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Solar Thermal Panels

Solar thermal technology

Solar thermal technology is very simple: the solar thermal collectors take advantage of the sun’s energy by transforming it into usable heat for heating domestic water or to supplement heating. Solar energy is harnessed for everyday use. Gas and electricity are used only for brief periods and as aids in case of long periods without sunlight. You can make a solar panel system in two different ways:

  • the first is by connecting the solar thermal system to a gas boiler, thereby combining the two systems. In doing so you get considerable energy and economic savings.
  • the second, should it be impossible to use the existing boiler, is to insert an electric resistance, of at least 1kW with a thermostat calibrated at 40°C, into the water tank.

A solar thermal system can easily replace a gas or electric heater and will produce hot water in abundance at a temperature of roughly 70°C (the temperature needed for taking a shower is roughly between 40-45°C). In summer you can heat an entire swimming pool and there is of course a considerable saving in the electricity bill.

There are three different types of technology that exploit the sun’s rays in order to produce heat: at low, medium and high temperatures. They differ from each other based on performance and the material with which they’re built. The most common solar thermal collectors are:

  • Open plastic collectors: this type of collector is used in seasonal systems (to heat swimming pools, for showering and beach resorts etc.)
  • Glazed glass flat plate collector: a high performance collector.
  • Evacuated tube collector: this type of collector works extremely well, even in the colder regions of northern Italy.
  • Glazed glass flat plate vacuum collector: it is the highest performing collector in its category, and it is superior by 10% if filled with Krypton gas.

Solar thermal panels can substantially be divided into two categories:

  • by natural circulation  
  • by forced circulation
Natural circulation system
In a natural circulation solar heating system the antifreeze liquid, which comes from the solar collector, circulates naturally inside a heat exchanger that is installed in the boiler. Once the heat is released the liquid returns to the panel to be reheated. The heat exchanger transfers the antifreeze liquid’s heat to the hot water found inside the boiler. Once the water is hot it is sent to the consumer through the pressurized piping system. A special valve prevents the liquid from reversing its flow during the night.
Forced circulation system
In a forced circulation system the antifreeze liquid circulates by means of an electric pump rather than naturally. The electric pump is run by a control unit and it stops the circulation when the temperature from the panels is colder than the temperature in the water tank. This takes place at night for example. The forced circulation can be used not only for heating water but (where possible) it can also be used to supplement the heating system.

In order to establish what kind of system is best suited for a home you need to know how many people live in the home and not its size. It is estimated that every person uses between 30 and 70 liters of water daily.

A solar thermal system can be installed in a home in various ways. Choosing a system also depends on the geographic location of the house and where the panels are positioned (on the roof, on the facade, facing south, southeast etc.).

Solar panels should always be oriented as much as possible perpendicular to the sun’s rays. If you do decide to install the collectors on the rooftop you need to verify that: there is enough space on the roof for installing the panels, there is no overshadowing by trees, buildings etc., the roof is in good condition, the roof is ideally oriented and that special permission is not needed to install the panels.

During the winter, on days when the sun is fully shining, one square meter solar panel installed can heat roughly 80-130 liters of water at a temperature of 40°C. In the summer it can reach 60-80°C. Even without sunlight the solar panels continue to produce thermal energy. As a matter of fact it’s not just sun rays that have an impact on the panel’s radiation, it is also the radiations produced by day light. Needless to say however, panels have a higher performance in the presence of sunlight.

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