• Energy Research

The greatest sustainability challenge facing humanity today is the greenhouse gas emissions and the global climate change with fossil fuels led by coal, natural gas and oil contributing 61.3% of global electricity generation in the year 2020. The cumulative effect of the Stockholm, Rio, and Johannesburg conferences identified sustainable energy development (SED) as a very important factor in the sustainable global development. This study reviews energy transition strategies and proposes a roadmap for sustainable energy transition for sustainable electricity generation and supply in line with commitments of the Paris Agreement aimed at reducing greenhouse gas emissions and limiting the rise in global average temperature to 1.5°C above the preindustrial level. The sustainable transition strategies typically consist of three major technological changes namely, energy savings on the demand side, generation efficiency at production level and fossil fuel substitution by various renewable energy sources and low carbon nuclear. For the transition remain technically and economically feasible and beneficial, policy initiatives are necessary to steer the global electricity transition towards a sustainable energy and electricity system. Large-scale renewable energy adoption should include measures to improve efficiency of existing nonrenewable sources which still have an important cost reduction and stabilization role. A resilient grid with advanced energy storage for storage and absorption of variable renewables should also be part of the transition strategies. From this study, it was noted that whereas sustainable development has social, economic, and environmental pillars, energy sustainability is best analysed by five-dimensional approach consisting of environmental, economic, social, technical, and institutional/political sustainability to determine resource sustainability. The energy transition requires new technology for maximum use of the abundant but intermittent renewable sources a sustainable mix with limited nonrenewable sources optimized to minimize cost and environmental impact but maintained quality, stability, and flexibility of an electricity supply system. Technologies needed for the transition are those that use conventional mitigation, negative emissions technologies which capture and sequester carbon emissions and finally technologies which alter the global atmospheric radiative energy budget to stabilize and reduce global average temperature. A sustainable electricity system needs facilitating technology, policy, strategies and infrastructure like smart grids, and models with an appropriate mix of both renewable and low carbon energy sources.

The Sugar industry faces several sustainability challenges due to dumping of excess global production which cause stiff competition for high cost sugar producers like Kenya. Through diversification into cogeneration and ethanol production, sugar companies in high cost producing countries can remain competitive and survive in the market. In this study, the technical and economic feasibility of ethanol production is done for the case of Nzoia Sugar Company in Kenya whose milling capacity is 3000 tons of cane per day (TCD). Molasses is taken through a series of stages starting with pretreatment, followed by fermentation and distillation to produce ethanol. The ethanol formed is then transferred to the distillation columns for fractionation to remove water and hence have ethanol rich product. Through further distillation and molecular sieve dehydration the purity and quality of the final ethanol product is enhanced. The main equipment for the process includes the fermenter, boilers, condensers, and distillation columns, design to suit the product characteristics and design capacity of the plant. The analysis showed that ethanol production by a 3000 TCD sugar factory is a profitable venture. The study showed that investment is both technically and economically feasible and will improve the financial performance and sustainability of the sugar factory in a competitive market environment. Therefore, diversification into ethanol production is an important strategy in sustaining the sugar industry in a competitive global market.

Biogas is a renewable energy resource that can play a leading role in the sustainable energy transition through green electricity generation. Biogas can be converted to electricity and renewable fuels through different technologies and prime movers. Prime movers that can be used for biogas power generation include gas and steam turbines, diesel engines, Otto cycle engines, Stirling engines as well as direct conversion in fuel cells. Since biogas has high octane rating, it can be used directly or with minimal modifications in spark ignition or petrol engines, but needs several modifications for use in dedicated diesel biogas engines or dual fuel engines and bi engines. The dual fuel mode which uses biomethane or biogas and diesel requires little or no engine modifications unlike the conversion to a dedicated gas engine. The performance of biogas prime movers is greatly enhanced if enriched biogas or biomethane is used in place of raw biogas. Other than use in various engines, biogas can be cleaned and used in fuel cells and manufacture of renewable hydrogen. As renewable natural gas, biogas in the form of biomethane can be injected to the natural gas grids for domestic and industrial application as natural gas substitute in applications which include power generation.

The Levelized Costs of Energy/Electricity (LCOE) is widely used to compare different power generation technologies by considering the various fixed and variable costs as a single cost metric. The levelized cost of electricity (LCOE) measures the average net present cost of generating electric power over the power plants entire life. As a metric, the levelized cost of energy does not capture all costs that affect the cost of electricity like the system costs. For accuracy of cost analysis, the LCOE is modified to account for other costs e.g., system levelized cost which considers externalities. The value-adjusted levelized cost of electricity (VALCOE) is a metric developed by the International Energy Agency (IEA) that captures the cost and value to the electricity system since the same amount of power may be less or more valuable during peak demand. The levelized cost of storage (LCOS) is another metric applied in comparing alternative energy storage systems for specific energy scenarios i.e. long-term, short-term, and medium-term storage. Another related metric is the Levelized avoided cost of energy (LACE) which n captures information about how the grid operates without the new power plant or storage facility entering service making it more complex than LCOE or LCOS, but more insightful. The value-adjusted levelized cost of electricity (VALCOE) captures both cost and value to the electricity system. Another metric, the Levelized Full System Costs of Electricity (LFSCOE), metric is used to analyze the costs incurred to supply the entire energy market with one power source plus storage presented as one value just like the levelized cost of energy (LCOE). Therefore, the levelized cost of energy (LCOE) metric is universally accepted as a tool for preliminary cost evaluations of generation technologies, but for accurate and reliable assessment, various modifications of the levelized cost of energy/electricity must be applied.

Sugar industries have huge potential to contribute to the sustainable energy transition through electricity generation and production of biofuels. Sugar-producing countries generate huge volumes of sugarcane bagasse as a byproduct of sugarcane production. In this study, the performance of an operating traditional sugar factory is analyzed for electricity generation and export potential. The study presents characteristics and energy potential of modern and traditional sugar factories. The challenges facing a traditional sugar mill are inefficient boilers, less efficient and back pressure steam turbines, and wasteful and inefficient use of steam turbine drives as prime movers instead of modern electric drives for the mills and cane knives. Others are the use of inefficient and energy intensive cane mill rollers instead of the diffusers which have low energy requirements. It was demonstrated that the cogeneration potential of sugar factory is quite significant but currently underutilized. Sugar factories can make significant contribution towards mitigation of greenhouse gas emission mitigation through supply of green electricity to the public grid. The study showed that the factory uses very old and inefficient boilers aged over 39 years which contributes to poor performance and low electricity generation capacity. Modernization is required to increase the generation and electricity export capacity through investment in new and modern high-pressure boilers, replacement of inefficient back pressure boilers (BPSB) with more efficient condensing extraction turbines (CEST), and reduction of factory steam consumption by electrification of mills and cane knife turbine drives among other measures. This study showed that the 3,000 TCD factory can invest in a 15 MW power plant based on current average factory performance indicators and more if the throughput and overall performance is close to design parameters.

Geothermal energy has a significant role to play in the global transition to renewable and low-carbon energy systems because of its ability to supply steady and flexible electricity particularly for baseload demand because of its cost competitiveness compared to fossil fuel energy options. However, geothermal faces a challenge of long project development times with conventional power plant taking an average of 5–10 years and with high risks associated with drilling of unproductive wells which discourage private investment and quick deployment. Although geothermal energy has a huge potential for power generation, it currently contributes less than 1% of global electricity generation capacity. The generation capacity grew from 8.7 GWe in 2005 to 15.61 GWe at the end of the year 2020, representing average annual growth of 4.01%. The overall objective of this study was to determine the potential, features and application of wellhead power plants in electricity generation both to complement and substitute central powerplants. It was established that wellhead power plants can be used on temporary basis during the project development or permanently as grid connected or off grid generation facilities. With current technology, wellhead generators of up to 15 MW capacity can be installed on well pads of production wells for temporary or permanent electricity supply. Wellhead generators can facilitate optimum resource utilization especially for wells with unique conditions like too high or too low pressure and temperature compared to others in the same steam. They are generally inferior to central power plants due to lack of economies of scale hence higher unit cost of power. Successful adoption of wellhead powerplants for faster electrifications calls for state support and incentives in terms of subsidies, development of electricity gid, attractive feed in tariffs and tax incentives without which they won't compete favorably against the conventional central powerplants. Generally, wellhead powerplants can make geothermal electricity projects more feasible with reduced barriers in investment and early electricity and revenue generation for investors. However, investment on temporary basis makes reasonable economic sense if the time between drilling the first productive well and completion of a central plant is more than one year. Incentives like high feed in tariffs and tax incentives may be necessary to make them competitive against the superior conventional powerplants.

This study looked energy sustainability and sustainable development and measures necessary to ensure that electricity generation is sustainable. Current literature in form of published journal articles and conference proceedings as well as scientific and technical reports on the area of sustainable energy and development was examined. It was noted that there can be no development without energy and there can never be sustainable development without sustainable energy. There is need to sustainably exploit the energy resources to meet current energy needs and those of future generations in an environmentally friendly manner while noting that about 35% of the anthropogenic greenhouse gas emissions come from energy related activities in power generation. Technological advances which include smart grids and decentralization of generation as well as energy carrier technologies are rapidly providing electricity access options available beyond the traditional grid. The study showed that electrification of the global energy mix, electrification of the transport sector, energy efficiency measures and enhanced use of low carbon and renewable energy resources for electricity will play a significant role in the future sustainable energy transition. Additionally to realize energy sustainability effective measures include increased use of solar and wind for grid electricity, use of sustainable energy carriers like hydrogen, development and adoption of energy efficiency measures, limiting environmental impact of energy use including carbon sequestration and enhancing socioeconomic acceptability through community involvement and social acceptability, economic affordability and equity, lifestyles, land use and aesthetics. Whereas renewable energy is a solution to sustainable energy and electricity, current technology and limitation make it necessary to have an optimized mix of renewable and low carbon nonrenewable for sustainable grid electricity.

Kenyan sugar factories are facing challenges in the market from low cost sugar producers as a result of high cost of production. As a result, a number of factories have closed down while operating factories are struggling with cash flow problems. Diversification into both ethanol and export cogeneration is a promising solution to the challenges. In this study, the feasibility of export electricity generation for a Nzoia sugar factory in Western Kenya is undertaken. The 3000 tons of cane per day crushing capacity (TCD) factory has effective generation capacity of 2.8 MW for own internal consumption against installed capacity of 7 MW. The study showed that the factory can develop a continuous power plant of 15 megawatts (MW) but modernization of the factory is necessary to reduce steam consumption mainly by replacing steam turbine drives with electric drives, increase generation efficiency by use of a condensing extraction turbine. The three boilers which are over 30 years old should be replaced with more efficient modern boilers of steam pressure between 45–60 bars. A well negotiated power purchase agreement that captures the challenges facing the factory should then be signed with a utility company to avoid the challenges in implementation due to external factors.

Diesel power plants use diesel engines as prime movers powered mainly by heavy fuel oil or industrial diesel oil and with potential for conversion to gas engines or dual fuel engines. The global concerns over prices of diesel and heavy fuel oil and energy related greenhouse gas emissions have created demand for natural gas as an alternative fuel for power generation by diesel power stations. This study involved a performance analysis of an operating diesel power plant and its potential conversion to dual fuel engine power plant. Dual fuel engines have reduced fuel costs and greenhouse gas emissions since natural gas is the cleanest fossil fuel. For a conventional diesel engine to run on diesel, the fuel injection system is modified to handle gas and a mixture of gas and diesel. Other modifications are the introduction of an electronic control unit, reduction in air fuel ratio, installation of a fuel mixer, and reduction of compression ratio. The conversion requires provision for natural gas storage facilities and supply system which were introduced in the proposed design modification. The study showed that dual fuel engine power plants have better performance indicators like lower specific fuel consumption, higher indicated and brake thermal efficiency, cheaper power produced, less emissions per unit power and thus reduced environmental impact. Conversion to dual fuel engines will reduce the cost of electricity generation, reduce emissions particularly Sulphur dioxide while accommodating fuel flexibility like use of biofuel to substitute diesel.