Conversion into electricity

The great energy consumption, limited recources of traditional fuels and environmental problems have lead to intensive research on the conversion of solar energy during the last fifteen years. Conversion into electrical energy has been realized in technical devices consisting of pn-junction photovoltaic cells. Efficiencies of up to 20 % have been obtained with single crystal devices and around 9 % with polycrystalline or amorphous layers. 

There is yet another very important use of sunlight, i.e. its conversion into electricity or hydrogen. In this case also it is obvious that for practical applications sunlight is the only acceptable light source. 

Maximum power is a concept introduced in Chapter 5. Appreciate its application in models for solar energy conversion to wind energy and photothermal conversion into electricity. 

There are two main types of PEC cells, the regenerative type cells, and the photoelectrolysis cells. The first type also called liquid-junction solar cells, serve like solid-state cells for solar energy conversion into electricity. The same reaction proceeds at both electrodes of the cell, directed forward at the anode, backward at the cathode. Hence, composition of the solution is preserved unchanged. The other type, the photoelectrolysis cells serve for conversion of solar energy into chemical energy. Here, two different reactions proceed at the electrodes. As a consequence, certain substance in the cell is transformed in the course of its operation. These two types of the PEC cells are described in more detail below. 

The most widespread use of solar radiation is the conversion into electricity by means of photovoltaic (PV) cells. Simply stated, in a PV cell photons from sunlight knock electrons into a higher state of energy, creating electricity. Growth in installment of PV cells has been 30 percent over the past decade, but the baseline is small. Figure 10.2 shows the evolution... 

It is important to appreciate that even if a material possess desirable characteristics, as discussed in the previous sections, it may not exhibit the desired efficiency of light energy conversion into electrical energy. For example, in spite of semiconductor and redox electrolyte possessing desired Fermi levels experimentally determined contact potential might be much less than the anticipated value. Presence of surface state is one of the factors responsible to show these deficiencies. Hence, efforts are required to minimize the adverse effects of surface states. 

In the following, the most important types of reactors wiU be discussed briefly. In principle, a distinction has to be made between research reactors and reactors of nuclear power stations. The latter ones are built to produce heat for conversion into electric energy. Research reactors are used as intense neutron sources the energy set free, necessarily, is not used. Actually energy production in a research reactor is normally disturbing rather than helpful. Therefore, research reactors are generally small and compact. More detailed information, comprehensible also for the nonspecialist, may be found in IAEA (2000) for research reactors and in Zech (1988) concerning reactors for nuclear power stations. 

The RTG basic units include the radiation heat source (RHS), thermoelectric unit (TEU), radiation shielding (RS), and radiator. (Space systems need radiators also to cool them.) RTGs merits are determined by the following unique properties spontaneous release of thermal power, its direct conversion into electricity, a simple design, high-energy output, a long lifetime, the opportunity of employment practically in all scopes of activities under water, at the surface of the Earth and planets, and in space. 

As further use is made of natural gas, be it by liquefaction and transport, gas to liquid conversion, or gas to wire conversion into electric power, the use of floating... 

Efficiency Photovoltaic cell s efficiency is dependent on the incident light that is available for conversion into electrical energy and can be reduced by such factors as dust accumulation or an obstacle in the path of sunlight. 

Woody biomass could supply the nation with about 5 quads of its total gross energy supply by the year 2050 with the use of approximately 112 million hectare (an area larger than the state of Texas). A city of 100,000 people using the biomass from a sustainable forest (3 t/ha) for fuel would require approximately 220,000 ha of forest area, based on an average electrical demand of 1 billion kilowatthours (860 kcal = 1 kWh). More than 70% of the heat energy produced from burning biomass is lost in its conversion into electricity this is similar to losses experienced in coal-fired plants. The forest area required to... 

This is the voltage that would be achievable in a 100% efficient fuel cell. However, as we have mentioned, it is the Gibbs free energy that is available for conversion into electrical work in a fuel cell. 

Since the maximum electrical work in a fuel cell is limited by the available Gibbs free energy, the maximum thermodynamic or reversible efficiency of a fuel cell is defined as the ratio of Gibbs free energy change for conversion into electrical energy to the net fuel energy available in the form of enthalpy of formation as... 

The mechanism involved with adsorption of light and conversion into electrical current in a photovoltaic device involves the light adsorption creating an exciton, which decays into holes and electrons. If this occurs near or at an interface where the holes and electrons can be conducted towards the respective electrodes before recombination occurs, electrical current... 

The total COD (substrate) removal in MFC arises from three consumption approaches (i) conversion into electrical current (via the Coulombic... 

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