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IFToMM Technical Committee - Sustainable Energy Systems

I. Visa*

Transilvania University of Brasov Brasov, Romania

Abstract — Sustainable energy is a concept that integrates energy efficiency, energy saving and renewable energy systems, as a path towards a fully clean (and green) energy pattern. Implementing sustainable energy represents a must for sustainable development and, if well exploited, it can represent a significant source of economic growth. RTD is expected to bring the concrete solutions, able to be fast implemented in the industrial, and more largely in the economic areas. The development of high-tech products, designed, manufactured and working in energy efficient processes, without wastes, promoting and supporting the energy production from renewable sources represents a pre-requisite for advances in energy production, automotives, robotics, medical engineering, environment depollution, etc. In this frame, the science of machines and mechanisms is strongly involved and case studies on already existent products/processes are presented in the paper. At international level, to coagulate the efforts and harmonize the research, education and technology transfer results, obtained especially in the field of mechanisms in sustainable energy systems, a new IFToMM technical committee was approved. The aim, objectives and provisioned activities of this new TC, Sustainable Energy Systems, are presented in this work.

Keywords: Sustainable energy systems, Tracking systems, IFToMM Technical Committee

I. Sustainable Energy Concept

Sustainable energy represents a complex concept emerged in the past two decades as an answer to two major threats: the resources depletion (mainly related to fossil fuels) and the global warming as main result of greenhouse gases emissions from fossil fuel burning. Thus, this concept supports the transition from the actual energy pattern – fossil fuel based to a future “green energy” pattern, heavily based on renewable energy sources. This transition involves complementary measures for reducing the wastes during energy production and distribution (energy efficiency) and during energy use (energy saving), along with the continuous development of the renewable energy systems using as sources the sun, the wind, the water power, the geothermal or tidal power, etc. Thus, sustainable energy must be discussed in terms of renewable energy systems, (process) energy efficiency and energy saving (products).

* visaion@unitbv.ro

The implementation of this concept is today in different stages, between RTD and mass production, with various degrees of development; of course, energy efficiency and energy saving measures are mostly addressed in terms of products and processes re-design, although breakthrough is expected from RTD, [1]. The development of renewable energy systems reached a mature level for certain systems (large hydro systems, large wind turbines), but still requires plenty of RTD work for most of the applications (sun energy conversion, small wind turbines, small hydros, geothermal systems, etc.). The interest for this topic is far from being only conceptual: the long term target is represented by fundamental changes in the production and consumption model of the humankind but, on short term view, these changes, if well exploited can represent a source of economic growth and of new industries development, based on already existent professional skills. In Europe, in 2008, the European Parliament proposed the 20/20/20 directive; this came in force in 2010 providing concrete targets, by 2020, for each member state in terms of renewable energy systems implementation (an amount corresponding to an average 20% from the total energy consumption will be obtained from renewables), also considering a reduction of 20% of the greenhouse gases emissions and an increase by 20% in the energy efficiency, [2]. This is why European governments developed coherent action plans which set concrete targets for sustainable energy implementation, within this given timeframe. This trend was also adopted by other countries, all over the world, and the result is a complex of economic, technical and scientific actions aiming to develop solutions for sustainable energy, to develop an incentive policy for implementing them to the industrial actors (most of them are SMEs, [3]) and for activating the markets, and to develop the horizontal measures able to support them (education, adults training, societal awareness, etc.), [4]. In this global context, the science of machines and mechanisms has to respond to the new challenges for developing high-tech products, which strongly imply the need to develop, analyze and optimize the mechanisms considering the reduction of energy consumption during driving (Energy Efficiency), the decrease in energy losses during functioning (Energy Saving) and the development of novel solutions for Renewable Energy Systems with high conversion efficiency, maximizing the

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use of renewable energy sources (solar radiation, wind, water flow, biomass and biofuels, tides, geothermal energy, etc.). This also complies with the strong need for developing, in an interdisciplinary approach, novel concepts and results for high-tech applications, able to be transferred towards industry. The paper presents significant case-studies on the role of mechanisms in promoting Sustainable Energy Systems and details on the new IFToMM Technical Committee that was launched in November 2010, as a frame for promoting integrated RTD, education and awareness as an answer to this identified need.

II. Mechanisms in Sustainable Energy Systems – Case studies

A. Sun-Tracking Systems for Individual Modules

Solar energy conversion is intensively studied since this resource is readily available, all over the Globe distributed, and provides power (in photovoltaic – PV - systems) or heat (in solar thermal systems) without any by-products and wastes. This makes solar energy conversion one of the most promising alternatives for the “green energy future”. But, for large scale implementation, the conversion efficiency must be significantly improved and the systems costs must be lowered. The energy output obviously depends on the amount of solar radiation and on the decrease of losses during conversion. Solar radiation has two main components: the solar direct radiation (received directly, unperturbed from the sun and representing between 40…80% of the total radiation) and the diffuse solar radiation (received by scattering). One characteristic of the solar radiation is its variability: during one day (from sunrise to sunset), due to clouds, dust, water droplets, and during one year (seasonal variation). These affects the amount and quality of the solar radiation (and energy), especially the solar direct radiation which is essential in the photovoltaic conversion. To increase the amount of solar radiation received by a solar convertor (PV module, solar collector) one solution is to develop mechanisms to orient the convertor for getting the direct radiation normal to the convertor’s surface. These are called tracking systems and usually they are mono- or bi-axial mechanisms. The energy needed to drive the tracking mechanisms must be as low as possible, therefore stepwise tracking algorithms are recommended vs. the continuous ones. Adding a tracking mechanism obviously raises the costs, thus, the optimal devices must be as simple as possible (from a constructive point of view) and must reproduce the sun path with high accuracy (usually estimated by the tracking efficiency). These are the prerequisites of many studies developed in the past years, [5…8].

The studies started in the Transilvania University of Brasov, in 2004, covered a broad range of aspects related to the sun tracking mechanisms adapted to PV and solar-thermal panels, to PV platforms and to PV strings imposing a supplementary prerequisite, linked with the need to integrate the solar energy conversion systems into the built environment. This prerequisite was mirrored in the need to limit the mechanisms dimensions and to develop systems acceptable from an architectural point of view. Mechanisms based on actuator(s) and gears proved to be optimal for these applications. The single axis mechanisms have a simple construction and are recommended for solar-thermal convertors (especially for trough collectors) which use both the direct and the diffuse solar radiation. Using the Multibody System Method (MBS), the families of mono-axial tracking systems could be developed with various degrees of complexity. Between the mobility, M, the number of bodies, nb and the total number of geometric restrictions, Σrg, the following correlations can be developed, [9]: - for planar multibody systems:

3(nb -1)- Σrg = M (1)

- for spatial multibody systems 6(nb -1)- Σrg = M. (2)

The mono-axial tracking systems have M = 1 and, in the simplest design, have two bodies, nb = 2, Fig. 1:

Fig. 1. Mono-axial, two bodies tracking mechanisms

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Similarly, solutions with M= 1 and three number of bodies (nb = 3) were identified, as presented in Fig. 2. These solutions allow higher accuracy and, based on the conceptual design prerequisites, the adequate solution for a particular situation can be chosen, [10].

Fig. 2 Mono-axial, three bodies tracking mechanisms

The PV modules need a higher tracking accuracy, therefore, most of the studies were focused on bi-axial tracking systems. In the bi-axial tracking of the PV modules, there usually are used three angular systems, used in describing the current angular position of the sun-ray and in the structure of the bi-mobile open chains (BOC) of the tracking linkages, [11]: a) The Equatorial System based on (in this order) the hourly and the declination angles; the BOC, resulted by serial connection of the 2 rotations, is denominated as equatorial or polar BOC. Due to its complexity this solution is seldom applied;

b) The Pseudo-Equatorial System, Fig. 3, using the seasonal and the daily angles of the module with the sun; the BOC, obtained by serial connection of the 2 rotations in the given order, is called pseudo-equatorial or pseudopolar; the pseudo-equatorial BOC results from the equatorial BOC reversing the connection order of the 2 rotations.

c) The Azimuthal System, Fig. 4, using the azimuth and the altitude angles; the BOC, resulted by serial connection of the 2 rotations is called azimuthal BOC and is widely applied for tracking large platforms and strings.

In most of the existing trackers, the angular movements with strokes ≤ 90o are made with linear actuators while the angular movements with high strokes (≥180o) usually use rotary actuators, more expensive. Extending the use of the linear actuators for the movements with large angular strokes was proposed, [11] and proved efficient.

Fig. 3. Pseudo-equatorial tracking system with planar amplifier

mechanism, [9]

0

1

2

4

5

3F

E

G

D C

B

A

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Fig. 4. Azimuthal tracking system with planar amplifier mechanism, [9]

Using the Multibody System Method (MBS), the family of bi-axial tracking systems could be developed with various degrees of complexity, with three (see Fig. 5), and four bodies, (Fig. 6).

Fig. 5 Bi-axial tracking system with three bodies and two decoupled motions, chain RTRR, [12]

Developing a bi-axial tracking system using a single actuator for driving both motions represents the next step approached, under the demand of lowering the tracking costs, while insuring a good tracking accuracy. The

studies, [13 – 15] proved that the only possible configuration corresponds to an azimuthal tracking system.

0

3

4

5

2

1

AB

C

D

E

G

F

(a)

(b) Fig. 6 Bi-axial tracking system with four bodies and two decoupled

motions: (a) two mono-contour chains RTRR ┴ RRRR; (b) two mono-contour chains RTRR ┴ TRRR, [12]

The proposed azimuth adjustable solar tracking linkage using a single actuator for a bi-axial orientation, presented in Fig. 7 consists of a vertical pole (0), a fork (1), a PV module (2), a swing (3), a vertical shaft (4), a slide (5) and their links: the rotating joint (0, 1) describing the system azimuth axis (driven by a rotating actuator), the rotating joint (1, 2) defining the system elevation axis, the swing connections (2, 3) and (3, 4) consisting of two Hook joints, the rotating joint (4, 5) – parallel with the azimuth axis and the prismatic joint (5,

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0) driven by a screw mechanism that adjusts manually or motorized the relative position between pole (0) and slide (5), [16].

 

Fig. 7. The kinematical scheme of the bi-axial azimuthal tracking system with a single actuator

The working conditions imposes three restrictions, for the limitation of β1 elevation pressure angle, Fig. 8, and other two working restrictions for the β2 and β3 working angles, Fig. 9.

Fig. 8 PV Tracking system of azimuthal type with a single actuator – working angle 1, [16]

 

(a)

(b)

Fig. 9. Working angle 2 (a) and 3 (b) in the bi-axial azimuthal tracking system with a single actuator, [16]

Fig. 10. The available direct solar radiation (B-sun) and the direct solar radiation normally received by: the PV system tracked with the biaxial system with two actuators (B_2 axis), the PV system tracked with the biaxial system with one actuators (B_RRSS), and by a fix tilted PV

system (FixT.).

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The accuracy in reproducing the sun path (the tracking efficiency) is for this new solution of 93%, while an azimuthal tracking system with two actuators reaches as much as 99%. Still, the in-field data prove that under outdoor conditions, this efficiency is very good. Comparing to a fixed and optimally tilled module, the average increase of solar radiation normally received on the PV surface is close to 30%, Fig. 10. B. Sun Tracking Systems for PV Platforms

Tracking is particularly recommended to be used in PV platforms when a single mechanism drives a frame containing a number of modules. According to the needs and the implementation conditions, there already are developed and installed large PV platforms (40…200 modules), average platforms (10…40 modules) or small PV platforms (up to 10…12 modules), the latest being particularly suitable for integration in the built environment. Based on the studies developed for PV modules, the RTD group in Transilvania University of Brasov has developed various solutions for small PV platforms. The first platform developed and installed was designed as an outdoor testing stand for RTD purposes, [17] aiming to give answers to a complex of questions: which are the suitable PV modules (in terms of materials and manufacturing technologies) to be implemented in the mountain area; which is the optimal driving algorithm considering the location (mountain area), and the weather conditions (clouds, temperatures, frost, fog, etc.); which is the optimal connection among the modules, on the platform; which is the energy gain comparing to a fixed and optimally tilled platform. Therefore, the platform contains four types of modules (three silicon based and one ceramic – CIS) and has various connection patterns among the modules.

Fig. 11. Pseudo-equatorial tracking for a PV platform, [18]

The platform is tracked by a bi-axial tracking system of pseudo-equatorial type. The dynamic orientation mechanism is described in Fig. 11. The PV platform tracking combines a hydraulic rotational engine, for the daily motion, with a hydraulic cylinder for elevation adjustment for seasonal orientation. The PV platform was manufactured and installed in the university campus, Fig. 12, and the data already acquired allow significant conclusions about the average energy gain of about 18% (using as reference a three array, 10kWp fixed platform installed in the same area) and about weather parameters that strongly influence the photovoltaic conversion, especially temperature. The results prove that tracking, although insuring the maximum amount of direct radiation onto the module, also results in an increase of temperature on the module and thus a decrease in the solar-to-power conversion efficiency. This opens a broad field for new studies in the future.

Fig. 12. Tracked PV platform (front view) and fixed and tilled PV platform (background image) in the Transilvania University of Brasov

Increasing the solar energy amount on a PV module can also be done by using light amplifiers. These can be mirrors or lenses, insuring a magnification factor up to x5 (with mirrors) and up to x200 for lenses. Still, using lenses requires a special design, including a heat dissipater; therefore the use of lenses is recommendable in common, low cost applications. The concentrating PV systems (CPV) must combine a significantly increased

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efficiency with small overall dimensions, therefore, the optimal length and disposal of the mirror(s) is subject of optimizing. Supplementary, to be effective, the use mirrors must be combined with highly accurate tracking. Studies have proved that a doubling of the solar radiation amount can be expected by using a simple constructive system, with two mirrors laterally disposed to the module, as presented in Fig. 13:

Fig. 13. Low solar concentrating system build up by a photovoltaic or hybrid module and two laterally disposed mirrors, and (b) the energy

gain on the module, [19]

(a)

(b) Fig.14. Variations of total direct radiation that falls normal on PV, at

different values of angle θ, compared with the PV direct radiation without mirrors, at different values of angle υM :

a) υM= 1,875° and b) υM= 15°.

The value of the mirror angle inclination (θ) and of the solar ray incident angle (νM) must be subject of accurate control since they strongly influence the amount of solar radiation on the PV module. This is particularly important at low incidence angles, as presented in Fig. 14.

C. Other mechanisms in renewable energy systems

There are renewable energy systems directly converting the mechanical energy, from water or wind, into power. Small hydro-systems are therefore typical examples of fields where the science of machines and mechanisms can significantly contribute. Developing efficient speed increasers with conveniently high ratio, high efficiency and low cost, represents a research target. A patent lately submitted and under evaluation, [20], proposes a Turgo turbine with chain planetary speed increaser (one satellite gear) while other new openings are linked with precessional transmissions. A very small wind turbine (output power up to 1.5kW) was designed and developed, [21] for testing various solutions for the blades (materials, shape, positioning in the rotor). The tests on the stand, using a wind tunnel, proved that blades of composite materials, with trapezoidal shape can reach good conversion efficiencies, at very low production costs. The blade pitch motion allows the orientation according to the wind potential and speed, and contributes to the conversion efficiency. The prototype has a flexible design, allowing testing different types of blades, mounted at different angles, Fig. 15.

Fig.15. Small wind turbine prototype Small wind turbines (1.5….50 kW power output) can also be implemented in the built environment when, along with the efficiency, the design plays a key role. Most of the small wind turbines, integrated in the built environment are vertical axis wind turbines (Savonius, Darrieus, Musgrow, Evence). Many solutions were proposed and are still expected to emerge, combining

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mechanical efficiency with (many times) a futuristic design.

D. Sustainable energy systems in the car industry

The car industry is one of the most dynamic sectors, where RTD results are fast implemented. Developing sustainable transportation, especially targeting the cars, requires a complex of actions. Specific constructive modifications for the vehicle must be considered when discussing sustainability [22]. As usual, one path is to increase the energy efficiency; the improvement of the engine can decrease the fuel consumption per 100 km in internal combustion engines (ICE). On the other hand, energy saving, particularly energy recuperation can represent another alternative, [23]. Kinetic energy recovery can be done from the breaking system and stored in a fly-wheel system while thermal energy can be recovered from the exhaust gases resulted from the engine and used for electrical energy production. At the same time cars involving renewables (especially photovoltaic modules) were developed at prototype stage and could be a future alternative for hybrid or electrical cars. To have these type of cars in large scale production (at an affordable cost) all the components should be re-designed in a certain degree, focusing on weight reduction and increasing efficiency and the science of machines and mechanisms is expected to bring valuable solutions. All these openings, most of them at RTD stage, must be supported by adequate education and training, providing the human resources able to bring breakthroughs via research. Afterwards, professionals are needed to take up the RTD results and implement them in manufacturing systems; once at mature stage, professionals are needed to design, implement and insure the maintenance of the sustainable energy systems. Thus, the approach in studying machines and mechanisms must include these new trends and should be based on a combination of fundamentals and software design. Project based learning (with concrete project subjects) and team working are also necessary for the today’s and tomorrow’s professionals.

III. The IFToMM Technical Committee: Sustainable Energy Systems

Based on extended analysis of various case studies, it became clear that there is needed to develop a structure supporting the trend of sustainable energy systems. In October 2009, during the IFToMM – SYROM Conference the idea of a new TC emerged and was well received by the IFToMM officials participating in the conference. In January 2010, a group from ARoTMM

(the Romanian Branch of IFToMM) coming from the Transilvania University of Brasov submitted a draft proposal to the IFToMM board and the feedback received in February contained valuable improvement solutions. After an intensive work, involving the initiative group and the IFToMM board (especially the President, Prof. Ceccarelli, the General Secretary, Prof. Cajun and Prof. Rooney), the new TC got a provisional approval, in August 2010, and the coordinator of the initiative group, Prof. Visa was invited to present this initiative to the IFToMM EC, in November 2010, in Tunis, when the new TC was unanimously approved by all the EC members. The Technical Committee Sustainable Energy Systems has formulated a set of objectives, aiming to develop a collaborative framework for research and education on machines and mechanisms, considering the sustainable energy concepts for Energy Efficiency, Energy Saving and Renewable Energy Systems: O.1. Promote research and development in the field of

Machines and Mechanisms considering the Sustainable Energy action lines.

O.2. Broaden contacts among persons and organizations of different countries and territories engaged in scientific or engineering work in the field of Machines and Mechanisms, designed for energy efficiency, energy saving and applications in renewable energy systems.

O.3. Promote the exchange of scientific and engineering information and experts in the field of advanced machines and mechanisms for sustainable energy.

O4. Promote the Sustainable Energy concept in IFToMM conferences and events, in scientific journals and other special publications.

O.5. Encourage the visits of experts and students amongst countries and territories, either as individuals or as teams.

O.6. Establish the necessary relationships with other international organizations and unions whose activities are of interest to the TC Sustainable Energy Systems.

These objectives will be put in force by specific activities: A1. Develop a collaborative frame of working groups,

active in the field of mechanical systems for sustainable energy; networking amongst research, education and industry groups is a pre-requisite for successful activities, with real impact in the economic area.

A2. Joint development of complex projects, strengthening the resources, experience and expertise of the groups.

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A3. Joint development of education and training guidelines and courses, preparing graduates for the real needs identified in the labor market.

A4. Organizing of thematic scientific events as part of IFToMM events and/or developing specific events in the frame of IFToMM.

A5. Developing the instruments for dissemination of the TC activities: web-site, specific publications (monographs, journal).

So far, this new TC has 19 members from 14 countries (in alphabetical order): Canada, Germany, India, Italy, Japan, Mexico, Moldavia, Poland, People’s Republic of China – Beijing, People’s Republic of China – Taipei, Romania, Singapore, Spain and United States. During the next months the kick-off meeting of the new TC is planned and the Action Plan will be formulated in its final form. One first action was to ask the 2011 IFToMM Congress organizers to include a specific section, with emphasis on sustainable energy systems, which was approved and is now running.

IV. Conclusions

1. Sustainable energy represents a complex concept, aiming to insure the transition from the fossil fuel based pattern of a full green energy model. This concept embedded renewable energy systems with increased energy efficiency in the process and with performant energy saving products.

2. Sustainable energy systems are containing novel

solutions developed for increasing the energy efficiency, decreasing the losses and/or developing renewable energy systems.

3. Applications of sustainable energy systems are

many, ranging from new/advanced solutions for solar energy conversion (tracking systems for photovoltaic or solar-thermal systems, tracked solar radiation concentrators) or for small hydros (speed increasers) and small wind turbines, up to automotives, robotics, etc.

4. For developing sustainable energy systems,

RTD, education and training are needed for new openings, for design and manufacturing, for implementation and maintenance.

5. Recognizing this need, IFToMM launched a new Technical Committee, Sustainable Energy

Systems, that aims to integrated develop the frame and instruments for promoting these systems world-wide.

References

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[17] Comsit M., Visa I., Duta A., Tracked PV Platform System For Outdoor Testing, 23 EU PVSEC, Valencia, 2008, (CD based proceedings).

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[23] Duta, A, Visa, I., How sustainable is the sustainable transportation?, Proceedings of CONAT, 3, 2010,pp. 299 – 307.