Solar Thermal: How it Works, Types And Advantages

The Solar Thermal System represents a sustainable solution for the production of Domestic Hot Water (DHW), suitable in some cases also for domestic heating. It is a technology that allows you to transform solar energy into Thermal Energy, exploiting the solar thermal system to enjoy sustainable comfort and reduce your CO2 footprint.

Today the Cost of a Solar Thermal System is quite competitive, also thanks to the tax breaks that can be used by installing systems with which to benefit from clean energy, as is the case with photovoltaics. In this regard, to get an idea of ​​the average expense to be incurred, it may be useful to compare the costs of photovoltaic and solar thermal systems.

Naturally, to make an informed investment it is equally important to know the different types of Solar Heating Systems, the main components, and what advantages they bring to your home.

Solar Thermal for Heating

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Solar Thermal for Heating

Solar thermal with integration for heating constitutes support for winter air conditioning, covering up to 15-40% of the heating energy needs in very sunny contexts (For Example Southern Italy). However, the water used for winter air conditioning is not the same as that used for sanitary purposes, an aspect that requires the configuration of a combined system, a more expensive system than solar thermal for Domestic Hot Water alone.

The general operation is similar to that of solar thermal for Domestic Hot Water. Solar Energy, In fact, heats a particular heat convector fluid present in the solar panels, which passes inside a heat exchanger and heats the water in the tank. When the fluid releases all its heat to the domestic systems, this is then pumped back into the solar collectors, to repeat the cycle and continue to Heat the water.

In particular, it is a forced circulation system, in which the panels placed on the roof are separated from the tank installed inside the building. In this case, it is necessary to mount two tanks, one for the water of the closed heating circuit and the other for the Domestic Hot Water. 

Alternatively, it is possible to opt for a single tank divided into two smaller ones inside: the one for domestic hot water is placed at the top as it requires water at a higher temperature, while the one for heating is located at the bottom as it works at lower temperatures.

The Solar Thermal System 

The most suitable Solar Thermal Panel for heating is the vacuum or glazed one, while the most efficient air conditioning system to combine with this technology is the underfloor radiant panel system, as it works at lower temperatures similar to those of the solar thermal system (approximately 30-40°C). Very often a main boiler is required, for example, a condensing model or a heat pump to supplement the heat that the solar thermal system alone cannot provide.

Solar Thermal For Hot Water

The main and most used technology is the solar thermal system for the production of domestic hot water. Depending on the geographical area, this system can cover up to 100% of the Domestic Hot Water requirement in certain summer periods. The Solar Thermal Panel for hot water can be a flat or vacuum collector, depending on the climatic conditions of the area and the required thermal performance.

Solar Thermal For Hot Water

The type of system, however, can be a natural or forced circulation system. In the first case, the solar thermal panels are positioned on the roof and connected to a tank located above the collectors, exploiting the properties of water according to which the fluid heated by solar radiation rises upwards so that it enters the tank to give heat to the sanitary water. 

A forced circulation system instead uses a pump to manage the movement of the fluid, as the tank is located inside the building. In this last case, it is a configuration that involves higher costs for the purchase of the system and installation but is necessary in places that are not very sunny during the course of the year.

The Components of Solar Thermal

The components of a Solar Thermal System are different, each of which performs a precise function:

  • Solar collector
  • Storage tank
  • Heat convector fluid
  • Pump for fluid circulation
  • Heat exchanger
  • Control unit

Transform Solar Energy Into Thermal Energy

The solar collector is used to transform solar energy into thermal energy. Flat panels are the cheapest and most widespread, used above all for the production of domestic hot water, they are rather simple to install and do not require particular maintenance interventions. They have a glass top covering, a surrounding structure covered in insulating material, and an internal heat absorber that heats the convector fluid present in the copper tubes. 

Vacuum panels are considered high-efficiency collectors, capable of operating even with very low external temperatures and little solar radiation. They are also more expensive than flat panels and can reach high temperatures close to 100°C. They consist of a series of glass tubes, inside which there is a second glass tube and in the middle an air void which works as insulation and reduces heat loss. This is a reliable technology, also suitable for integration with a radiant panel heating system.

Summer Season and Areas with High Solar Radiation

Alternatively, there are also flat non-glazed panels, with a covering made of plastic material. They are very economical but not very efficient collectors, suitable only for the summer season and areas with high solar radiation. For example, it is used to supply DHW to establishments and campsites or to heat the water of an outdoor swimming pool.  

Another fundamental component of solar thermal is the storage tank, i.e. the container of hot water, heated through the exchange of heat with the heat convector fluid. In natural circulation systems, the storage is positioned on the roof above the panels, while in forced circulation systems it is located inside the building and separated from the collectors. It can have different dimensions based on the capacity required, with an internally stratified structure to increase the performance of the system, or enameled or vitrified. 

An important Component is the Heat Exchanger

The convector fluid, on the other hand, is usually a mixture of water and antifreeze liquid, to prevent it from freezing in the pipes during the winter, while the pipes can be made of stainless steel or copper. An important component is the heat exchanger, which transfers the heat from the convector fluid heated by the panels to the domestic or heating water. 

In forced circulation systems there is also a pump to push the fluid from the collectors to the tank, finally, there is also a control unit with a digital display for managing the system and the other connected systems (heat pump, condensing boiler, valves for integration with the heating).

Solar Thermal: The Advantages

The advantages of solar thermal are numerous

  • Reduction of CO2 emissions
  • Possibility of combined use for DHW and heating
  • Savings on bills
  • Minimal maintenance
  • High duration (on average 20 years)
  • Wide range of configurations.

For the Purchase and Installation of Solar Thermal, it is also possible to take advantage of some discounts and incentives. One solution is the 65% tax deduction provided by the Ecobonus, valid for interventions that increase the energy efficiency of the building. 

Otherwise, it is possible to opt for the Conto Termico 2.0, an incentive managed by the GSE (Energy Services Manager) with which to obtain a reimbursement of 5 thousand euros for the production of thermal energy from renewable sources.