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Elettromeccanica CMC srl has been an industrial partner in the research project funded by the Ministry of Education with ERDF funds and FdR of R & C PON.

This project, called IN.TE.R.RA, has as its objective the study and the development of technological and process innovations for irrigation reuse of urban wastewater and agro-industrial one for the purpose of sustainable management of water resources.

The partners of the project include University of Foggia, University of Bari, Polytechnic University of Bari, University of Salento, Council of Research and Experimentation in Agriculture (CRA), Mediterranean Agronomic Institute and the National Research Council (CNR), as well as other Apulian business realities.

Within this project Elettromeccanica CMC srl aims at innovating its own DWS system thanks to a more advanced automation, based on strictly scientific methods with a double result:

1) Optimize and rationalize water resource distribution thanks to withdrawals made according to actual cultivation needs;

2) Provide final users with a tool capable of autonomously managing irrigation according to cultivation needs and therefore optimize business management both in terms of time and money.

More specifically, Elettromeccanica CMC srl will develop an automatic water distribution system capable of planning irrigation by monitoring levels of soil humidity measured through wireless sensors opportunely placed on the cultivation area.

Humidity measurements shall be integrated by crop temperatures by means of infrared sensors capable of providing information by a radio transmission system. We will address technical problems relating to sensor arrangement on field (topology), and we will verify the most appropriate communication protocols as well as a use of hardware and software solutions capable of ensuring the best conditions for transmission of measured data, by minimizing device energy consumption.

This second-generation thermodynamic solar project is implemented by using three well-established and tested technologies with excellent results:

These three technologies are:
a) Solar concentration with sensing systems provided with parabolic mirrors heating receiver tubes suitable for molten salts transportation;
b) Storage of molten salts in isolated tanks provided with an hydraulic circuit for molten salts circulation (T=550°C);
c) Exothermic motors named Stirling, powered with water-cooled molten salts, with an efficiency of 24%-32% (24-32% of introduced thermal energy is converted in electric energy).

To date the use of Stirling motors coupled with molten salts coming from molten salt tanks has not been implemented yet in any renewable energy production plant.

Actually, molten salt technology was implemented by Professor Rubbia to feed plants with a power higher than 20 Mw by coupling the molten salt circuit with a hydraulic circuit provided with heat exchangers generating saturated steam to be introduced in steam turbines connected to 3-phase alternators. This technology is characterised by four limitations:

1) these plants are water-scooping plants even though they are equipped with condensers and coolers of the cooling tower type. Water losses for steam are equal to 27% of total used water.
2) Maximum plant efficiency does not exceed 18%. (18% of introduced thermal energy is converted into electrical energy).
3) High conversion losses, equal to about 29% of thermal energy contained in heat exchanger steam circuit.
4) Plant size. A size smaller than 20 Mw makes the construction of such plants not particularly cost effective.

Process Innovation proposed in the second-generation thermodynamic solar project.
The use of Stirling motors allows a drastic reduction in size since the accumulation tanks are not grouped, but distributed. Such accumulation tanks 8×3mt large and 3mt high have a low cost and allow accumulation of 72 m3 of molten salts.
There is no need for tank interconnection since a stand-alone system will feed Stirling motors for 48 hours with a global production power of 200 kw.
Stirling motor cooling is obtained through a water circuit feeding a radiator and allows a thermal spread from 80°C to 35°C.

The modular structure of the plant allows replication without significantly increasing final plant complexity.
Energy losses due to waste heat are of about 16%.
Molten salt hydraulic system complexity is limited thanks to the absence of parallel connection pipes leading to the only storage centralized tank.
Product Innovation proposed in the second-generation thermodynamic solar project.

The following products were studied, designed and innovated.
a) Molten salt tank with diffuser and aluminium pipe pre-heater
b) Support structure of mirrors and heating pipe located in dish focal point
c) Stirling motor for the production of electric power with a rated capacity of 35 Kw and a weight of 400 kg
d) Molten salt heat exchanger (T=550°C)
e) Water heat exchanger (T=300°C).
f) 3-phase linear alternator with mobile permanent magnets, operating at 350°C

Second-generation thermodynamic solar project prototyping

Prototyping will be split into two phases:
The first phase will concern construction of Stirling motor, heat exchangers and 3-phase linear alternators and performance of tests and measurements relevant to alternator motor system for 500 hours of operation.
The second phase will concern construction of a CSP plant with accumulation tanks for molten salts, pumps, valves and automation of pump and valve control devices, test and measurements relevant to the CSP plant system and of an accumulation tank for 500 hours of operation.

Wind turbines are the most common wind powered system and considered as a wind machine by definition.

The main issue with these generators is not represented by low energy that air masses can provide but rather by their irregularity. Actually, energy contained in air masses does not increase linearly with speed but has an exponential trend. This means that a speed of 2 m/s produces a pressure on blades equal to 8 kg/m2 whilst if wind speed raises to 3 m/s pressure immediately jumps to 27 kg/m2, or if speed is of 4 m/s pressure reaches 64 kg/m2, and so on.

If we reflect upon this data we can notice that if wind speed doubles (from 2 to 4 m/s), pressure on blades becomes 23 times greater (from 8 to 64 kg/m2). If winds were constant, it would be sufficient to calibrate wind turbine according to the pressure exerted, but often winds change their direction and intensity and change from strong burst to light breezes. Therefore, the main issue is not to sense the wind but to safeguard wind turbine integrity, particularly generator rotors when the wind blows hard or with burst, and well control it in order to maintain the most suitable direction.

The first issue, that is a wind speed higher than the “cut off” speed, can be addressed by acting in such a way to have a zero yawing angle of blades, or by rotating wind turbines so that they do not fight against the wind. The other wind turbine characteristic speeds, in addition to “cut off” speed, are the rated speed, that is a speed allowing generator to operate at full design load; and “cut in” speed, that is the minimum wind speed under which it is not worth to produce energy, and no power is obtained from the wind turbine.

Conversely, limit speed is a safety speed, that is a speed for which the wind turbine was designed from the structural point of view; beyond such speed, structure mechanical resistance could collapse and irreparably damage the wind turbine.

Wind turbine power control system with stall is based on yaw control.

A yaw control system of wind turbine provides for a limitation of power in response to nacelle rotation in the wind in order to maintain the rotor in a direction that is no longer orthogonal to flow. Such “yaw controlled” system is used only for horizontal axis turbines provided with stall. It must be noted that a passive stall control system is the only method for power control available for horizontal axis turbines. Such technology permits less accurate controls with respect to an active system and, generally cannot leave aside the use of mechanical or aerodynamic brakes able to stop the rotor in case of emergency.

The designed yawing control system can be implemented on any wind turbine provided with stall and envisages the use of an electronic speed control device and of a motor-driven device for controlling windvane- additional rotor reference system and of an additional rotor-nacelle control system.

The additional rotor-nacelle control system is directly regulated and controlled by the original wind turbine control system, whilst the windvane-additional rotor control system is regulated and controlled by an ad hoc electronic device, which considers power limitation imposed by a user as well as electric power produced by an electric generator.

IN SUMMARY

The “cmc-yawc” power controller with wind turbine active stall, through nacelle yaw control is a universal control system based on microprocessors, allowing control of power as a function of wind conditions, air density, etc. It is added to wind turbine control system, originally deprived of pitch control, in order to lower power to the desired value, for example to the maximum power available for feeding the grid.

When wind conditions tend to exceed threshold power, the controller intervenes by controlling turbine yaw in order to reduce the mechanical power transferred to generator.

This system functions electronically without installing any heat sink or other power devices. It will be supplied already programmed for the desired power control (e.g.: 150 kW generator, maximum power to be delivered: 60 kw).

Prototyping provides for:

1) Construction of a wind generator, 1:5 in scale of a size comprised between 3 and 6 kw provided with yaw control and of a 3-phase asynchronous generator for wind turbine control system.

2) Construction of a yaw control system separated from turbine control.

3) 500 hours’ test of yaw control system and output electric power regulation when environmental conditions change.