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Preprint from the 28 x' ILEE Photovoltaic Specialists Conference, Anchorage, Sept. 2000
PV HYBRID VRLA BATTERY TEST RESULTS FROM A TELECOMMUNICATIONS SITE
Thomas D. Hund and John W. Stevens
Sandia National Laboratories, PO Box 5800
Albuquerque, New Mexico 87185-0753
A new valve regulated lead-acid (VRLA) gel motive
power battery and PV system power center have been
tested in the laboratory and at a PV hybrid
telecommunication site. The power center provides battery
charge control, system remote communications, and data
acquisition at the field test site. Extensive laboratory and
field-test data were used to improve battery performance
by optimizing regulation voltages, finish-charge, and
system design. After 1.5-years of service, battery and
charge controller performance have met all performance
requirements for the remote communications site at Sandia
The Mt. Washington communication site near Sandia
National Laboratories was established more than 25 years
ago and was powered by an ac cable laid over a quarter of
a mile of very steep rugged mountainous terrain. The
theory was that this cable would be replaced with an
overhead line at some future date. The area traversed by
the cable recently became a training ground for military
personnel, presenting a hazard both to the cable and the
personnel. Sandia's Facilities staff estimated the cost to
install an overhead line up the mountain, and Sandia's
Photovoltaic Systems Assistance Center (PVSAC)
provided a cost estimate for serving the site with
photovoltaics. The solar option was about half the cost of
a line installation, so the Facilities group asked the PVSAC
to assist it in preparing a bid package and in evaluating
proposals. Direct Power and Water, an Albuquerque-
based photovoltaic systems designer/installer, was
awarded a contract to install a photovoltaic hybrid system,
which began operation in March of 1999 (see Fig. 1).
TEST OBJECTIVES FOR THE SYSTEM
The Mt. Washington site is being monitored to
evaluate the performance of the new Deka valve-regulated
lead-acid (VRLA) G-75 gel battery and the Digital Solar
MPR-9400 system charge controller and power center.
Previous experience with photovoltaic systems identified
the battery and charge controller as the source of the most
common performance and life-cycle cost drivers [1,2]. The
evaluation is part of an effort to improve system design,
charging strategies, . battery technology for photovoltaic
Sandia is a multiprogram laboratory operated by Sandia Corporation,
Energy under Contract DE-AC04-94AL85000.
systems and reduce life-cycle cost using both laboratory
and field test data.
1. Sandia's Mt. Washington Telecommunication
DESIGN OF THE SYSTEM
The Mt. Washington telecommunication site is
designed to be a stand-alone 48-volt DC system with an
engine generator backup for emergency power. The loads
consist of DC to DC converters for 12-volt radio
transmitters, a 48-volt microwave phone, and a small AC
inverter for 120 V lighting and room cooling fan. PV power
is provided by three Solec 48-volt photovoltaic arrays at
502 tilt for a peak power of 1,600 watts. The PV array
provides more than enough power for the 50 amp-hours
(Ah) load even during the minimum solar resource month.
The site has a conservative energy design to ensure
adequate battery charging and minimal generator run time.
With an average December solar resource at tilt for
Albuquerque of 5.5 kWh/m2, the photovoltaic array is
calculated to provide an average of 129 Ah/day in
December. Based on the above solar and load Ah
numbers, the minimum system array Ah to load Ah ratio is
calculated to be about 1.6. The array-to-load Ah ratio is
important to determine available energy for battery
recovery and finish-charge. In this case the battery will
spend about 6-h at regulation voltage on a clear day. At
array-to-load ratios significantly below 1.3, battery recovery
and finish-charge has been shown to be marginal (see Fig.
4) because it will spend less than 3-h at regulation voltage
on a clear day.
a Lockheed Martin Company, for the United States Department of
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HUND,THOMAS D. & STEVENS,JOHN W. PV Hybrid VRLA Battery Test Results from a Telecommunications Site, article, September 25, 2000; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc718238/m1/1/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.