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More collectors = more free energy

With a higher number of solar collectors, the system is able to cover a greater part of the energy need for heating (solar fraction).

The graph below shows the percentage of needed energy that can be covered by different solar thermal systems.

The grey area represents the energy need for heat production. It slightly differs during the year, dipending on consumption and other parameters such as the cold water temperature. The colored curves represent the percentage of the energy need that can be fulfilled  by solar thermal surfaces.

Without a solar collector, the energy need would therefore be covered in full by traditional means (gas, heating oil, electricity,...).



A traditional/pressurized system is normally sized to supply 85% of the theoretical need calculated at the best time of the year (yellow line).
A pressurized installation, designed to achieve 100% of the theoretical need at the best time of the year (red line) could suffer severe degradation.


As this phenomenon does not affect drainback systems (blue lines), such systems can be sized larger in order to achieve a much greater solar fraction and as a consequence, achieve greater overall savings.



The calculation of the Optimum Sizing draws on this basic principle

The combination of a technology that avoids overheating problems with an optimised collector area provides you with maximum solar energy throughout the year.

On the basis of our calculation tools, Sunoptimo recommends the ideal number of solar thermal collectors that need to be installed to achieve an economic optimum. The calculation is based on hot water consumption, the area on the roof available and what is specifically sought in a solar thermal system (energy independence, maximizing the financial return on the investment, a fast return on the investment, ... ).

Thanks to drainback, the installation can exceed the traditional limit of 40-45% of the annual solar fraction recommended by most prescribers to avoid overheating of pressurised installations in summer. The more collectors you install, the more the solar system is able to cover a significant portion of your hot water energy needs (solar fraction).

The advantages of Optimum™ Sizing are therefore numerous:


  • Lower installation price for a solar thermal system
  • Cheaper price per kWh hour
  • Significant savings for water heating
  • Independence from increases in the price of oil, gas and electricity
  • Security thanks to drainback
  • Quickest return on investment

Got a solar thermal project in mind?