When designing a solar PV system, one key decision is sizing the inverter—the device that converts the direct current (DC) power generated by solar panels into usable alternating current (AC) power for your home or business. A common practice is to slightly “oversize” the solar array compared to the inverter, meaning the panel capacity (measured in kilowatts, or kW) exceeds the inverter’s capacity.
At first glance, this might seem counterintuitive—why would you pair a smaller inverter with a larger solar array? The answer lies in how solar PV systems generate electricity. Solar panels rarely produce their maximum rated power due to factors like weather, shading, and time of day. Oversizing allows the inverter to operate more efficiently by optimising energy production during these less-than-perfect conditions.
This article explores how an oversized array improves efficiency during non-peak hours, enhancing your system’s overall performance and maximising your return on investment.
1. Capturing Low Irradiance Levels More Effectively
Solar panels generate electricity by converting sunlight into energy, but they don’t produce the same amount of power throughout the day. During non-peak hours—such as early morning, late afternoon, or cloudy days—there is less sunlight available for the panels to convert into electricity. This reduced sunlight is called low irradiance.
In a typical solar system, the inverter is designed to convert the electricity from the panels into usable power for your home. However, inverters work most efficiently when they are operating near their maximum capacity. When the array is undersized—meaning the solar panels don’t produce enough power—the inverter may not be able to operate at its peak efficiency. This can cause the inverter to waste energy or work inefficiently.
On the other hand, with an oversized array (where the number of solar panels exceeds the inverter’s capacity), there is more solar power available even during low irradiance conditions. The extra capacity from the additional panels means that the inverter can receive more power to convert into usable energy, even when sunlight is weaker. This helps the inverter run more smoothly and closer to its optimal performance range, improving overall efficiency and ensuring that more energy is produced.
In simple terms, oversizing the solar array allows the system to work better during the times when sunlight is less intense, ensuring that the inverter remains active and efficient for longer periods, rather than being underpowered.
2. Extending Productive Hours
Oversizing enables the solar array to “wake up” the inverter earlier in the morning and keep it active later into the evening. With more panels feeding the system, the array can generate enough voltage and current to meet the inverter’s minimum operating thresholds sooner and sustain them longer. This extends the system’s daily energy production window.
For example, an array matched to the inverter’s size might only start producing usable power at 9:00 am and stop by 4:00 pm. An oversized array could extend these times to 7:30 am and 5:30 pm, increasing total energy generation.
3. Compensating for Seasonal and Weather Variations
In regions with variable weather or seasonal changes, sunlight intensity fluctuates significantly. An oversized array ensures that even during these suboptimal conditions, the inverter can still operate efficiently. For instance, on cloudy days, the extra panel capacity compensates for reduced sunlight, allowing the inverter to produce usable energy rather than idle or operate inefficiently.
4. Boosting Midday Efficiency on Overcast Days
On cloudy days, light intensity never reaches peak levels, meaning a right-sized array might struggle to deliver adequate energy to keep the inverter in its most efficient operating range. An oversized array ensures that even under diffused light, enough power is generated to maximise inverter performance.
5. Addressing Panel Degradation Over Time
Solar panels naturally degrade, losing a small percentage of efficiency each year (typically 0.5–1%). An oversized array compensates for this gradual loss, ensuring the inverter continues to receive sufficient energy to operate efficiently over the system’s lifespan.
6. Improving Energy Yield During Partial Shading
Partial shading—caused by trees, buildings, or clouds—can reduce the output of some panels in the array. An oversized array minimises the impact of shading because the additional panels ensure the inverter receives enough power from the unshaded portion of the system.
7. Reducing Idle Time
Inverters have a minimum operating threshold. If the array’s output drops below this threshold during non-peak hours, the inverter shuts off temporarily, resulting in zero energy production. An oversized array is less likely to fall below this threshold, keeping the inverter active for longer and reducing idle time.
Conclusion
Oversizing inverters is a strategic choice that leverages the extra capacity of solar panels to enhance the performance of the entire solar power system. During non-peak hours, when sunlight is less intense—such as early mornings, late afternoons, or on cloudy days—the energy produced by the solar panels can be less than the system’s maximum potential. However, by installing a larger solar array than the inverter’s rated capacity, the system ensures that even during these low-light or variable conditions, the inverter receives enough power to operate efficiently.
This approach helps keep the inverter functioning closer to its optimal performance range, even when sunlight isn’t at its peak. As a result, the system doesn’t lose power when conditions aren’t perfect. Instead, it continues to convert more energy into usable electricity, maximising daily production and extending the hours of effective energy generation.
Additionally, oversizing allows for greater flexibility in the system’s energy production. When the panels generate more power than the inverter can handle during peak sunlight hours, the inverter may “clip” the output, meaning some energy is wasted. However, oversizing reduces the chances of this happening during non-peak times, as the inverter can more effectively manage fluctuations in power generation.
Overall, oversizing the inverter ensures a higher level of consistency in energy production, optimises system efficiency, and improves the long-term performance of the solar PV system. For those looking to maximise their return on investment and ensure their solar system works efficiently all day long, this is a smart design choice that can provide greater value over time.
