on the cover solar market development
JOHN J. MOSESSO/PUBLIC DOMAIN PHOTO DEP T OF INTERIOR
A power plant operated by the Northern Indiana Public service Co. draws cooling water from Lake Michigan and sends water vapor into the atmosphere. A
u.s. Geological survey report estimates that, in 2000, power stations evaporated roughly 10. 5 million gallons daily from the Great Lakes Basin (see tinyurl.
com/yg85dfz).
So thank the sun every time you cool your feet
in a mountain stream, and every time a stream is
diverted to cool a coal or nuclear plant.
It’s possible to design a
concentrating solar power
system that consumes
a negligible amount of water.
The possibility that climate change may exacerbate droughts in critical areas bumps right up
against the ongoing search for new energy supplies. As a result, Congress and state governments are beginning to pay attention and may
take action. The Energy and Water Integration
Act of 2009, introduced by Sens. Jeff Binga-man, D-N.M., and Lisa Murkowski, R-Alaska,
proposes a new focus on gathering data about
the water-energy nexus and calls for planning
by the departments of Energy and Interior and
the Environmental Protection Agency. In Texas,
House Bill 2406 was introduced in 2009 and
would have required power plant developers to
disclose their source of water as part of the air-quality-permitting process.
Where does solar energy fit in here? We know
that the sun drives nature’s global water cycle:
Taikan Oki at the University of Tokyo in 1999
calculated that the sun evaporates about 430 gigatons of water every year, distilling it to support all
terrestrial life on earth. The solar energy used to
drive the global water cycle amounts to twice the
annual primary energy consumption of humans.
Energy-Water Nexus Hurts Solar
Water shortages may limit production by
concentrating solar power (CSP) plants. The
reason is that many CSP technologies operate
steam-based thermal heat cycles and are more
efficiently cooled using water rather than air. The
problem is compounded by the fact that the best
solar resources are in desert areas. You quickly
see the conundrum.
To deal with this issue, a tremendous amount
of research has been done in the use of dry- and
hybrid-cooling towers to cool steam cycles even
in desert environments. The systems cost more
because more equipment and surface area is
required to dissipate the same amount of heat
as an equivalently rated wet-cooling tower. A
wet-cooling tower with a CSP trough or power
tower can consume roughly 800 gallons of water
per megawatt-hour (MWh) of power generated
(compared to roughly 600 gallons per megawatt-
