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The Expert replies

What are solar thermal panels?

There is a difference between solar thermal panels and solar photovoltaic panels. Solar thermal panels heat domestic water for everyday use without using gas or electricity. They are based on a very simple principle: they use heat produced by the sun for heating a space or for producing hot water that can reach temperatures up to 70° in the summer, far more than the 40°-45° needed to take a shower.

How does a solar thermal panel work?

A solar panel (or solar collector) consists of a radiator which is capable of absorbing heat from the sun’s rays and transferring it to the water tank. The movement of water from the tank to the domestic water tap is achieved by natural or forced circulation. In the latter case the solar panel uses an electric hydraulic pump.

In Italy we are lucky to have an average insulation of 1500 kWh/m2 every year. An average solar panel efficiency of 160,000 sq m of panels installed in any Italian Region would help save 8 million cubic meters of natural gas used for gas boilers or roughly 80 Gwh of electric energy needed for electric water heaters.

How long does it take to heat the water?

A solar panel takes roughly 10 hours to heat the tank water. The time required varies considerably depending on sun exposure, season, weather conditions and latitude. When the sky is covered in winter the solar panel performance drops from 80 ° to 40 °. At night you can only use water heated earlier in the day. Once all the water is used you must wait for a new day and the relevant number of hours needed to heat the water again. For these reasons combining solar panels and gas boilers is recommended.

How many solar panels are needed to heat the water?

The number of solar panels is determined by the domestic needs and the local climate. One square meter solar panel can produce an average of 80-130 liters of hot water per day at an average temperature of 40 °. The average consumption of hot water per person is roughly 30-50 liters per day, so one square meter solar panel should be able to meet the hot water needs of 1-2 people.

Do panels work at night and during bad weather?

Technology has overcome these obstacles for some time now. The heated water is kept in insulated tanks to ensure autonomy for may hours. This explains why many European countries with considerably lower levels of solar irradiation than Italy have already invested in solar panels much more than our sunny country! Solar panels, or thermal collectors, have become an everyday reality in Germany and Austria where the amount of space taken up by the solar panels is far greater than that currently used in Italy. Another country leading in this field is Greece.

Are solar panels a substitute for the boilers?

Solar panels are not a substitute for the boiler but a complementary system in order to reduce gas consumption required for heating water. It is therefore recommended to have a gas furnace or an electric water heater installed along side solar panels. In many cases it is possible to connect the solar panel and the boiler in order to make the boiler work less and as a result save on gas consumption. This combination provides constant hot water and is ideal for any emergency situation.

How much do panels cost?

Growth in the European market for solar products is contributing to a rapid reduction of the purchase price of the panels. This is also due to fierce competition between producers and installers. The price can vary considerably depending on the panel’s technology.

Types of models on the market

The main models of solar thermal panels (or solar collectors) are divided into three types:

  • glass solar panels
  • vacuum solar panels
  • open solar panels

Regional contributions

Installing solar panels is a private choice which benefits society as a whole. Every property owner evaluates the installation of solar collectors on the basis of future economic benefits. A private choice that reduces the State’s energy dependency and limits the importance of oil or gas. The use of the panels will also reduce public health costs or environmental costs needed to confront damages caused by pollution. The State encourages the purchase of solar panels by providing supportive contributions and tax relief on private expenditure. Occasionally Regions grant contributions towards installing thermal collectors. We suggest you check your Region’s web site. In numerous cases however the contributions expired many years ago.

Fortunately, the purchase price of a solar thermal panel is not too high. Even without the Region’s contributions installing a solar thermal system can be worthwhile.