The present invention refers to an automatic plant and a process for producing electric energy from solar irradiation in combination with a fuel-type auxiliary plant and a system for storing thermal energy. All disclosed values, sizes, pressures and temperatures, are approximate and can change from project to project .

For producing electric Energy more or less efficient systems are used. The nuclear system, the only one which could produce enough energy for everybody, is opposed by many because it produced radioactive waste, difficult to dispose of, part of which remains radioactive for more than one hundred thousand years, and due to the dangers witnessed in Chernobil and Fukushima disasters. Fossil fuels, the major source of electric energy and at the same time the major responsible for atmospheric pollution, are not renewable and it is foreseen that shortly they will be exhausted. They produce a high amount of polluting products, fumes, fine particulates, sulphur and nitrogen oxides, aromatic hydrocarbons.

As alternative to the production of electric energy with nuclear or by burning fossil fuels, the electric energy can be obtained by renewable sources: from an hydroelectric source with water which moves from a level to a lower level in forces ducts, on the river course or due to a dam, to exploit the geothermal energy below the earth, due to wave motion and floods, or producing energy from biomasses, with the concentration-type solar plants, from wind and from photovoltaic systems. The last two systems produce energy intermittently, only when there is wind or light. Renewable energy sources, sun, wind, water do not produce atmospheric pollution.

Sun is the source of energy which has allowed life on earth. Sun energy is not here considered which has been capitalized during millions of years in fossil fuels or present in all vegetable and animal forms of life, but the current sun energy which earth receives from sun. Insulation is the measure of the amount of radiation emitted by the sun which reaches a given earth surface per time unit. It is expressed as average radiance in watt/m2. It is defined as solar constant, with a value of 1.367 W/m2 at the borders with atmosphere and can range from 7% during the year as consequence of the longer or shorter distance of earth from sun. The solar irradiation intensity is attenuated by the passage through the atmosphere. At Italy latitudes, at midday and with clear sky, insulation is about 1,000 W/m2. Considering the alternation between day and night, cloudiness and seasons, the average insulation on 24 hours is in Italia of circa 200 W/m2, to which, on the 300,000 km2 of national territory, a power of over 1.000 times the Italian energy need, currently of about 50 GW, corresponds. Similar computations can be done for other areas.

The target of all Countries for the next years is a substantial increase of energy obtained by renewable sources, with the consequent reduction of the emission of carbon dioxide and various pollutants. The present embodiment is a step forward along that direction.

What makes the electric market complex and particular is that the electric energy cannot be stored, if modest contributions of batteries are excluded. Every instant what is requires must be produced. All systems must therefore be coordinated so that it is possible to have available the necessary power for the requests of the territory, which change during the day, between working days and holidays, between one month and the other. Big thermoelectric plants and nuclear plants are those producing energy at the lowest cost and operate continuously; less efficient hydroelectric plants and thermoelectric plants operate with full power for less hours and modulate the power during rush hours, corresponding to the peak of daily consumptions. The electric energy produced by sun, light and wind is instead volatile and not programmable, but has the advantage of having dispatching priority; if the plant is connected to the electric mains, the production must always be absorbed.

There are people stating that obtaining electric energy by the sun is an illusion and that the current contribution from sun energy for the production of electric energy is marginal and will be still more in the future. It is certainly true that currently this contribution is small, but there is no reason for concluding that it will also be such in the future. It is legitimate to assume that the right technology has not been located. When the technical evolution will make it economically convenient, the thermal energy freely provided by the sun can be used. The problem is that the amount of energy which arrives on the ground is enormous, ma scarcely concentrated. It is necessary to collect energy from very wide areas to have meaningful amounts and this makes it difficult to have acceptable efficiencies and costs. The proposed hybrid plant has building features which increase the contribution of the sun, reduce the costs for kWh produced and strongly reduce C02 emission and other pollutants. In general, regarding social costs, the advantages of an energy produced with reduced atmospheric pollution and lower system risks would be enormous, but contrary interests in play prevents its success.

From the economic point of view, the statement of a system with respect to other ones will depend on the cost per kWh produced, taking into account the factors determining it, the used capital, the length of the plant working life, the operating costs, the maintenance costs, the fuel cost, the waste disposal cost, the mains connection costs and the system operating houses .

Also the contribution of electric energy obtained in hybrid plants will depend on the cost per k h produced. The chance of wide-spreading on the territory small plants with poker from 100 to 300 kW and more will be able to determine a more important position with respect to energy produced from other sources. With the same investment, a plant which can deliver a power of 100 kW where the average insulation is 200W/m2 on 24 hours could give more where insulation is greater, with a maximum in the band included in the tropics.

The primary sun energy is a free resource available practically unlimitedly, but its exploitation is not easy. The development of technologies adapted to make the use of sun Energy possible and economical is a very active search sector, but so far has not produced revolutionary results.

Sun energy is used:

1. in the photovoltaic field to directly obtain electric energy from light, and for producing few kW for family uses and in big power plants. Photovoltaic yields are small and the cost per kW produced is greater than the one of other systems. At efficiency level, photovoltaic panels reach a percentage of converted energy included between 7% and 15% and producing relevant amounts of energy from the photovoltaic requires the coverage of wide surfaces of territory with panels exposed to the sun, in addition to the fact that the photovoltaic produces electric energy only when there is sun light. in solar panels for producing hot water, substantially for family uses. The percentage of converted energy can reach 80%, but the solar panels cannot produce electric energy and collect thermal energy only when there is solar irradiation . in collectors with parabolic disk which produce electric energy with Stirling motors, also in this case dxscontinuously depending on the solar irradiation. in solar, concentration-type plants, with tower plants or linear parabolic collectors. Sun radiation is captured and concentrated in a spot for heating a thermal carrier fluid (mineral oil, melted salts) and take it to temperatures of hundreds of degrees. The stored thermal energy is afterwards used for generating the steam which a turbine uses for producing electric energy. The principle is correct and the presence of a thermal energy store allows keeping the plant operating also with a temporary absence of solar irradiation. Plants in the thermo-dynamic field are costly, complex must be located in areas with strong insulation and have high control and maintenance costs. The cost per kWh produced is the highest in absolute terms. Concentration-type solar plants however have pointed out that, if it is not possible to store electric energy, it is however possible to store thermal energy to produce it.

To obtain electric energy from sun, light or wind, the inconstancy of their presence must be taken into account. With the exception of concentration solar plants, currently no plants are available which store energy reserves and use them for keeping the plant active, at least temporarily, when irradiation is lacking. The contribution of batteries and of other energy recovering systems is marginal. The diffusion of hybrid plants for producing electric energy is therefore possible provided that a meaningful percentage of energy is supplied by the sun and the fuel-type auxiliary system for keeping the plant active has an impact which is as much as possible small on the cost per kWh produced.

The problem with this type of plant is that, from at sunrise and at sunset, the sun rays strike the collector with an angle of few degrees and scarce thermal energy, since insulation is reduced depending on the angle sinus. The unit cost of the power produced in one year by the plant is high. Trigonometric computations point out that the thermal addition increases by 50% if the plane collector is replaced by a collector with certain profiles. For increasing the received thermal energy, the present invention provides that the collector has not a plane surface, but has, every 80 mm, 4 cylindrical profiles with a diameter of 10 mm projecting by 5 mm (Figure 3a), obviously arranged with a North-South axis. The profiles can be created with repeating milling with a pitch of 80 mm on the aluminium sheet module or by extrusion. In this case, the extruded profile can contain many 80-mm figures, for example 10.

Irradiation on 480 mq of a plane collector can guarantee the plant operation for 8 average insulation hours, while the modified collector equipped with profile can guarantee 12. The coverage for the 8 or 12 hours in which there is no insulation must be provided by the auxiliary plant and its capability of storing thermal energy. The thermal energy supplied by the sun and the combustion system concurs to heating water. The pressurized steam accumulated in the top vessel part is conveyed to the turbine after a pressure reduction to values designated by the turbine's manufacturer adapted to guarantee the production of electric energy required by the plant. This function is given to a pressure regulator placed in the duct which communicates tank and turbine. The delta between the two values is the pressure reserve which keeps the plant operating till the minimum defined threshold is reached. Upon starting the plant, the system is taken to the maximum pressure for which the tank is designed, and afterwards left automatically operating. A thermostatic actuator is used to deactivate the auxiliary system, for example at 20 bar and re-activate it at the pressure of 10 or 12 bar. The plant can operate with methane, where available, with GPL or with other fuel. To produce 100 electric kW, it will therefore be necessary to have 300 thermal kW continuously available.

Who builds, assembles and start the plant supports costs of 500,000 Euros for a plant with plane collector. The costs rise to 550,000 Euros for a plant with collector with profiles. Who builds the plant can also be its manager, but normally builds the plant on a licence and sells it to a manager, applying a recharge, for example equal to 30%.

There are two possible types of plant with a collector of 480 sqm: the one with plane collector piano and the one with collector with profiles. The third column on the right in the following table points out the results for the same plant with profiles placed in a place in which the average insulation is 300W/m2 on 24 hours. It is possible to compare the results.

In the collector bands, from one to four excavations, some centimetres wide and 5 millimetres deep, are also longitudinally obtained in the 10 mm of depth of the collector. Metal section with high conductivity are housed in these excavations, which include the water flowing pipe, like in Figure 2c, which transports heat by convection. The strict connection between the parts, necessary to guarantee a good conduction between collector and metal section, is obtained with elastic bands for fastening to the collector.

Comparison table:

TOTAL 1, 537, 500 1, 622, 500 1, 622, 500 kWh produced 8, 760, 000 13, 140, 000 17, 520, 000 in 10 years

Reduced due to 8, 300, 000 12, 450, 000 16, 600, 000 stops to

Cost per kWh 0.185 0.130 0.098

Incentive 0.22 0.22 0.22 price

Profit per kWh 0.035 0.09 0.122

Profit kWh

per year

29,050

(x 830,000)

Profit kWh per

year

112,050

(x 1,245,000)

Profit kWh per

year

202,520

(x 1,660,000)

Market price 0.12 0.12 0.12

Loss per kWh 0.65

Loss per year

(x 830,000) 53, 50 Loss per kWh 0.01

Loss per year

(x 1,245,000)

12, 450

Profit per kWh 0.022

Profit kWh per

year

36,520

X 1,660,000

Note (1) . The basic plant cost remains unchanged. Costs are added for making the profiles and other related costs.

Note (2) . The cost for fuel is reduced because, after having reached the maximum pressure and temperature value, the thermostat deactivates the auxiliary system. Fuel consumption restarts when accumulated thermal reserves have been spent.

The table points out that the sale of energy with an interesting price produces profits, while the sale at market price produces losses in the two plants, even with the plant with collector equipped with profile (in a small amount) . The plant with plane collector is therefore to be deemed a wrong investment to avoid. The fuel costs are (or would be) :

If the plant were operated only with fuel excluding the sun, there will be a consumption of Euro 11.76 x 24 hours x 365 days, with a yearly expense of 103,018 Euros

With 8 hours of thermal energy supplied by the solar plant on 480 m2 of plane collector, in the 16 hours in which there is no irradiation, the kW obtained by the auxiliary plant would imply a fuel expense of 11.76 for 16 hours x 365 days = 68,678 Euros

With 12 hours of thermal energy supplied by the solar plant on 480 m2 of the collector with profiles, the 12 remaining hours must be supplied by the auxiliary plant with a fuel expense of Euro 11.76 x 12 hours x 365 days = 51, 508 Euros. The necessary time to spend the accumulated thermal reserves and to make the temperature and pressure values decrease from their maximum value to the one which restarts the fuel system is 50%, with a fuel expense reduced by about 25,750 Euros.

The plant with plane collector can produce profits till the electric energy can be sold at an interesting price, here assumed equal to 0.22 Euros per kWh. At a market sales price here assumed equal to 0.12 Euros, it generates losses.

With completed depreciations and wholly paid financial burdens, residual fuel and managing costs remain to be paid every year for 25,750 + 30,000 Euros every year for a tot of 55,750 Euros.

Profit per year 142,760

(x 1,660,000)

The collector surface could be substantially reduced with the same result, with high savings in terms of material and work, but the results would be the same as with 480 mq of collector with plane surface.

Keeping the collector surface at 480 mq, with the modification of the profiles, guarantees the operation with thermal energy received from the sun for over 12 hours of insulation .

Object of the present invention is increasing the contribution of the sun thermal energy for producing electric energy with a new system and process for producing electric energy 24 hours on 24, which can be simply and economically used, with particular care to the environment and the costs of produced energy. The plant can be stand-alone, or connected to the electric mains ("grid-connected") .

Another object of the invention is defining a process which automatically operates due to simply physical principles, with practically null assistance and maintenance costs. Proceeding southwards in our hemisphere, insulation increases and the same plant will be able to produce more power till a maximum in the band between cancer tropic and equator. Similarly in the austral hemisphere, between Capricorn tropic and equator. The system can therefore express powers from 200 k to 300 kW and more depending on its location, excluding its use in the coldest areas of the plant towards the poles.

The above and other objects and advantages of the invention, as will result from the following description, are obtained with a system and a process as claimed in the respective independent claims. Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims .

It is intended that all enclosed claims are an integral part of the present description.

The present invention will be better described by some preferred embodiments thereof, provided as a non-limiting example, with reference to the enclosed drawings, in which:

Figure 1 shows the general system with vertical tank. With an horizontally arranged tank, the system is functionally identical. The structure comprises the following components:

1. Pressure-resistant tank body containing water

2. Tank bearing feed with regulating system

3. Tank closing cover for the cases in which the upper cover is separated and screwed through a flange to a cylindrical part equipped with a similar flange afety valve/s team turbine ressure regulator upstream of the turbine, where provided carcely reflecting glasses as collector cover olar collector and auxiliary plant connected to the common hydraulic circuit for circulating water nsulating layer between collector and bearing plane lane yard for bearing the collector ater outlets of solar and auxiliary circuits olar circuit pump uxiliary circuit pump uel-type auxiliary plant connected to the hydraulic circuit ot water returns in solar and auxiliary circuits ircuit for overheating the steam, where provided ondenser ank refill water itting pipe to the pressurized tank with pump asement erimeter walls 22. Room ceiling

23. Apparatuses for controls, regulations and mains connection.

Figure 2a shows the plant placed North of the collector to avoid shadows on it. Figure 2b shows the plant in plan view with the collector, for example composed of 40 6-sqm modules in the 150 x 400 cm format .

Figure 2c shows in plan view the enlargement of a band of the solar collector with 150 x 400 cm on whose length there are the profiles of Figure 3, repeated on every panel. Moreover, at 90 degrees, for half the thickness and some centimetres wide, one or more channels are obtained to house the profile with the water circulating pipe.

Figure 2d shows a sectioned detail of the channel and of the profile with the same width which inserted therein. The strict connection between metal section and collector is ensured by elastic straps and connecting screws.

Figure 3a shows, in a 1:1 scale, the collector section which is repeated every 80 mm of the profiles, specifying the amounts of plane parts and parts occupied by profiles.

Figure 3b shows a scaled portion of the collector with the profiles to receive the irradiation at sunrise and at sunset, when transmitted heat is lower, with rays reaching the collector with an acute angle.

Figure 4 shows the diagram of the hydraulic circuit common to solar and auxiliary systems.

As previously mentioned and as will more clearly result from the following description, the present invention can be advantageously applied for producing electric energy without interruptions due to the integration of two systems, a solar and an auxiliary one, and a thermal energy store. With reference to the Figures, it can be noted that the automatic plant 10 according to the present invention comprises: the solar energy collector 8. To receive the thermal energy of the sun, the plant exposes to irradiation a metal plate with high conductivity and reduced cost, probably aluminium, whose thickness is for example equal to 10 mm. Such collector is preferably composed of modules cut at the size of 4, 000 x

1, 500) mm (6 m2) since they are sturdy, but sufficiently lightweight and easy to manage. The modules are laid in parallel bands orientate on the East - West axis. Such bands can also be obtained from a continuous ribbon. The solar collector is painted black or subjected to selective processes to absorb more heat from the sun. Its surface extension is computed depending on the site insulation and on the plant power. A layer of insulating material 9 is placed between collector and bearing yard. The collector is placed horizontally, the simplest and safest building solution, since possible vertical or slanted parts would require a cumbersome and uncertain fastening. the auxiliary system. The plant comprises a fuel-type auxiliary system 14 for heating water and guaranteeing the continuity of services in the periods of absence of insulation. Where available, fuel can be methane, GPL or other fuel. GPL has a calorific power of 6,070 kcal/litre, equal to 7.3 kWh. Assuming a cost per litre of 0.84 Euros, with 14 litres of GPL we have about 100 kWh with a cost of 11.76 Euros . the thermal energy stores. Essential component for the plant, they are a capable tank 1 resistant to positive pressures and containing water. The tank is the main store of thermal energy. Other thermal energy reserves are in the collector, in the hollow space between collector and covering glass and in the pressurized steam. The vessel made of steel, treated in its internal faces to resist to corrosion, is thermally insulated in compliance with the outside environment and is placed North of the collector to avoid shadows thereon. On the tank top, an opening can be obtained for letting a man pass, closed by a sealed cover for periodic inspections and cleaning from inside. The vessel volume and the amount of water contained, anyway of some tens of m3, is an important data for design. Water is the main store of thermal energy in the plant. The water level in the tank is controlled by a floater (not shown) or by another level control system. The pressure resistance of the vessel can approximately be equal to 20-22 atmospheres. The tank is placed in a closed room with perimeter walls 21 and a bellows 22 and abuts on a basement 20 with feet 2 equipped with regulating screws. Control, regulating and energy transfer instruments 23 are placed in the room. the turbine. A turbine 5 actuated by the steam keeps in motion a dynamo which supplies one or more batteries aimed to the various services of the plant and an alternator for producing the foreseen power. The turbine is in communication with the tank through a duct in which a pressure regulator 6 is placed, which regulates the pressure to the turbine. The automatic operation of the plant keeps pressures and temperatures at their maximum levels, activating with thermostat the auxiliary system to 10 or 12 bar and de-activating it next to 20 bar. With this plant management, the produced electric energy is kept at constant values. Without pressure regulator, the turbine would be activated at the pressure value which is allowed and would progressively produce more energy till its maximum pressure and temperature. The auxiliary system is disconnected due to the intervention of a thermostat next to 20 bar and the plant consumes the accumulated reserves with a progressive reduction of pressure and temperature. Upon reaching the lower set values, the auxiliary circuit is automatically restarted. the hydraulic circuit. The hydraulic circuit is common to solar and auxiliary systems in a collector, composed for example of 4 adjacent bands of 1.5 x 40 metres. In each band, there are one or more profiles with water passing pipe arranged on the whole length. From the tank 1 four pipes go out, two for withdrawing water identified with 11 and one for the return of heated water from solar and auxiliary circuits, identified with 15. In the solar circuit, the pump 12 pushes water into the circuit, similarly to the pump 13 for the auxiliary circuit. The two pumps have a variable flow-rate for the necessary regulations. In the solar circuit, piping in which water flows are placed in contact with the collector heated by radiation to absorb by conduction heat with the aluminium section, 5 millimetres thick, which mimics the excavation obtained in the collector and comprises the water pipe which transports heat by convection. The profile, as states, mimics on the bottom the excavation obtained in the collector to which is strictly connected with a system which allows a sliding due to heat. Heat transmission occurs with three modes: collector irradiation; conduction between collector and aluminium section with the ware flowing pipe as shown in Figure 2c; and by convection for water flowing in the pipes. The hydraulic circuit is composed of round pipes and aluminium, elbow or three-way fittings, obtained through melting or machined. The connections between pipes and fittings can be obtained through welding, but the preferred system employs metal dilatation of pipes due to produced heat. At ambient temperature, coupling is not possible. The female pipe, or an end thereof, is then brought back at a temperature of some hundreds of degrees to allow coupling. The resulting joint, after cooling, is stable, safe and resistant without leakages at every pressure which can occur in the circuit.

- one or more scarcely reflecting glasses 7 overlapped to the collector to exploit the greenhouse effect and protect the plant from adverse atmospheric events. Part of the energy which reaches the collector is re-inserted as infrared radiations whose wave length is greater than the sun Energy one. The glass cover is almost completely opaque to this type of radiations and the thermal energy reains trapped between glass and collector.

- at least one safety valve 4 for the overpressures.

- a possible independent system 16 for overheating the steam, placed between vessel 1 and turbine 5. The saturated steam is inserted into a chamber heated by a burner. Inside the chamber, a bunch of pipes is travelled by steam which, along the path, improves its title and reduce damages to the turbine blades.

- one or more batteries - a condenser 17 for recovering the evaporated water. The spent steam at the turbine outlet is channelled to the condenser.

- a vessel 18 for water coming from the condenser for following refilling; a pipe 19 which re-inserts it into the tank, when it receives the consent from the water level meter in the tank.

The present invention further refers to a process for producing electric energy, through an automatic plant 10 as previously described. In particular, the process according to the present invention allows producing energy without interruptions, exploiting the sun energy and a fuel-type auxiliary plant, and using water as thermal vector. In particular, the process according to the present invention comprises the steps of: a) filling with some m3 of water the capable, pressure- resistant vessel b) heating water contained therein both with the fuel-type auxiliary plant and with the solar system which receives the irradiation on a metal collector with high conductivity equipped with a plurality or round profiles which increase its irradiated surface with the same horizontal area being occupied c) circulating water in the hydraulic circuit common to the two system, withdrawing it from the vessel and returning it after having heated it. d) automatically activating the auxiliary plant 14 with thermostatic system when temperatures and pressures fall below a defined level and de-activating it to maximum values allowed by the pressure resistance of the tank e) using the thermal reserves accumulated in the vessel, in the collector, in the space between collector and glass and in the pressurized steam to keep the plant active till they are spent.

With respect to known techniques, the automatic plant 10 has the following innovative features: it allows operating the plant and producing energy also during the night and in periods of prolonged lack of irradiation it directly uses the solar thermal energy receiving the irradiation on a metal collector with high conductivity, having a surface exposed to the sun computed depending on the plant power and in the site insulation it increases the thermal amount of irradiation, creating round profiles on the collector which offer to sun rays faces which are always arranged orthogonally thereto it reduces the production cost per kWh it overlaps to the collector glasses with low emissions to exploit the greenhouse effect and protect it from adverse atmospheric events it uses water as single thermal vector. Water is heated separately or simultaneously in the two solar and auxiliary systems and circulates in the common hydraulic circuit it generates and keeps steam inside a pressure-resistant tank instead of directly transferring steam to the turbine, thereby avoiding continuous pressure and temperature variations. Temperatures and pressures do not depend on continuous and accurate regulation checks for air and fuel in the boiler and on the supply of water to be vaporized it creates thermal energy reserves in the tank, in the collector, in the space between collector and glass, in hydraulic circuits and in the pressurized steam it uses thermal energy reserves to shorten the intervention times of the fuel system and reduce the fuel consumption it uses all three heat transmitting systems, irradiation, conduction and convection it does not produce pollutants and does not increase C02 when it operates with the sun it makes available plants from 100 to 300 kW and more for producing electric energy widely directly from the solar irradiation, everywhere insulation so allows, excluding the coldest areas of the planet towards the poles.

The system is simple and the plant operates automatically, producing energy with reduced managing and maintenance costs. It does not require the use of fuel materials, does not generates residuals to be disposed of, has a logistics which does not require the presence of personnel, has no components subjected to wear. The plant can be installed everywhere there is enough solar irradiation, has a low visual impact, is silent, respects the environment and produces a minimum atmospheric pollution.

The present invention further refers to a process for producing electric energy, with an automatic plant 10 as previously described. In particular, the process according to the present invention allows producing energy without interruptions. In particular, the process according to the present invention comprises the steps of:

1) filling with some m3 of water the capable, pressure- resistant vessel

2) heating water contained in the vessel both with the fuel- type auxiliary plant and with the solar system which receives irradiation on a metal collector with high conductivity equipped with a plurality of round profiles which increase the irradiated surface with the same horizontal areas occupied, exposing the reflecting surfaces always orthogonally to the sun rays circulating water by withdrawing it from the vessel and returning it after having heated it and circulating it in an hydraulic circuit common to the two systems automatically activating the auxiliary system 14 with thermostatic system when temperatures and pressures drop below a defined level and de-activating it at maximum values allowed by the pressure resistance of the tank using the accumulated thermal reserves to keep the plant active till the reserves accumulated in the vessel get spent, in the collector, in the space between collector and glass and in the pressurized steam.