EKISTICS is the science that draws on
combined talents of the professional design community
to shape and define future settlements.
Continuing as one of the best industrial uses of photovoltaic power, worldwide
for 2007-2008, the PV telecommunications market segment has the following
· Stand-alone systems
· Hybrid systems, with Generator-set backup
· Utility-connected sub-stations
Stand-alone photovoltaic systems have no mechanical backup charging. All
generation is provided by the solar electric array. Load autonomy during
inclement periods is provided by energy stored in the battery and the solar
array is sized to meet the load requirement for the month with the least
Stand-alone PV systems are designed to provide excess energy for the rest
of the year, and may still be more cost effective than other generator technologies.
Life cycle cost analyses generally project that these systems will produce
power at $4.30 to $5.00 per KWh.($US). The installed price of a stand-alone
photovoltaic (PV) system is currently less than or similar to that of a
thermal electric generator (TEG) installation. TEGs continuously consume
fuel and require frequent maintenance.
For applications where the daily load is large or in areas where winter
sunlight is scant, the PV and batteries required to maintain a site's entire
electrical design load may render a stand-alone PV system too costly. In
such cases a solar-hybrid system can help reduce the initial system cost
while maintaining low operating costs and required liability.
By integrating a back-up charging system into the design, the photovoltaic
array can be sized so that its output is used by the load for most of the
year. Whenever this smaller array falls short of meeting the load requirement,
or if the load were to expand, the "on-demand" back up charging
system will operate intermittently to supply the required generation. In
a PV -generator set hybrid systems, the generator is allowed to operate
only at its optimum level, so when the genset runs, it is producing power
at its lowest possible cost per KWh.
Advancements continue in the electronic controls necessary to reliably and
automatically manage the start/stop cycles of motor generator sets (gensets)
optimize the genset as a reliable back-up battery charging source, when
coupled with a high output industrial charger.
Hybrid systems of this sort allow the solar array and the battery bank to
be reduced substantially. Properly designed, the back-up genset in a PV
hybrid will need to run less than an hour a day, averaged annually. At this
small usage, a good diesel generator will require basic maintenance and
fuel deliveries only once per year and an overhaul won't be necessary for
10 to 20 years. Additional photovoltaic modules can always be added at a
later time to even further reduce its run time.
EXAMPLE: Onyx Peak Microwave Link in California. Typical of many sites,
it is now a completely automated photovoltaic system with a backup charging
subsystem. Steady users include the Highway Patrol, Sheriff's
Department and Department of Forestry. The old power system used three 7.5
KW diesel generator sets. Two were always on site; one at 100 percent duty
cycle, the other rotated weekly with the one on line. The third rotated
out for maintenance. Fuel consumption to drive the generators amounted 7,000
U.S. gallons annually. By integrating a backup generator set with the primary
photovoltaic array, the solar plant size could be significantly reduced
over a stand-alone photovoltaic station. And, fuel consumption was dramatically
reduced from 7,000 gallons to 156 gallons annually.
EXAMPLE: Papua New Guinea has one of the most modern telecom networks in
the world based on energy efficient microwave relays powered by solar electric
arrays. Thousands of photovoltaic systems are in operation there, both hybrid
and stand-alone, powering large scale telecommunications, two-way radios,
and navigational systems for aircraft and marine traffic.
EXAMPLE: KIHX FM in Prescott Valley, Arizona, was the first commercial solar
electric FM station in the United States. In addition to the FM station,
PV also provides electricity for an expanded paging network and public safety
repeater antennas. (Intermountain Communications, TelePage).
A 4.5 kWp PV array, stored in large batteries with backup genset charging.
UTILITY-CONNECTED PHOTOVOLTAIC SUB-STATIONS (also known as distributed power stations),
are constructed near the point of end use, and feed power back into the utility grid.
Generally speaking, these have no mechanical backup charging, and all end-use load
generation is provided by the utility. The solar
array may be sized to meet the load requirement for the month with the least
sunshine, and then incrementally constructed, over time, in a modular fashion, to fit fiscal budgeting requirements,