Biomass Residue-Fueled Micro-Grid for a Rural Community in Puerto Rico

Abstract

Ecology - Agriculture in the tropics is challenging in large part because of low-fertility soils that are highly weathered, acidic, and have few nutrients which are prone to leaching during heavy rainfall. A potential solution to this dilemma is the use of biochar as a soil amendment to raise pH and increase nutrient availability for plants. To test the efficacy of biochar in enhancing soil fertility and plant growth, we built a gasifier to create biochar through pyrolization of wood from inga trees. Resulting biochar was used to create eight soil treatments in which bush bean plants were grown from seed in an outdoor greenhouse. Treatments consisted of four different amounts of biochar and the presence or absence of an organic calcium-containing fertilizer. After measuring the growth of individual plants over the course of 45 days, soil pH levels in pots were measured, beans were harvested, then plants were oven dried and weighed to determine biomass. Results showed that biochar amendments lead to significant increases in plant biomass and soil pH. A 4% amendment of biochar to soil without fertilizer increased plant biomass by 73% on average while the same 4% amendment of biochar in combination with fertilizer increased plant biomass by 173%. Unamended soil had an average pH of 5.1, soil amended with only the calcium containing fertilizer had a pH of 5.7, and soil amended only with 4% biochar a pH of 5.75. Engineering - On September 20, 2017, Hurricane Maria struck Puerto Rico, destroying most of its energy infrastructure and triggering an 11-month blackout. This research looks to micro-grids and their potential for energy stability in hopes of revitalizing Puerto Rico’s energy system and making further sustainable improvements. Said micro-grids will be powered by already-existing solar panels and newly-constructed biomass gasifiers located at the headquarters of Puerto Rican NGO, Casa Pueblo, and within the community of El Hoyo, Adjuntas. The gasifiers will utilize locally available agricultural waste, such as coffee husks and tree prunings, and help communities develop energy independence and resilience in the face of future storms. To gather the data needed to create feasibility models assessing the implementation of potential micro-grids, interviews were conducted within El Hoyo, and data was collected from Casa Pueblo’s generation and load demand. The data showed that El Hoyo will not have a high enough baseline demand to add a gasifier to their current electrical system, and a purely solar and storage micro-grid would have the lowest NPC ($50,205.39) and LCOE ($0.2425/kWh), even if providing the highest amount of excess electricity (49,767 kWh/yr, 73.7%). Additionally, Casa Pueblo’s solar production was found to be underutilized with an excess electricity of 19,836 kWh/yr (91%). Installing a micro-grid with neighboring buildings would put excess electricity to use and also has the potential to be supplemented by a gasifier.