Patent Description:
More precisely, the present invention concerns a compact solar system comprising a hydraulic circuit adapted to activate or deactivate an area of thermal energy storage.

In the state of the art, solar systems for the production of domestic hot water (DHW) are known, which are divided into two macro-families: forced circulation systems and natural circulation systems. The former provide solar collectors (hereinafter also called just collectors) connected, via a hydraulic circuit with circulator, to an insulated energy storage located in a technical room. In the latter, the energy storage element is generally placed near the collector and the energy collected by the collector is transferred on site to the storage, by natural circulation.

The latter systems are in turn divided into systems with the storage separated from the collector and systems with an integrated storage (called in English Integrated Collector Storage or more briefly ICS or compact solar systems), used to reduce the architectural impact, in order to try to limit the size of the solar system as much as possible.

In these systems, solar energy is collected by collecting surfaces (S), covered by highly selective material which transmit part of this energy to an energy storage volume (V) containing a primary heat transfer fluid, for example technical water, or directly a secondary fluid, such as domestic hot water (DHW). De facto, the system receives solar energy in the form of light (electromagnetic) energy and stores part of this energy in the form of thermal energy, increasing the temperature of the fluid stored in the storage tank; generally the outer surface of the storage itself actively participates in the solar energy absorption stage, or in any case the collector and the storage are integrated and are not clearly distinguishable from the outside, all forming a compact system.

The state of the art of ICS systems provides for the division into two families of systems based on the method of control of heat dispersions towards the environment: in the former, heat dispersions are reduced by using a glass cover (for example in patent documents <CIT>, <CIT>), in the latter by using vacuum gaps in order to cancel convective motions. In this latter type of known ICS systems, glass pipes having vacuum gaps are used both as elements collecting solar energy and as elements containing the storage of hot water. In fact, inside them there is the storage or hydraulic tank where the energy absorbed by the selective collecting surface and stored in the glass pipes is transferred. This technique of control of thermal dispersions allows for a high efficiency in the solar energy storage process, since the amount of dissipation towards the environment is reduced to a minimum; in fact, the vacuum gap reduces convective heat exchanges and only involves dissipation by irradiation. Examples of this type of ICS systems are well known in the state of the art, for example in patent documents <CIT> and <CIT>.

In most of the state-of-the-art ICS compact systems, for safety reasons of the components (such as circulators, gaskets, etc.), and given the technical operating limits of the mixing valve of the downstream sanitary system and for avoiding excessive pressures or generation of steam by lamination at ambient pressure, the upper limit of the temperature of the storage fluid is fixed at approximately <NUM>° - <NUM>. Beyond this limit it is necessary to adopt a protection system. Commonly, this protection system consists of dissipating the thermal energy generated, originating from the collection of solar radiations, when the storage temperature reaches its limit values.

Some examples of ICS systems with this safety system, adapted to dissipate the energy stored when the temperature reaches its limit values, are described in the following patent documents:.

Generally, in known solar systems, the collection of solar energy takes place in the form of light (electromagnetic) energy converted into thermal energy, increasing the temperature of the fluid stored in the storage and of the system components. In periods of more favourable weather conditions, it is possible that the system reaches overheating conditions due to excessive stored thermal energy, which leads to a possible malfunction of the solar system components and therefore of the system itself. State-of-the-art safety systems are adapted to prevent the reaching of operating extreme temperatures. They have the objective of dissipating the excess energy if a DHW withdrawal is not made on the user side (in fact, during the withdrawal, water at the grid temperature, for example at <NUM>-<NUM>, is introduced into the system, cooling it accordingly), thus preserving the integrity of the system.

Although these safety systems prevent the system from reaching critical temperature values, they do not allow the excess solar energy incident on the system to be used, as this is dispersed and released into the surrounding environment.

The process of heating a fluid using compact solar systems also depends on the nature and volume of the fluid stored in the system. In particular, for most cases where the working fluid is water, the ratio between the volume of the stored fluid (V) and the collecting surface (S), here indicated as V/S, represents a critical factor for the efficiency of such systems.

In fact, the value of the ratio between storage volume and collection surface, referred to as V/S, must fall within an optimal range, which however can vary based on the conditions of use and weather conditions. In particular, if the V/S value is too high, the solar energy may not be sufficient to heat the system and therefore to guarantee the withdrawal of DHW at the minimum design temperature (typically the system must deliver hot water at a temperature not lower than <NUM> - <NUM>). On the contrary, if the V/S value is too low, the heating process leads to frequent overtemperature conditions; this is because the collected solar energy corresponds to a low storage volume, therefore, there is a greater risk of increasing the fluid temperature to unacceptable values. Furthermore, due to the extreme variability and unpredictability of solar energy, it is not possible a priori (during the design stage) to choose a V/S fixed value that avoids such critical conditions, especially because an ideal system must have a V/S value that allows the availability of domestic hot water even with limited irradiation windows or in conditions of poor irradiation.

The aim of the present invention is to maximise all the solar energy incident on the system, by reducing the dissipation of the incident energy to a minimum, without compromising the performance of the system throughout the year, under both more unfavourable weather conditions and favourable weather conditions.

Furthermore, an aim of the present invention is to allow the compact solar system to store excess energy, without reaching the maximum operating temperature values.

Another aim of the present invention is to allow a rapid heating of the compact solar system under any condition of irradiation and user profile.

Again, an aim of the present invention is to operate the system, as far as possible, at an average temperature of the stored fluid lower than <NUM>, which allows the efficiency of the system itself to be increased (less dispersions towards the environment), to limit the thermal stress of the system components and reduce the limescale formation processes.

An object of the present invention is a compact solar system for heating a first heat transfer fluid; said solar system includes an external frame, inside which the following elements are contained: a main tank for containing a heat transfer fluid; collecting means for collecting the incident solar radiation, which, being in heat exchange with said main tank, make it possible to transfer the collected thermal energy to the heat transfer fluid stored in the main tank; and a first hydraulic circuit for the circulation of the first heat transfer fluid, which includes an inlet portion for the inlet of the first heat transfer fluid and an outlet portion for the outlet of the first heat transfer fluid.

Furthermore, the solar system includes an additional tank inside the frame to contain a heat transfer fluid, thermally isolated from the collecting means, and in that the volumetric ratio between the volume of the additional tank and the volume of the main tank is defined by the following relationship: <MAT> where V<NUM> is the volume of the main tank and V<NUM> is the volume of the additional tank.

Furthermore, the first hydraulic circuit provides a first heat exchange portion, in heat exchange with the heat transfer fluid contained in the additional tank, and a second heat exchange portion in heat exchange with the heat transfer fluid contained in the main tank.

The first and second heat exchange portions are in fluid connection with each other via a connecting conduit and a first return conduit.

Furthermore, the compact solar system is characterised in that it provides flow adjusting means, arranged in the first hydraulic circuit, to allow the circulation of the first heat transfer fluid from the second heat exchange portion to the first heat exchange portion through the first return conduit, when a threshold temperature of a heat transfer fluid contained in the main tank is reached.

Possibly according to the invention, the first heat exchange portion of the first hydraulic circuit can be the additional tank. The additional tank can therefore be adapted to contain the first heat transfer fluid, and be in fluid connection with the connecting conduit and with the first return conduit of the first hydraulic circuit and with the inlet portion.

Possibly according to the invention, the second heat exchange portion of the first hydraulic circuit can be the main tank, which can be adapted to contain the first heat transfer fluid and be in fluid connection with the connecting conduit and the first return conduit of the first hydraulic circuit and with the outlet portion.

In particular, according to the invention, the main tank can contain a second heat transfer fluid, not in fluid connection with the first heat transfer fluid.

Alternatively, according to the invention, the solar system can include a second hydraulic circuit for the circulation of the second heat transfer fluid. The second hydraulic circuit can be a closed circuit composed of the main tank and a recirculation conduit. Furthermore, the solar system can include a heat exchanger, wherein the recirculation conduit of the second hydraulic circuit and the second heat exchange portion of the first hydraulic circuit can be arranged, in heat exchange with each other.

Again, according to the invention, the solar system can include a second circulation pump arranged in the second hydraulic circuit, to be able to activate the circulation of said second heat transfer fluid in said second hydraulic circuit. Furthermore, it can include means for detecting the circulation of the first heat transfer fluid, in particular a flow switch, in the first hydraulic circuit. Said detecting means can be in connection with the second circulation pump and the solar system can furthermore be configured to activate/deactivate said second circulation pump on the basis of the values detected by the detecting means.

Preferably according to the invention, the second heat exchange portion of the first hydraulic circuit can be arranged inside the main tank.

In particular, according to the invention, the additional tank can contain a second heat transfer fluid, not in fluid connection with the first heat transfer fluid, wherein the first heat exchange portion of the first hydraulic circuit can be arranged inside the additional tank itself.

Still according to the invention, the flow adjusting means, arranged in the first hydraulic circuit, can be a first circulation pump and a non-return valve, wherein said non-return valve can be arranged on the first return conduit between the two heat exchange portions.

Again, according to the invention, the first circulation pump can be arranged on one of the connecting or return conduits, between said two (first and second) heat exchange portions.

Alternatively, according to the invention, the flow adjusting means can be arranged in the first hydraulic circuit and can be a thermostatic valve or an electrovalve, arranged in the first return conduit, between said two heat exchange portions.

Furthermore, according to the invention, the main tank can include a plurality of main storage ducts in fluid connection with each other.

More particularly according to the invention, the second heat exchange portion can include a plurality of heat exchange conduits, in fluid connection with each other; each of which can be inserted into a respective main storage duct of the main tank.

Furthermore, according to the invention, the collecting means of the solar system can be a plurality of pipes having an outer vacuum gap.

In particular, according to the invention, each main storage duct of the main tank can be inserted into a respective pipe having an outer vacuum gap.

Preferably according to the invention, the additional tank can include at least two additional storage ducts in fluid connection with each other.

In particular, according to the invention, the ratio between the sum of the volumes of the main and additional tanks and the surface of the collecting means is defined by the following relationship: <MAT> where V<NUM>+V<NUM> represents the sum of the volumes of the main and additional tanks while S represents the surface of the collecting means.

Further according to the invention, the solar system can include a control unit connected to the flow adjusting means arranged in the first hydraulic circuit. The control unit can be configured to act on the flow adjusting means on the basis of the temperature of the heat transfer fluid contained in the main tank, when said threshold temperature is reached.

In particular, the threshold temperature can be defined by the following formula: <MAT>.

Preferably according to the invention, the solar system can include temperature detecting means, arranged in said main tank, for detecting the temperature of the heat transfer fluid contained therein.

Furthermore, according to the invention, the flow adjusting means can include a thermal switch, for detecting the temperature of the heat transfer fluid contained in the main tank, and a first circulation pump electrically connected to said thermal switch. Furthermore, said first circulation pump can be arranged in the first hydraulic circuit and the thermal switch can be arranged in the main tank, in direct or indirect contact with the heat transfer fluid contained therein.

More specifically, according to the invention, the temperature detecting means or the thermal switch can be inserted into a possible thermowell.

Finally, according to the invention, the solar system can be adapted to assume a first use configuration, wherein the first heat transfer fluid can be adapted to flow into said first hydraulic circuit from the inlet portion to the outlet portion, passing through the first and the second heat exchange portion passing only through the connecting conduit. Furthermore, the solar system can assume a second use configuration, wherein the first heat transfer fluid can circulate in the first hydraulic circuit between the first and second heat exchange areas, passing through both the connecting conduit and the first return conduit. Furthermore, during use, the solar system can assume said second use configuration when the temperature of the heat transfer fluid contained in the main tank exceeds said threshold temperature.

The invention will now be described for illustrative but non-limiting purposes, with particular reference to the drawings of the attached figures, wherein:.

As previously mentioned, the process of heating a fluid by compact solar systems depends on the ratio between the volume of the stored fluid (V) and the collecting surface (S).

The importance of the V/S ratio can be better understood with a numerical example, wherein the energy transferred to the volume of stored fluid can be expressed in the form: <MAT>.

After a simple mathematical step, it can be noted that, by increasing the solar energy G, with the same V/S ratio, the value of ΔT and therefore the temperature difference of the stored fluid will increase.

If, however, an increase in G also corresponds to an increase in V/S, it can be seen from the equation that the ΔT value will increase less than in the previous case.

Below are some numerical examples having the aim of calculating the actual ΔT values, using specific fixed G, V/S, η values of a solar system adapted to simulate true environmental and use conditions (grid temperature <NUM> and minimum final DHW outlet temperature in the range <NUM> - <NUM>).

"Blue sky" winter day (in Italian "cielo blu", name for a day of favourable solar irradiation): <MAT> <MAT> <MAT> <MAT>.

"Blue sky" summer day: <MAT> <MAT> <MAT> <MAT>.

Therefore, in summer the system in a single day of solar energy storage can be in overtemperature conditions.

If, however, in summer a solar system having a higher V/S value equal to, for example, <NUM>/m<NUM> is taken into consideration,.

In this case, reaching overtemperature conditions is avoided and at the same time all the daily solar energy is stored.

Imagining adopting only the same solar system of V/S value = <NUM>/m<NUM>, we are considering a day with little irradiance, technically known as "grey sky day" (in Italian "giornata di cielo grigio"). The solar energy values can also be halved, so the calculation becomes:
"Grey sky" winter day: <MAT> <MAT> <MAT> <MAT>.

That is, the design DHW temperature conditions are not reached.

Instead, if a solar system with a V/S value = <NUM>/m<NUM> is adopted again, we obtain:
Grey sky winter day <MAT> <MAT> <MAT> <MAT>.

Therefore, in this case a temperature is reached that falls within the design range of <NUM> - <NUM>°.

Moreover, if a secondary circuit for heating a secondary fluid by heat exchange with a primary fluid (for example by a heat exchanger) is used, it is important that the solar system has a more conservative V/S value, because it is necessary to bring the primary storage to high temperature to allow an optimal primary/secondary exchange. In other words, having a primary fluid at <NUM> - <NUM> is not sufficient to guarantee a heat exchange with the secondary circuit such as to bring it to design DHW conditions of <NUM> - <NUM>, unless using a heat exchanger having a high exchange surface, which would make the objective of creating a compact system difficult and would also be anti-economic.

In the context of systems wherein there is a constant transfer of energy from the collection area to the storage area, the solar system according to the present invention provides the possibility of having a dynamic V/S ratio value over time, therefore variable depending on weather conditions.

In <FIG> and <FIG>, <FIG> and <FIG> a solar system according to the invention is shown, in a first embodiment, indicated with the numerical reference <NUM>.

The solar system <NUM> according to the invention is of the compact type, as previously described, and is adapted to heat a first heat transfer fluid, in particular a secondary fluid, for example domestic hot water (DHW). The solar system <NUM> includes an external frame <NUM>, inside which the following elements are contained, described herein below.

A main tank <NUM> necessary to contain a heat transfer fluid, collecting means <NUM> for collecting the solar radiation incident on them, a first hydraulic circuit <NUM> for the circulation of the first heat transfer fluid, and an additional tank <NUM> for containing a heat transfer fluid.

In the present embodiment, the main tank <NUM> and the additional tank <NUM> are adapted to contain the same heat transfer fluid, in particular said first heat transfer fluid. In other embodiments, as will be seen below, a second heat transfer fluid can be provided, possibly contained in one of the two tanks.

The collecting means <NUM> are in heat exchange with the main tank <NUM> in order to transfer the collected thermal energy to the heat transfer fluid contained in the main tank <NUM>. The first hydraulic circuit <NUM> in turn includes an inlet portion <NUM> for the inlet of the first incoming heat transfer fluid and an outlet portion <NUM> for the outlet of the first outgoing heat transfer fluid on the user side.

Furthermore, the additional tank <NUM> is thermally insulated from the collecting means <NUM>. The main tank <NUM> and the additional tank <NUM> are such that the volumetric ratio between their respective volumes V<NUM> and V<NUM> is defined by the following relationship: <MAT>.

Moreover, the first hydraulic circuit <NUM> provides a first heat exchange portion <NUM>, which is in heat exchange with the heat transfer fluid contained in said additional tank <NUM>, and a second heat exchange portion <NUM>, which instead is in heat exchange with the heat transfer fluid contained in the main tank <NUM>. Said first <NUM>, <NUM>' and second <NUM>, <NUM> heat exchange portions are in fluid connection with each other via a connecting conduit <NUM> and a first return conduit <NUM>. In the specific embodiment, the two heat exchange portions coincide respectively with the additional tank <NUM> and the main tank <NUM>, as both are adapted to contain the same first heat transfer fluid which, by circulating and mixing between the two tanks at different temperatures, act as heat exchange areas.

The compact solar system <NUM> according to the invention also provides flow adjusting means <NUM>, <NUM> arranged in the first hydraulic circuit <NUM>, used in order to allow the circulation of the first heat transfer fluid from the second heat exchange portion <NUM> to the first heat exchange portion <NUM> through said first return conduit <NUM>, when a threshold temperature Ts of a heat transfer fluid contained in said main tank <NUM> is reached.

Preferably, said solar system <NUM> can be adapted to assume a first use configuration wherein the first heat transfer fluid is adapted to flow into said first hydraulic circuit <NUM> from said inlet portion <NUM> to said outlet portion <NUM> through said first <NUM> and second <NUM> heat exchange portions passing only through said connecting conduit <NUM>, and a second use configuration wherein the first heat transfer fluid circulates into said first hydraulic circuit <NUM> between said first <NUM> and second <NUM> heat exchange areas passing through both said connecting conduit <NUM> and first return conduit <NUM>. Again, during use, said solar system <NUM> assumes said second use configuration when the temperature T<NUM> of the heat transfer fluid contained in the main tank <NUM> exceeds said threshold temperature Ts.

In the embodiments described herein the collecting means are a plurality of vacuum collecting pipes <NUM> having an outer gap. In other embodiments, the collecting means can be of a different type, for example the main tank <NUM> can be directly painted with a highly selective material and protected by a non-vacuum glass cover, or the collecting means can be absorbers consisting of a sheet of metallic material coated by a highly selective material, which is placed in heat exchange with the main tank <NUM>.

Furthermore, in the present embodiment the main tank <NUM> includes a plurality of main storage ducts <NUM>, in fluid connection with each other, for the storage of the secondary fluid to be heated.

Again, in the present embodiment, a corresponding main storage duct <NUM> is preferably arranged inside each collecting vacuum pipe <NUM> with an outer gap. Said plurality of main storage ducts <NUM> are in fluid connection with each other, via a plurality of further connecting conduits <NUM>, to form the main tank <NUM>.

Furthermore, in the present embodiment the additional tank <NUM>, which is in fluid connection with said main tank <NUM>, is arranged adjacent thereto, preferably in the lower portion of the solar system <NUM>.

Said additional tank <NUM> can include one or more additional storage ducts in fluid connection with each other or a single duct, as shown for the first embodiment. Said additional tank <NUM> is shielded from solar radiation by a suitable opaque surface (which can also be the frame <NUM> of the system <NUM> itself) and is suitably insulated to reduce heat dissipation towards the environment external to the tank <NUM> itself. Said additional tank <NUM> is separated from the main tank <NUM> and the separation space is suitably insulated.

The additional tank <NUM> can be arranged in the upper part of the solar system <NUM>, in the lower part of the solar system <NUM> or in any central area of the solar system <NUM>, both in a horizontal position and in a vertical position if it is elongated in shape.

Furthermore, the additional tank <NUM> can have a cylindrical shape but also any shape that ensures a structural resistance to the hydraulic pressure of the contained fluid.

Furthermore, the material of the additional tank <NUM> can be stainless steel but also any material that is compatible with the temperatures and intended use of the contained fluid.

In the present embodiment, the first hydraulic circuit <NUM> includes said additional tank <NUM>, said plurality of main storage ducts <NUM> and said plurality of further connecting conduits <NUM>. Furthermore, said first hydraulic circuit <NUM> provides a connecting conduit <NUM> for the fluid connection of the additional tank <NUM>, in correspondence with an additional outlet portion <NUM> of said additional tank <NUM>, with said main tank <NUM>, in particular with at least one duct of said plurality of main storage ducts <NUM>, in correspondence with a main inlet portion <NUM> of said main tank <NUM>, in particular of a duct of said plurality of main storage ducts <NUM>.

Furthermore, said first hydraulic circuit <NUM> includes a first return conduit <NUM> for the fluid connection of the main tank <NUM>, in correspondence with its main outlet portion <NUM>, with the additional inlet portion <NUM> of said additional tank <NUM>. Preferably, in the described embodiment, in correspondence with said first return conduit <NUM> there is arranged a first circulation pump <NUM> adapted to move the first heat transfer fluid from said main tank <NUM> to said additional tank <NUM>. Said first circulation pump <NUM> can be connected to a control unit (as shown for the first control system in <FIG>). Alternatively, a different control system can be provided wherein the first circulation pump <NUM> is connected to a thermal switch which activates it depending on the temperature value detected by the switch itself (as shown in <FIG>).

Furthermore, said first return conduit <NUM> in turn comprises a non-return valve <NUM>, arranged between said two heat exchange portions <NUM> and <NUM>, in particular it is arranged between said main outlet portion <NUM> of the main tank <NUM> and said additional inlet portion <NUM> of the additional tank <NUM>.

During use, when the first heat transfer fluid is withdrawn from the outlet portion <NUM>, the first heat transfer fluid is simultaneously introduced through the inlet portion <NUM> at the same flow rate.

According to the invention in a first use configuration (shown in <FIG>), as long as it is not necessary to transfer the stored solar energy from the main tank <NUM> to the additional tank <NUM>, the latter will not participate in the process of storing the incident solar energy. In other words, the first heat transfer fluid flows into the first hydraulic circuit <NUM> from the inlet portion <NUM> to the outlet portion <NUM> without passing through the first return conduit <NUM> between the main storage <NUM> and the additional one <NUM> (which in <FIG> has not been shown as it is not operational, like the first circulation pump <NUM>), therefore the energy present in the main tank <NUM> is transferred only to the user downstream of the outlet portion <NUM>. In this condition, the solar energy, transferred to the heated fluid, is stored only in the main tank <NUM> exposed to solar radiation. In this condition, the additional tank <NUM> acts solely as an inlet passage conduit for the first heat transfer fluid coming from the hydraulic grid.

Again, according to the invention, the solar system <NUM> is able to assume a second use configuration (shown in <FIG>), if temperature conditions are reached such that said solar system <NUM> risks overheating. Thanks to the additional tank <NUM> and said first dedicated hydraulic circuit <NUM>, in particular thanks to the first return conduit <NUM>, it is possible to also make the additional tank <NUM> participate in the storage of solar energy and therefore to increase or decrease the value of the V/S ratio of the solar system <NUM> according to the invention on the basis of the weather conditions, since the collected solar energy can be redistributed not only in the volume V<NUM> of the main tank <NUM>, but also in the volume V<NUM> of the additional tank <NUM>.

When the extreme conditions of use are reached, i.e. when a threshold temperature Ts of the fluid placed inside the main tank <NUM> is reached, the fluid connection between the main tank <NUM> and the additional tank <NUM> is activated also via the first return conduit <NUM> of said first hydraulic circuit <NUM>, (as shown in <FIG>) by activation of flow management means <NUM>, for example said first circulation pump <NUM>, which were deactivated in said first use configuration. By activating the first circulation pump <NUM>, the first heat transfer fluid flows between said additional inlet portion <NUM> of said additional tank <NUM> and said main outlet portion <NUM> of said main tank <NUM>, passing through said first return conduit <NUM>. This therefore allows the energy transfer between the volumes V<NUM> and V<NUM> of said tanks <NUM> and <NUM>. In other words, the first hydraulic circuit <NUM> becomes a closed circuit wherein the first heat transfer fluid by passing through the first return conduit <NUM>, which acts as a recirculation conduit, allows the circulation of the first heat transfer fluid between the two tanks <NUM> and <NUM>, thus also heating the first heat transfer fluid contained in the additional tank <NUM>.

This transfer can take place via passive control, for example by opening and closing of electromechanical elements, or active control, for example via electronics and control logic.

It may also happen that, during the energy transfer, the user needs DHW, therefore grid water is introduced through the inlet portion <NUM> and hot water is delivered through the outlet portion <NUM>. This can also occur in conjunction with the activation of the first circulation pump <NUM> and therefore in conjunction with the energy transfer, without compromising the transfer itself or the quality of the DHW delivered on the user side.

<FIG> and <FIG> show three variants of the embodiment of <FIG> associated with alternative control systems for describing some principles of activation of the circulation conduits in the recirculation branches, in particular in the first return conduit <NUM>, arranged for transferring energy between the main tank <NUM> and the additional tank <NUM>.

In particular, <FIG> shows a schematic showing a first control system for controlling the first circulation pump <NUM> via a control unit or control panel <NUM>. The control unit <NUM> has means for detecting the temperature <NUM>, in particular a temperature sensor <NUM>, which detect the value of the temperature T<NUM> of the fluid contained in the main tank <NUM>, in particular in one of the ducts of said plurality of main storage ducts <NUM>, which is compared with the value of the threshold temperature Ts. The comparison can be made via threshold/hysteresis logic or via more complex logics, such as PID, PD, PI. The temperature sensor <NUM> can be either in direct or indirect contact with the fluid contained in the main tank <NUM> or more simply in indirect contact with this fluid, for example by placing it in a thermowell <NUM> (as shown in <FIG>) or in contact with the material of which the ducts of said plurality of main storage ducts <NUM> are made. Therefore, the control unit <NUM> decides whether to activate the second use configuration, by electrically powering the first circulation pump <NUM> or not. The first circulation pump <NUM> therefore guarantees the hydraulic head useful for circulating the fluid (by putting the fluid under pressure) through the non-return valve <NUM> and overcoming pressure losses throughout the recirculation circuit.

In <FIG>, alternatively to the control unit of <FIG>, there is a second control system comprising a thermal switch <NUM> which detects the temperature T<NUM> of the fluid contained in the main tank <NUM> or more simply in indirect contact with this fluid, for example by placing it in a thermowell <NUM>, in particular in the plurality of main storage ducts <NUM>, and on the basis of this value the thermal switch <NUM> closes or not the electrical power circuit of the first circulation pump <NUM>. The thermal switch <NUM> is preferably arranged in indirect contact with the fluid contained in the plurality of main storage ducts <NUM>, for example by inserting it into a thermowell <NUM> (as shown in <FIG>) or in contact with the material of which the ducts of said plurality of main storage ducts <NUM> are made.

Furthermore, <FIG> shows an alternative schematic of the system including a third control system, wherein in the first return conduit <NUM> there is an electrovalve <NUM>". The latter, if de-powered, is able to stop the circulation of the heat transfer fluid inside said first return conduit <NUM>, while, when powered, the electrovalve <NUM>" allows the passage of fluid. Therefore, similarly to the control of the first circulation pump <NUM> of the solution of <FIG>, the control unit <NUM> can electrically power or not power the electrovalve <NUM>" and allow the transfer of energy between the main tank <NUM> and the additional tank <NUM> by means of a natural circulation motion of the fluid.

The described solutions have no limitations on the methods of controlling the energy transfer between the main tank <NUM> and the additional tank <NUM>, any alternative solutions that have the same functional purpose are considered to be equivalent.

In cases where there is the active control, the threshold temperature Ts can be set by the installer or the customer by means of the electronic device supplied with the system, i.e. a control device that allows the adjustment of the system operating parameters and the principle of operation of the additional tank <NUM>. In any case, a set of recommended default values can be indicated by the manufacturer.

In cases where there is the passive control, components are chosen that intervene at a specific threshold temperature Ts.

Preferably the threshold temperature Ts is between <NUM> and <NUM>.

In further embodiments, the volume of the additional tank can be composed of a plurality of storage ducts that can be activated in cascade, for example the transfer to a first additional tank can be activated when the threshold temperature Ts in the main tank is reached, in turn the transfer to a second additional tank can be activated once the threshold temperature has been reached in the first additional storage and so on. Of course, the choice of the number of additional storage ducts depends on the balance between benefits and costs.

<FIG>, <FIG>, <FIG> and <FIG> show a second embodiment of the solar system <NUM> according to the invention comprising two additional storage ducts <NUM>', <NUM>" which form said additional tank <NUM>.

This makes it possible to obtain a dimensional compactness. In this case, the first circulation pump <NUM> can be arranged in a second return conduit <NUM>' which connects the two additional ducts <NUM>' and <NUM>". In this embodiment, the first hydraulic circuit <NUM> can have a third return conduit <NUM>", wherein a non-return valve <NUM>' is arranged. This third return conduit <NUM>" also connects the at least two additional storage ducts <NUM>' and <NUM>". The function of this third return conduit <NUM>" is to reduce the pressure losses and not force the incoming heat transfer fluid to pass only through the first circulation pump <NUM> which, for functional reasons, offers a high impediment to the fluid if it is not active.

The first circulation pump <NUM> allows the withdrawal of the first heated heat transfer fluid, for example hot water, from the main tank <NUM> through the first return conduit <NUM> which connects the main outlet conduit <NUM> of the main tank <NUM> and the additional inlet portion <NUM> of the second additional storage duct <NUM>". In turn, the energy is transferred from the second additional storage duct <NUM>" to the first additional storage duct <NUM>' through the second return conduit <NUM>'. The hydraulic recirculation circuit closes via the connecting conduit <NUM> between the additional outlet portion <NUM> of the first additional storage duct <NUM>' and the main inlet portion <NUM> of the main tank <NUM>.

The non-return valves <NUM> and <NUM>' prevent hydraulic short circuits and guarantee the anti-clockwise recirculation flow, as shown in <FIG>.

Returning, therefore, to the operation of the solar system <NUM> according to the invention, once the energy transfer between the main tank <NUM> and the additional tank <NUM> has taken place (for example as shown in <FIG>), the energy of the main tank <NUM> is redistributed. Then, according to the thermodynamic equilibrium equations, the system approaches the theoretical condition, wherein the final temperature T"<NUM> of the main tank <NUM> is equal to the final temperature T"<NUM> of the additional tank <NUM>: <MAT>.

Where T'<NUM> and T's are equal to the initial temperatures of the volumes V<NUM> and V<NUM> of the two tanks <NUM> and <NUM> before the heat exchange with each other.

This redistribution leads to a decrease in the temperature of the fluid contained in the main tank <NUM>. In fact, since the additional tank <NUM> is shielded from solar radiation, the fluid contained therein is certainly at an initial temperature T'<NUM> lower than the initial temperature T'<NUM> of the fluid contained in the main tank <NUM>. Therefore, the fluid contained in the main tank <NUM>, once cooled, can continue to absorb solar energy, in correspondence with the collection area, without facing extreme conditions of use, in other words without overheating. At this point, when the first heat transfer fluid is withdrawn on the user side, it will be possible to benefit directly from the energy transferred to the additional tank <NUM> since the inlet of fluid to the system takes place at the inlet portion <NUM>. In this way, advantageously, the system will operate at a lower average temperature, increasing its efficiency and decreasing its dissipation towards the external environment.

The initial temperature T'<NUM> of the fluid contained in the additional tank <NUM> affects the final equilibrium temperature T" of the fluid contained in the solar system <NUM> during the energy transfer between the main tank <NUM> and the additional tank <NUM>: the higher the initial temperature T'<NUM> of the fluid contained in the additional tank <NUM>, the higher the final equilibrium temperature T". Therefore, with the repetition of storage processes, a point will be reached at which said transfer will no longer be beneficial. Therefore, when this condition is reached, the main tank <NUM> will continue to increase its temperature regardless of whether the recirculation circuit is activated and will potentially be able to reach the critical conditions of use (this is possible in conditions of high irradiation and particularly high external temperatures). The solar system <NUM> can therefore include a dissipator element, for example like those described in the state of the art, in order to avoid reaching this extreme condition of extraordinary use or a protection element with a safety valve that discharges hot fluid from the system automatically reintroducing cold fluid from the water grid.

The solar system <NUM> is preferably designed in such a way that, in the event that the user withdraws the first heat transfer fluid every <NUM>/<NUM> hours, this extreme condition of extraordinary use is not likely.

To support this observation, the value of the volume V<NUM> of the additional tank <NUM> can therefore be indicated in relationship to the volume V<NUM> of the main tank <NUM> via the following relationships. As anticipated, the ratio between the volume V<NUM> of the additional tank <NUM> and the volume V<NUM> of the main tank <NUM> is included in the following range of values: <MAT>.

Furthermore, the ratio between the total volume of solar system <NUM>, V<NUM> + V<NUM>, and the collecting surface S, defined as per the UNI EN ISO <NUM> standard which defines the geometric references to be used for calculating the collecting surface, can be included in the following range of values: <MAT>.

Furthermore, the invention concerns a specific control strategy/algorithm for the activation or not of the circuitry of said volume V<NUM> of the additional tank <NUM>. <FIG> shows the flow diagram of the control strategy for the switch of the solar system <NUM> according to the invention between the first and second use configuration, possibly also based on time windows within which allowing the system to execute the energy transfer logic.

The diagram shows a first option indicated with the reference Xllla wherein the threshold temperature Ts is entered by the user or installer during the installation stage. In this configuration, in the event that the temperature T<NUM> of the fluid in the main tank <NUM> is greater than a threshold temperature Ts and the time of reaching this condition is within the time range allowed by the user or installer during the installation stage, the system switches to the second use configuration, i.e. the energy transfer between the main tank <NUM> and the additional tank <NUM> is activated. Otherwise, the volume of the additional tank <NUM> does not store heated fluid and is not involved in the thermal process of the solar system <NUM>. The hourly intervals selectable by the user or installer can respond to different needs, for example it is not recommended to keep the energy transfer function active close to sunset time, since it could happen that the final temperatures T"<NUM> and T"<NUM> of the fluid in tanks <NUM> and <NUM> are such that an optimal value for the DHW production cannot be guaranteed the following morning, due to the night-time cooling. After a stage of heating of the volume of fluid contained in the main tank <NUM> and transferring of energy to the fluid contained in the volume of the additional tank <NUM>, if the temperature T<NUM> of the fluid contained in the main tank <NUM> is lower than said threshold temperature Ts then the system returns to the first use configuration, i.e. the hydraulic recirculation flow is stopped.

In the event that the temperature T<NUM> of the fluid contained in the main tank <NUM> is greater than said threshold temperature Ts, it is further checked whether the system is operating within a time limit or not, respectively keeping the system for transferring energy to the additional tank volume <NUM> active or not.

The flow diagram of <FIG> further shows a second option indicated with the reference Xlllb with the same options and logic as the first option Xllla, but with the difference that the threshold temperature Ts is adjusted in real time, as better explained herein below.

The temperature T<NUM> of the fluid contained in the main tank <NUM> adapted to carry out the energy transfer is linked to the inlet temperature Tgrid of the secondary fluid (grid temperature) via said inlet portion <NUM> and also by the ratio between the volumes V<NUM>/V<NUM> of the main tank <NUM> and additional tank <NUM> of solar system <NUM>, according to the following relationship: <MAT>.

Which leads to the following equation (whose relationship between values is shown in the graph of <FIG>): <MAT>.

Where Ts is the threshold temperature of the fluid contained in said main tank <NUM>, following which the system switches to the configuration of transfer of energy to the additional tank <NUM>.

Tuser means the set outlet temperature of the fluid on the user side through said outlet portion <NUM>, set by the user or installer.

Conceptually, the above set out equation has the following meaning: if I bring the volumes V<NUM> and V<NUM> into equilibrium, with the fluid in the volume V<NUM> of the additional tank <NUM> at the grid temperature Tgrid, the final equilibrium temperature T" must always be higher than the user temperature Tuser, so that the system can deliver hot water at the temperature chosen by the user.

So, for example, considering Tgrid = <NUM>°C, Tuser = <NUM>°C with a ratio <MAT> we obtain from the equation <MAT>.

Of course, the Ts, with Tgrid (<NUM>) and Tuser (<NUM>) both fixed, can depend on varying the V<NUM>/V<NUM> ratio chosen by the manufacturer (as also shown in the graph of Figure <NUM>): <MAT>.

Or Ts, with Tuser (<NUM>) and V<NUM>/V<NUM> ratio (<NUM>) both fixed, can depend on the variation of the grid temperature Tgrid (as shown in the graph of <FIG>): <MAT>.

With which the Ts can be varied, as the grid temperature Tgrid has variable temperatures based on the season or the different location/climate zone.

Thanks to that logic it is therefore possible to take advantage of the possibility of varying the V/S ratio on the basis of the weather conditions or the climate zone, in such a way as to guarantee a fluid withdrawal in the design conditions (i.e. <NUM>°-<NUM>) and maximise the solar energy collected by reducing overtemperature conditions that require the dissipation of excess energy.

Referring to <FIG>, a third embodiment of the solar system <NUM> according to the invention can be observed. The same components of the solar system <NUM> according to the first embodiment will be indicated with the same numerical references.

The third embodiment differs from the first embodiment due to the different arrangement of the flow management means <NUM>, for example said first circulation pump <NUM>. This first circulation pump <NUM> is in fact arranged in correspondence with said connecting conduit <NUM>, upstream from the direction of flow of the first heat transfer fluid and from the main portion of inlet <NUM> to the plurality of main storage ducts <NUM>. This solution would be advantageous for making the first circulation pump <NUM> work at a lower temperature, extending its useful life as the stress to which the component is subjected is reduced. In this case, however, the pressure losses are aggravated at the time of the DHW withdrawal on the user side, therefore it is necessary to have a hydraulic pressure in the aqueduct sufficient to guarantee the DHW flow rate desired by the user.

In relation to <FIG>, a fourth embodiment of the solar system <NUM> according to the invention can be observed. The same components of the solar system <NUM> according to the first embodiment will be indicated with the same numerical references.

This embodiment differs from the previous embodiments since the activation system of the additional tank <NUM> is not in forced circulation, but takes place through natural circulation. In fact, the first hydraulic circuit <NUM> provides a thermostatic valve <NUM> which is arranged in said first return conduit <NUM>.

In the first use configuration, the thermostatic valve <NUM> prevents the passage of the first heat transfer fluid from said main outlet portion <NUM> of said main tank <NUM> to the additional inlet portion <NUM> of said additional tank <NUM>.

When said threshold temperature Ts is detected, the thermostatic valve <NUM> allows the passage of the first heat transfer fluid through said first return conduit <NUM> and the first hydraulic circuit <NUM> switches into said second use configuration, putting in fluid connection the main outlet portion <NUM> of the main tank <NUM> with the additional inlet portion <NUM> of the additional tank <NUM>. In this configuration a closed circuit is created wherein the first heat transfer fluid circulates in the first hydraulic circuit <NUM> by natural circulation.

This solution is advantageous from an economic and installation point of view, since the system does not require electrical power. However, the energy transfer efficiency is lower than the forced convection circuit.

Referring to <FIG>, a fifth embodiment of the solar system <NUM> according to the invention can be observed.

As in the previous embodiments, this solar system <NUM> provides collecting means <NUM>, in particular a plurality of vacuum collecting pipes <NUM>, inside each of which a respective duct of said plurality of main storage ducts <NUM> is arranged for the storage of a second heat transfer fluid or a primary heat transfer fluid, for example a <NUM>% water and glycol solution. Said plurality of main storage ducts <NUM> are in fluid communication with each other, in particular via said plurality of further connecting conduits <NUM> to form the main tank <NUM>.

The plurality of connecting conduits <NUM> preferably connect said main storage ducts <NUM> in series. Furthermore, said main storage ducts <NUM> are connected with each other via a recirculation conduit <NUM> in such a way as to form a second hydraulic circuit <NUM>'. This second hydraulic circuit <NUM>' is a closed circuit inside which the second heat transfer fluid flows in correspondence with the collection area of the solar system <NUM>.

A second circulation pump <NUM>' is arranged in said recirculation conduit <NUM> for activating the circulation of said second heat transfer fluid.

Again, the solar system <NUM> provides an additional tank <NUM> for the storage of the first heat transfer fluid or secondary fluid, in particular domestic water, arranged alongside said plurality of vacuum collecting pipes <NUM>. As per the described embodiments, the additional tank <NUM> is shielded from solar radiation and insulated. Furthermore, the additional tank <NUM> provides an additional inlet portion <NUM>, in fluid connection with said inlet portion <NUM>, and an additional outlet portion <NUM> of the secondary fluid. The outlet portion <NUM> of the heated secondary fluid is in fluid communication with the additional outlet portion <NUM> of the additional tank <NUM>. Said first return conduit <NUM> is also provided between said additional inlet portion <NUM> and additional outlet <NUM> from said additional tank <NUM>, to form said first hydraulic circuit <NUM> wherein the secondary fluid flows.

In correspondence with said first return conduit <NUM>, a non-return valve <NUM> and said first circulation pump <NUM> are provided.

This embodiment differs in the mode of transfer of thermal energy from the main tank <NUM> to the additional tank <NUM>, which takes place by means of a heat exchanger <NUM>.

The heat exchange takes place between a portion of the further recirculation duct <NUM> of the second hydraulic circuit <NUM>', where the primary fluid flows, and between a portion <NUM> of the connecting conduit <NUM>, which corresponds to the second heat exchange portion of the first hydraulic circuit <NUM>.

Furthermore, this embodiment can provide an activation flow switch <NUM>, arranged alongside the first hydraulic circuit <NUM>, which activates the second circulation pump <NUM>' in order to guarantee the forced circulation of the second heat transfer fluid inside the heat exchanger <NUM>, during the DHW withdrawal by the user (the forced circulation of the secondary fluid is guaranteed by the grid pressure). The flow switch <NUM> is in fact activated by the circulation of the first heat transfer fluid, which is guaranteed by the grid pressure. The flow switch <NUM> acts in DHW withdrawal conditions, as it guarantees the circulation of the two fluids in the heat exchanger <NUM> when the user opens the taps and therefore sends the secondary fluid into circulation, moved by the grid pressure.

Since the second heat transfer fluid flows inside said plurality of main storage ducts <NUM>, the described embodiment makes it possible to reduce, even eliminate, the problems of corrosion and limescale in the plurality of main storage ducts <NUM> and in the plurality of further connecting conduits <NUM>. Furthermore, this embodiment allows the use of less noble materials for producing said plurality of main storage ducts <NUM>. The aforementioned problems are confined to the inside the heat exchanger <NUM> and to the additional tank <NUM>, which are typically at lower temperatures and are also more easily replaceable.

During a first use configuration, the first heat transfer fluid is heated following the passage through the heat exchanger <NUM> where the energy is transferred via heat exchange between the recirculation conduit <NUM> and the second heat exchange portion <NUM>, included in the connecting conduit <NUM>, of said second <NUM>' and first <NUM> hydraulic circuits, respectively. In the first use configuration, the first circulation pump <NUM> is deactivated.

When a threshold temperature Ts of the fluid in the main tank <NUM> is reached, the control unit activates the second circulation pump <NUM>' and the first circulation pump <NUM> (the latter activates the circulation of the first heat transfer fluid through the first return conduit <NUM>), thus activating the recirculation of the first heat transfer fluid in the additional tank <NUM> after the heat exchange in said heat exchanger <NUM> with the second heat transfer fluid circulating in the second hydraulic circuit <NUM>'. Therefore, the first hydraulic circuit <NUM> switches into a second use configuration.

This advantageously allows the excess energy of the second heat transfer fluid contained in the plurality of main storage ducts <NUM> to be stored in the additional tank <NUM>.

Referring to <FIG>, a sixth embodiment of the solar system <NUM> according to the invention, which is an alternative to the previous ones, can be observed. The same components will be indicated with the same numerical references.

This embodiment, similarly to the fifth embodiment, involves the use of two fluids. A second heat transfer fluid is contained in a plurality of main storage ducts <NUM>, each arranged in the respective collecting pipe of said plurality of vacuum pipes <NUM>, and which are not in fluid connection with each other, but which form a main tank <NUM> of the second heat transfer fluid.

A first heat transfer fluid is instead contained in an additional tank <NUM> arranged similarly to the previous embodiment but forming part of a first hydraulic circuit <NUM> similar to that one described for the first embodiment.

In this case, a plurality of heat exchange conduits <NUM> are provided, which form said second heat exchange portion <NUM> of the first hydraulic circuit <NUM>, in fluid connection with each other. Said heat exchange conduits <NUM> are arranged inside the main storage ducts <NUM> to allow the heat exchange with the second heat transfer fluid contained therein. Each heat exchange conduit <NUM> of said second heat exchange portion <NUM> is preferably a corrugated pipe.

In this embodiment two use configurations are provided. In a first configuration the additional tank <NUM> is deactivated, as long as it is not necessary to transfer the solar energy stored in the main tank <NUM>. In this configuration the first heat transfer fluid flows into the first hydraulic circuit <NUM> from the input portion <NUM> to the outlet portion <NUM> without passing through said first return conduit <NUM> and wherein said additional tank <NUM> acts solely as an inlet passage duct for the first heat transfer fluid coming from the hydraulic grid. Furthermore, in this embodiment, said connecting conduit <NUM> is provided, wherein the first heat transfer fluid flows between the additional outlet portion <NUM> of the additional tank <NUM> and the main inlet portion <NUM> of the main tank <NUM>, in fluid connection with the plurality of heat exchange conduits <NUM> in correspondence with said second heat exchange portion <NUM>, adapted to absorb the thermal energy from the second heat transfer fluid, contained inside the plurality of main storage ducts <NUM>. In a second use configuration, however, when the extreme conditions of use are reached, i.e. when a threshold temperature Ts of the second heat transfer fluid is reached, the fluid connection between the main tank <NUM> and the additional tank <NUM> is also activated via the first return connecting conduit <NUM> of said first hydraulic circuit <NUM>, via the activation of flow management means, for example said first circulation pump <NUM>, which were deactivated in said first use configuration. By activating the first circulation pump <NUM>, the first heat transfer fluid coming out of the plurality of heat exchange conduits <NUM>, flows between said additional inlet portion <NUM> of said additional tank <NUM> and said main outlet portion <NUM> of said heat exchanger <NUM> from said main tank <NUM>, passing through said first return conduit <NUM>. This therefore allows the transfer of energy between the volumes of said main <NUM> and additional <NUM> tanks. In other words, the first hydraulic circuit <NUM> becomes a closed circuit wherein the first heat transfer fluid passing through the first return conduit <NUM>, which acts as a recirculation conduit, allows the circulation of the first heat transfer fluid between the additional tank <NUM> and the plurality of heat exchange conduits <NUM> inserted in the main tank <NUM>, thus also cooling the second heat transfer fluid contained in the main tank <NUM>, de facto allowing the system to operate at a lower average temperature, if temperature conditions are reached such that said solar system <NUM> risks overheating.

This embodiment, compared to the fifth one, allows the plurality of heat exchange conduits <NUM> to be integrated, in fluid connection with each other, inside said plurality of main storage ducts <NUM> of said main tank <NUM> wherein the second heat transfer fluid, thus the solar system <NUM> is more compact.

Furthermore, the presence of the second primary circulation pump <NUM>' and the flow switch <NUM> described previously is not necessary. On the other hand, the length of the plurality of heat exchange conduits <NUM> is limited by the volume of the main storage ducts <NUM>, therefore the exchange area between the second heat transfer fluid and the first heat transfer fluid is more constrained. Furthermore, the second heat transfer fluid carries out the heat exchange in natural convection; therefore, the heat exchange efficiency is also lower than in the case wherein a circulator, dedicated to the second heat transfer fluid, is adopted.

Referring to <FIG>, a seventh embodiment of the solar system <NUM> according to the invention can be observed, wherein inside the plurality of main storage conduits <NUM> and inside the additional tank <NUM>, a second heat transfer fluid is present, in particular a primary fluid as previously described. The same components of the solar system <NUM> according to the first and fifth embodiments will be indicated with the same numerical references.

A second heat transfer fluid is contained in a plurality of main storage ducts <NUM>, each arranged in the respective collecting pipe <NUM> and not in fluid connection with each other, but forming a main tank <NUM> of the second heat transfer fluid.

Furthermore, a second heat transfer fluid is also contained in an additional tank <NUM>, not in fluid connection with said plurality of main storage ducts <NUM>.

In this case, a first heat exchange portion <NUM>' of the first hydraulic circuit <NUM> is provided, inside said additional tank <NUM>, comprising a second heat exchange conduit <NUM> placed inside said additional tank <NUM> wherein a first heat transfer fluid, introduced via an additional inlet portion <NUM>, flows in fluid connection with the inlet portion <NUM> of the first heat transfer fluid from the hydraulic grid and with a first return conduit <NUM>, or recirculation branch <NUM>. This second heat exchange conduit <NUM> is in fluid communication with said connecting conduit <NUM> in correspondence with said additional outlet portion <NUM>.

Furthermore, a second heat exchange portion <NUM> of the first hydraulic circuit <NUM> is provided, coinciding with the main tank <NUM>, with a plurality of heat exchange conduits <NUM>, arranged inside said plurality of main storage conduits <NUM> wherein the first heat transfer fluid flows, introduced through a main inlet portion <NUM>, in fluid connection with said connecting conduit <NUM> from the first heat exchange portion <NUM>', and a main outlet conduit <NUM> in fluid connection with the outlet portion <NUM> and with the first return conduit <NUM>. Said plurality of heat exchange conduits <NUM> is preferably composed of a plurality of corrugated pipes, connected in series or in parallel via the plurality of further connecting conduits <NUM>.

Furthermore, in the present embodiment the first return conduit <NUM> is adapted to allow the recirculation of the first heat transfer fluid between the main outlet portion <NUM> and the additional inlet portion <NUM>.

A first circulation pump <NUM> and a non-return valve <NUM> are provided in correspondence with the first return conduit <NUM>.

In a first use configuration, the additional tank <NUM> is deactivated, as long as it is not necessary to transfer the solar energy stored in the main tank <NUM>. In this configuration the first heat transfer fluid first flows into the first hydraulic circuit <NUM> in correspondence with the first heat exchange portion <NUM>' and then into the plurality of heat exchange conduits <NUM>, from the inlet portion <NUM> to the outlet portion <NUM> without passing through said first return conduit <NUM>. If the second heat transfer fluid contained in the additional tank <NUM> has a temperature higher than the grid temperature Tgrid, the first heat exchange area <NUM>' acts as a pre-heating area for the first heat transfer fluid introduced into system <NUM>.

In a second use configuration, instead, when the extreme conditions of use are reached, i.e. when a threshold temperature Ts of the second heat transfer fluid contained in the main tank <NUM> is reached, the first return conduit <NUM> is activated by the first circulation pump <NUM>, therefore the first heat transfer fluid is set in motion in the closed circuit operating between the portions <NUM>, <NUM>, <NUM> and <NUM> of the first hydraulic circuit <NUM>. In this way the excess energy in the plurality of said main storage ducts <NUM> is transferred to the additional tank <NUM> by means of the plurality of heat exchange conduits <NUM> and the second heat exchange conduit <NUM>.

Compared to the solution described in the previous schematics, the solution of <FIG> allows the use of a second low pressure heat transfer fluid in the additional tank <NUM>, therefore the additional tank <NUM> can be made of a generic shape and therefore be more easily integrated into the compact system. On the other hand, the use of a plurality of heat exchange conduits <NUM> and of the second heat exchange conduit <NUM> introduces heat exchange efficiency factors, therefore the second heat transfer fluid must always be at a temperature a few degrees centigrade higher than the first heat transfer fluid in each heat exchange area. This implies that at the end of the withdrawal on the user side it is necessary to leave the second heat transfer fluid at a temperature higher than that one resulting in the systems wherein the first heat transfer fluid is present inside the tanks.

Advantageously, the invention makes it possible to use the excess incident solar energy stored in the system, at the same time preventing it from reaching an extreme use temperature value, and to operate at a lower average temperature, increasing efficiency and decreasing dissipation towards the external environment.

Again, the invention advantageously makes it possible to obtain a V/S volume-to-collection surface ratio that is dynamic over time, variable on the basis of the weather and/or use conditions, for example that can be increased in overtemperature conditions and decreased in conditions of low solar irradiation.

Moreover, the invention presents a control strategy, based on the calculation of a Ts beyond which a dedicated circuit activates/deactivates the energy transfer between the main tank and the additional tank, allowing an efficient use of the system even in conditions of an excessive solar radiation, storing the excess temperature of the fluid, or in conditions of poor solar radiation, preventing the heat exchange between the main tank and the additional one and allowing the solar system to heat the fluid sufficiently to the design conditions.

Furthermore, according to the invention in some of its embodiments it provides the use of a primary fluid inside said storage ducts and/or inside the additional storage tank, allowing the use of less noble materials for manufacturing the ducts.

Again, thanks to the division of the additional storage volume into a plurality of additional ducts, and to the possibility of carrying out the heating process of the heat transfer fluid contained in the additional storages in a sequential manner, this advantageously makes it possible to use all the solar energy for heating the heat transfer fluid contained in the main storage, in direct thermal contact with the absorber element or collecting means, and then in a sequential manner for heating the heat transfer fluid contained in the other additional storages. This makes it possible to "stratify" the thermal energy and make hot water available at the design temperature first.

Claim 1:
A compact solar system (<NUM>) for heating a first heat transfer fluid, said solar system (<NUM>) comprising an external frame (<NUM>), inside which are contained
a main tank (<NUM>) for containing a heat transfer fluid,
collecting means (<NUM>) for collecting the solar radiation, said collecting means (<NUM>) being in heat exchange with said main tank (<NUM>) for transferring the collected thermal energy to the heat transfer fluid contained in said main tank (<NUM>), and
a first hydraulic circuit (<NUM>) for the circulation of said first heat transfer fluid, comprising an inlet portion (<NUM>) for the inlet of the first heat transfer fluid and an outlet portion (<NUM>) for the outlet of the first heat transfer fluid,
said solar system (<NUM>) further comprising inside said frame (<NUM>)
an additional tank (<NUM>) for containing a heat transfer fluid, said additional tank (<NUM>) being thermally isolated from said collecting means (<NUM>),
the volumetric ratio between the volume (V<NUM>) of the additional tank (<NUM>) and the volume (V<NUM>) of the main tank (<NUM>) being defined by the following relationship: <MAT>
wherein said first hydraulic circuit (<NUM>) provides a first heat exchange portion (<NUM>, <NUM>') in heat exchange with the heat transfer fluid contained in said additional tank (<NUM>) and a second heat exchange portion (<NUM>, <NUM>) in heat exchange with the heat transfer fluid contained in said main tank (<NUM>),
said first (<NUM>, <NUM>') and second (<NUM>, <NUM>) heat exchange portions being in fluid connection with each other through a connecting conduit (<NUM>) characterised in that said first (<NUM>, <NUM>') and second (<NUM>, <NUM>) heat exchange portions are further in fluid connection with each other through a first return conduit (<NUM>),
and in that it provides flow adjusting means (<NUM>, <NUM>; <NUM>, <NUM>; <NUM>; <NUM>") arranged in said first hydraulic circuit (<NUM>) for allowing the circulation of said first heat transfer fluid from the second heat exchange portion (<NUM>, <NUM>) to the first heat exchange portion (<NUM>, <NUM>') through said first return conduit (<NUM>), when a threshold temperature (Ts) of a heat transfer fluid contained in said main tank (<NUM>) is reached.