Delivering cost savings and environmental benefits with hybrid power

In the developing world electrical grids are still unavailable in many areas, and when they are available their reliability is sometime a major concern for telecom operators who have wireless sites. The choice of a reliable method of generating the power for those sites is of course vital for the operation of the Base Transceiver Station, but this choice can also have significant impact on the site operating costs. The selection of the energy source can also impact the site's environmental footprint at a time when the wireless industry is striving to reduce CO emissions to limit climate change. In Sub-Saharan Africa for example, off-grid sites are usually powered by two diesel generators operating alternately to ensure a reliable power source. Such a solution, greedy in fuel, results in high operating costs and, for the more remote sites, the refueling and periodic maintenance of the generators creates logistical problems and results in significant additional expenditure. Hybrid systems, with a diesel generator combined with a dedicated cycling battery operating alternately can reduce operating costs for fuel and maintenance by up to 66%, while also cutting CO emissions in the same range. A complete hybrid system of this type will be packed in an "energy container" to offer a turnkey solution for easy and quick installation in more remote locations. To ensure the lowest Total Cost of Ownership of the hybrid solution, the different sub-systems such as genset, rectifier, controller and battery must be carefully selected and sized to permit the highest system efficiency. The use of a battery technology with a proven high level of reliability will allow a single diesel generator to be used. This will maintain system reliability while reducing capital expenditure, with part of the cost of the battery being covered by the elimination of the second generator. The addition of solar panels or possibly a wind turbine enable an increase in cycling time and will consequently extend the calendar life of the battery and generator while also increasing the environmental benefits. This paper discusses technical aspects such as application needs, complete system design and optimization, and advanced battery, rectifier and controller choices. It also covers laboratory testing to optimize the operating profile and field trials for validation. Results of the different tests are also analyzed and discussed. The paper also includes a Total Cost of Ownership analysis of the hybrid system proposed in comparison to existing systems with two diesel generators.