Does the efficiency of solar panels offer an attractive proposal?

How to optimise solar panel output

A solar panel's output depends on several factors, such as the materials chosen, the amount of sunshine and the angle of installation, just to give a few examples.

Solar panels are made from silicon. This semiconductor material captures sunlight and converts it into photovoltaic energy. As this process creates a direct current, an inverter is used to convert it to an alternating current. This then powers the various electrical appliances in the building and is also used for hot water and heating. For a profitable, long-lasting installation, using professionals who work with high-quality products that meet the needs of users is strongly recommended. 

To ensure that each photovoltaic cell offers a high level of efficiency, a south-facing orientation and an angle of 30° should be chosen. This is the ideal configuration for optimal solar panel performance. 

Solar panels work using daylight. To maximise their output, they should never be in the shade and should be kept clean. Maintenance of the various elements should also be considered when using photovoltaic panels, in order to capture the maximum amount of sunlight for optimum performance.

How efficient is a photovoltaic panel?

The efficiency of solar panels depends on the various criteria detailed above, but also on how the panels themselves are manufactured. With this in mind, a monocrystalline photovoltaic panel provides an efficiency of between 16% and 24%, while a polycrystalline photovoltaic panel offers an efficiency between 14% and 20%. The efficiency of solar panels is always expressed as a percentage. This percentage represents the amount of light energy converted into alternating current compared to the amount of light captured by each photovoltaic cell in the solar panel. 

The efficiency of a photovoltaic panel is therefore equivalent to the electrical power produced (expressed in Watt peak [Wp]) divided by the solar power. To calculate its solar power, the panel's surface area (in m2) is multiplied by 1000.

For example, for a solar panel with a photovoltaic power of 300 Wp and a surface area measuring 1.5 m2: 300/1500 = 0.20 or 20%. This photovoltaic panel will therefore be 20% efficient under optimal conditions.

How profitable are solar panels?

The profitability of solar panels varies depending on the overall installation and maintenance costs, as well as on the amount of photovoltaic power installed and its efficiency. However, it also depends on the price per kWh for any power sold back to the grid, whether any financial assistance was granted for installation and also on the warranty.

On an existing building, solar panels will be fitted on top of the current roof, whereas they will be integrated into the structure for a partial roof replacement or new construction. Integration into the building is a little more expensive but the price of the solar panels remains the same. 

In order to estimate electricity requirements as accurately as possible and benefit from maximum solar panel efficiency, normal consumption should be used as a starting point before defining the number of solar panels and the amount of photovoltaic power necessary for self-consumption, with or without selling surplus energy to an electricity supplier.

There are two possible options: 

• Total self-consumption with energy stored in batteries so the building can still be powered even when it is dark or light levels are too low.
• Total or partial self-consumption under the same conditions but with more energy being produced than consumed, with a view to sell it back to the grid. 

For the first option, the profitability of the solar panels is guaranteed as soon as the amount of energy not taken from the power grid equals the overall cost of the photovoltaic installation. 

In the second, the installation generates a passive income. The profitability of the solar panels is then also linked to the price per kWh when energy is sold back to the grid.