Hybrid Power Systems Deliver Efficient Energy Management for Off-Grid BTS Sites

The continuous increase in fuel costs for generators is driving organizations that use power in off-grid locations to search for more cost-effective ways of powering their sites. This is especially the case within the telecoms sector where grid supply is unreliable. Therefore, choosing a reliable method (including equipment) to generate electricity to run sites is vital to successfully operate equipment. In the case of telecoms operators this means ensuring the Base Transceiver Station (BTS) has power and functions. However, choosing the right technology to achieve this can have a major impact on the site's operating costs. Furthermore, the wrong choice of technology can not only be expensive to run, but also have a negative impact on a site's environmental footprint - which is not ideal when you consider the "wireless industry" is striving to play a positive role in dealing with climate change by reducing its CO2 emissions. One solution to this problem is for organizations to use a hybrid system that integrates a variable speed diesel DC generator (genset) with a deep cycling Li-ion battery. This can offer an extremely energy efficient alternative to using an AC generator operating 24/7. The generator simultaneously charges the battery and powers the site load. When the battery has been fully charged the generator shuts down and the battery takes over as the primary source of power. By reducing the genset runtime down to typically 4 hours per day, this approach offers major savings in fuel consumption - usually up to 74 percent savings compared with a standard genset. It also reduces CO2 emissions while increasing refuelling and service intervals. A complete hybrid system of this type can be packaged in a compact and light "energy container" to offer a turnkey solution that is quick and easy to install in remote locations. Moreover, achieving both optimum system efficiency ratings and Total Cost of Ownership (TCO) reductions comes down to a careful selection of the right equipment making up the hybrid system. This includes selecting the right sub-systems comprising the best DC diesel generator, controller and battery for the task at hand. Typical factors that need to be considered include: The high-density cycling battery must be temperature-resistant, maintenance free, highly energy efficient, charge quickly and deliver a large number of deep discharge cycles The DC generator must be based on Permanent Magnetic Generation (PMG) technology so that the system can keep its weight and size to a minimum. This helps achieve an overall compact design that achieves optimum global efficiency and system reliability The controller must be equipped with its own dedicated software that enables the operating profile of the battery and generator to be optimized, thus delivering the lowest possible operating cost. The addition of PV (photovoltaic) panels or possibly wind turbines will allow further significant reductions in operating costs (OPEX) while also increasing environmental benefits. This paper discusses technical aspects of hybrid systems such as application needs; complete system design and optimization including DC generator, advanced battery, and controller choices. It will also review and analyse the results of various filed tests implemented to validate this concept. It concludes with a Total Cost of Ownership (TCO) analysis of a proposed hybrid system compared with existing systems based on continuously operating diesel generators.