Energy conversion difference

Most increases in temperature observed in a plant environment are as a result of energy conversion (friction to heat, chemical reaction to heat, etc.). A common example of energy conversion difference is when the resistance of a poor coimection converts electric current to heat. This results in a real temperature change at the target surface. 

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A fuel cell is equivalent to a generator it converts a fuel s chemical energy directly into electricity. The main difference between these energy conversion devices is that the fuel cell acccomplishes this directly, "without the two additional intermediate steps, heat release and mechanical motion. 

Ocean thermal energy conversion (OTEC) power plants generate electricity by exploiting the difference in temperature between warm water at the ocean surface and colder waters found at ocean depths. To effectively capture this solar energy, a temperature difference of 35°F or more between surface waters and water at depths of up to 3,000 feet is required. This situation can be found in most of the tropical and subtropical oceans around the world that are in latitudes between 20 degrees north and 20 degrees south. 

Electrochemical power sources differ from others, such as thermal power plants, by the fact that the energy conversion occurs without any intermediate steps for example, in the case of thermal power plants fuel is first converted in thermal energy, and finally electric power is produced using generators. In the case of electrochemical power sources this otherwise multistep process is achieved directly in only one step. As a consequence, electrochemical systems show some advantages, such as energy efficiency. 

Fig. 3. Calculated activation energies at different conversion levels of waste PSP.

The band edges are flattened when the anode is illuminated, the Fermi level rises, and the electrode potential shifts in the negative direction. As a result, a potential difference which amounts to about 0.6 to 0.8 V develops between the semiconductor and metal electrode. When the external circuit is closed over some load R, the electrons produced by illumination in the conduction band of the semiconductor electrode will flow through the external circuit to the metal electrode, where they are consumed in the cathodic reaction. Holes from the valence band of the semiconductor electrode at the same time are directly absorbed by the anodic reaction. Therefore, a steady electrical current arises in the system, and the energy of this current can be utilized in the external circuit. In such devices, the solar-to-electrical energy conversion efficiency is as high as 5 to 10%. Unfortunately, their operating life is restricted by the low corrosion resistance of semiconductor electrodes. 

There might be various reasons that lead to finding an apparent instead of the true activation energy. The use of power-law kinetic expressions can be one of the reasons. An apparent fractional reaction order can vary with the concentration, i.e. with conversion, in one experimental run. Depending upon the range of concentrations or, equivalently, conversions, different reaction orders may be observed. As an example, consider the a simple reaction ... 

The recent experimental developments on dark and photoinduced ET reactions give support to the previous speculations on the relevance of these interfaces in such fields as catalysis and solar energy conversion. These disciplines have been, and still are centered on processes at solid solution interfaces. However, particular applications require molecu-larly defined interfaces, where reactants exhibit different solubility properties. In this section, we shall consider some of these systems and the advances reported so far. 

Note There is really a fundamental underlying unity in energy, which is always conserved although it can be interconverted amongst its different forms. All types of energy conversion, except nuclear, are associated with biological as well as human machinery. 

The rate of H2 production by one unit of photobioreactor s volume is not useful for estimation of strain capabilities or for measurements of efficiency of light energy conversion. However, it is useful unit of measurements for optimization of hydrogen production by particular photobioreactor. From practical point of view it does not matter how much cells are in the photobioreactor or how much hydrogen is produced by one unit of illuminated surface. The rate of hydrogen production by the whole photobioreactor is of first importance. For a comparison of different photobioreactors it is better to express rate of hydrogen photoproduction per unit of its volume. So, it is practical unit for estimation of actual hydrogen photoproduction. 

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