Energy and Human Ambitions on a Finite Planet, 2021a

13 Solar <strong>Energy</strong> 224
successful contribution to PV current, starting with a green photon
leaving the sun <strong>and</strong> ending with an electron crossing the junction.
16. Many people have an instinctive reaction to discount the < 20%PV
panel efficiency as disappointingly low—perhaps thinking they
should hold out for higher. Present a multi-point argument about
why the efficiency is actually pretty good, <strong>and</strong> why in practice it is
plenty good enough to be practical.
17. If aiming for a particular power output 109 from a PV array, describe 109: Make up your own number if it helps.
explicitly/quantitatively how PV panel efficiency interacts with
the physical size (area) of the array. For instance, what happens
if the efficiency doubles or is cut in half, while keeping the same
target output?
18. Make the connection between Figure 13.4 <strong>and</strong> Figure 13.6 by
drawing a zoom-in of the bottom left corner of one of the cells in
Figure 13.6.
19. Figure 13.7 shows operational curves of a PV cell for different
levels of illumination. If the illumination is low <strong>and</strong> the panel
continues to operate at maximum power, 110 which changes the
most compared to full-sun operation: the voltage or the current?
Why might lower light (fewer photons) directly connect to a lower
current based on the physics of PV operation?
110: . . . largest rectangle that fits in curve
20. Replicate the calculation on page 206 (showing work) that starts
with the surface of the sun being 5,770 K <strong>and</strong> finds that we receive
1,360 W/m 2 at Earth.
21. According to Figure 13.8, which continent appears to have the
most solar potential? How would you rate China? Do the largest
populations <strong>and</strong>/or largest energy consumers in the world tend
to be well-aligned to the best solar resources?
22. Examine Figure 13.9 to determine the insolation at the “four
corners” location where Arizona, New Mexico, Utah, <strong>and</strong> Colorado
touch. Express this in both kWh/m 2 /day <strong>and</strong> in W/m 2 , showing
how to convert from one to the other.
Just using this location as an unambiguous
spot on the map.
23. What is a typical value for hours of full-sun-equivalent 111 of solar 111: . . . full sun meaning 1,000 W/m 2
exposure in the U.S. based on the map <strong>and</strong> native units in Figure
13.9? Explain how you arrive at this.
24. A 30 year study by the National Renewable <strong>Energy</strong> Lab 112 indicates 112: . . . called the Redbook study: [88]
that in San Diego, a typical year delivers an annual average of
5.0 kWh/m 2 /day of insolation for a flat panel facing straight up.
Convert this to W/m 2 .
25. The same study mentioned in Problem 24 finds that worst year
in San Diego delivered an annual average of 4.7 kWh/m 2 /day
© 2021 T. W. Murphy, Jr.; Creative Commons Attribution-NonCommercial 4.0 International Lic.;
Freely available at: https://escholarship.org/uc/energy_ambitions.