Chemical Energy Sources Transformations by Remote Experiment

The paper describes the first experience with the set up, functioning and data evaluation of the remote experiment “Energy transformation” accessible via Internet (http://remotelab10.truni.sk ) as a part of the e-laboratory at the Department of Physics, Faculty of Education, Trnava University in Trnava, Slovakia. The remote experiment control and data acquisition is based on the system ISES (Internet School Experimental System) and its control program and www page are built using the environment Easy Remote ISES. The main goal of the experiment is the elucidation of the energy transformations of three types of well known energy sources – photovoltaic cell (solar energy to electrical energy), electrolyzer (electrical to chemical energy of hydrogen) and fuel cell (chemical energy of hydrogen to electrical energy) and finding optimal regimes for their maximum efficiencies. The perspective of the improvement of the experiment and its exploitation is given.


INTRODUCTION
The energy is one of the most important physical quantities, but in the general sense it constitutes one of the most vital topics in contemporary society [1]. Surprisingly, little is known and still less is taught at all types of schools about functioning, for society vital, devices that serve as transducers of one type of the energy to another and/or means for energy storing [2].
Remote labs can expand the capability of conventional laboratories also in the field of energy transformation by increasing the number of possibilities in which a student can perform experiments [3,4], while also increasing the availability of the laboratory to many students.
The purpose of the present work is the characterization of several well known energy transducers using interactive remote experiment (RE) "Energy transformation" (http://remotelab10.truni.sk). The experiment is built and located at the Trnava University in Trnava, Faculty of Education, Department of physics, as a part of Internet Natural Science Remote e-Laboratory -INRe-L [5].
The layout of the paper is following. First, we give briefly the construction of the RE with the set of energy transformation devices, followed by its technical realization and brief description of the corresponding physical basis. In the last part of the paper we show the measured data and their evaluation of the individual energy transducers, characterized by their energy transformation efficiencies (solar cell, electrolyser and fuel cell (FC)).

II. EXPERIMENT WITH ISES
For the building of RE Internet School Experimental System (ISES) was used [6]. ISES consists of the plug and play physical software (SW) and hardware (HW) for school experimentation. The physical HW is composed of the ISES panel and the set of easily interchangeable sensing modules and sensors (relevant details are described in [7]).
The physical HW of the RE experiment "Energy transformation" is in Fig. 1. The technical arrangement is composed of the ISES panel (1) with the set of ISES modules: 2x ISES V-meters, 2x ISES A-meters and the analogue input on the ISES panel. The physical HW include the several additional modules: photovoltaic panel JT010(17)P360x296 (2), electrolyser "V#U-TU OSTRAVA PC001" with the solid Proton Exchange Membrane (PEM) (3), hydrogen flow meter OMEGA FMA1802 (4) and hydrogen fuel cell from NTL company DT775-1B "inno" (5). In the Fig. 1 is not visible the solar simulator.
To transform the hands-on experiment to RE using the communication scheme server-client we used the environment Easy Remote ISES (ER ISES) enabling the compiling of RE control program and clients web page without programming using the approach of plug and play based on the Java applets (in later versions Javscript) [8].

A. Energy efficiency of the solar cell
The radiant energy transformation to the electrical energy is the demanding physical process. The efficiency of this conversion is described by the relation between the maximal electrical power P elmax , to the external load (here electrolyser) and the P radiation power radiation el efect photo (1) The conversion efficiency may be expressed as a product of partial efficiencies [9] FF where ! r = P abs /P rad = 0.70 is the efficiency factor expressing the part of the reflected radiation (taking average reflectivity to be 0.30 [10]), defined by the quotient of the absorbed flux to the impinging flux (P rad = P abs + P refl ), ! e = 1 -T / T lamp = 0.77 is the Carnot efficiency, T = 300 K and T lamp = 1300 K is the temperature of the source; ! p = 0.15 [11] is the efficiency factor due to the loss of a part of the radiation due to the mismatch of bandgap to the spectrum of the lamp (taken as blackbody radiator at the temperature T lamp = 1800 K); ! el is the efficiency due to the cumulative electronic parameters of the cell, accessible to the measurements, where I sc is the short circuit current of the cell, U oc is the open circuit voltage, FF is the fill factor and U m, I m are the voltage and current for the maximum electrical power.

B. Efficiency of the Electrolyser
Electrical energy obtained in the first energy transformation step (solar energy $ electrical energy) is transformed in the following step into the chemical energy in the form of hydrogen and oxygen by the process of electrolysis. The principal part of the experiment is the proton exchange membrane (PEM) of the electrolysis unit. The following reaction occurs in the electrolyser: In electrolysis, the applied voltage must be at least as large as theoretical cell voltage in order for a current to flow. Hence, from mentioned facts we can calculate the theoretical value of this voltage from the free enthalpy of reaction %G (F -Faraday's charge (C&mol -1 )) From the point of view of the thermal balance it is important to know the value of threshold voltage of the cell . Up to this voltage (6) the electrolyser works without heat generation and when exceeded, the electrolyser starts to produce heat and its efficiency drops. The efficiency of the electrolyser with respect to the delivered electrical energy per unit time (power P PV ) is defined where E V of H2 -combustion energy of produced H 2 (J) per time unit and the E PV -electrical energy from PV panel (J) per time unit.

C. Efficiency of the Fuel cell
In the fuel cell the chemical energy of the hydrogen and oxygen is directly converted via chemical reaction into electrical energy. Hydrogen and oxygen react to form water, giving up free charge carriers and the heat PAPER CHEMICAL ENERGY SOURCES TRANSFORMATIONS BY REMOTE EXPERIMENT The maximum theoretical efficiency of the fuel cell The efficiency of the fuel cell with respect to the produced H 2 by electrolyser, may be defined by two efficiencies, the electrical efficiency ! FC-el and the chemical efficiency (also referred as Faraday's) ! FC-chem of the generated hydrogen where E el -electrical energy supplied to the load per time unit, E V of H2 -energy content of hydrogen per time unit, V th -theoretical volume of produced H 2 , V exp -measured volume of produced H 2 .

A. Efficiency of the solar cell
Maximum electrical power P el of the PV panel as determined from the data in Fig. 3 and corresponding current and voltage for the maximum electrical power I m = 0.456 A and U m = 3.63 V.

B. Efficiency of the electrolyser
The efficiency of the electrolyser can be calculated using (7) where value of E PV (electrical power from PV panel) calculated as the integral of power supply (P el in Fig. 4) (15).
The value of E V of H2 is determined from Fig. 4 where /min ml 53 .  The second efficiency -Faraday efficiency (! FC-chem ) is the ratio between the theoretically calculated volume (V th ) of hydrogen consumed by FC and the experimentally calculated volume of hydrogen consumed (V exp ). At the standard pressure and temperature, the volume of H 2 is 24000 ml/mol. The electrical charge of one mole of electrons is given as 96500 C. Since there are two moles of electrons involved, the electrical charge deliver by one mol of H 2 is 96500 C x 2 = 193000 C.  At the present stage of the remote experiment "Energy transformation" the remote experimentators study the energy transformation of the photovoltaic panel at the fixed illumination at several predetermined light intensities. In the next development of the experiment we intend to build in the rotation of the light source and continuous change of irradiation of the photovoltaic panel as a next parameter for optimizing the experiment. Thus, the hydrogen output and working regime of fuel cell may be studied and optimized.
VII. CONCLUSIONS 1. Experiment and experimentation is a vital component of any science subject. In spite of this the experimentation at starting courses of universities and secondary schools is limited for different reasons, lack of time and experimental equipment, to mention two predominant [12,13]. This is the reason for building management systems for remote laboratories (RLMS [14]), that bring to the teacher the RE in question removing both obstacles.
2. RE "Energy transformation" aims at the free accessible remote experimentation in the field of energy and its transformations with the possibilities to demonstrate the physical phenomena involved.
3. By RE "Energy transformation" the teachers can show three typical energy transformations solar energy $ electrical energy (photovoltaic cell), electrical energy $ chemical energy (water electrolyser) and chemical energy $ electrical energy (fuel cell).
4. Envisaged changes of the experiment increase the range of possibilities to study and measure energy transformations of the individual energy sources in a wider range of parameters.
5. On top of this RE "Energy transformation" may be with advantage used in the laboratory exercise to determine the energy conversion of individual energy transducers, as every process of the energy transformation is with the data outputs, enabling work with and processing of the corresponding data towards the assignment -finding conversion efficiencies of all energy transducers in RE. PAPER CHEMICAL ENERGY SOURCES TRANSFORMATIONS BY REMOTE EXPERIMENT 6. RE "Energy transformation" may be with advantage used for basic courses of physics and sciences subjects at Universities [15] and also is suitable for the secondary school level [16]. It may be used for distance education students and students of Open universities [17].