Dissertations / Theses on the topic 'Energy resources'

Tanzania has a characteristic developing economy, which is dependent on agricultural productivity.  About 90% of the total primary energy consumption of the country is from biomass.  Since the biomass is mostly consumed at the household level in form of wood fuel, it is marginally contributing to the commercial energy supply.  However, the country has abundant energy resources from hydro, biomass, natural gas, coal, uranium, solar, wind and geothermal.  Due to reasons that include the limited technological capacity, most of these resources have not received satisfactory harnessing.  For instance: out of the estimated 4.7GW macro hydro potential only 561MW have been developed; and none of the 650MW geothermal potential is being harnessed.  Furthermore, besides the huge potential of biomass (12 million tons of oil equivalent), natural gas (45 million cubic metres), coal (1,200 million tones), high solar insolation (4.5 – 6.5 kWh/m²), 1,424km of coastal strip, and availability of good wind regime (> 4 m/s wind speed), they are marginally contributing to the production of commercial energy.  Ongoing exploration work also reveals that the country has an active system of petroleum and uranium.  On the other hand, after commissioning the 229km natural gas pipeline from SongoSongo Island to Dar es Salaam, there are efforts to ensure a wider application in electricity generation, households, automotive and industry.

Due to existing environmental concerns, biomass resource is an attractive future energy for the world, Tanzania inclusive.  This calls for putting in place sustainable energy technologies, like gasification, for their harnessing.  The high temperature gasification (HTAG) of biomass is a candidate technology since it has shown to produce improved syngas quality in terms of gas heating value that has less tar.

This work was therefore initiated in order to contribute to efforts on realizing a commercial application of biomass in Tanzania.  Particularly, the work aimed at establishing characteristic properties of selected biomass feedstock from Tanzania.  The characteristic properties are necessary input to thermochemical process designers and researchers.  Furthermore, since the properties are origin-specific, this will provide baseline data for technology transfer from north to south.  The characteristic properties that were established were chemical composition, and thermal degradation behaviour.  Furthermore, laboratory scale high temperature gasification of the biomasses was undertaken.

Chemical composition characteristics was established to palm waste, coffee husks, cashew nut shells (CNS), rice husks and bran, bagasse, sisal waste, jatropha seeds, and mango stem.  Results showed that the oxygen content ranged from 27.40 to 42.70% where as that of carbon and hydrogen ranged from 35.60 to 56.90% and 4.50 to 7.50% respectively.  On the other hand, the elemental composition of nitrogen, sulphur and chlorine was marginal.  These properties are comparable to findings from other researchers.  Based on the results of thermal degradation characteristics, it was evident that the cashew nut shells (CNS) was the most reactive amongst the analyzed materials since during the devolatilization stage the first derivative TG (DTG) peak due to hemicellulose degradation reached (-5.52%/minute) compared palm stem whose first peak was -4.81%/minute.  DTG first peak for the remaining materials was indistinct.

Results from the laboratory gasification experiments that were done to the coffee husks showed that gasification at higher temperature (900°C) had an overall higher gasification rate.  For instance, during the inert nitrogen condition, 7% of coffee husk remained for the case of 900°C whereas the residue mass for the gasification at 800 and 700°C was 10 and 17% respectively.  Steam injection to the biomass under high temperature gasification evolved the highest volumetric concentration of carbon monoxide.  The CO peak evolution at 900°C steam only was 23.47 vol. % CO whereas that at 700°C was 21.25 vol. % CO.  Comparatively, the CO peaks for cases without steam at 900°C and 2, 3, and 4% oxygen concentrations were 4.59, 5.93, and 5.63% respectively.  The reaction mechanism of coffee husks gasification was highly correlated to zero reaction order exhibiting apparent activation energy and the frequency factor 161 kJ/mol and 3.89x10⁴/minute respectively.

Increased share of Renewable Energy Sources (RES) in the generation mix requires higher flexibility in power system resources. The intermittent nature of the RES calls for higher reserves in power systems to smooth out the unpredictable power fluctuations. Grid-tied energy storage systems are practical solutions to facilitate the massive integration of RES. The deployment of Battery Energy Storage Systems (BESS) on the power grids is experiencing a significant growth in recent years. Thanks to intensive research and development in battery chemistry and power conversion systems, BESS costs are reducing. However, much more advancements in battery manufacturing as well as additional incentives from the market side are still needed to make BESS a more cost-effective solution. Planning and operation of the BESS significantly influence its profitability. It is quite important to find optimal sizes of batteries and inverters. Sizing of the BESS for two different applications is addressed in this work. In the first application, the BESS is co-located with Pumped Storage Hydro (PSH) to meet the Day-Ahead (DA) schedule of wind generation. In the second application, a method for BESS sizing in the presence of PV-induced ramp rate limits is proposed. In this thesis, two methods based on Receding Horizon Control (RHC) for the optimal operation of the BESS are introduced. A co-located BESS and wind farm is considered in both methods. In one method, electricity market participation is not considered, and the goal is solely meeting the DA schedule utilizing the BESS. A novel predictive control method is proposed in this part and the efficiency of the method is evaluated through long-run simulations using actual historical wind power.

In the second scenario, market participation of the BESS is taken into account. The deviation from the DA schedule can be compensated through the BESS, or by purchasing power from the real-time electricity market. The optimization problem based on physical and operational constraints is developed. The problem is solved through an RHC scheme while using updated wind power and electricity price forecasts. In this thesis, a Ridge-regression forecast model for electricity price and an ARIMA forecast model for wind power are developed. Simulation results using actual historical data for wind power and electricity price demonstrate that the proposed algorithm increases the average daily profit. In order to evaluate the impact of the BESS lifetime and price on average daily profit, different scenarios are defined and simulated. Although they increase the complexity of the problem, much more realistic result might be obtained when all details and constraints are considered.

With the increasing attention and support behind plug in hybrid electric vehicles, research must be conducted to examine the impacts of vehicles on electric distribution and transmission systems. This research aims first to model the behavior of vehicle battery chargers during system disturbances and mitigate any impacts. A distribution test system example is modeled and several different vehicle charger topologies are added. Faults are applied to the distribution system with vehicle chargers connected and the results are examined. Based on these results, a control strategy to mitigate their negative impacts is suggested. Photovoltaic panels are then added to the system and the study is repeated.

Several services that plug in hybrid electric vehicles are capable of providing to the electric system are presented in order to allow electric vehicles to be seen as an asset to electric systems rather than a burden. These services are particularly focused on an electric system such as might be found on a college campus, which in this case is represented by the Clemson University electric distribution system. The first service presented is dynamic phase balancing of a distribution system using vehicle charging. Distribution systems typically face problems with unbalance. At most large car parks, a three phase electric supply is expected even though current standardized chargers are single phase. By monitoring system unbalance and choosing which phase a vehicle is allowed to charge from, unbalance between phases is reduced in a distribution system. The second service presented is a decentralized vehicle to campus control algorithm based on time of use rates. Using time of use electricity prices, discharging vehicle batteries during high prices and recharging at low prices is explored. Battery degradation as well as limits placed by required vehicle range availability are included in the decision on whether to charge or discharge. Electric utilities will also benefit from a reduction of load at peak times if vehicles discharge back to the campus. A comparison with stationary battery energy storage is included.