COMBINED ENERGY SYSTEMS APPLIED TO PRODUCTIVE SECTORS: THE CASE OF DAIRY FARMS IN CENTRAL BOLIVIA

Sammanfattning: Most energy solutions in developing countries focus primarily on solving domestic energy demands of their growing populations without due consideration of sustainable development. On the other hand, in most of these countries, a segment of energy users that has not received enough attention from governments and institutions regarding appropriate energy solutions is the productive sector. This sector is mainly composed by small and medium-sized industries and ventures that greatly contribute to the countries’ economy, as in the case of Bolivia. However, the low investment capacity, the lack of knowledge, training and insufficient support from local and national governments do not allow these solutions to arrive as expected. Although many of these sectors have the potential to apply energy solutions utilizing alternative energy sources, as the waste generated by the activity, this work has not materialized. This is the case of the dairy farmers in central Bolivia, who do not have an adequate management of farm waste. This problem contributes negatively to the contamination of the local and global environment. This study explores solutions of combined energy systems applied to the dairy sector of Bolivia. The two cases under investigation consider the utilization of waste from farms to produce biogas, which drives the proposed systems. The first solution focuses on a polygeneration system featuring either an internal combustion engine or internally fired microturbine for the simultaneous provision of biogas for cooking, electricity, refrigeration, and fertilizer. The second system involves trigeneration i.e. absorption chiller integrated to an externally fired microturbine for supplying electricity, refrigeration and hot water. Analysis methods include determination of levelized cost of services, payback period, primary energy rates and energy saving rates. The techno-economic assessment for the polygeneration system shows that the costs of the supplied services are still attractive when compared to subsidized prices of fossil fuel-based services in the market if the investment capital of this system is partially subsidized. The biogas cost from the system is lower than the cost of conventional gas used for cooking. The use of the internal combustion engine results in a lower electricity cost than using the microturbine. The refrigeration cost is slightly higher than conventional refrigeration for both cases. A sensitivity analysis shows that the cost for feedstock (cow dung) can be increased while maintaining an attractive price of biogas, and that subsidies on investment capital cause a reduction in the services costs. In the case of energy performance evaluation of the trigeneration system it was found to be more efficient in terms of energy utilization than conventional fossil fuel-based solutions, and this leads to energy savings.  Finally, it is shown that combined energy systems applied to the Bolivian dairy sector are competitive in terms of their economic feasibility and energy performance.