, resulting in a lower AC rating.
Electrical Losses:
As electricity travels from the solar panels to the inverter and then to your appliances, there are inherent losses along the way. These losses occur due to resistance in the wires, connections, and other electrical components. These losses further contribute to the reduction in the AC rating compared to the DC rating.
In the solar industry, it is considered best practice to undersize an inverter for a solar electric system. Undersizing refers to selecting an inverter with a lower AC power rating than the total DC power output of the solar panels. Let's delve into the reasons behind this approach.
Improving Inverter Efficiency:
Inverters are electronic devices that convert the DC electricity generated by solar panels into usable AC electricity. They have an efficiency range within which they operate optimally. By choosing an inverter that is slightly smaller than the total DC capacity of the solar panels, it operates closer to its peak efficiency range. Undersizing helps reduce the inverter's operational stress, leading to improved efficiency and potentially lower energy losses during the conversion process.
Maximizing Power Harvesting:
Solar panels rarely operate at their maximum capacity due to various factors such as shading, temperature, and soiling. By undersizing the inverter, it aligns the system's output with the average power production of the solar panels. This ensures that the inverter operates closer to its optimal efficiency even during periods when the solar panels are not generating at their peak. As a result, the system can capture and utilize a larger percentage of the available solar energy, increasing overall kilowatt-hour energy harvest and system performance.
Cost Savings:
Inverters are a significant component of a solar electric system and can be a considerable expense. Undersizing the inverter allows for the use of a smaller, less expensive model compared to an inverter matched exactly to the total DC capacity of the solar panels. This cost reduction can contribute to overall project savings without significantly impacting system performance.
Enhanced Reliability:
Inverters are electronic devices that have a lifespan and may require maintenance or replacement over time. By undersizing the inverter, it operates with reduced stress and potentially experiences less wear and tear. This can contribute to increased reliability and longevity, reducing the risk of inverter failure or the need for premature replacement.
Main Panel Upgrade Avoidence:
In some cases, when the total AC capacity of the solar electric system exceeds the capacity of the main electrical panel, a main panel upgrade may be required to accommodate the additional power. However, by undersizing the inverter, the AC power output matches or falls below the capacity of the main panel, eliminating the need for a costly upgrade. This can be particularly advantageous for homeowners looking to install solar electric systems without making extensive modifications to their electrical infrastructure.
Conclusion:
Undersizing an inverter in the solar industry is a common practice that offers several benefits. It improves inverter efficiency, maximizes power harvesting, provides cost savings, allows for system flexibility and enhances overall reliability. By carefully selecting an inverter that aligns with the average power output of the solar panels, you can optimize the performance and cost-effectiveness of your solar electric system.