Page 346 - A Comprehensive Guide to Solar Energy Systems

17

Energy and Carbon Intensities of

Stored Solar Photovoltaic Energy

Charles J. Barnhart
WESTERN WASHINGTON UNIVERSITY, BELLINGHAM;
INSTITUTE FOR ENERGY STUDIES, WESTERN WASHINGTON UNIVERSITY,
BELLINGHAM, WA, UNITED STATES
charles.barnhart@wwu.edu

17.1 The Need for Storage

The world needs affordable, accessible, sustainable, and low-carbon energy resources [1–3].
Of the renewable resources, solar photovoltaic (PV) and wind turbines have the highest
technical potential to satisfy this need, but these technologies generate electricity from
variable, weather-dependent resources [4–7]. Fig. 17.1 provides a compelling visualization
of 30 days of superimposed power demand time series data [black (red in the web ver-
sion)] wind energy generation data [light gray (blue in the web version)] and solar insola-
tion data [gray (yellow in the web version)]. Supply correlates poorly with demand. What
will be the amount of storage needed for the operation of electrical grids incorporating
increasing amounts of variable resources is a critical yet complicated question. It is com-
plicated for two reasons: (1) the electrical grid, composed of myriad power sources and
sinks, is conducted as a whole in real-time, and (2) the number of technologies and prac-
tices, their varied and evolving characteristics, and their possible implementations under
differing and shifting policy landscapes presents a grossly underdetermined problem with
several solutions.
Technologies and practices positioned to ensure grid-reliability include flexible con-
ventional generation (e.g., natural gas combustion turbines and diesel generation sets),
flexible renewable generation (e.g., curtailment, hydropower, and concentrated solar
power with thermal storage), flexible load (e.g., demand-side management), energy stor-
age, and resource sharing (e.g., diversity and transmission). In the future, when green-
house gas (GHG) emissions are constrained, flexible generation will need to be achieved
using low-carbon energy supplies.
Studies have made efforts to determine the amount of renewable generation an electri-
cal grid can support by bundling these technologies and practices into an abstract resource:
grid flexibility, defined as the percentage of generation and load capable of being readily
dispatched or halted [5]. Less flexible grids harbor high percentages of so-called baseload
A Comprehensive Guide to Solar Energy Systems. http://dx.doi.org/10.1016/B978-0-12-811479-7.00017-8 351
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