Purpose. The study aims to outline and compare various renewable energy alternatives in view of the global warming crisis and depletion of fossil fuels which cause emissions of carbon dioxide. Carbon dioxide is a major source of pollution and is an absorbent for radiation. Methods.Literature surveys and analysis of benefits and drawbacks of the competing technologies should include the capital costs, running costs and carbon footprint. Liquid fuels have high energy to weight ratio compare to say solar panels or thermal absorbers, but what is neglected is the large refinery and other processing machinery behind the liquid fuel which is adding to the carbon footprint.Findings. Producer gas and bacterial engines are suggested as possible pollution reducing and cost effective methods for power generation. Coal, biomass, geothermal and hydroelectric have the lowest running cost, but carbon footprint cost is neglected. Solar chimneys, with low mechanical efficiency have low running costs, and no pollution. Modification of internal combustion engines to use producer gas and alcohol may reduce overall carbon footprint.Originality. Many researches focus on energy and mechanical efficiency. Bacterial engines have yet to be fully developed, and these are wonderful chemical factories but not understood in terms of classical thermodynamics. For all technologies, return on investment is more appropriate since capital costs are also included, which are neglected in mechanical efficiency calculations.Practical implications. Depletion of forest cover which acts as a greenhouse gas sink contributes to global warming. Worldwide, million of cars with internal combustion engines consuming petroleum, if converted to alternative fuels, can help in reducing the carbon gas emissions and ultimately to a slowdown in the global warming rate.

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Background and objectives Reducing glycerol production, a major by‐product produced during fermentation by yeast Saccharomyces cerevisiae, can improve the ethanol productivity in corn dry grind process. This study investigates the potential of glycerol reduction using an advanced engineered yeast strain and determines the effect of enzyme dosage, pH, and temperature on the granular starch hydrolysis (GSH) process efficiency using both conventional yeast and advanced yeast. Findings Ethanol yields in GSH process were found maximum at enzyme dosage 4.8 kg/MT grains and remained unchanged with further increase in dosage. The glycerol production was reduced by more than 50% with use of advanced enzymes compared to the conventional yeast and resulted in 2.2–3.8% higher final ethanol concentrations. Performances of both yeast were reduced and lead to stuck fermentation at 36°C temperature. Conclusions Use of advanced yeast strains can improve the ethanol yields by reducing glycerol production in GSH process; however, the ethanol yields are highly dependent on the process conditions, especially enzyme loadings and temperature. Significance and novelty GSH process is expected to produce lower glycerol compared to conventional dry grind process. This research demonstrated that advanced engineered yeasts can reduce the glycerol production in GSH process also, improving the process yields and profitability.

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