Solar Thermal: How It Works and How to Integrate It with a Thermal Battery to Maximize Efficiency

Solar thermal is a mature, sustainable, and versatile technology, suitable for various applications: production of domestic hot water (e.g. for showers), support for space heating, and pool heating. However, to make the most of the solar energy captured by the panels, it is essential to adopt an efficient thermal storage strategy.

In certain contexts, a PCM thermal battery like the one developed by I-TES can replace traditional buffers, improve energy efficiency, and address hygiene-related issues such as the proliferation of Legionella by eliminating stagnant water.

How a Solar Thermal System Works

The solar thermal circuit consists of several key components:

Solar thermal panel (collector)
Absorbs solar energy and converts it into heat, transferring it to a heat transfer fluid. There are flat plate and vacuum tube collectors, depending on the required efficiency level.
Circulation pump
Circulates the heated fluid from the collector to the heat exchanger and/or storage.
Monitoring and control unit
Regulates system operation: it activates the circulation pump and controls the opening and closing of any valves in the solar circuit.
Heat exchanger (in closed-loop systems)
Transfers heat from the solar circuit fluid to domestic water or to technical water for the space heating system.
Thermal storage system
Stores heat by accumulating water. This water remains stagnant and is maintained at temperatures that can reach 70°C until needed.
Optional backup boiler or heat pump
Complements heat production during periods of low solar irradiation, ensuring continuous service delivery.

Systems can be:

In combination with heating systems (e.g. heat pumps)
Or used exclusively for domestic hot water production

To further explore the comparison between buffer tanks/flywheels and thermal batteries, read our dedicated article: Flywheel Storage: How It Works and Why Thermal Batteries Are More Efficient

Open or closed: which system to choose?

There are two main types of solar thermal systems:

Open systems
The fluid circulating in the collector is the same water that, once heated, goes directly to the end user.
The main advantage is system simplicity and the absence of thermal losses due to transferring heat between fluids.
However, they have two significant limitations:
- The risk of freezing water in the collectors in low temperatures
- The formation of limescale, which can damage the system
Closed systems
In these systems, the circuit of the fluid that passes through the solar collector and the water going to the user (hot domestic water or water for the heating system) are two separate circuits. Heat is transferred via a heat exchanger.
These are safer, more reliable, and suitable for cold climates or professional installations.

Small or large: the exchanger also changes

In smaller systems (e.g. family homes), heat exchangers like immersion coils or tube bundles are used.
In larger systems, plate heat exchangers are used instead – more efficient, modular, and suitable for high flow rates.

Integration of the I-TES Thermal Battery: When It’s the Right Choice

The I-TES thermal battery can replace traditional water-based storage systems, offering:

Instant domestic hot water production, without stagnant technical water. The battery delivers thermal energy instantly, reducing stored water volume and hygienic risks.
Elimination of Legionella risk
There is no stagnant water in tanks, thus preventing the proliferation of harmful bacteria such as Legionella, often found in traditional water-based storage (like buffers or boilers).
No thermal stratification
Energy is delivered uniformly, with no need for complex systems to keep cold water at the bottom of the tank separate from hot water at the top.
Less maintenance and greater safety
In the right configuration, there are fewer components to manage, resulting in lower risk of malfunction and reduced maintenance needs.
Flexible and scalable installation
I-TES batteries are modular: they adapt to different spaces and demands, and can be easily added or removed as needed.

Integration is ideal for:

Hospitality structures (hotels, campsites)
They cover peak thermal demands at specific times (e.g. morning and evening), improving guest comfort.
Apartment buildings
They allow centralized and stable management of heating and domestic hot water, with lower costs for residents.
Public buildings
They optimize the use of renewable energy in schools, hospitals, offices—where demand varies and efficient management is needed.
Sanitary services in industrial facilities
They cover peaks in domestic hot water demand during worker shift changes.

As you’ve seen, solar thermal is an effective and well-tested technology, but in certain configurations, its smart integration with innovative storage systems can make a big difference. Our thermal battery, thanks to PCM technology, allows you to:

Avoid heat waste → solar surplus is not lost but stored intelligently
Improve system efficiency → fewer auxiliary activations and optimized cycles
Eliminate Legionella risk → hygiene ensured without additional treatments
Simplify daily system management → fewer checks, lower costs, greater reliability