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Solar Thermal Energy

The solutionfor producinghot water to suit your needs
Iberdrola Solar Thermal Energy for your home

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Offer, Financial aspects ...

Offer: Enjoy domestic hot water and save money with solar thermal energy

Solar thermal energy is clean and inexhaustible and can be used to heat domestic water and swimming pools or for low-temperature heating, among other uses.

With solar thermal energy you can enjoy domestic hot water in your home and save energy and money. In addition, if you sign up for solar thermal energy with Iberdrola we provide advice on the best solution for your home and offer you the all the experience of a leader in renewable energy:

  • Installation by leading companies in the renewable energy sector.

  • Optimisation of the installation's size, avoiding oversizing problems.

Financial aspects: Make the most of solar energy

The benefits of solar energy are based on the use of a clean, inexhaustible and free source of energy for heating, instead of using traditional fuels. This reduces energy costs.

The materials, the design and the installation account for most of the costs involved in solar energy, since the supporting system only operates a few hours a year, unlike conventional heating systems.

With the current prices of traditional fuels, you can pay off a solar installation in just 5 to 10 years (depending on its location and use). However, the fact that the initial outlay required for installing solar thermal systems is relatively high is a barrier to their large-scale expansion in existing homes, and obviously a psychological and financial obstacle. To overcome that barrier, some regional and local governments offer financial incentives for installing solar thermal systems.


Technical Aspects: Find out more about solar thermal energy

Domestic hot water production is undoubtedly the most widespread application of solar energy today.

The systems are designed to meet 100% of users’ hot water needs in summer and between 50% and 80% throughout the year. Forced circulation systems or thermosyphons are used for this application. They usually have an auxiliary conventional water heater to meet the user's needs when the solar system is unable to do so.

The thermosyphons used for domestic hot water in a standard single-family home have a 2-5 m2 panel and a 100-300 litre deposit, while forced circulation systems usually have a total panel surface area of between 2 and 6 m2 and a 150-500 litre storage heater.

But there are also large installations that serve multi-family buildings, apartment blocks, hotels or office buildings. In these systems the panel surface area can vary from 10 to hundreds of m2.

The installation consists of a number of solar thermal panels that use solar energy to heat a fluid (usually water) that runs inside the panels. Once heated, the fluid is used to meet the home's needs (hot water, heating…), thus reducing the use of traditional fuels.

The basic operating principle common to all solar thermal systems is simple: solar radiation is captured and the heat is transferred to a heat-carrying medium, usually a fluid, water or air. The heated medium can be used directly, for instance, in the case of swimming pools. It can also be used indirectly through a heat exchanger that transfers the heat to its final destination, for example, for heating a room.


The most common system for making use of solar energy is the solar collector, which absorbs the sun's radiation and transmits the absorbed energy to a carrying fluid (mainly water, although air or a mixture of water and other fluids can also be used). In addition to absorbing solar radiation, the collector emits thermal radiation and loses energy by conduction and convention. The solar collectors sold today have a high degree of absorption (minimising reflection and transmission) and a low level of heat losses. If the collector is connected to a storage deposit, the fluid carries the heat to the deposit, where the fluid's temperature increases.

A number of advanced solar thermal collectors have been designed in order to increase the amount of energy absorbed and reduce losses. The most common ones are flat collectors, which use water and have a glass cover. Evacuated tubular solar collectors are also used today, which enable higher temperatures to be achieved. Other types of collectors use air as a fluid.

The operating principle of the solar collector is based on the heat trap that a glazed surface produces (known as greenhouse effect). The sun's short-wave incident radiation goes through the glass and is absorbed by a surface that heats up. This surface, in turn, emits long-wave thermal radiation that is trapped by the glass, which prevents it from going through.

A distinction can be made between two main groups of systems for harnessing solar energy, depending on whether or not they require an additional contribution of energy for enabling the solar energy captured to be used as thermal energy where needed:

  • SOLAR SYSTEMS WITH ADDITIONAL CONTRIBUTION OF ELECTRIC POWER FOR AUXILIARY COMPONENTS: The systems used for harnessing solar energy often need some type of additional source of energy for operating the fluid circulation elements. This is the case with domestic hot water and/or heating installations, whether they use flat or evacuated tubular collectors. This is known as forced circulation. Using a circulation pump, the solar accumulator can be located inside a building, enabling better system integration. These are more flexible, but also more complex, since they require a pump and a controller.

  • SOLAR SYSTEMS WITHOUT ADDITIONAL CONTRIBUTION OF ELECTRIC POWER FOR AUXILIARY COMPONENTS: One of the most elementary examples of these systems is a room with a glazed opening facing south. The solar radiation enters the room through the glazing, heating the air and the walls, and only a small fraction of the incident radiation reaching the glazed surface is sent outside.

These systems also include the thick wall of a building facing the sun during the day. The wall absorbs the radiation, acting as an accumulator. At night it releases the accumulated energy. More sophisticated versions of absorbent walls have been designed, adding glazing outside and making the air circulate between the glass and the wall.


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