Energy flow in a Hybrid Wind/ Hydrogen System for Kampala and Tororo towns in Uganda

University essay from KTH/Energiteknik

Author: Godfrey Ssajja Ssali; [2015]

Keywords: ;

Abstract: This report presents modeling for energy flow of a distributed renewable energy system based on an integrated wind power and hydrogen production system supplying a local electric load connected to an electric grid. The system consists of a 200kW wind generator, an Electrolyzer with a maximum production capacity of 5kg of hydrogen per 24h and a 3.5kW peak electric load. There is an external connection to the electric grid, assumed large enough to serve as a back-up supply, and whose electricity source of the system is unknown.The main objective of this research was to simulate optimal control strategies that regulate the flow of power from the wind generators to the grid at wind power peaks and from the grid to the Electrolyzer at low wind speeds thereby enabling production of 4-5kg of electrolytic hydrogen for transportation and stationary applications using a renewable resource.The system inputs are hourly wind speed, hourly load demand, and hourly hydrogen demand. The wind generator is modeled as an energy conversion device, which follows the cubic law with cut-in and a maximum speed of 25m/s. The Electrolyzer and compressor are modeled as energy consuming units. The system fully exhausts the wind generator power to meet hydrogen production and electric load requirements per day. The excess power is supplied to the grid while shortages are sourced from the grid. The system outputs are hydrogen production per hour and the power exported to and imported from the grid. The controller thus monitors energy flows from the system and optimizes utilization of the renewable energy source. A computer program using MATLAB for this integrated system is developed, where Energy and hydrogen flow are balanced at each time step depending on the specified strategy. An economic assessment was done to get the annualized costs and the cost of electricity from wind energy in comparison with the electric grid. The system is experimented with hypothetical wind speed data and then validated using wind speed data from two towns in Uganda, Kampala and Tororo Towns.The validation of the model was carried out using wind speeds for Kampala City and Tororo Town in Uganda; the monthly average wind speed were sourced from the RETScreen software with embedded NASA data measured/estimated at 10m above the ground. The Weibull distribution was then used to simulate random hourly data for 24 hours in a day for each particular month of the year as required by the Matlab program. The smart grid application of this model in the production of hydrogen has been investigated and found feasible. The model monitors hydrogen flow within storage and optimizes the flow of power to meet the hydrogen demand for the day. The economic assessment done showed that the cost of electricity from the wind generator was not competitive with the commercial electricity production within the country though there is an environmental benefit in using the wind energy in production of hydrogen, as there are more than 140,000 kg of CO2 emissions saved. Therefore, the results obtained here confirm that such an integrated system has the potential to support remote investments in the production of electrolytic hydrogen from a non-polluting source.

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