Energy and Human Ambitions on a Finite Planet, 2021a

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13 Solar <strong>Energy</strong>
Now we come to the main attraction. As we saw in Chapter 10, all of
the strictly renewable energy options are ultimately derived from the
sun. The two resources of the last two chapters—hydroelectricity <strong>and</strong>
wind—represent tiny crumbs of the overall solar input to the planet.
Practically speaking, it is difficult to concoct ways to harness more than
a few terawatts of power from hydroelectric or wind-based resources.
Similar limitations apply to biologically-derived energy, geothermal,
tidal, ocean currents, wave energy, etc. This may be worrisome considering
that human society currently dem<strong>and</strong>s 18 TW. Meanwhile, the
sun delivers 83,000 TW to the earth’s surface (Fig. 10.1; p. 167, Table
10.2; p. 168). That’s almost 5,000 times more than the dem<strong>and</strong>. By the
numbers, then, the sun seems to offer all we might ever need. In fact,
the quantitative imbalance is so extreme as to make one wonder why
we would ever mess around doing anything else.
Yet at present, the U.S. gets only about 0.9% of its energy from solar
power, or 2.3% of its electricity. Similarly for the world, 1.2% of global
energy is solar (2.1% of the electricity). It would seem to be vastly
underutilized.
13.1 The <strong>Energy</strong> of Light ......197
13.2 The Planck Spectrum .... 199
13.3 Photovoltaics ......... 201
Theoretical Efficiency .... 202
13.4 Insolation ........... 206
13.5 Incredible Solar Potential ..211
13.6 Residential Considerations 213
Configurations ........ 213
Sizing <strong>and</strong> Cost ........ 213
13.7 Photovoltaic Installations . 215
Pros <strong>and</strong> Cons of PV .....217
13.8 Solar Thermal ......... 218
Passive Solar Heat ...... 218
Solar Thermal Electricity . 219
Pros <strong>and</strong> Cons of ST ..... 221
13.9 Upshot for Solar ....... 221
13.10Problems ............ 222
This chapter explains the nature of solar energy, its potential for use,
practical considerations, <strong>and</strong> looks at the state of installations. While
most of the focus is on photovoltaic (PV) panels that directly generate
electricity from light, solar thermal power generation is also covered.
13.1 The <strong>Energy</strong> of Light
Sec. 5.10 (p. 79) introduced the basics of the energy of light. This section
acts as a refresher <strong>and</strong> lays the foundation for the rest of the chapter.
Photovoltaic cells, showing grid contacts <strong>and</strong> crystal domains. Photo Credit: Tom Murphy
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.