Vacuum collectors have one advantage and disadvantages. Their advantage is primarily linked to their performance at high temperatures. Their disadvantages are

    • Reduced performance at nominal yield and therefore for the lower temperature deltas.
    • More fragile
    • Loss of performance over time due to the fact that the vacuum disappears.
    • For a given area, available on the roof, vacuum collectors do not provide the same optical surface (usable surface) as flat collectors.
    • Vacuum collectors are in general more expensive than flat collectors.
    • Vacuum collectors generally do not permit the use of Drainback technology, only flat collectors allow it. As a consequence, correct sizing of the installation is not possible, at the risk of generating severe problems with overheating.

    The more collectors that are installed, the greater will be the savings, but the greater the initial outlay for the solar thermal system. It is by calculating the total cost of water heating accurately over a given period of analysis, taking into account both the cost of the solar installation as well as the cost of the residual supplementary energy required (the cost of which will change over time) that the ideal area you need to install can be determined with accuracy. Sunoptimo has developed very advanced calculation tools that can be used to determine the "Optimum™ Sizing" accurately. Don't hesitate to ask us to carry out a preliminary study of your project by completing the form.

    Both technologies are complementary. When financial resources and space on the roof allow it, both technologies have their place.

    Photovoltaic performance is between 12% and 18% depending on the modules chosen. This performance decreases once the modules heat up. The nominal yield for solar thermal is 80%.

    This performance will decrease when the temperature difference between the inside and outside of the collectors increases to reach 60% for example, when the temperature difference between the outside and inside is 50°C (if it is 20°C outside, this means that the temperature of the water in the hot water cylinder circulating through the collectors is 70°C). In other words, if the sun provides 1000 kWh on 1 m², this photovoltaic area will theoretically supply in the region of 120 to 180 kWh, while this same thermal area will theoretically supply from 600 to 800 kWh.

    By contrast, since solar thermal is not able to supply its energy to the "grid" and being standalone, at different times of the year there will be a "loss" of performance related to the fact that solar energy can no longer be used to heat the water, the hot water cylinder having reached its maximum. As a general rule, this area in terms of m² of thermal solar collectors will supply in the region of from 400 kWh to 500 kWh due to this loss of performance linked to their non-use; however, this is still 4 to 5 times more energy than photovoltaic.

    Without a public grant, it is therefore much more cost-effective to install solar thermal for water heating. However, financial incentives and local legislation sometimes distort this reasoning. From a purely financial point of view, there is a need to analyze the different laws in force to determine the most cost-effective solution. From an energy and ecological perspective, it is solar thermal that is the most cost-effective.

    • A more cost-effective system because you can size the installation more efficiently (no overheating problems).
    • More reliable in the long-term.
    • Requires less maintenance.
    • Permits sizing of the installation to obtain an economic optimum.
    • Safe when stopped, no risk during a power cut, etc.
    • Less heat transfer fluid required.
    • Should work be required on the collectors, system empties when stopped.