Environmental Engineering Reference
In-Depth Information
power demand over 24 h for the State of California on a hot day is illustrated in
Figure 10.5. (The pattern will differ on a weekend or on a cold day when air
conditioning is not needed.) But, approximately, the electric power demand is
doubled during the day over that at night. So, a large portion of the variation could
be accommodatedwithout storage by equal amounts of photovoltaic andwind electric
power.
The combined renewable power scenario for average demand 500 GW to be
provided solely by equal amounts of solar and wind power would cost $250 billion
(for wind) plus $845 billion
0.5 (205/1000)
ΒΌ
$86.6 billion for solar. The cost of the
total on this estimate is $337 billion.
To bemore realistic, wemight double these numbers to allow for a period of cloudy
weather, for example. The extra capacity on good (sunny and windy) days would be an
opportunity to generate hydrogen, which might eventually fuel automobiles, and
otherwise has a market value. If we ask about the total energy usage in the United
States we multiply this number by 6.9.
10.6
The Importance of Storage and Grid Management to Large-Scale Utilization
In spite of the comment above, storage capacity is an essential need for large use of
either solar or wind energy. The primary storage need is with solar, because the sun is
absent at night. Storage is also a (reduced) problem with wind power, since the wind
blows more strongly at night, and weather is variable. Clouds greatly reduce the
power output from a photovoltaic facility. The question of variability in renewable
energy sources is being addressed in China, which has unquestionably decided it
needs as much power as it can get, with strong planned growth in hydropower
(demonstrated by the Three Gorges Dam hydropower plant) and solar and wind
farms. Chinas State Grid is the largest power grid in the world and is expanding. Its
President, Liu Zhenya, is quoted as saying that the multiple Three Gorges of Wind
that are to be built in China will have to be bundled with natural gas, coal, and
nuclear [134]. This does not mention storage, but it is likely that there is considerable
pumped hydro storage in China (Figure 1.11).
Hydrogen storage is sensible as a means of storage for both wind and solar electric
power. This is not presently being done. Hydrogen storage can be done locally on
almost any scale, from the personal or family house scale addressed by Nocera (see
Section 9.2) to large scales as appropriate for wind or solar farms. The grid-scale
storage that is most common is pumped hydroelectric capacity currently at 27GW in
the United States (see Figure 1.11.) The use of hydrogen as an energy intermediary,
including its use with fuel cells to power electric cars, has been discussed in
Chapter 9.
The PV-based hydrogen energy storage approach can also be envisioned on a small
scale, in the vision of Nocera discussed in Chapter 9, similar to Figure 10.7. Nocera is
working with (http://uk.ibtimes.com/articles/20110328/leaf-mimicking-catalyst-
inventor-signs-huge-contract-with-tata-group-hydrogen-from-water-device.htm) the
