Energy and Human Ambitions on a Finite Planet, 2021a

13 Solar <strong>Energy</strong> 218
◮ PV technology has no moving parts or steam; panels are robust
<strong>and</strong> last a long time;
◮ PV is one of the few resources that can fit on a rooftop <strong>and</strong> provide
self-contained electricity generation;
◮ PV efficiency is rather good: close to theoretical expectations <strong>and</strong>
much better than biology has managed at getting energy from
sunlight;
◮ PV technology works well, <strong>and</strong> despite expense has been deployed
on rooftops across the world;
◮ Life-cycle CO 2 emissions are 15 times smaller than that of traditional
fossil fuel electricity [68];
◮ PV is often a good solution when utility electricity is far away.
[68]: (2020), Life Cycle GHG Emissions
And now the less attractive aspects:
◮ PV is intermittent, <strong>and</strong> not well-matched to energy dem<strong>and</strong>; it
would be hard to “balance” the electrical grid if too much of
the input came from such an intermittent source, <strong>and</strong> storage is
difficult;
◮ PV is still expensive 90 relative to prevailing energy resources—
especially important in terms of up-front cost;
◮ Electricity alone is not well-suited to many of our current energy
dem<strong>and</strong>s, like transportation <strong>and</strong> industrial heat/processing;
◮ St<strong>and</strong>-alone operation requires batteries, at least doubling the cost
<strong>and</strong> adding maintenance/replacement dem<strong>and</strong>s;
◮ Even partial shading can be disproportionally disruptive;
◮ PV manufacturing involves environmentally unfriendly chemicals;
◮ PV deployment can harm habitats if installed in undeveloped
areas.
90: Cost has been a major barrier, but may
cease to be so as prices fall further.
13.8 Solar Thermal
Photovoltaics (Section 13.3) convert sunlight directly into electricity, but
this is not the only way to harness energy from the sun. Solar energy
can also be used for heat. We’ll first have a brief look at home heating,
then turn to electricity generation from solar heat.
13.8.1 Passive Solar Heat
Full sun delivers something like 1,000 W/m 2 at the earth’s surface. Now
imagine a window in a house intercepting 1.5 m 2 of sunlight, in effect
admitting 1,500 W into the home—like a space heater, <strong>and</strong> it’s free!
Depending on window construction, some of the infrared energy may be
blocked, so maybe not all 1,000 W/m 2 will make it inside, but a sizable
portion will. Clever design has south-facing windows for receiving
low-angle winter sun, but an overhang to keep out the high summer sun
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.