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Previous Work/Current Work

Improved Hybrid Solar Collector Has Higher Efficiency, Longer Lifespan

ScienceDaily (July 17, 2011) — For his graduation project, TU Delft student of Sustainable Energy Technology Stefan Roest developed a new type of hybrid solar collector with a higher efficiency and a longer lifespan than the current hybrid systems. Hybrid solar collectors combine photovoltaic solar cells that convert sunlight into electricity with a solar heater that provides warm water. Roest built a prototype and also built an actual solar simulator that he used to test the efficiency of his prototype. There turned out to be considerable commercial interest in this solar simulator. This motivated Roest and a partner to start the TU Delft spin-off company Eternal Sun, so they could put the solar simulator on the market. Eternal Sun recently came out on top at the European finals of the BE.Project, a competition for student-entrepreneurs. A hybrid solar collector is a combination of a photovoltaic solar panel and a thermal solar collector. The residual heat from the PV solar panel is used to heat water. The water flows through a system of pipes on a copper sheet. A great deal of heat is needed to heat the water in the pipes. That is why the solar collector has been fitted with a transparent cover that helps to retain the heat. Unfortunately, the material used in the PV solar cell degrades quickly under temperatures of around 120 degrees. As a result, its efficiency is reduced by around 20 per cent and it has a lifespan of between five and ten years. For his graduation research as part of a Master's degree in Sustainable Energy Technology, Stefan Roest developed a new type of hybrid solar collector with increased electrical efficiency and a longer lifespan. For a start, Roest's solar collector does not require a transparent cover. The water flows through a large number of small aluminium channels directly under the solar panel instead of through copper tubing and a copper sheet. Consequently, less heat is required to heat the water sufficiently for household use. Roest also chose not to use a crystalline silicon PV solar panel, opting for a thin film solar panel instead. It is easier to draw heat from this type of solar cell. Getting rid of the cover meant that the heat of the solar panel could be limited to around 80 degrees. An additional benefit of thin film solar panels is that these perform relatively well at high temperatures. At a temperature of 80 degrees, an efficiency loss of around 10 per cent occurs, instead of the 20 per cent in the case of crystalline silicon solar panels. Roest's hybrid solar collector has an estimated lifespan of 15 to 20 years. Roest developed the new solar collector under the supervision of the professor of Photovoltaic Materials and Devices, Miro Zeman, who comments: "This innovative design could play an important role in the development of affordable and efficient hybrid systems for household use."

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Theoretical

Photovoltaic

     Alexandre-Edmond Becquerel (24 March 1820 – 11 May 1891), known as Edmond Becquerel, was a French physicist who studied the solar spectrum, magnetism, electricity, and optics. He is known for his work in luminescence and phosphorescence. He is credited with the discovery of the photovoltaic effect, the operating principle of the solar cell, in 1839. He was the son of Antoine César Becquereland the father of Henri Becquerel.

      Charles Fritts was the American inventor credited with creating the first working solar cell in 1883.Fritts coated the semiconductor material selenium with an extremely thin layer of gold. The resulting cells had a conversion electrical efficiency of only about 1% owing to the properties of selenium, which in combination with the material's high cost prevented the use of such cells for energy supply. Selenium cells found other applications however, for example as light sensors for exposure timing in photo cameras, where they were common well into the 1960s. Solar cells later became practical for power uses after Russell Ohl's 1941 development of silicon p/n junction cells that reached efficiencies above 5% by the 1950s/1960s.

Thermoelectric

      Thomas Johann Seebeck; (9 April 1770 – 10 December 1831) was a physicist who in 1821 discovered the thermoelectric effect. Seebeck was born in Reval (today Tallinn, Estonia) to a wealthy Baltic German merchant family. He received a medical degree in 1802 from the University of Göttingen, but preferred to study physics. In 1821 he discovered the thermoelectric effect, where a junction of dissimilar metals produces an electric current when exposed to a temperature gradient. This is now called the Peltier–Seebeck effect and is the basis of thermocouples and thermopiles.

      Jean Charles Athanase Peltier  (French; February 22, 1785, in Ham – October 27, 1845, in Paris) was a Frenchphysicist. He discovered the calorific effect of electric current passing through the junction of two different metals. This is now called the Peltier effect or Peltier–Seebeck effect. The Peltier effect, where current is forced through a junction of two different metals, forms the basis of the small 12/24 volt heater/coolers sold for vehicle use. By switching the direction of current, either heating or cooling may be achieved. It also forms the basis of the rather expensive, but very stable, junction heated soldering irons, and is used for spot cooling of certain integrated circuits. Junctions always come in pairs, as the two different metals must be joined at two points. Thus heat will be moved from one junction to the other. To make a usable heat pump, multiple junctions are created between two plates. One side will get hot and the other side cold. An effective heat dissipation device must be attached to the hot side to maintain a cooling effect on the cold side. This is usually a heatsink and fan assembly.

tE eFFect

The term "thermoelectric effect" encompasses three separately identified effects: the Seebeck effect, Peltier effect and Thomson effect. This separation derives from the independent discoveries of French physicist Jean Charles Athanase Peltier and balt-German physicist Thomas Johann Seebeck. Joule heating, the heat that is generated whenever a voltage is applied across a resistive material, is related though it is not generally termed a thermoelectric effect. The Peltier–Seebeck and Thomson effects are thermodynamically reversible, whereas Joule heating is not.

 

            The Seebeck effect is the conversion of temperature differences directly into electricity and is named for the balt-German physicist Thomas Johann Seebeck, who, in 1821 discovered that a compass needle would be deflected by a closed loop formed by two metals joined in two places, with a temperature difference between the junctions. This was because the metals responded differently to the temperature difference, creating a current loop and a magnetic field. Seebeck did not recognize there was an electric current involved, so he called the phenomenon the thermomagnetic effect. Danish physicist Hans Christian Ørsted rectified the mistake and coined the term "thermoelectricity". The voltage created by this effect is of the order of several microvolts per kelvin difference. One such combination, copper-constantan, has a Seebeck coefficient of 41 microvolts per kelvin at room temperature.

            The Peltier effect is the presence of heat at an electrified junction of two different metals and is named for French physicist Jean-Charles Peltier, who discovered it in 1834. When a current is made to flow through a junction composed of materials A and B, heat is generated at the upper junction at T₂, and absorbed at the lower junction at T₁.

            The Thomson effect was predicted and subsequently observed by Lord Kelvin in 1851. It describes the heating or cooling of a current-carrying conductor with a temperature gradient. Any current-carrying conductor (except for a superconductor) with a temperature difference between two points either absorbs or emits heat, depending on the material.

            In metals such as zinc and copper, whose temperature is directly proportional to their potential, when current moves from the hotter end to the colder end, there is a generation of heatand the positive Thomson effect occurs. Conversely, in metals such as cobalt, nickel, and iron, whose temperature is inversely proportional to their potential, when current moves from the hotter end to the colder end, there is an absorption of heat and the negative Thomson effect occurs. If the Thomson coefficient of a material is measured over a wide temperature range, it can be integrated using the Thomson relations to determine the absolute values for the Peltier and Seebeck coefficients. This needs to be done only for one material, since the other values can be determined by measuring pairwise Seebeck coefficients in thermocouples containing the reference material and then adding back the absolute thermopower of the reference material. Lead is commonly stated to have a Thomson coefficient of zero; in fact, it is non-zero, albeit being very small. In contrast, the thermoelectric coefficients of all known superconductors are zero.

 

            For monitoring the performance of photovoltaic and thermoelectric, LabView has been used. Basically each renewable energy plant or system plants needs the monitoring control systems. Same as hybrid system, where the performances and parameters must be closely monitored and controlled, thus allow adequate data acquisition system.  The data acquisition system requires large number of measured data where very frequent recording necessary needs to be automated to eliminate the probability of human error as well as to save time. This project is mainly about computer based real time monitoring system center which use LabView as Graphic User Interface (GUI) to provide graphical display output chart, graph or pie chart.

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Research

            Photovoltaics are best known as a method for generating electric power by using solar cells to convert energy from the sun into electricity because of the increasing efficiency and ease of use. PV modules come in a huge variety of types and sizes and are used as the power solution for many different applications including residential and commercial grid-tie solar power systems as well as off-grid and industrial systems.

            Made most commonly using the  Silicon Crystal , solar cells essentially create electricity by converting photons of light into electrons. The "photovoltaic effect" occurs when photons of light from the sun strikes these cells, a portion of the energy is absorbed into the silicon, displacing electrons which then begin to flow. In order to harness this flow, the electrons are drawn into a magnetic field generated by positively- and negatively-charged metal contacts on the top and bottom of the cell. producing direct current, or DC, electricity. Using a DC to AC inverter, the DC current is converted to alternating current, or AC, which can then be used to power electrical appliances.

            Solar cells (SC) produce direct current electricity from sunlight, which can be used to power equipment or to recharge a battery.  Nowadays, the majority of photovoltaic modules are used for grid connected power generation. In this case an inverter is required to convert the DC to AC.

            A photovoltaic system consists of multiple components, including cells, mechanical and electrical connection and mountings and means of regulating and modifying the electrical output. Due to the low voltage of an individual solar cell typically 0.5V, several cell are combined into photovoltaic modules, which are in turn connected together into an array.

            Photovoltaic power systems are generally classified according to their functional and operational requirements, their components configurations and how the equipment is connected to other power sources and electrical loads. The three principal classifications are grid connected or utility interactive systems, photovoltaic hybrid system and PV stand alone systems. Photovoltaic system can be design to provide DC and AC power service, can operate interconnected with or independent of the utility grid and can be connected with other energy source and energy storage system. 

Advantages Photovoltaic

• No pollution and totally silent in process energy compare wind and water based from turbine and very noisy
•  Low cost maintenance and have a long lifetime
•  Not required large space to build. The solar panel can put on the roof top
•   Appropriate to use in Malaysia

The figure above show the solar panel which cell connected in series and parallel

           

 Thermoelectric is a device that converts heat into electricity and it is a two-way process. It can refer either to the way a temperature difference between one side of a material and the other can produce electricity, or to the reverse: the way applying an electric current through a material can create a temperature difference between its two sides, which can be used to heat or cool things without combustion or moving parts.

The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice-versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, it creates a temperature difference. At the atomic scale, an applied temperature gradient causes charge carriers in the material to diffuse from the hot side to the cold side.

            Thermoelectric modules are solid-state heat pumps that operate on the Peltier effect. A thermoelectric module consists of an array of p-type and n-type semiconductor elements heavily doped with electrical carriers. The array of elements is soldered so that it is electrically connected in series and thermally connected in parallel. This array is then affixed to two ceramic substrates, one on each side of the elements. Electrons can travel freely in the copper conductors but not so freely in the semiconductor. As the electrons leave the copper and enter the hot side of the p-type, they must fill a "hole" in order to move through the p-type. When the electrons fill a hole, they drop down to a lower energy level and release heat in the process. Essentially the holes in the p-type are moving from the cold side to the hot side. Then, as the electrons move from the p-type into the copper conductor on the cold side, the electrons are bumped back to a higher energy level and absorb heat in the process. Next, the electrons move freely through the copper until they reach the cold side of the n-type semiconductor. When the electrons move into the n-type, they must bump up an level in order to move through the semiconductor. Heat is absorb when this occurs. Finally, when the electrons leave the hot side of the n-type, then can move freely in the copper. They drop down to a lower energy level and release heat in the process.