Transcript ch08c

FIGURE 8.11 A parabolic mirror system focuses sunlight on a Sterling cycle heat engine that produces electrical power. (By permission of
DOE/NREL-PIX.)
Energy and the Environment
James A. Fay / Dan S. Golomb
Copyright © 2011 by Oxford University Press, Inc.
FIGURE 8.12 A spherical mirror system consisting of individual focusing mirrors arrayed around a central tower that collects the focused light.
(By permission of DOE/NREL-PIX.)
Energy and the Environment
James A. Fay / Dan S. Golomb
Copyright © 2011 by Oxford University Press, Inc.
FIGURE 8.13 A cylindrical collector mirror focuses sunlight on a glass pipe containing fluid. (By permission of DOE/NREL-PIX.)
Energy and the Environment
James A. Fay / Dan S. Golomb
Copyright © 2011 by Oxford University Press, Inc.
FIGURE 8.14 The elements of a photovoltaic cell of area A exposed to a solar irradiance Is and supplying a total current jA to an external load
at an electric potential difference V. The current density, electric current per unit area, in the cell is j.
Energy and the Environment
James A. Fay / Dan S. Golomb
Copyright © 2011 by Oxford University Press, Inc.
FIGURE 8.15 The maximum fraction f of the transmitted solar irradiance that can be converted to electric power in the external circuit as
a function of the dimensionless photovoltaic cell energy gap xg of Equation (8.10).
Energy and the Environment
James A. Fay / Dan S. Golomb
Copyright © 2011 by Oxford University Press, Inc.
FIGURE 8.16 (a) The open circuit voltage Voc and short circuit current density jss of a photovoltaic cell as functions of solar irradiance. (b)
The voltage versus current density characteristics of a photovoltaic cell for a fixed value of solar irradiance, showing the point of maximum
power.
Energy and the Environment
James A. Fay / Dan S. Golomb
Copyright © 2011 by Oxford University Press, Inc.
FIGURE 8.17 The flow of wind having a speed V and passing through a wind turbine whose blade radius is R is slowed to a speed Vt at
the turbine disk and even further to a speed Vw in the wake region downstream of the turbine.
Energy and the Environment
James A. Fay / Dan S. Golomb
Copyright © 2011 by Oxford University Press, Inc.
FIGURE 8.18 The motion of the wind relative to a turbine blade consists of an axial speed Vt and a tangential speed 2πrf that generates a
lift force L and drag force D.
Energy and the Environment
James A. Fay / Dan S. Golomb
Copyright © 2011 by Oxford University Press, Inc.
FIGURE 8.19 The power coefficient of a wind turbine of fixed pitch is a function of the ratio of the tip speed to wind speed. Its maximum
value is less than the theoretical value of 16/27 = 0.593.
Energy and the Environment
James A. Fay / Dan S. Golomb
Copyright © 2011 by Oxford University Press, Inc.