OFF-GRID TELECOMMUNICATION STATIONS IN MALAYSIA

Typically, telecommunications service operators have to locate some of their stations at sites without existing mains or grid electricity supply. Such a connection may be too expensive due to the distance involved, or may take too long to install. Typical "problem installations" are repeater stations or cellular phone base stations. The latter are generally regarded as power hungry, so the standard approach is to use stand-alone diesel generator sets. Appropriate Energy  has considerable experience in providing electricity for the telecommunications industry. One of SPC's more recent projects is described below.

CELLULAR BASE STATIONS IN NORTH BORNEO

In December 1995, a leading cellular phone service operator in Malaysia invited SPC to provide alternative power solutions for its off grid base stations. About 30 such stations within peninsular Malaysia were off the grid. Expansion into East Malaysia would result in many more such stations. Each of the existing affected base stations were powered by a pair of diesel generator sets operating on an alternating 12-hour cycle.

The major problems identified with operating stand-alone diesel generator sets were cost and reliability. The operation and maintenance contract costs of providing electricity to these stations amounted to 6 - 8 times the electricity costs of similar base stations powered by the grid.

In addition to the financial problem, reliability was a major issue. Typical problems were generator set starting failure, necessitating unscheduled site visits for fault rectification. Generator engine life also proved unsatisfactory, with overhaul intervals being reduced to as little as 60% of the manufacturer's specifications.

SPC installed dataloggers in several base stations to determine typical power demand and load characteristics of such installations. These investigations showed that over 95% of the power and energy consumption were by the station radio transceivers and airconditioners. Typical results are shown in Figuress 1 and 2.

Surprisingly, the radio transceivers accounted for about 40% of the power demand, and the airconditioners about 60%. The data also showed that the maximum radio transceiver loading (when all voice channels are in use) was twice the minimum loading (when no voice channels are in use). The airconditioners displayed much greater variation, as their power demand depends on compressor cut in and out, which in turn depends on thermostat settings.

Figure 3 shows total station load and its variation over one day.

The conclusions were as follows:

• Variation in power demand through the daily load cycle was very high. Maximum power required was 5 times greater than minimum.
• This caused the stand-alone diesel generator sets to operate in an underloaded state, i.e. below 50% of their rating, approximately 18 hours out of every 24.
• Such prolonged underloaded operation of diesel generator sets invariably leads to engine coking and glazing. This, in turn, results in poor fuel economy, reduced reliability and shortened engine life.
• The high operation and maintenance costs were largely a function of the generator set service requirements, not fuel.

AEI proposed a diesel hybrid solution which would reduce operating and maintenance costs by over 50%. This proposal was accepted, and is presently being implemented in the East Malaysian State of Sabah located at the northern end of the island of Borneo.

A typical AEI solution for cellular base stations is shown in schematic form in Figure 4. It is capable of being installed with any of 3 energy sources, i.e. diesel, wind and solar (PV). Both AC and DC buses are provided to accommodate typical telecommunications station loads.

In its most basic diesel hybrid form, the diesel generator set operates between 8 and 12 hours per day at most, whilst providing a 24-hour power supply. In addition, the generator set is always operated at an optimum load regardless of actual load. This solves all the problems associated with stand-alone diesel operation, whilst remaining reasonable in capital investment terms.

For installations that are so remote that fuel and fuel transport costs become significant, renewable options such as wind turbines or PV panels may be added. This may reduce generator set operating time to as little as an hour a day, or even zero operation. AEI provides such systems in various power and energy ratings depending on the requirements of the telecommunications equipment.

AEI has provided such power systems for telecommunications stations requiring up to 50kWh per day rated at 20kVA, and is capable of customising solutions to fit both capital investment and operating budgets.