System oversizing: how to exploit the most of energy

The oversizing of the system consists of the possibility to produce more energy from the panels than what the inverter can transform to AC side.

Sometimes it might seem like a wrong choice: why use so much power when I can’t convert it all to the AC side? In reality, this is not the case.

Photovoltaic system production

During the day, the production of a photovoltaic system is not constant. There are time slots that, more than others, allow you to have a greater amount of energy available, with the same climatic conditions.

Generally, at the beginning of the day, the plant’s production is very low compared to the panels’ potential. Production increases gradually throughout the morning, reaching its peak around noon.

During the afternoon this goes down again until the system is switched off in the evening.

Why is it convenient to oversize a system?

The non-constant production of the plant does not depend only on the time slot. Many other factors affect the amount of energy that a certain number of panels can produce in a certain amount of time.

• Climatic conditions: one of the causes that influence the production of a plant is the presence or absence of the sun. In rainy conditions or in general with little irradiation, the overall power drops.
• Temperatures: the maximum power is shown in the technical data sheets of each photovoltaic panel. It is measured under standard test conditions, usually at 25° C. As the cell temperature increases, the module loses a certain amount of energy, which can be calculated from the temperature coefficient of the maximum power.
• Period of the year: during the winter months, production is lower than in the rest of the year

For these factors, it is advisable to size the peak power of the panels not based on the inverter output power, but in higher quantities.

The choice on “how much to oversize” must be made based on the conditions and place of installation, such as SOUTH / EAST / NORTH / WEST orientation, high/low irradiation conditions, etc …

Guidelines for optimizing production

The maximum input voltage and current are indicated in the technical sheet of each inverter. On most occasions, there is also the maximum recommended power, especially useful if there are batteries connected to a hybrid inverter.

When oversizing it must be taken into account that each inverter works in optimal conditions when the voltage from the strings is as close as possible to the nominal voltage of the inverter itself.

Another important aspect to consider is the cut power. By oversizing the peak power of the panels compared to the output on the AC side, it has advantages in the winter months.

At the same time, however, this could lead to cuts in the summer months, where production is on average higher.

One aspect to consider is to make sure that the advantages do not outweigh the disadvantages: specifically, that the cut power is not greater than that gained in the rest of the year.