Steve Donovan, Head of Technical (UK & Ireland), and Giulio Stangarone MIET, Technical Engineer, at Segen Ltd, explain why a larger solar array can often deliver better performance, improved economics and a more consistent generation profile.
When designing an effective solar photovoltaic (PV) system, it is worth considering oversizing the array. This approach allows the system to generate power more consistently throughout the day and maintain better performance during the winter months. The result is higher overall energy output and, in many cases, better project economics.
Inverters are rated by their AC output, which you’ll find on the data plate. For example, a 3.6 kW inverter can deliver a maximum of 3.6 kW of AC power to the load and to the grid. However, most inverters will accept a higher DC input from the solar array than the AC rating of the unit. This means you can connect more solar panels to the same inverter – a strategy known as oversizing.
When designing a PV system, always consult the inverter datasheet. There you will find the recommended maximum DC input relative to the rated AC output, which can be as high as 150% or even 200%. This headroom exists for a reason. Panels rarely operate at nameplate output. Temperature losses, seasonal irradiance, orientation and shading all eat into real-world performance. Designing at a 1:1 ratio assumes conditions that almost never occur. However, any oversizing must comply with the limits set out by the manufacturer of your chosen product. It is also essential to review designs with a suitably qualified technical specialist before installation.
Design considerations: hybrid inverters and east-west arrays
Oversizing is particularly beneficial when using a hybrid inverter with battery storage. As a rule of thumb, the default operating mode of many hybrid inverters is to charge the battery first and then export any excess energy. Once the battery is full, generation will drop to the maximum limit that can be exported on the AC side.
It’s worth noting that you won’t get the full benefit of oversizing by pairing a PV inverter with an AC-coupled battery inverter. In this setup, the bottleneck will be the rating of the PV inverter. While the AC-coupled battery inverter can draw excess power from the PV inverter’s AC output, a system with separate AC-coupled inverters will not deliver the same DC oversizing advantages as a hybrid inverter.
Oversizing is also particularly beneficial for east-west configurations. Typical solar systems are angled south to maximise irradiance at midday, but an east-west setup has some panels facing east and others facing west. The east-facing panels produce more energy in the morning, while the west-facing panels produce more in the afternoon, meaning the system is less likely to reach the inverter’s theoretical maximum DC rating at one sharp midday peak.
East-west configurations are growing in popularity because they provide more energy outside peak hours, which can increase export value and boost self-consumption. When designing such a system, remember to observe the inverter’s minimum and maximum voltage limits, and keep the east and west arrays on separate MPPTs (maximum power point trackers) to ensure correct system performance.
Grid benefits: smoother energy supply
By undersizing the inverter, it is also possible to help reduce grid congestion. The wider, flatter generation curve from the solar system can result in more consistent energy being supplied to the grid and fewer sharp peaks in power. At scale, this can help grid operators by reducing the duck curve effect.
The duck curve describes the shape of daily electricity demand excluding solar generation, specifically the swing between high and low demand. In the morning, when there is little solar, demand is relatively stable. Then, at midday, when solar generation is high, demand drops, only to rise again to the daily peak in the late afternoon. These daily differences make energy trading complex and expensive, as operators may need to bring peaking power plants online to cover the demand peak.
By oversizing solar arrays, system designers can contribute, albeit modestly, to a smoother and more consistent power supply in the afternoon, helping to delay the use of peaking plants. This effect becomes even more significant when paired with battery storage systems that can shift energy over time.
Managing excess energy: clipping
As mentioned previously, solar panels rarely operate at their nameplate output. However, in an oversized array there are times – typically on very sunny days – when the panels can produce more DC power than the inverter can handle. The excess energy is managed through a process called clipping.
During clipping, the inverter adjusts the maximum power point along the I-V curve, with the MPPT deliberately operating at a slightly suboptimal voltage. This reduces the power drawn from the array, keeping the inverter within its AC rating. Any energy above this threshold is clipped and cannot be converted, although in systems with a hybrid inverter, the surplus can instead be directed to charge the battery.
Despite these brief losses, oversizing can still increase total daily energy production and extend the periods during which the inverter operates at its maximum capacity.
The bottom line: better utilisation, but only within the limits
To conclude, oversizing a PV array can improve utilisation of the inverter’s AC-rated output, increase annual energy yield and deliver a more consistent output profile throughout the day and across the year. In the right design, it can also reduce the levelised cost of electricity produced, while hybrid inverters and battery storage can further improve self-consumption.
But the gains are not automatic. Oversizing works best where the additional DC capacity improves usable output without creating excessive clipping. If the array is pushed too far, or beyond the manufacturer’s stated limits, the design can introduce avoidable losses as well as technical and compliance risk.
As always, ensure the design stays within the limits of the equipment. If there is any uncertainty, refer to the manufacturer’s specifications and design tools, and seek appropriate technical advice where needed.
