Waste to Work: Powering Cold Storage Systems Using Biomass and Solar Energy

Abstract

Generating electricity from sources outside of fossil fuels is more important now than ever before. With global temperatures rising, it is vital to the future health of our planet’s ecosystems to reduce the amount of carbon being emitted into the atmosphere. Our system, named "Waste to Work," uses organic waste and the sun’s rays as energy inputs, and outputs electricity for cold storage. It is intended to supply developing areas of the world with the necessary refrigeration for their agricultural products. Anaerobic co-digestion of biomass (food waste and sewage sludge) was accomplished primarily by keeping the temperature of the digester in the mesophilic temperature range and the pH above 7.0. Our 12 gallon digester produced biogas at a maximum rate of 0.81 liters per hour with a methane content of 48%. Using water scrubbing as a method of "cleaning" the biogas significantly increases the relative methane content by removing carbon dioxide and hydrogen sulfide [1]. Power is produced by running the clean biogas through a generator with an efficiency of 52% and a computed fuel flow rate of 0.22 m3/hr, providing up to 1,200 watts (W). An array of solar panels, acting as the second source of power, provides 200 W to power a 40 W refrigerator with a volumetric capacity of 2.2 ft3. This accounts for approximately 40 kg of cold storage capacity. Running in a parallel configuration, the generator and solar panels power the refrigeration system. Through the use of intelligent autonomous control, the system is capable of switching being the two sources of energy independent of human intervention. The energy levels of the solar source are constantly monitored using an Arduino microcontroller that shifts the energy source using a doubleswitch as needed, ensuring uninterrupted supply of electricity to the cold storage system.