POWER May 2011 - 14

loop at the Arvada, Colo., site of contractor
Barber Nichols Inc. has been running
and producing approximately 240 kWe during
the developmental phase that began
in March 2010. The second loop, at Sandia
in Albuquerque, N.M., has been focused
on understanding issues of compression,
bearings, seals, and friction that exist
near the critical point, where the CO2
has
the density of liquid but otherwise has
many of the properties of a gas.
" The supercritical properties of carbon
dioxide at temperatures above 500C and
pressures above 7.6 megapascals enable the
system to operate with very high thermal
efficiency, exceeding even those of a large
coal-fired power plant and nearly twice as
efficient as that of a gasoline engine (about
25%), " researchers say. The combination of
low temperatures, high efficiency, and high
power density allows for the development
of very compact, transportable systems
that are more affordable because only standard
engineering materials (stainless steel)
are required, less material is needed, and
the small size allows for advanced, modular
manufacturing processes.
Sandia admits that it is not alone in
the field but says it is " in the lead. " The
lab will test the capability of the concept,
particularly its compactness, efficiency,
and scalability to larger systems. Future
plans call for commercialization of the
technology and development of an industrial
demonstration plant at 10 MWe.
Interest, Funding Buoys
Floating Solar Power Plants
Like most forms of generation, solar power
has its disadvantages. Two cited most by
critics of photovoltaic (PV) or concentrating
solar power facilities are that they require
large expanses of land and that solar
cell fabrication and maintenance costs are
high. Several companies have been assessing
a new approach to tackling these factors:
installing solar plants on water. Two
projects in recent months have garnered
government and industry backing, indicating
growing interest in the concept.
Aquasun, developed by a collaboration
between Israeli firm Solaris Synergy and
France's EDF Group, is a PV array that uses
200-kW modules that can be installed on
existing industrial water basins. Developers
say that costs will be reduced because Aquasun
uses a mirror-based concentrating system,
cutting down on the number of panels
needed. It also employs a " creative cooling
system " using the water on which the panels
float so it can use cheaper silicon cells.
The floating solar array has environmental
14
7. Floating a ray. Australia's Sunengy recently partnered with India's Tata Power to pilot a
floating concentrating photovoltaic module. A thin plastic focusing concentrator lens rotates
slowly to track the sun both daily and seasonally. A minimal number of silicon (or other types of)
photovoltaic cells are housed in a container that sits in the water where the cells are kept cool
through convective heat flow to the surrounding water. Courtesy: Sunengy
benefits, too, the developers claim: It works
as a " breathing surface through which oxygen
can penetrate " the water, ensuring the
viability of underwater life.
The project has gained the support of
Eureka, a 39-member intergovernmental
network that promotes market-oriented
research and development and innovation
projects. The Israeli Ministry of Industry,
Trade and Labor has also pitched in.
The project's design phase ended in
March 2010, and fabrication of a prototype
is now under way. The implementation
phase is slated to begin in September
2011 on waters near a hydropower facility
in Cadarache, southeast France. The prototype
will operate onsite for nine months,
and researchers hope the technology will
be ready for market by June 2012.
In late March, meanwhile, Australian
solar company Sunengy Pty Ltd. entered
into a partnership with Tata Power, India's
largest integrated private power utility, to
build a pilot plant for its Liquid Solar Array
(LSA). The project essentially uses PV
concentrators that float on water, mounted
on anchored rafts (Figure 7).
Inventor Phil Connor, who is also
Sunengy's chief technology officer, claims
that an LSA installation located with or
combined with hydro dams could match
the power output of a typical hydro plant,
using less than 10% of the dammed water's
surface area. The solar installation
could thereby supply an additional six
to eight hours' worth of power per day.
LSA effectively turns a dam reservoir into
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a very large battery, he said, pointing
to company modeling that shows that a
240-MW LSA system could increase annual
energy generation at the Alqueva hydropower
plant in Portugal by 230%.
Construction of a pilot in India will begin
in August this year. Sunengy plans to
establish a larger LSA system in Australia's
Hunter Valley in mid-2012 before going
into full production.
POWER Digest
ABB, BHEL to Deliver $1.1B Multi-Terminal
UHVDC Line in India. Zurich-based
ABB and Indian state-owned company
Bharat Heavy Electricals Ltd. (BHEL)
said on March 23 that they had been selected
by Power Grid Corp. of India Ltd.
(PGCIL) to deliver an ultrahigh-voltage direct
current (UHVDC) transmission system
to convey hydropower from northeastern
India to the city of Agra over a distance
of 1,728 kilometers (km). The $1.1 billion
project (ABB's contract is valued at $900
million) will have an 8,000-MW converter
capacity, which ABB says is " the highest
ever built. " The firm also claims that the
system will be the world's " first UHVDC
link with three converter stations. " It will
include two " sending " stations to convert
power from AC to DC for transmission over
a single power line that will pass through
the narrow Siliguri Corridor and deliver
electricity to the third, " receiving " station
in Agra, where it will be converted back
into AC for distribution to end users.
POWER | May 2011

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POWER May 2011

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