Question

A group is considering installing a solar power station and has asked you for your recommendation for a photovoltaic system or a solar thermal system. At this stage you are asked not to include cost factors. The single point design condition they have given you is for an incident solar radiation on the collector of 550 W/m2, a surrounding temperature of 18 C. The dead state for this problem should be taken as To = 291 K, Po = 1 bar. You can perform your analysis at steady state conditions. In addition to determining the power output and first law efficiency of the options, you have been requested to determine the exergy destroyed for each of them. The photovoltaic system has an efficiency of 0.15 defined as the power output/incident solar radiation. The basic photovoltaic collector is 1.1 m2 and losses heat from both the front and back surface. The edge area can be neglected. The convective heat transfer coefficient is 10 W/m2 K. The inverter and signal conditioning device used to connect the photovoltaic collector to the grid and household has an efficiency of 0.87. The inverter operates isothermally. The solar thermal collector will heat the working fluid from a temperature of 32 C and has a concentration factor of 10,000. The concentration factor is the ratio of the incident solar radiation on the heat transfer surface to the incident solar radiation area. It is a concentrating collector with an opening of 1.1 m2 and a heat transfer area of 0.05 m2. The mass flow rate of the working fluid through the system is 0.009 Kg/s. The heat transfer area is not equal to the area of absorption. The convective heat transfer coefficient is 1.0 W/m2 K. The heat transfer from the collector can be considered to be at the average temperature of the working fluid, (Tin + Tout)/2. The specific heat of the working fluid is 678 J/(Kg K). The useful energy from this collector system is the change in the enthalpy of the flow through the system. The working fluid enters a heat engine with an efficiency of 0.30 that is connected to a generator with an efficiency of 0.90. The generator operates isothermally.

Answer the following:

a) Determine the power output for each type of system for a basic collector area.

b) Determine the exergy destroyed for each type of system.

c) Which system would you recommend on this analysis? This question neglects the costs.

Answer 1

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